Assuming you have the proper amount of fluid in the system, Is there any risk in popping delicate rubber bits in the master cylinder (bladders or...
Assuming you have the proper amount of fluid in the system, Is there any risk in popping delicate rubber bits in the master cylinder (bladders or some such) by going up to a thicker rotor?
I like my Curas, but I’d like them to feel a bit firmer earlier in the lever stroke. Clearance is already pretty tight between OE rotors and pads, so not sure this is a good idea.
Formula Monolitic rotors come in 2.3mm thickness and they have not redesigned the caliper since it was released so you will be fine with 2.3 rotors...
Formula Monolitic rotors come in 2.3mm thickness and they have not redesigned the caliper since it was released so you will be fine with 2.3 rotors. Assuming you are OK with the 100g+ weight penalty. Those grams add up! Next you will be running inserts front and rear with DH casing tires and you will need to buy a new trail bike because your enduro bike no longer "does-it-all" like it used to!
Just teasin! We are all enjoying riding bikes in the woods and there is nothing wrong with that no matter how thick you let your rotors get.
Hey Guys!
Replying to some comments and adding mine:
I am just parted ways with my Formula Cura 4 brakes. As per many websites, some rotor sizes are 2.3mm, like the 203mm size, but some sites state the 203mm is 2.0mm thick.. I am speaking of their Monolitic rotors.
As I found out the 180mm rotor was only like 1.8 or 1.9 thick. This is why I always felt longer lever throw on my Cura 2 and later Cura 4 on the rear too.
I bought a TRP 2.3mm rotor for the rear, also 180mm (Niner Rip9 RDO accepts 180 max at the rear due to clearance with the swingarm) and with new pads, and pistons pushed back all the way in to their bores, it was such a tight fit I opted not to run them.
I had issues with the lever, so I rebuilt it, then tha caliper, although I rebuilt the caliper it still had some issues, so those brakes are gone.
In came the Hayes Dominion A4-s. Original rotors should be 1.95mm, but I had a brand new set of Magura Storm HC discs 203/180, so I opted to run those with the Hayes. They fit well, and have enough pad retraction that it doesnt rub after setting up the brake. It seems the pad/rotor surface matches as well. I saw some guys in forums using Magura Disc with Hayes Dominions too.
Hayes also compatible with Galfer Shark 2.0mm rotors, the Atherton Racing Team use this combo for a very long time. They are on Hayes brakes since they ditched the Trickstuff Maxima brakes.
Other out of the topic stuff, on adaptors.
Hayes adaptors, pretty hard to find (at least in Europe, I am from Hungary) and Shimano PM 203 adaptor (from 180 to 203 PM) do fit the large caliper of the Dominion. At the rear, neither the Formula PM 180 (160 to 180) nor the Shimano fit. So I searched and the Magura QM40 does fit, so I have one coming towards me.
One point regarding long term disability, if you are turning your rotors blue (especially deep blue/ purple) from heat you are affecting the heat treating of...
One point regarding long term disability, if you are turning your rotors blue (especially deep blue/ purple) from heat you are affecting the heat treating of the rotor.
This can make them wear faster and more likely to warp.
Rotor bluing not cause for concern with quality rotors and is standard in motorsports. For automotive road racing, bluing the rotor when bedding in new brakes is when you know the bedding procedure is done properly. Rotors were always blue on all of my race bikes back when I roadraced motorcycles. Cheap rotors might have inconsistencies in the material so they might warp under such heat, hence the importance of quality rotors.
It seems there is less expertise or interest in learning here. Instead those searching for comfirmation bias of their purchases.
Trying to save weight on brakes and rotors is just plain stupid. I have never finished a ride and thought if only i had bought those...
Trying to save weight on brakes and rotors is just plain stupid. I have never finished a ride and thought if only i had bought those xc 2pots I could have saved 200 grams and shaved 2.5 seconds of my climb.
If you think I recommended XC brakes for enduro bikes, then you didn't read the posts. Having far too much braking potential than what you need is also stupid. Debating parts selection on a mountain bike is based on performance, and just like with everything in competition, it is about optimization and efficiency. If you are plodding along the trails and want massive braking power, go for it. That is a subjective opinion. But when racing a clock, I want exactly what I need for optimum performance, nothing more and nothing less, and that is not an uncommon demand for racing.
One point regarding long term disability, if you are turning your rotors blue (especially deep blue/ purple) from heat you are affecting the heat treating of...
One point regarding long term disability, if you are turning your rotors blue (especially deep blue/ purple) from heat you are affecting the heat treating of the rotor.
This can make them wear faster and more likely to warp.
Rotor bluing not cause for concern with quality rotors and is standard in motorsports. For automotive road racing, bluing the rotor when bedding in new brakes...
Rotor bluing not cause for concern with quality rotors and is standard in motorsports. For automotive road racing, bluing the rotor when bedding in new brakes is when you know the bedding procedure is done properly. Rotors were always blue on all of my race bikes back when I roadraced motorcycles. Cheap rotors might have inconsistencies in the material so they might warp under such heat, hence the importance of quality rotors.
It seems there is less expertise or interest in learning here. Instead those searching for comfirmation bias of their purchases.
There is a big difference between the surface slightly bluing on a carbon steel rotor (on a car) during bedding in and turning an entire rotor dark blue on a MTB. A similar bedded in look on a MTB rotor (let's call it light blue) is not cause for concern, similar to cars. Deep bluing could be.
MTB rotors being much thinner and stainless (most rotors on cars are carbon steel, I don't know about motorcycle rotors) are much less durable.
My experience with changing heat treatment is from my day job, firearms manufacturing. If you turn stainless steel deep blue you have affected any heat treatment that part had previously.
Does that practically effect MTB rotors, in the real world? Is the change enough to matter? Maybe / maybe not.
My point was mainly that if you are bluing your rotors on your MTB, it is a sign you could use more thermal capacity so larger / thicker rotors are likely a good idea.
I am completely on the other end of the spectrum here. Martin Maes is the only validation I can think of right now. I have done...
I am completely on the other end of the spectrum here. Martin Maes is the only validation I can think of right now. I have done quite a few Enduro races in my day (30 years wrenching, riding, and racing) and I have run 180 rotors front and rear forever for my Enduro bike. Currently on Galfer Shark rotors (standard Thickness) and Galfer Pro pads in Magura MT5 E-Stops (Just an MT5 with silver caliper piston pucks instead of black ano and stupid plastic color rings) with the HC brake lever option. I have never felt like I needed more braking power. Here in the northeast US, when it is steep, it is usually janky so 'dragging' brakes isn't a safe option, pick a braking spot, and brake hard and short, otherwise stay off the brakes. Modulation is key here. You really need to gauge the grip of the roots, rocks, etc and brake accordingly. Even with that method, I have blued the rotors on steep, long runs of tech terrain but didn't feel a dropoff in performance, if anything, they bit harder. Prior rotors I have used are Galfer Wave, Magura Storm, and Swiss Stop, all with good results. All of them blued at some point and either still in use, or tossed because they got too thin. Haven't warped a rotor in over a decade. I have used Cura 4s (still on a different bike) Codes (don't like the feel, weight, and finish of Sram brakes), and Shimanos but swore off Shimanos with the servo-wave (or whatever they call it) for the wandering bite point and too much power with poor modulation.
I am assuming that the OP is not a World Cup DHer and is likely riding the bike in his profile pic for "enduro" all-mountain, trail, blah blah. I can get behind the bending resistance of thicker rotors, but as long as you are using quality rotors and pads, I have not had heat issues that led to a performance problem. I have plenty of braking power with my little rotors and they are half (or less) of the rotating, unsprung weight of larger rotors so my suspension can follow terrain a small percentage better and I don't have to slog around weight I don't need when I have to get on the gas. I am 42, 185 pounds, 5'8" riding a Specialized Enduro for...well...enduro, big mountain...hiking trail jank riding...whatever you want to call it. Stumpy Evo is my trail bike that sees some spicy lines and that only has Magura Trail Sports with a 2-piston rear caliper and 180mm rotor! With the stock organic pads no less! Took forever for them to bed in and make full power though. Still no complaints.
