Brake Rotor thickness vs size talk

I think the thicker rotors have a stiffer feel when braking at the lever, larger rotors offer more bite and consistency from heat over the run.

Personally I run 200 or 203 front TRP 2.3 with a pad that has less bite(like red Hope).  Then 220-223 rear 2.3 rotor. Either TRP or Galfer Shark.  These offer more bite and power.  

This combination gives me the best usable braking power.  I choose for less bite in the front so I can drag the brake without locking it or knifing the front, this also keeps the suspension to pitching dramatically and losing balance coming into corners.

Just curious here... With these huge rotor sizes, are we talking DH bikes? Or are you guys running them on enduro or trail bikes? If so it seems like overkill and very dangerous for rock strikes damaging your rotors.

I run Galfer's shark rotors: 220mm up front and 200 rear on a NP Giga. Love them. To me, the more powerful the brake the better. It is of course a very personal thing, but for me the brake feel, and being confident with them is the most important aspect of any part of bike set-up. I'm able to ride around other poor set up issues but I don't ride confidently if the brakes are shite. I have never felt over-braked, never had any issues with fork diving or tyres breaking traction/front locking. I also find it less fatiguing as I need less power on the lever to get a decent amount of slowing- esp in winter, compared to brakes where you have to really yank on the levers to get power into them. Not sure I have ever hit a rotor on a rock either - but then most of my riding is in Ireland and Scotland, so not the rockiest of terrain compared to some places.

Edit: to answer the OP's actual question - to me a larger diameter gives more powerful braking, but a thicker rotor is less likely to deform and warp, and will deal with heat better on longer descents. Non-scientific opinion there, but that's how I see it. Makes sense if you're going bigger to go thicker too.

Increasing rotor mass increases thermal capacity, that works both for thicker and/ or larger diameter rotors. Generally this is a positive but taken to the extreme it can mean that the pads and rotors don't reach effective operating temperature. Think xc bike running 2.3mm thick 220 diameter rotors. For most people this isn't a problem. 

Thicker rotors will also feel more responsive / have less dead stroke on a lot of brakes. In my experience thicker rotors also stay true better.

Larger diameter rotors also increase the leverage of the disc. This increases bite and overall power. Mountain bike disc brakes are the only place I've ever seen rotor size alone discussed as a tool to increase braking power.

All this, 100%. 
 

I have 9” / 8” rotors on my big eeb, the thick TRPs. Using those MTX carbon/metal pads and they are so sick. BUT: they really do need to get to temp before they work, makes me appreciate why more and more racers are using resins…no brakes for the first minute of Fort William or whatever. I’d be dead. 
 

but yeah: I’ve never felt over-braked and I doubt I’ll ever get there. Actual fast people obviously feel differently. 

If you like the 220 rotors you have, I would not recommend going down in rotor size at all. If you'd like to mess with 2.3mm rotors, get them in a 220 size. It sounds like you're picky about brake feel (which is great by the way, no shade) and I think you're going to immediately notice the lack of power if you go down in rotor size. I certainly did.

For those going to thicker disks are you rebleeding your calipers with thicker blocks to maintain rotor and piston gap/caliper throw?

On my codes there's about 1mm clearance on either side of the disk. Centerline at 1.8mm to something like the TRP at 2.3mm eats up a lot of that space. Even with bite adjustment a lot of the range would not be unusable. Right?

If you reset your pistons, pad retract is always relative to the braking surface so you have the same pad clearance regardless of rotor thickness. Increasing rotor thickness will only impact the clearance/dead stroke if you don’t reset the pistons, but over time as your pads wear it will work its way to the same spot. 

The one issue with going up to 220s I've noticed is that they tend to warp easier (at least the shoddy HS2s I've been using).  The 200s tend to stay a bit straighter for me.  Plus 220 and metallic pads definitely take longer to get up to temperature.

Coming in a little late, and others have essentially said this, but larger diameter rotors will give you greater power and heat management than sizing down but going thicker.

The 2.3mm thick rotors add additional heat management, but I think the more important thing is bending/ warping resistance.

@Big Bird- I have been using 203mm rotors for a couple of years on my 167/170mm Knolly Chilcotin. I've never felt like they're too much, and while I have definitely hit rocks with them the 2.3mm thick rotors are none the worse for wear.

Need to reiterate the comment about brakes getting up to temp. 
If you don't live in a place with mountains or 'real' descents, you may not be getting big ass rotors up to temp. 
I have seen people in the Midwest (USA), following the cool trend and running thicc 200 or 220mm rotors and their bike never sees more than a 20 second not-so-steep descent. Those brakes are never getting up to temp and therefore full power. They'd be better off with some 160mm or 180mm HS2s or similar. Good balance between bit thicker than old school and not so large that they won't get up to temp. On most Midwest descents (not steep, under 30 seconds) a 160mm HS2 (2.0mm) rotor will provide as much power (because it gets up to temp) and better feel than a 200mm 2.3mm rotor. 

