Cornering sitting and standing is a completely different thing. You want to keep the mechanics the same, what you're proposing is not it. So the cornering should be done standing up in both cases with the bike being leaned over and the rider mostly upright.
Cornering sitting and standing is a completely different thing. You want to keep the mechanics the same, what you're proposing is not it. So the cornering...
Cornering sitting and standing is a completely different thing. You want to keep the mechanics the same, what you're proposing is not it. So the cornering should be done standing up in both cases with the bike being leaned over and the rider mostly upright.
We're talking about taller BB and placing riders weight higher up, not about frame construction and weight distribution within, right?
No, about the effect of wheel size on cornering. And I'm saying it doesn't have an effect, if the geometries of the two bikes are the same (which is never the case when swapping wheel sizes). And I'm claiming that you roll the bike around the CoG height. Thus two different bikes with different wheels but the same CoG height should corner similarly, but the same bike should corner differently if the CoG height changes. Therefore the test with a significant weight (~10 % or more of the unsprung weight) mounted either high up or low down to change the CoG heights.
No, about the effect of wheel size on cornering. And I'm saying it doesn't have an effect, if the geometries of the two bikes are the...
No, about the effect of wheel size on cornering. And I'm saying it doesn't have an effect, if the geometries of the two bikes are the same (which is never the case when swapping wheel sizes). And I'm claiming that you roll the bike around the CoG height. Thus two different bikes with different wheels but the same CoG height should corner similarly, but the same bike should corner differently if the CoG height changes. Therefore the test with a significant weight (~10 % or more of the unsprung weight) mounted either high up or low down to change the CoG heights.
I went mixed wheel size from 27.5 by installing longer ATC 29er fork and a wheel. HTA went from 65.5 to 64 and BB rose by 17 mm (i now only use low geo mode and it feels great). I can now more easily cut a tighter radius turn. I thought this was due to smaller trailing wheel size. How would you explain this effect? I don’t quite get how a higher COG would have an impact.
Turning radius is not something that is relevant to mountainbiking.
Maybe i used the wrong terminology. i wasnt trying to compare my bike turns to a car with a shorter front/rear wheel base having a tigther turning radius. I meant that when i lean the bike to turn through the same berms (and in other places, it is just very noticeable in berms i am very familiar with) compared to before the mixed wheel change, i can now more easily cut a tighter turn and/or hold my speed and still make the turn. At least it really feels that way and i know the feel of this bike quite well.
Regarding the former turning radius i mentioned, it does not apply to this mixed wheel convo but of course wheel base/ turning radius effect tight switchbacks and slow tech riding. I havent found the change to make anything unrideable but it certainly does effect line choice.
Let me get it straight.. You changed wheelsize, wheel weight, ATC, trail, offset, head angle, wheelbase, front center, stack, reach, bar roll or your bike and attribute the change in behaviour to the different wheelsize?
Let me get it straight.. You changed wheelsize, wheel weight, ATC, trail, offset, head angle, wheelbase, front center, stack, reach, bar roll or your bike and...
Let me get it straight.. You changed wheelsize, wheel weight, ATC, trail, offset, head angle, wheelbase, front center, stack, reach, bar roll or your bike and attribute the change in behaviour to the different wheelsize?
Stack and reach stayed about the same as i swapped headset spacer to lower the stem/ bars. Yes, a lot of geo changes occurred, i know that. I was just supposing that out of all the factors at play, the smaller rear wheel may have had the biggest benefit on turning. Thats why i listed bb height and HTA and just asked what others think is impacting the turning and how a higher COG would come into play given Primoz’s comments. I didn’t bother to mention ever geo detail you decided to toss out there. Instead of trying to talk down to me we could just have a conversation and you could attempt to answer my question if you want to be constructive. Thanks.
I did a similar thing last year, went for 29" front end, didn't change the geometry so drastically, dropped 20mm of fork travel.
My initial feeling of the change in behaviour on flat supported corners (Finale Ligure) was also similar to yours.
On the topic of counter-steering, the only way to initiate a corner on a bicycle is counter-steering. Newton says that any force creates an equal and...
On the topic of counter-steering, the only way to initiate a corner on a bicycle is counter-steering. Newton says that any force creates an equal and opposite force, so when a rider wants to go left they have to begin the process by sending the bike to the right. Counter-steering typically isn't conscious- it's not like you're going to think about turning right every time you turn left- but it always happens.