My fatbike and beater hardtail get 160mm china sram knockoff rotors and they still work well when bed in properly so I'm not a rotor snob. Shit, sometimes they hit the same negative gradients as the big bikes and it is just that much extra spicy.
Not to sound like a dick but I hope most people ignore this.
1) Martin is one of one. You don't ride a bike like him and neither do I.
2) According to the telemetry data I've seen, most (good) riders do in fact use their brakes for ~85% of a descent. Even Neko just noted at the WC level guys are on their brakes 80% of a run.
3) The whole point of a brake is to take kinetic energy and turn it into thermal energy. The more "room" a system has with respect to heat management, the better it will perform over longer descents. This isn't all that complicated.
4) The more a person can have confidence in their brakes without adding to hand/arm fatigue the safer they will be and more fun they'll have.
5) Nobody at a race is going "oh, this is a 900 foot descent not a 1,400 foot descent, I'll go down to a 1.8mm rotor" (or similar). If you think this is how real world privateer type racers do anything you are severely misguided. Yes, you'll have an outlier like Martin or Troy trying something weird on the brake side of things but these are guys chasing fractions of a percent and there is zero real data to suggest these wonky decisions actually paid off in the first place. Your standard everyday Joe, even the kind racing at the pro level, is much better off with more brake than they need than trying to toe some imaginary line of "baby-bear brake optimization".
As to if you'll notice a few fractions of a mm in rotor thickness, I don't know. It's all iterative at the end of the day. If I have to pick thickness or size vs weight, I'm taking the weight penalty all day long on everything but m XC bike. Size of rotor plus thickness of rotor all equals a better braking experience.
I loved Dak on the Inside Line this fall talking about how far behind he feels our brakes really are for what we do. I agree. I want brakes that are as effective for my mtb as my moto brakes are for my dirt bike. We have a little ways to go IMO.
Trying to save weight on brakes and rotors is just plain stupid. I have never finished a ride and thought if only i had bought those...
Trying to save weight on brakes and rotors is just plain stupid. I have never finished a ride and thought if only i had bought those xc 2pots I could have saved 200 grams and shaved 2.5 seconds of my climb.
If you think I recommended XC brakes for enduro bikes, then you didn't read the posts. Having far too much braking potential than what you need...
If you think I recommended XC brakes for enduro bikes, then you didn't read the posts. Having far too much braking potential than what you need is also stupid. Debating parts selection on a mountain bike is based on performance, and just like with everything in competition, it is about optimization and efficiency. If you are plodding along the trails and want massive braking power, go for it. That is a subjective opinion. But when racing a clock, I want exactly what I need for optimum performance, nothing more and nothing less, and that is not an uncommon demand for racing.
If you're commenting on a vital forum post I'm pretty sure you're not a pro racer who would be able to actually notice 20-50 grams saved on 180mm rotors. You can't have too much braking power on an enduro / trail bike, however you can have an inexperienced "racer" who doesn't know how to properly use his brakes. More braking power / mechanical advantage from larger discs or better brakes means less force required on the finger and usually less arm fatigue.
This is a little off topic, but how do people feel about more powerful braking system vs larger rotors. Both weigh more and deliver more braking...
This is a little off topic, but how do people feel about more powerful braking system vs larger rotors. Both weigh more and deliver more braking force, but which is best?
In the past I've stuck with whatever cheap calipers my bike came with e.g. codes, and bumped the rotor up from 200mm to 220mm. That's an easy win of 10% more braking force (ignoring heat issues which might give more or less advantage depending on whether your brakes were too hot/cold to start with). For me this has always been a simple upgrade path: buy a couple of rotors and caliper adapters, job done!
I'd be interested to hear from people who have invested money in stiffer caliper with better mechanical advantage which can also deliver more braking force but without having to bump up rotor size. What are the pros/cons? Anyone tried both and compared?
Mentioning Codes specifically, R feels like garbage to me, RSC works. I'd rather have 180 mm rotors on RSC brakes than 220 mm rotors on R brakes. Because of feel alone.
Worth mentioning that brake power is relative to rotating weight. As your rim, tire, and potentially tire insert get bigger and heavier, your wheel is significantly harder to stop, which necessitates bigger rotors. That sounds a little conspiracy hat-ty, but it's real. I felt this as I upgraded to 29" from 27.5", and as I started moving towards downhill tires and later inserts on my trail bikes, and I believe this is why 4-piston brakes are now standard on trail and even XC bikes, when 2 piston brakes were fine on many 26" enduro bikes. I'd also bet my bottom dollar that 180mm rotor guy from Maine is on EXO or EXO+ tires, no inserts, and maybe even carbon rims.
Added point, the same sized rotor is less effective on a 29 inch wheel compared to smaller wheels. Look at the rotor size in relative terms to the wheel diameter instead of absolute sizes of 180, 200, etc. mm.
@jeff.brines considering you're also a moto guy, how is braking done on a moto? One finger or two finger? What are pad clearances like on motor bikes? Etc.
Certainly not Martin Maes or Troy Brosnan level of rider here, and most likely not near @jeff.brines either, but here's what I have found in 26 years as a bike mechanic, 30+ years of riding offroad.
If you're primarily riding in terrain that has short descents or very short braking zones, 180mm rotors are probably big enough. Larger rotors might take you too long to heat up enough to get the full power out of them. On the other hand, if like me you live in a mountainous area with 5-10+ minute descents being the norm, and weigh more than 150lbs, you may find that you're overheating rotors regularly.
Comparing the heat capacity of MTB vs. motorsports braking systems is unhelpful. The sheer mass of the rotors, calipers, and the huge volume of fluid in motorsports brakes is made possible by the amount of power that the engine creates. This all means that heat control on motorsports systems can be much greater than on a bicycle. If you're heating your brakes to the point that you're discoloring the rotor means that you're heating the fluid in your brake a lot more than is optimal, and will degrade the entire system. Yup, even the high boiling point of DOT 5.1 (260°C, assuming there's no water absorption...) can be reached on a long descent without larger and/or thicker rotors.
Added point, the same sized rotor is less effective on a 29 inch wheel compared to smaller wheels. Look at the rotor size in relative terms...
Added point, the same sized rotor is less effective on a 29 inch wheel compared to smaller wheels. Look at the rotor size in relative terms to the wheel diameter instead of absolute sizes of 180, 200, etc. mm.
@jeff.brines considering you're also a moto guy, how is braking done on a moto? One finger or two finger? What are pad clearances like on motor bikes? Etc.
You and @TEAMROBOT both bring up the necessary point of the rotational mass of the wheel system.
I'm not an offroad moto guy either, and would be interested to hear about braking methods. When I've ridden street bikes, I would two-finger brake on the front and rarely use the rear (foot) brake very much as it was easy to lock up the rear tire with so much mas shift to the front.
That's a big reason why moto brakes are so much more powerful then. We've discussed quite a few times already that you have a certain throw of the finger and a certain force that it can generate, so you're more or less limited by the amount of energy that can be input into the system. It's either pad clearance or high braking force when talking about a given rotor size.
Mechanical advantage (swing links and servo wave) improves this as it makes the behaviour more progressive, but you can't make something out of nothing - cars use brake boosters for a reason.
If motor bikes have hardly any pad clearance of course the brakes can be that much more powerful. So the easiest way to improve braking power is to run a bigger rotor...
Added point, the same sized rotor is less effective on a 29 inch wheel compared to smaller wheels. Look at the rotor size in relative terms...
Added point, the same sized rotor is less effective on a 29 inch wheel compared to smaller wheels. Look at the rotor size in relative terms to the wheel diameter instead of absolute sizes of 180, 200, etc. mm.
@jeff.brines considering you're also a moto guy, how is braking done on a moto? One finger or two finger? What are pad clearances like on motor bikes? Etc.
This makes sense. Bigger wheel = bigger lever, which in turns requires a bigger rotor to act as a bigger lever in response. All I know is that my longstanding dual piston XT brakes were NOT cutting it when I switched to 29" wheels.
I view it as disc size controlling for brake power/modulation AND thermal capacity, while disc thickness controls for thermal capacity only.
It also seems to be pretty well settled that you need more thermal capacity on the rear per articles like this and in my own experience.