Even in the mountains, if it's cold (<45deg) and wet I need a solidly steep descent that I can drag the brakes for a bit, to get them up to temp. My 200mm HS2s have noticeably less bite and power until they heat up. I don't weigh a lot though. In the summer months they get hot quicker and stay hot so I never really notice it. 

Wet NW winter: these mtx golds are runaway train whistles for the first bit. It’s remarkable how drastic the change is when they’re up to temp. Love them!

That’d me nuts to never be able to heat them up. Overbraked so far you’re underbaked. 

I would be inclined to size for power and brake performance you want (ie. diameter) and use the thickness to manage heat if necessary.

Braking make 3mm thick rotors. I have one on the rear in 180mm. Tried 203mm but felt it was too grabby so got the 180mm thicker rotor. Did have to file down my shimano rear caliper a tad to make it fit .

https://www.lordgun.com/braking-wave-fix-3-mm-disc-rotor-1

Whoa. Did not know 3mm thick rotors existed. That's getting close to double the industry standard of 1.8mm.

Aren't hope vented rotors also 3 mm thick? In either case, I'm guessing caliper width might become an issue with rotors that thick. At least Hope's were only compatible with their calipers. 

Hope Vented are 3.3mm! They say they only fit the V4 calipers.I have smoked 203mm rotors but only 1.8mm Shimano ones in the rear on hot days and steeps.

I will look at the Hope 2.3mm ones on my next build coming up. Saint Calipers could benefit with the feel at initiation using a thicker rotor.

From a compliance perspective, more fluid in the caliper=squishier brake lever feel, so a good reason to change rotor thickness might be to get preferred lever compliance.

I rode Hope Vented rotors in 203mm for a whole season & those where great never had any bad things to report, they never warped no matter how hot they got and the thickness of more then 3mm they are stronger then most rotors. They now come in the new 220mm size for those that want to go even bigger with the vented rotors.

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.

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.

I should clarify my opinion here: Rotors are getting far too heavy and thick for anything less than trails and riding at the top-tier of difficulty and racing. And even there, those guys and gals aren't working the brakes as much as Joe and Jane Average rider. "Which caliper piston diameter is better," "which master cylinder piston size is better," "which lever actuation ratio..".....and so on are all questions that have multiple variables attached to them so anecdotal isolation is damn near impossible.

Assuming the same brake, the same rotor with exactly the same material ingredient list, exact same surface area for the pad contact, essentially the ONLY difference being the thickness and/or size, then the answer is simple: smaller rotor has less leverage therefore less power. Thicker rotor has better heat dissipation so it can be more consistent throughout a long and brutal run.

The problem is that usually these thicker rotors also have fewer cutouts so they have greater surface area for the pad so they feel like they have more power, which they do, but it is because of that increased contact patch with the pad. 

I love "enduro" type riding but it sure did bloat the acceptable weight for bikes real quick. Some might be justified for the format, but alot is marketing. Just as long as someone comes out with a dual-front-rotor and caliper setup (think sportbikes) for the heavy ebikes I will excuse all of the marketing mantra.

Lets also contemplate that the further the caliper gets from its mounting point, the more it deflects. With those massive stacks of spacers and ultra-long bolts, sometimes even bolts to hold onto the adapter so you can attach more bolts exerting excruciating force on the poor 12ish mm of thread engagement at the caliper posts. The more it deflects and potentially binds, it creates additional braking force through the action of binding and flexing the rotor in addition to clamping. That could be a valid argument FOR thicker rotors as you get to 200+.

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.

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. 

https://www.acfloby.com/about-us/#lightweight

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. 

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?

Investing in a stiffer caliper seems like a limited marginal gain vs. investing in better temperature management. Anyone have a clear explanation in how much extra heat is absorbed/lost by larger, thicker rotors?

From my experience temperature management is so key for DH- for parks & long descents- for consistent brake points and minimizing arm pump. On my saints I invested in the MT-RT905 (XTR) 203s ice-tech rotors that most shimano WC teams run, coming from the base deore 203s. The XTRs take slightly more time (maybe 5-6 corners vs. 3-4) to get up to temp but I have yet to exceed their operating window on any descent, whereas the old rotors could definitely exceed the window then fade. Keeps the friction coefficient high and therefore braking force much more predictable and higher over the descent. Same size, big performance difference (much bigger than expected, no caliper or pad change).