I agree with Primoz that contact patch is more important than axle position for cornering. But, if we assume that axle height doesn't affect cornering at all, then wheel size wouldn't matter for cornering. For instance, if axle position doesn't matter, a bike with 20" wheels and a bike with 36" wheels would corner the same if the contact patches were in the same place relative to the bb. I don't think that's true in practice.
And yes, I know a 20" tire and a 36" tire have different contact patch sizes and thus one would generate more traction, but that's not really what we're talking about here, so I oversimplified. For instance, no one is saying "I can't ride a mullet, I need my rear tire's contact patch to be 4% larger!!"
How much of an effect does wheel size and the way a bike with a given wheel size turns have to do with the geometry that...
How much of an effect does wheel size and the way a bike with a given wheel size turns have to do with the geometry that a certain wheel size demands? We haven't seen an ultra long, low, slack enduro bike, designed to fit 20" wheels after all... I mean it's not like leaning of the bike (I'm guessing with countersteer you mean flipping the contact patches outward, 'counter' to the cornering direction as opposed to just leaning into the corner around the contact patch?) is done around the axles, it happens around the horizontal, length-wise line through the CoG of the system rotating, mostly the bike in this case. And I do agree that you can't just flop over, you have to rotate the bike around that line.
I guess testing that would be simple, tie about a kilo of lead to either the top tube or around the BB and compare how the bike turns.
@SB14 regarding pressures, I'd say no, it's not the same area on a 2,2" and a 4" tyre at the same pressure. This is mostly gut feeling, haven't tested it, but we know for a fact that the tyre carcass plays a role here. But even with the exact same carcass, the diameter of the 2,2" tyre will be much smaller than the 4" tyre, so the support from the same pressure will not be the same. The effective shape-caused stiffness of that same carcass will be different. Lower pressures ran on bigger tyres makes me think the contact patch on the 2,2" tyre will actually be bigger due to more deformation. Maybe.
As for rollover, another benefit might (must?) be also rolling resistance. I see little other reason for modern EVs going to 20+" wheels and tyres, when we were happily chugging along on 15 to 17s just 10 to 20 years ago, not beating an eye. Higher weights and wider tyres to carry the load better might also have something to do with it too though...
Physics says contact patch size is dictated by tyre pressure and will be the same for a 2.2" or 4" tyre.
Thing is, you don't run them at the same pressure. You can run the 4" tyre at about half the pressure so you get double the contact patch.
Wheel diameter doesn't change the size of the contact patch either, but it changes the shape. A larger diameter will give you a longer, skinnier contact patch.
Physics says contact patch size is dictated by tyre pressure and will be the same for a 2.2" or 4" tyre.
Thing is, you don't run...
Physics says contact patch size is dictated by tyre pressure and will be the same for a 2.2" or 4" tyre.
Thing is, you don't run them at the same pressure. You can run the 4" tyre at about half the pressure so you get double the contact patch.
Wheel diameter doesn't change the size of the contact patch either, but it changes the shape. A larger diameter will give you a longer, skinnier contact patch.
Contact patch shape does change how the bike rides too. I rode a 26" fat bike and could not keep the ride stable at low psi, my poor pedalling 'circles' caused me to bounce all the time. That was not the case on a 27.5" fat bike; the tires were a touch smaller but I wasn't on a make-your-own merry-go-round anymore.
I'm sure that the casing also plays a role, as the tire isn't a uniform piece of rubber and may influence things somewhat
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this above, hell, I wouldn't be surprised if the same model, same casing, same rubber tyres were mounted to the same rim with the same pressure, the patch shape would be different.
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this...
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this above, hell, I wouldn't be surprised if the same model, same casing, same rubber tyres were mounted to the same rim with the same pressure, the patch shape would be different.
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will feel different. A much stiffer casing would probably reduce the contact patch slightly.
If you leave all the other variables alone, contact patch size is directly correlated to tyre pressure. Tyre pressure in pounds per square inch. Vertical load in pounds. contact area supporting this load in square inches.
Please don't try to argue against basic physics.
The difference in feel between 29 and 27.5" tyres is not well understood by most people and the reasons for the differences that most people state are wrong. It's not about angle of attack or a bigger contact patch.