With that in mind, I've settled on a 180mm 2.3mm rotor front with a 200mm 2.3mm rear on a 29er enduro bike using Hope T4V4. The hopes are pretty dang strong and wanted more modulation on the front.
I feel like I'm reading a Seb Stott/Henry Quinney article get created before my eyes.
Y'all've seen two basic principles gt raised here. Here are a couple visual aids I made to help show the relationships I see people using to help solve the OP's question.
The stars show the particular contrast being made: a brake system near it's optimum temperature giving some level of performance greater than a brake noticeably below that optimum temp. The blue dots are just some ways we might fill in the relationship for other temps. Note that this is a relationship (as the posters here are writing it and as I'm drawing it) that doesn't show data. There are no units and no numbers because this is a principle, not a data set. We think it's a true principle, and so data should look like this, but the difference is important to bear in mind.
Here's the other principle people are invoking to help answer the OP. 'Dimensions' here collapses a number of different size differences being discussed, like rotor thickness or rotor diameter. Again these aren't data but the principle is something there seems to be agreement on. So far so good. Taking it to the next step, you see people in the thread combining these two principles and saying something like (and correct me if I'm mischaracterizing you, please) that the idea here is to think about heat inputs from rider size and bike speed and especially terrain, and heat dissipation from the several different dimensional choices, so that a given bike is rolling downhill with its brake system inside the window, the goldilocks zone of not too cold and not too hot. Chapeau. Upvotes all around.
Except the OP's question, entirely reasonably, is about concrete differences between real products. Diameter differences of 20 or 40 mm. Thickness differences of 0.2 or 0.4 mm. And those specific numbers are not in the data set. The principles are 'factual' or 'scientific' or whatever you want to say, but the conclusions, e.g. 180 rotor for midwest blues and 220 rotor for steeps, are--and I'm using the kindest professional language I can muster here--undersupported by the evidence. There is nothing in the combination of the two principles that lets anyone zoom in and determine yes, the optimum window for brake performance at slower speeds vs higher speeds falls perfectly at the dimensional difference between the 180 mm rotor and the 220 mm rotor. That's pure Stott-Quinney pseudoscience. It's believable, if you happen to find it so, because it's what you might've guessed before all the wanking on about heat -- it's what you'd believe without the science! Making the whole, long, bike mag-filling word count padding effort nothing more than a performance. You can't answer the OP's question with the data provided. Cultivate the skill of saying you don't know. Don't be a science poser
I am completely on the other end of the spectrum here. Martin Maes is the only validation I can think of right now. I have done...
I am completely on the other end of the spectrum here. Martin Maes is the only validation I can think of right now. I have done quite a few Enduro races in my day (30 years wrenching, riding, and racing) and I have run 180 rotors front and rear forever for my Enduro bike. Currently on Galfer Shark rotors (standard Thickness) and Galfer Pro pads in Magura MT5 E-Stops (Just an MT5 with silver caliper piston pucks instead of black ano and stupid plastic color rings) with the HC brake lever option. I have never felt like I needed more braking power. Here in the northeast US, when it is steep, it is usually janky so 'dragging' brakes isn't a safe option, pick a braking spot, and brake hard and short, otherwise stay off the brakes. Modulation is key here. You really need to gauge the grip of the roots, rocks, etc and brake accordingly. Even with that method, I have blued the rotors on steep, long runs of tech terrain but didn't feel a dropoff in performance, if anything, they bit harder. Prior rotors I have used are Galfer Wave, Magura Storm, and Swiss Stop, all with good results. All of them blued at some point and either still in use, or tossed because they got too thin. Haven't warped a rotor in over a decade. I have used Cura 4s (still on a different bike) Codes (don't like the feel, weight, and finish of Sram brakes), and Shimanos but swore off Shimanos with the servo-wave (or whatever they call it) for the wandering bite point and too much power with poor modulation.
I am assuming that the OP is not a World Cup DHer and is likely riding the bike in his profile pic for "enduro" all-mountain, trail, blah blah. I can get behind the bending resistance of thicker rotors, but as long as you are using quality rotors and pads, I have not had heat issues that led to a performance problem. I have plenty of braking power with my little rotors and they are half (or less) of the rotating, unsprung weight of larger rotors so my suspension can follow terrain a small percentage better and I don't have to slog around weight I don't need when I have to get on the gas. I am 42, 185 pounds, 5'8" riding a Specialized Enduro for...well...enduro, big mountain...hiking trail jank riding...whatever you want to call it. Stumpy Evo is my trail bike that sees some spicy lines and that only has Magura Trail Sports with a 2-piston rear caliper and 180mm rotor! With the stock organic pads no less! Took forever for them to bed in and make full power though. Still no complaints.
My fatbike and beater hardtail get 160mm china sram knockoff rotors and they still work well when bed in properly so I'm not a rotor snob. Shit, sometimes they hit the same negative gradients as the big bikes and it is just that much extra spicy.
Not to sound like a dick but I hope most people ignore this.
1) Martin is one of one. You don't ride a bike like him...
Not to sound like a dick but I hope most people ignore this.
1) Martin is one of one. You don't ride a bike like him and neither do I.
2) According to the telemetry data I've seen, most (good) riders do in fact use their brakes for ~85% of a descent. Even Neko just noted at the WC level guys are on their brakes 80% of a run.
3) The whole point of a brake is to take kinetic energy and turn it into thermal energy. The more "room" a system has with respect to heat management, the better it will perform over longer descents. This isn't all that complicated.
4) The more a person can have confidence in their brakes without adding to hand/arm fatigue the safer they will be and more fun they'll have.
5) Nobody at a race is going "oh, this is a 900 foot descent not a 1,400 foot descent, I'll go down to a 1.8mm rotor" (or similar). If you think this is how real world privateer type racers do anything you are severely misguided. Yes, you'll have an outlier like Martin or Troy trying something weird on the brake side of things but these are guys chasing fractions of a percent and there is zero real data to suggest these wonky decisions actually paid off in the first place. Your standard everyday Joe, even the kind racing at the pro level, is much better off with more brake than they need than trying to toe some imaginary line of "baby-bear brake optimization".
As to if you'll notice a few fractions of a mm in rotor thickness, I don't know. It's all iterative at the end of the day. If I have to pick thickness or size vs weight, I'm taking the weight penalty all day long on everything but m XC bike. Size of rotor plus thickness of rotor all equals a better braking experience.
I loved Dak on the Inside Line this fall talking about how far behind he feels our brakes really are for what we do. I agree. I want brakes that are as effective for my mtb as my moto brakes are for my dirt bike. We have a little ways to go IMO.
Edit for point 5
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular belief or your own opinions. Shirking the "bigger is better" rotor mentality works for an apparent minority of people. And I am fairly certain I don't have freakishly strong index fingers.
Your point 5 seems to imply that I am suggesting some razor-thin margin where vertical feet of a descent is part of an equation to establish what braking setup you need for that particular descent. That is nowhere my posts. I stated that I have ridden and raced the same setup for years regardless of trail conditions, gradient, or descent length. I would have bumped up rotor size if there was a power or heat issue but there hasn't been. For over a decade. I may be an outlier, but I have 100% confidence in my braking setup no matter what I am dropping into and I know I am not alone riding 'baby' rotors at an decent pace and I am confident others would have the same experience if "I wish it had larger rotors" wasn't such a common refrain in MTB media.
My main point is that it is about more than just rotor size and thickness.
The missing part of your kinetic to thermal reference, friction, is the most important part of braking power. Which is why quality rotors and pads are crucial in order to ensure enough friction. I mentioned that there truly are a myriad of variables when talking about braking power and heat management and these are a couple that don't seem to get mentioned in this thread much at all. The pad material, and rotor contact surface area have a much larger impact on braking power than the thickness of the rotor.
Moto (dirtbike) brakes have been the same for decades. They are two-piston floating calipers in the front with semi-floating rotors and usually only a single-piston caliper in the rear with a solid rotor. They are far simpler than mtb brakes, there are no leverage cams employed like Shimano or SRAM, they rely on the additional friction of a massive (compared to MT
pad contact patch and thick rotors with alloy carriers to shed heat. I have seen the floating calipers freeze up and absolutely nuke the pad on one side from dragging all the time. I certainly do not want that for my MTB but there is definitely an argument for having a larger pad for MTB brakes which would be a whole new standard for the rotor contact patch. That could be a great innovation for a brand. However, I have noticed alot of the thick rotors have minimal cutouts so they are maximizing the friction potenial of the tiny pads we currently employ in MTB.
If you have heat problems to the point of brake fade or your lever is pumping up there are more solutions than simply increasing rotor thickness or size. You might need a bleed, your current pads might have alloy backing plates transfering heat to your pistons and fluid too quickly, your pads might be glazed or might simply be the wrong material for your application. You could move to higher performance pads, Galfer, Trick Stuff, MTX, Ice-tech if you are Shimano, etc. Or your rotors might not shed heat effectively and there are quite a few rotors out there now with thermal dissipation as a design function.
If you have power issues, a larger rotor isn't the only solution and rotor thickness won't add leverage. Moving to a more aggressive pad material is an option as well as rotors with a better contact patch for your pad profile. Sometimes mixing and matching caliper and rotor brands end up with a poor contact patch mate.
Lets keep our minds open about solutions and ideas. Being tribal about everything is silly.
I feel like I'm reading a Seb Stott/Henry Quinney article get created before my eyes.
Y'all've seen two basic principles gt raised here. Here are a...
I feel like I'm reading a Seb Stott/Henry Quinney article get created before my eyes.
Y'all've seen two basic principles gt raised here. Here are a couple visual aids I made to help show the relationships I see people using to help solve the OP's question.
The stars show the particular contrast being made: a brake system near it's optimum temperature giving some level of performance greater than a brake noticeably below that optimum temp. The blue dots are just some ways we might fill in the relationship for other temps. Note that this is a relationship (as the posters here are writing it and as I'm drawing it) that doesn't show data. There are no units and no numbers because this is a principle, not a data set. We think it's a true principle, and so data should look like this, but the difference is important to bear in mind.
Here's the other principle people are invoking to help answer the OP. 'Dimensions' here collapses a number of different size differences being discussed, like rotor thickness or rotor diameter. Again these aren't data but the principle is something there seems to be agreement on. So far so good. Taking it to the next step, you see people in the thread combining these two principles and saying something like (and correct me if I'm mischaracterizing you, please) that the idea here is to think about heat inputs from rider size and bike speed and especially terrain, and heat dissipation from the several different dimensional choices, so that a given bike is rolling downhill with its brake system inside the window, the goldilocks zone of not too cold and not too hot. Chapeau. Upvotes all around.
Except the OP's question, entirely reasonably, is about concrete differences between real products. Diameter differences of 20 or 40 mm. Thickness differences of 0.2 or 0.4 mm. And those specific numbers are not in the data set. The principles are 'factual' or 'scientific' or whatever you want to say, but the conclusions, e.g. 180 rotor for midwest blues and 220 rotor for steeps, are--and I'm using the kindest professional language I can muster here--undersupported by the evidence. There is nothing in the combination of the two principles that lets anyone zoom in and determine yes, the optimum window for brake performance at slower speeds vs higher speeds falls perfectly at the dimensional difference between the 180 mm rotor and the 220 mm rotor. That's pure Stott-Quinney pseudoscience. It's believable, if you happen to find it so, because it's what you might've guessed before all the wanking on about heat -- it's what you'd believe without the science! Making the whole, long, bike mag-filling word count padding effort nothing more than a performance. You can't answer the OP's question with the data provided. Cultivate the skill of saying you don't know. Don't be a science poser
I love it. Whether you love or loathe my tirade, yours was great.
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular...
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular belief or your own opinions. Shirking the "bigger is better" rotor mentality works for an apparent minority of people. And I am fairly certain I don't have freakishly strong index fingers.
Your point 5 seems to imply that I am suggesting some razor-thin margin where vertical feet of a descent is part of an equation to establish what braking setup you need for that particular descent. That is nowhere my posts. I stated that I have ridden and raced the same setup for years regardless of trail conditions, gradient, or descent length. I would have bumped up rotor size if there was a power or heat issue but there hasn't been. For over a decade. I may be an outlier, but I have 100% confidence in my braking setup no matter what I am dropping into and I know I am not alone riding 'baby' rotors at an decent pace and I am confident others would have the same experience if "I wish it had larger rotors" wasn't such a common refrain in MTB media.
My main point is that it is about more than just rotor size and thickness.
The missing part of your kinetic to thermal reference, friction, is the most important part of braking power. Which is why quality rotors and pads are crucial in order to ensure enough friction. I mentioned that there truly are a myriad of variables when talking about braking power and heat management and these are a couple that don't seem to get mentioned in this thread much at all. The pad material, and rotor contact surface area have a much larger impact on braking power than the thickness of the rotor.
Moto (dirtbike) brakes have been the same for decades. They are two-piston floating calipers in the front with semi-floating rotors and usually only a single-piston caliper in the rear with a solid rotor. They are far simpler than mtb brakes, there are no leverage cams employed like Shimano or SRAM, they rely on the additional friction of a massive (compared to MT
pad contact patch and thick rotors with alloy carriers to shed heat. I have seen the floating calipers freeze up and absolutely nuke the pad on one side from dragging all the time. I certainly do not want that for my MTB but there is definitely an argument for having a larger pad for MTB brakes which would be a whole new standard for the rotor contact patch. That could be a great innovation for a brand. However, I have noticed alot of the thick rotors have minimal cutouts so they are maximizing the friction potenial of the tiny pads we currently employ in MTB.
If you have heat problems to the point of brake fade or your lever is pumping up there are more solutions than simply increasing rotor thickness or size. You might need a bleed, your current pads might have alloy backing plates transfering heat to your pistons and fluid too quickly, your pads might be glazed or might simply be the wrong material for your application. You could move to higher performance pads, Galfer, Trick Stuff, MTX, Ice-tech if you are Shimano, etc. Or your rotors might not shed heat effectively and there are quite a few rotors out there now with thermal dissipation as a design function.
If you have power issues, a larger rotor isn't the only solution and rotor thickness won't add leverage. Moving to a more aggressive pad material is an option as well as rotors with a better contact patch for your pad profile. Sometimes mixing and matching caliper and rotor brands end up with a poor contact patch mate.
Lets keep our minds open about solutions and ideas. Being tribal about everything is silly.
No, I'm not squashing your point of view because it runs counter to popular opinion. I'm squashing it because its generally not the best way to think about brakes. You are making this way (way) too hard. For most riders on a run of the mill SRAM/Shimano OEM stoppers on a trail/enduro/DH bike you are likely going to have a better time out there with larger 200 or 220 rotors that are on the thiccc(er) side of things.
TL;DR - Go bigger if you want more power and more heat dissipation. Go thicker if you want to stop bending rotors and a little more heat management too. And of course, experiment with pads if you want! Tons of options out there and they can have a big impact on how a brake feels, sounds and wears. However, most people are going to run OEM pads because that's what the bike shop carries (and they work fine tbh).
There was nothing "tribal" about what I was saying. I'm speaking in broader generalities. You seem to have a formula that works for you, which is awesome. But your n=1 anecdote is more important for you than it is a resource for others to lean into. I feel very strongly if I were to poll most professional caliber riders, top tier riders with a lot of experience and bike testers they'd all say gravity focused bikes (trail, enduro, DH) should aim to have 200 or 220mm rotors (depending on preference) and the trend toward thicker rotors is a good one. I'm so confident on this, I'd even be willing to bet a friendly wager on it
EDIT: My point about moto was not to say we should borrow the exact engineering. My point was to say dirt bike brakes work better with more power for longer periods of time than my mountain bike brakes. That's all I was saying.
Im heavy at 6’4 250lbs and typically run TRP brakes with their 2.3mm 223mm rotors with good results.
I tried the 246mm 2.3mm Galfer rotors and it was a big fail. Halfway down a descent they would warp wildly from the heat - like 10mm out of true. I realize I’m an outlier size wise but there is DEFINITELY something to the rotor size vs. thickness ratio. I think at 223mm we are probably at the limit for 2.3mm thickness.
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular...
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular belief or your own opinions. Shirking the "bigger is better" rotor mentality works for an apparent minority of people. And I am fairly certain I don't have freakishly strong index fingers.