The blog post by Joe from Starling linked earlier in this thread by SB14 explains this really well.
Back to the main topic, I would love to see some research into the gyro effects and turning arcs of different diameter wheels on cornering.
My anecdotal evidence is that mullets do corner better. I love my new mullet bike (thanks Joe, the Twist is fantastic!)
It would be awesome to have a full understanding of why.
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this...
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this above, hell, I wouldn't be surprised if the same model, same casing, same rubber tyres were mounted to the same rim with the same pressure, the patch shape would be different.
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will...
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will feel different. A much stiffer casing would probably reduce the contact patch slightly.
If you leave all the other variables alone, contact patch size is directly correlated to tyre pressure. Tyre pressure in pounds per square inch. Vertical load in pounds. contact area supporting this load in square inches.
Please don't try to argue against basic physics.
The difference in feel between 29 and 27.5" tyres is not well understood by most people and the reasons for the differences that most people state are wrong. It's not about angle of attack or a bigger contact patch.
The blog post by Joe from Starling linked earlier in this thread by SB14 explains this really well.
Back to the main topic, I would love to see some research into the gyro effects and turning arcs of different diameter wheels on cornering.
My anecdotal evidence is that mullets do corner better. I love my new mullet bike (thanks Joe, the Twist is fantastic!)
It would be awesome to have a full understanding of why.
So as a thought experiment of sorts, to compare one aspect of 29 vs 27.5 wheel, if all other factors were adjusted/ equivalent (contact patch etc…) if each wheel were on an axle tilted to the same angle and then rotated forward, their tracks in the ground would create a circle of the same circumference (i think). The 29 wheel would complete the circle with less roll out than the 27.5, so to maintain the same pace, the 27.5 would have to spin faster. So perhaps the rear 27.5 on a mixed wheel bike is forced to accelerate to keep up with the front wheel, thus making it feel like it turns faster..??? I doubt this is the definitive explanation, my example simplifies all of the factors at play but i feel like this has something to do with it.
Totally based on anecdotal evidence but I just recently made my new stumpy evo into a mullet and I did notice that it turns MUCH better now compared to the full 29er setup (easier to lean over, holds grip better and is easier to do back to back turns with). I kept the geo the same and with the link installed most other variables are controlled for besides the tires being different between the two of them.
I would have to say that the mullet does most things better compared to the full 29er setup based on my first impressions. Acceleration, general maneuverability, leaning the bike over, and it gives you a bit of extra clearance on jump landings. EXCEPT on the fast and chunky stuff it gets knocked around more which seems logical to me and potentially worth it in the end.
Totally based on anecdotal evidence but I just recently made my new stumpy evo into a mullet and I did notice that it turns MUCH better...
Totally based on anecdotal evidence but I just recently made my new stumpy evo into a mullet and I did notice that it turns MUCH better now compared to the full 29er setup (easier to lean over, holds grip better and is easier to do back to back turns with). I kept the geo the same and with the link installed most other variables are controlled for besides the tires being different between the two of them.
I would have to say that the mullet does most things better compared to the full 29er setup based on my first impressions. Acceleration, general maneuverability, leaning the bike over, and it gives you a bit of extra clearance on jump landings. EXCEPT on the fast and chunky stuff it gets knocked around more which seems logical to me and potentially worth it in the end.
My experience would agree with this. Especially on lean over in corners.
The mullet really rewards a bit more lean angle. Loads of grip and great transition between corners.
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this...
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this above, hell, I wouldn't be surprised if the same model, same casing, same rubber tyres were mounted to the same rim with the same pressure, the patch shape would be different.
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will...
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will feel different. A much stiffer casing would probably reduce the contact patch slightly.
If you leave all the other variables alone, contact patch size is directly correlated to tyre pressure. Tyre pressure in pounds per square inch. Vertical load in pounds. contact area supporting this load in square inches.
Please don't try to argue against basic physics.
The difference in feel between 29 and 27.5" tyres is not well understood by most people and the reasons for the differences that most people state are wrong. It's not about angle of attack or a bigger contact patch.
The blog post by Joe from Starling linked earlier in this thread by SB14 explains this really well.
Back to the main topic, I would love to see some research into the gyro effects and turning arcs of different diameter wheels on cornering.
My anecdotal evidence is that mullets do corner better. I love my new mullet bike (thanks Joe, the Twist is fantastic!)