Your point 5 seems to imply that I am suggesting some razor-thin margin where vertical feet of a descent is part of an equation to establish what braking setup you need for that particular descent. That is nowhere my posts. I stated that I have ridden and raced the same setup for years regardless of trail conditions, gradient, or descent length. I would have bumped up rotor size if there was a power or heat issue but there hasn't been. For over a decade. I may be an outlier, but I have 100% confidence in my braking setup no matter what I am dropping into and I know I am not alone riding 'baby' rotors at an decent pace and I am confident others would have the same experience if "I wish it had larger rotors" wasn't such a common refrain in MTB media.
My main point is that it is about more than just rotor size and thickness.
The missing part of your kinetic to thermal reference, friction, is the most important part of braking power. Which is why quality rotors and pads are crucial in order to ensure enough friction. I mentioned that there truly are a myriad of variables when talking about braking power and heat management and these are a couple that don't seem to get mentioned in this thread much at all. The pad material, and rotor contact surface area have a much larger impact on braking power than the thickness of the rotor.
Moto (dirtbike) brakes have been the same for decades. They are two-piston floating calipers in the front with semi-floating rotors and usually only a single-piston caliper in the rear with a solid rotor. They are far simpler than mtb brakes, there are no leverage cams employed like Shimano or SRAM, they rely on the additional friction of a massive (compared to MT
pad contact patch and thick rotors with alloy carriers to shed heat. I have seen the floating calipers freeze up and absolutely nuke the pad on one side from dragging all the time. I certainly do not want that for my MTB but there is definitely an argument for having a larger pad for MTB brakes which would be a whole new standard for the rotor contact patch. That could be a great innovation for a brand. However, I have noticed alot of the thick rotors have minimal cutouts so they are maximizing the friction potenial of the tiny pads we currently employ in MTB.
If you have heat problems to the point of brake fade or your lever is pumping up there are more solutions than simply increasing rotor thickness or size. You might need a bleed, your current pads might have alloy backing plates transfering heat to your pistons and fluid too quickly, your pads might be glazed or might simply be the wrong material for your application. You could move to higher performance pads, Galfer, Trick Stuff, MTX, Ice-tech if you are Shimano, etc. Or your rotors might not shed heat effectively and there are quite a few rotors out there now with thermal dissipation as a design function.
If you have power issues, a larger rotor isn't the only solution and rotor thickness won't add leverage. Moving to a more aggressive pad material is an option as well as rotors with a better contact patch for your pad profile. Sometimes mixing and matching caliper and rotor brands end up with a poor contact patch mate.
Lets keep our minds open about solutions and ideas. Being tribal about everything is silly.
No, I'm not squashing your point of view because it runs counter to popular opinion. I'm squashing it because its generally not the best way to...
No, I'm not squashing your point of view because it runs counter to popular opinion. I'm squashing it because its generally not the best way to think about brakes. You are making this way (way) too hard. For most riders on a run of the mill SRAM/Shimano OEM stoppers on a trail/enduro/DH bike you are likely going to have a better time out there with larger 200 or 220 rotors that are on the thiccc(er) side of things.
TL;DR - Go bigger if you want more power and more heat dissipation. Go thicker if you want to stop bending rotors and a little more heat management too. And of course, experiment with pads if you want! Tons of options out there and they can have a big impact on how a brake feels, sounds and wears. However, most people are going to run OEM pads because that's what the bike shop carries (and they work fine tbh).
There was nothing "tribal" about what I was saying. I'm speaking in broader generalities. You seem to have a formula that works for you, which is awesome. But your n=1 anecdote is more important for you than it is a resource for others to lean into. I feel very strongly if I were to poll most professional caliber riders, top tier riders with a lot of experience and bike testers they'd all say gravity focused bikes (trail, enduro, DH) should aim to have 200 or 220mm rotors (depending on preference) and the trend toward thicker rotors is a good one. I'm so confident on this, I'd even be willing to bet a friendly wager on it
EDIT: My point about moto was not to say we should borrow the exact engineering. My point was to say dirt bike brakes work better with more power for longer periods of time than my mountain bike brakes. That's all I was saying.
I conceed. You are spot on here. I enjoy making things more complicated! But I like my bike simpler. I believe having the best rotors and pads with the least unsprung, rotating weight is a worthy balance to strive for. Mostly everyone likes sensitive suspension and any unsprung weight reduction will help that. Some of these thicker rotors are brutally heavy on top of the additional spacers and bolts required to mount them. Older calipers also might not be compatible. I am also mullet, so my 180 rotor has more leverage on my little wheel than a 29er so I effectively have a "larger" rotor on the rear relative wheel size. I am certainly being a contrarian here, and it is a much simpler (and possibly cheaper) solution to simply click 'buy' on larger rotors and be done with it for people, especially those that are riding 99% with gravity rather than against it or competing against a clock. "Enduro racing still includes pedalling in places on many courses much to everyone's dismay.
You got me thinking about moto in terms of scraping area. Scraping area doesn't necessarily equal power but it does aid consistency and modulation. (measurements are rough and not accounting for radiused edges on the pads)
2020 CRF450 front pad surface area: 1809sq.mm per pad, 3618 for the pair
Rear pad SA: 2220 (pair)
Shimano 2-pot: 400sq.mm per pad, 800 pair
Formula Cura 4: 552sq.mm per pad, 1104 total
Assuming the average system weight for a moto is 240lbs bike, and 160lbs rider (400 total), and 35lbs bike, 160 rider (195 total) for mtb we get the following:
CRF450 front brake: 9.045sq.mm of scraping surface per pound of system weight.
CRF450 rear brake: 5.55sq.mm of scraping surface per pound of system weight
Shimano 2-pot: 4.1sq.mm per pound of system weight
Cura 4 (similar pad size to code): 5.66sq.mm per pound.
With MTB, rider weight more heavily skews this ratio so that's a big deal. These numbers would somewhat explain the perceived consistency of moto brakes, however, a quick scan of moto forums reveals alot of bitching about their brakes as well. My experience with moto (to a lesser extent) and sportbikes, is that the braking is very predictable in all situations.
Buuuut, to increase scraping area we need to increase caliper piston size which means we also need to increase master cylinder piston size as well as the reservoir size and then our teensy-weensy brake lines (a size standard established by cable brake housing sometime during the caveman days) are the choking point for this increased fluid flow requirment so our hoses need to be larger but then the stupid internal routing ports in all our frames are too small so we all need to buy new bikes...dammit!
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular...
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular belief or your own opinions. Shirking the "bigger is better" rotor mentality works for an apparent minority of people. And I am fairly certain I don't have freakishly strong index fingers.
Your point 5 seems to imply that I am suggesting some razor-thin margin where vertical feet of a descent is part of an equation to establish what braking setup you need for that particular descent. That is nowhere my posts. I stated that I have ridden and raced the same setup for years regardless of trail conditions, gradient, or descent length. I would have bumped up rotor size if there was a power or heat issue but there hasn't been. For over a decade. I may be an outlier, but I have 100% confidence in my braking setup no matter what I am dropping into and I know I am not alone riding 'baby' rotors at an decent pace and I am confident others would have the same experience if "I wish it had larger rotors" wasn't such a common refrain in MTB media.
My main point is that it is about more than just rotor size and thickness.
The missing part of your kinetic to thermal reference, friction, is the most important part of braking power. Which is why quality rotors and pads are crucial in order to ensure enough friction. I mentioned that there truly are a myriad of variables when talking about braking power and heat management and these are a couple that don't seem to get mentioned in this thread much at all. The pad material, and rotor contact surface area have a much larger impact on braking power than the thickness of the rotor.
Moto (dirtbike) brakes have been the same for decades. They are two-piston floating calipers in the front with semi-floating rotors and usually only a single-piston caliper in the rear with a solid rotor. They are far simpler than mtb brakes, there are no leverage cams employed like Shimano or SRAM, they rely on the additional friction of a massive (compared to MT
pad contact patch and thick rotors with alloy carriers to shed heat. I have seen the floating calipers freeze up and absolutely nuke the pad on one side from dragging all the time. I certainly do not want that for my MTB but there is definitely an argument for having a larger pad for MTB brakes which would be a whole new standard for the rotor contact patch. That could be a great innovation for a brand. However, I have noticed alot of the thick rotors have minimal cutouts so they are maximizing the friction potenial of the tiny pads we currently employ in MTB.
If you have heat problems to the point of brake fade or your lever is pumping up there are more solutions than simply increasing rotor thickness or size. You might need a bleed, your current pads might have alloy backing plates transfering heat to your pistons and fluid too quickly, your pads might be glazed or might simply be the wrong material for your application. You could move to higher performance pads, Galfer, Trick Stuff, MTX, Ice-tech if you are Shimano, etc. Or your rotors might not shed heat effectively and there are quite a few rotors out there now with thermal dissipation as a design function.
If you have power issues, a larger rotor isn't the only solution and rotor thickness won't add leverage. Moving to a more aggressive pad material is an option as well as rotors with a better contact patch for your pad profile. Sometimes mixing and matching caliper and rotor brands end up with a poor contact patch mate.
Lets keep our minds open about solutions and ideas. Being tribal about everything is silly.
No, I'm not squashing your point of view because it runs counter to popular opinion. I'm squashing it because its generally not the best way to...
No, I'm not squashing your point of view because it runs counter to popular opinion. I'm squashing it because its generally not the best way to think about brakes. You are making this way (way) too hard. For most riders on a run of the mill SRAM/Shimano OEM stoppers on a trail/enduro/DH bike you are likely going to have a better time out there with larger 200 or 220 rotors that are on the thiccc(er) side of things.
TL;DR - Go bigger if you want more power and more heat dissipation. Go thicker if you want to stop bending rotors and a little more heat management too. And of course, experiment with pads if you want! Tons of options out there and they can have a big impact on how a brake feels, sounds and wears. However, most people are going to run OEM pads because that's what the bike shop carries (and they work fine tbh).
There was nothing "tribal" about what I was saying. I'm speaking in broader generalities. You seem to have a formula that works for you, which is awesome. But your n=1 anecdote is more important for you than it is a resource for others to lean into. I feel very strongly if I were to poll most professional caliber riders, top tier riders with a lot of experience and bike testers they'd all say gravity focused bikes (trail, enduro, DH) should aim to have 200 or 220mm rotors (depending on preference) and the trend toward thicker rotors is a good one. I'm so confident on this, I'd even be willing to bet a friendly wager on it
EDIT: My point about moto was not to say we should borrow the exact engineering. My point was to say dirt bike brakes work better with more power for longer periods of time than my mountain bike brakes. That's all I was saying.
I conceed. You are spot on here. I enjoy making things more complicated! But I like my bike simpler. I believe having the best rotors and...
I conceed. You are spot on here. I enjoy making things more complicated! But I like my bike simpler. I believe having the best rotors and pads with the least unsprung, rotating weight is a worthy balance to strive for. Mostly everyone likes sensitive suspension and any unsprung weight reduction will help that. Some of these thicker rotors are brutally heavy on top of the additional spacers and bolts required to mount them. Older calipers also might not be compatible. I am also mullet, so my 180 rotor has more leverage on my little wheel than a 29er so I effectively have a "larger" rotor on the rear relative wheel size. I am certainly being a contrarian here, and it is a much simpler (and possibly cheaper) solution to simply click 'buy' on larger rotors and be done with it for people, especially those that are riding 99% with gravity rather than against it or competing against a clock. "Enduro racing still includes pedalling in places on many courses much to everyone's dismay.
You got me thinking about moto in terms of scraping area. Scraping area doesn't necessarily equal power but it does aid consistency and modulation. (measurements are rough and not accounting for radiused edges on the pads)
2020 CRF450 front pad surface area: 1809sq.mm per pad, 3618 for the pair
Rear pad SA: 2220 (pair)
Shimano 2-pot: 400sq.mm per pad, 800 pair
Formula Cura 4: 552sq.mm per pad, 1104 total
Assuming the average system weight for a moto is 240lbs bike, and 160lbs rider (400 total), and 35lbs bike, 160 rider (195 total) for mtb we get the following:
CRF450 front brake: 9.045sq.mm of scraping surface per pound of system weight.
CRF450 rear brake: 5.55sq.mm of scraping surface per pound of system weight
Shimano 2-pot: 4.1sq.mm per pound of system weight
Cura 4 (similar pad size to code): 5.66sq.mm per pound.
With MTB, rider weight more heavily skews this ratio so that's a big deal. These numbers would somewhat explain the perceived consistency of moto brakes, however, a quick scan of moto forums reveals alot of bitching about their brakes as well. My experience with moto (to a lesser extent) and sportbikes, is that the braking is very predictable in all situations.
Buuuut, to increase scraping area we need to increase caliper piston size which means we also need to increase master cylinder piston size as well as the reservoir size and then our teensy-weensy brake lines (a size standard established by cable brake housing sometime during the caveman days) are the choking point for this increased fluid flow requirment so our hoses need to be larger but then the stupid internal routing ports in all our frames are too small so we all need to buy new bikes...dammit!
Fun stuff.
Not a moto guy but commuted on a street bike for a while.
One key difference might be intensity of use. If you’re riding steeps on an MTB you’re on the brakes in some fashion nearly constantly for the whole track (5min?).
Gravity is our throttle and it’s always WIDE OPEN.
Hey Guys!
Replying to some comments and adding mine:
I am just parted ways with my Formula Cura 4 brakes. As per many websites, some rotor sizes are 2.3mm, like the 203mm size, but some sites state the 203mm is 2.0mm thick.. I am speaking of their Monolitic rotors.
As I found out the 180mm rotor was only like 1.8 or 1.9 thick. This is why I always felt longer lever throw on my Cura 2 and later Cura 4 on the rear too.
I bought a TRP 2.3mm rotor for the rear, also 180mm (Niner Rip9 RDO accepts 180 max at the rear due to clearance with the swingarm) and with new pads, and pistons pushed back all the way in to their bores, it was such a tight fit I opted not to run them.
I had issues with the lever, so I rebuilt it, then tha caliper, although I rebuilt the caliper it still had some issues, so those brakes are gone.
In came the Hayes Dominion A4-s. Original rotors should be 1.95mm, but I had a brand new set of Magura Storm HC discs 203/180, so I opted to run those with the Hayes. They fit well, and have enough pad retraction that it doesnt rub after setting up the brake. It seems the pad/rotor surface matches as well. I saw some guys in forums using Magura Disc with Hayes Dominions too.
Hayes also compatible with Galfer Shark 2.0mm rotors, the Atherton Racing Team use this combo for a very long time. They are on Hayes brakes since they ditched the Trickstuff Maxima brakes.
Other out of the topic stuff, on adaptors.
Hayes adaptors, pretty hard to find (at least in Europe, I am from Hungary) and Shimano PM 203 adaptor (from 180 to 203 PM) do fit the large caliper of the Dominion. At the rear, neither the Formula PM 180 (160 to 180) nor the Shimano fit. So I searched and the Magura QM40 does fit, so I have one coming towards me.
Hope I helped some of you
Rotor bluing not cause for concern with quality rotors and is standard in motorsports. For automotive road racing, bluing the rotor when bedding in new brakes is when you know the bedding procedure is done properly. Rotors were always blue on all of my race bikes back when I roadraced motorcycles. Cheap rotors might have inconsistencies in the material so they might warp under such heat, hence the importance of quality rotors.
It seems there is less expertise or interest in learning here. Instead those searching for comfirmation bias of their purchases.
If you think I recommended XC brakes for enduro bikes, then you didn't read the posts. Having far too much braking potential than what you need is also stupid. Debating parts selection on a mountain bike is based on performance, and just like with everything in competition, it is about optimization and efficiency. If you are plodding along the trails and want massive braking power, go for it. That is a subjective opinion. But when racing a clock, I want exactly what I need for optimum performance, nothing more and nothing less, and that is not an uncommon demand for racing.
There is a big difference between the surface slightly bluing on a carbon steel rotor (on a car) during bedding in and turning an entire rotor dark blue on a MTB. A similar bedded in look on a MTB rotor (let's call it light blue) is not cause for concern, similar to cars. Deep bluing could be.
MTB rotors being much thinner and stainless (most rotors on cars are carbon steel, I don't know about motorcycle rotors) are much less durable.
My experience with changing heat treatment is from my day job, firearms manufacturing. If you turn stainless steel deep blue you have affected any heat treatment that part had previously.
Does that practically effect MTB rotors, in the real world? Is the change enough to matter? Maybe / maybe not.
My point was mainly that if you are bluing your rotors on your MTB, it is a sign you could use more thermal capacity so larger / thicker rotors are likely a good idea.
Not to sound like a dick but I hope most people ignore this.
1) Martin is one of one. You don't ride a bike like him and neither do I.
2) According to the telemetry data I've seen, most (good) riders do in fact use their brakes for ~85% of a descent. Even Neko just noted at the WC level guys are on their brakes 80% of a run.
3) The whole point of a brake is to take kinetic energy and turn it into thermal energy. The more "room" a system has with respect to heat management, the better it will perform over longer descents. This isn't all that complicated.
4) The more a person can have confidence in their brakes without adding to hand/arm fatigue the safer they will be and more fun they'll have.
5) Nobody at a race is going "oh, this is a 900 foot descent not a 1,400 foot descent, I'll go down to a 1.8mm rotor" (or similar). If you think this is how real world privateer type racers do anything you are severely misguided. Yes, you'll have an outlier like Martin or Troy trying something weird on the brake side of things but these are guys chasing fractions of a percent and there is zero real data to suggest these wonky decisions actually paid off in the first place. Your standard everyday Joe, even the kind racing at the pro level, is much better off with more brake than they need than trying to toe some imaginary line of "baby-bear brake optimization".
As to if you'll notice a few fractions of a mm in rotor thickness, I don't know. It's all iterative at the end of the day. If I have to pick thickness or size vs weight, I'm taking the weight penalty all day long on everything but m XC bike. Size of rotor plus thickness of rotor all equals a better braking experience.
I loved Dak on the Inside Line this fall talking about how far behind he feels our brakes really are for what we do. I agree. I want brakes that are as effective for my mtb as my moto brakes are for my dirt bike. We have a little ways to go IMO.
Edit for point 5
If you're commenting on a vital forum post I'm pretty sure you're not a pro racer who would be able to actually notice 20-50 grams saved on 180mm rotors. You can't have too much braking power on an enduro / trail bike, however you can have an inexperienced "racer" who doesn't know how to properly use his brakes. More braking power / mechanical advantage from larger discs or better brakes means less force required on the finger and usually less arm fatigue.
Are the 220’s noticeably more jangly than 200? Ie when you bounce through a rock garden do you hear the cling-cling-cling noise? I hate that sound
Mentioning Codes specifically, R feels like garbage to me, RSC works. I'd rather have 180 mm rotors on RSC brakes than 220 mm rotors on R brakes. Because of feel alone.
Worth mentioning that brake power is relative to rotating weight. As your rim, tire, and potentially tire insert get bigger and heavier, your wheel is significantly harder to stop, which necessitates bigger rotors. That sounds a little conspiracy hat-ty, but it's real. I felt this as I upgraded to 29" from 27.5", and as I started moving towards downhill tires and later inserts on my trail bikes, and I believe this is why 4-piston brakes are now standard on trail and even XC bikes, when 2 piston brakes were fine on many 26" enduro bikes. I'd also bet my bottom dollar that 180mm rotor guy from Maine is on EXO or EXO+ tires, no inserts, and maybe even carbon rims.
Added point, the same sized rotor is less effective on a 29 inch wheel compared to smaller wheels. Look at the rotor size in relative terms to the wheel diameter instead of absolute sizes of 180, 200, etc. mm.
@jeff.brines considering you're also a moto guy, how is braking done on a moto? One finger or two finger? What are pad clearances like on motor bikes? Etc.
Certainly not Martin Maes or Troy Brosnan level of rider here, and most likely not near @jeff.brines either, but here's what I have found in 26 years as a bike mechanic, 30+ years of riding offroad.
If you're primarily riding in terrain that has short descents or very short braking zones, 180mm rotors are probably big enough. Larger rotors might take you too long to heat up enough to get the full power out of them. On the other hand, if like me you live in a mountainous area with 5-10+ minute descents being the norm, and weigh more than 150lbs, you may find that you're overheating rotors regularly.
Comparing the heat capacity of MTB vs. motorsports braking systems is unhelpful. The sheer mass of the rotors, calipers, and the huge volume of fluid in motorsports brakes is made possible by the amount of power that the engine creates. This all means that heat control on motorsports systems can be much greater than on a bicycle. If you're heating your brakes to the point that you're discoloring the rotor means that you're heating the fluid in your brake a lot more than is optimal, and will degrade the entire system. Yup, even the high boiling point of DOT 5.1 (260°C, assuming there's no water absorption...) can be reached on a long descent without larger and/or thicker rotors.
You and @TEAMROBOT both bring up the necessary point of the rotational mass of the wheel system.
I'm not an offroad moto guy either, and would be interested to hear about braking methods. When I've ridden street bikes, I would two-finger brake on the front and rarely use the rear (foot) brake very much as it was easy to lock up the rear tire with so much mas shift to the front.
On a moto- single finger is plenty to do a stoppie.
Pad clearance is about zero- wheel rotates a few times when spun off the ground… Not acceptable for a bicycle.
That's a big reason why moto brakes are so much more powerful then. We've discussed quite a few times already that you have a certain throw of the finger and a certain force that it can generate, so you're more or less limited by the amount of energy that can be input into the system. It's either pad clearance or high braking force when talking about a given rotor size.
Mechanical advantage (swing links and servo wave) improves this as it makes the behaviour more progressive, but you can't make something out of nothing - cars use brake boosters for a reason.
If motor bikes have hardly any pad clearance of course the brakes can be that much more powerful. So the easiest way to improve braking power is to run a bigger rotor...
This makes sense. Bigger wheel = bigger lever, which in turns requires a bigger rotor to act as a bigger lever in response. All I know is that my longstanding dual piston XT brakes were NOT cutting it when I switched to 29" wheels.
I view it as disc size controlling for brake power/modulation AND thermal capacity, while disc thickness controls for thermal capacity only.
It also seems to be pretty well settled that you need more thermal capacity on the rear per articles like this and in my own experience.
With that in mind, I've settled on a 180mm 2.3mm rotor front with a 200mm 2.3mm rear on a 29er enduro bike using Hope T4V4. The hopes are pretty dang strong and wanted more modulation on the front.
I feel like I'm reading a Seb Stott/Henry Quinney article get created before my eyes.
Y'all've seen two basic principles gt raised here. Here are a couple visual aids I made to help show the relationships I see people using to help solve the OP's question.
Here's the other principle people are invoking to help answer the OP. 'Dimensions' here collapses a number of different size differences being discussed, like rotor thickness or rotor diameter. Again these aren't data but the principle is something there seems to be agreement on. So far so good. Taking it to the next step, you see people in the thread combining these two principles and saying something like (and correct me if I'm mischaracterizing you, please) that the idea here is to think about heat inputs from rider size and bike speed and especially terrain, and heat dissipation from the several different dimensional choices, so that a given bike is rolling downhill with its brake system inside the window, the goldilocks zone of not too cold and not too hot. Chapeau. Upvotes all around.
Except the OP's question, entirely reasonably, is about concrete differences between real products. Diameter differences of 20 or 40 mm. Thickness differences of 0.2 or 0.4 mm. And those specific numbers are not in the data set. The principles are 'factual' or 'scientific' or whatever you want to say, but the conclusions, e.g. 180 rotor for midwest blues and 220 rotor for steeps, are--and I'm using the kindest professional language I can muster here--undersupported by the evidence. There is nothing in the combination of the two principles that lets anyone zoom in and determine yes, the optimum window for brake performance at slower speeds vs higher speeds falls perfectly at the dimensional difference between the 180 mm rotor and the 220 mm rotor. That's pure Stott-Quinney pseudoscience. It's believable, if you happen to find it so, because it's what you might've guessed before all the wanking on about heat -- it's what you'd believe without the science! Making the whole, long, bike mag-filling word count padding effort nothing more than a performance. You can't answer the OP's question with the data provided. Cultivate the skill of saying you don't know. Don't be a science poser
God I love you bunch of nerds.
To summarize:
The heavier (you + bike), faster (you) or steeper terrain- You benefit from larger and thicker rotors.
If you are lighter,ride flatter terrain- You can get away with smaller and thinner rotors.
Let's go back to rim brakes, no circle on a bike is bigger than a wheel! Psst... 220mm disks.
true, some of the shit we used to ride down on Cantilever and V-Brakes makes me wonder how I'm alive today.
These "youth" don't know how good they have it.
Ever ride Canti's in the rain..... JESUS TAKE THE WHEEL!
Like this...
https://www.youtube.com/watch?v=djm3OF0C-R4
maybe 20 years after seeing this on TV I rode the trail for the fist time myself and could not believe what these people were doing on those brakes.
It didn't come off dickish but it also isn't productive to attempt to broadly squash a point of view simply because it runs counter to popular belief or your own opinions. Shirking the "bigger is better" rotor mentality works for an apparent minority of people. And I am fairly certain I don't have freakishly strong index fingers.
Your point 5 seems to imply that I am suggesting some razor-thin margin where vertical feet of a descent is part of an equation to establish what braking setup you need for that particular descent. That is nowhere my posts. I stated that I have ridden and raced the same setup for years regardless of trail conditions, gradient, or descent length. I would have bumped up rotor size if there was a power or heat issue but there hasn't been. For over a decade. I may be an outlier, but I have 100% confidence in my braking setup no matter what I am dropping into and I know I am not alone riding 'baby' rotors at an decent pace and I am confident others would have the same experience if "I wish it had larger rotors" wasn't such a common refrain in MTB media.
My main point is that it is about more than just rotor size and thickness.
The missing part of your kinetic to thermal reference, friction, is the most important part of braking power. Which is why quality rotors and pads are crucial in order to ensure enough friction. I mentioned that there truly are a myriad of variables when talking about braking power and heat management and these are a couple that don't seem to get mentioned in this thread much at all. The pad material, and rotor contact surface area have a much larger impact on braking power than the thickness of the rotor.
Moto (dirtbike) brakes have been the same for decades. They are two-piston floating calipers in the front with semi-floating rotors and usually only a single-piston caliper in the rear with a solid rotor. They are far simpler than mtb brakes, there are no leverage cams employed like Shimano or SRAM, they rely on the additional friction of a massive (compared to MT
pad contact patch and thick rotors with alloy carriers to shed heat. I have seen the floating calipers freeze up and absolutely nuke the pad on one side from dragging all the time. I certainly do not want that for my MTB but there is definitely an argument for having a larger pad for MTB brakes which would be a whole new standard for the rotor contact patch. That could be a great innovation for a brand. However, I have noticed alot of the thick rotors have minimal cutouts so they are maximizing the friction potenial of the tiny pads we currently employ in MTB.
If you have heat problems to the point of brake fade or your lever is pumping up there are more solutions than simply increasing rotor thickness or size. You might need a bleed, your current pads might have alloy backing plates transfering heat to your pistons and fluid too quickly, your pads might be glazed or might simply be the wrong material for your application. You could move to higher performance pads, Galfer, Trick Stuff, MTX, Ice-tech if you are Shimano, etc. Or your rotors might not shed heat effectively and there are quite a few rotors out there now with thermal dissipation as a design function.
If you have power issues, a larger rotor isn't the only solution and rotor thickness won't add leverage. Moving to a more aggressive pad material is an option as well as rotors with a better contact patch for your pad profile. Sometimes mixing and matching caliper and rotor brands end up with a poor contact patch mate.
Lets keep our minds open about solutions and ideas. Being tribal about everything is silly.
I love it. Whether you love or loathe my tirade, yours was great.
Whoa.
No, I'm not squashing your point of view because it runs counter to popular opinion. I'm squashing it because its generally not the best way to think about brakes. You are making this way (way) too hard. For most riders on a run of the mill SRAM/Shimano OEM stoppers on a trail/enduro/DH bike you are likely going to have a better time out there with larger 200 or 220 rotors that are on the thiccc(er) side of things.
TL;DR - Go bigger if you want more power and more heat dissipation. Go thicker if you want to stop bending rotors and a little more heat management too. And of course, experiment with pads if you want! Tons of options out there and they can have a big impact on how a brake feels, sounds and wears. However, most people are going to run OEM pads because that's what the bike shop carries (and they work fine tbh).
There was nothing "tribal" about what I was saying. I'm speaking in broader generalities. You seem to have a formula that works for you, which is awesome. But your n=1 anecdote is more important for you than it is a resource for others to lean into. I feel very strongly if I were to poll most professional caliber riders, top tier riders with a lot of experience and bike testers they'd all say gravity focused bikes (trail, enduro, DH) should aim to have 200 or 220mm rotors (depending on preference) and the trend toward thicker rotors is a good one. I'm so confident on this, I'd even be willing to bet a friendly wager on it
EDIT: My point about moto was not to say we should borrow the exact engineering. My point was to say dirt bike brakes work better with more power for longer periods of time than my mountain bike brakes. That's all I was saying.
Im heavy at 6’4 250lbs and typically run TRP brakes with their 2.3mm 223mm rotors with good results.
I tried the 246mm 2.3mm Galfer rotors and it was a big fail. Halfway down a descent they would warp wildly from the heat - like 10mm out of true. I realize I’m an outlier size wise but there is DEFINITELY something to the rotor size vs. thickness ratio. I think at 223mm we are probably at the limit for 2.3mm thickness.
I conceed. You are spot on here. I enjoy making things more complicated! But I like my bike simpler. I believe having the best rotors and pads with the least unsprung, rotating weight is a worthy balance to strive for. Mostly everyone likes sensitive suspension and any unsprung weight reduction will help that. Some of these thicker rotors are brutally heavy on top of the additional spacers and bolts required to mount them. Older calipers also might not be compatible. I am also mullet, so my 180 rotor has more leverage on my little wheel than a 29er so I effectively have a "larger" rotor on the rear relative wheel size. I am certainly being a contrarian here, and it is a much simpler (and possibly cheaper) solution to simply click 'buy' on larger rotors and be done with it for people, especially those that are riding 99% with gravity rather than against it or competing against a clock. "Enduro racing still includes pedalling in places on many courses much to everyone's dismay.
You got me thinking about moto in terms of scraping area. Scraping area doesn't necessarily equal power but it does aid consistency and modulation. (measurements are rough and not accounting for radiused edges on the pads)
2020 CRF450 front pad surface area: 1809sq.mm per pad, 3618 for the pair
Rear pad SA: 2220 (pair)
Shimano 2-pot: 400sq.mm per pad, 800 pair
Formula Cura 4: 552sq.mm per pad, 1104 total
Assuming the average system weight for a moto is 240lbs bike, and 160lbs rider (400 total), and 35lbs bike, 160 rider (195 total) for mtb we get the following:
CRF450 front brake: 9.045sq.mm of scraping surface per pound of system weight.
CRF450 rear brake: 5.55sq.mm of scraping surface per pound of system weight
Shimano 2-pot: 4.1sq.mm per pound of system weight
Cura 4 (similar pad size to code): 5.66sq.mm per pound.
With MTB, rider weight more heavily skews this ratio so that's a big deal. These numbers would somewhat explain the perceived consistency of moto brakes, however, a quick scan of moto forums reveals alot of bitching about their brakes as well. My experience with moto (to a lesser extent) and sportbikes, is that the braking is very predictable in all situations.
Buuuut, to increase scraping area we need to increase caliper piston size which means we also need to increase master cylinder piston size as well as the reservoir size and then our teensy-weensy brake lines (a size standard established by cable brake housing sometime during the caveman days) are the choking point for this increased fluid flow requirment so our hoses need to be larger but then the stupid internal routing ports in all our frames are too small so we all need to buy new bikes...dammit!
Fun stuff.
Not a moto guy but commuted on a street bike for a while.
One key difference might be intensity of use. If you’re riding steeps on an MTB you’re on the brakes in some fashion nearly constantly for the whole track (5min?).
Gravity is our throttle and it’s always WIDE OPEN.
THIS!!! Even if the canti's "worked", the superball rubber narrow tires wouldn't do much anyway.
I don't think Jesus could help at that point.
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