It would be awesome to have a full understanding of why.
So as a thought experiment of sorts, to compare one aspect of 29 vs 27.5 wheel, if all other factors were adjusted/ equivalent (contact patch etc…)...
So as a thought experiment of sorts, to compare one aspect of 29 vs 27.5 wheel, if all other factors were adjusted/ equivalent (contact patch etc…) if each wheel were on an axle tilted to the same angle and then rotated forward, their tracks in the ground would create a circle of the same circumference (i think). The 29 wheel would complete the circle with less roll out than the 27.5, so to maintain the same pace, the 27.5 would have to spin faster. So perhaps the rear 27.5 on a mixed wheel bike is forced to accelerate to keep up with the front wheel, thus making it feel like it turns faster..??? I doubt this is the definitive explanation, my example simplifies all of the factors at play but i feel like this has something to do with it.
In isolation the smaller wheel will create a smaller circle when leaned over the same amount.
Tied together in a system like a bicycle they will be forced to carve a similar radius so if the smaller rear wheel follows the line of the front it will have to scrub a bit. This is one of the mechanisms put forward for the more lively cornering of a mullet.
The smaller wheel will turn more revolutions so have a higher angular velocity, but will still have less gyro effect than the bigger, heavier wheel and this might also help make it easier to lean over and turn.
A bit like the Yamaha R1 engine that spins reverse to conventional to counter the gyro effect of the wheel and reduce stability of the bike to make it more agile.
Lots of hypotheses getting around. It definitely needs a bit of scientific exploration to quantify all these effects.
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this...
Of course it does. So saying 'physics says contact patch size is dictated by tyre pressure' and it alone is not correct. I've written about this above, hell, I wouldn't be surprised if the same model, same casing, same rubber tyres were mounted to the same rim with the same pressure, the patch shape would be different.
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will...
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will feel different. A much stiffer casing would probably reduce the contact patch slightly.
If you leave all the other variables alone, contact patch size is directly correlated to tyre pressure. Tyre pressure in pounds per square inch. Vertical load in pounds. contact area supporting this load in square inches.
Please don't try to argue against basic physics.
The difference in feel between 29 and 27.5" tyres is not well understood by most people and the reasons for the differences that most people state are wrong. It's not about angle of attack or a bigger contact patch.
The blog post by Joe from Starling linked earlier in this thread by SB14 explains this really well.
Back to the main topic, I would love to see some research into the gyro effects and turning arcs of different diameter wheels on cornering.
My anecdotal evidence is that mullets do corner better. I love my new mullet bike (thanks Joe, the Twist is fantastic!)
It would be awesome to have a full understanding of why.
So if I set my pressure in bars, your example doesn't work? How much pressure do I have then?
I'm not sure you're looking at the whole picture when you're saying I shouldn't argue basic physics. I'm not. I'm just advising against going too basic. And don't worry, I'm well aware of what pressure does and the like. Don't believe me? Go through my post history, I think I don't need to type out my qualifications?
As for 'could vary construction and rim width', well... Yeah, you could. But the issue here is also that YOU vary it. By varying the tyre width, which by default varies the effective rim width, carcas shape, etc.
Don't get me wrong, all other variables staying the same does mean different pressure, different patch size. But like you said, all other variables staying the same. Different sized tyres is a changed variable, which is my point from the beginning, from the first mention of this (sub)topic.
Anywho, regarding wheel sizes, I've just been thinking a bit, a smaller wheel size is like a smaller side radius ona carving ski, X amount of lean angle will cause more 'turning' than on a larger wheel size, like you sorto of mentioned. But the thing is that a leaned over wheel rotating sort of 'falls down' as it turns - the smaller the diameter, the further it has to 'fall' to get into contact with the ground. Thus making a tighter radius.
Sure, diameter differences aren't that large between wheels when it comes to roll over differences, but this difference is increased (effectively) when leaned over.
All of you guys who think rollover angle/angle of attack/angle of impact isn't affected by wheel size are tripping. A well-tuned mountain bike rider who's in touch with their suspension is like the princess and the pea. You can feel the tiniest difference between a small root, a medium-sized root, and a small-ish but kinda medium-sized root through your feet, hands, and even your inner ear. Even if the difference in attack angle seems small between wheel sizes, it's still very noticeable when riding.
Going from 26" to 27.5" I specifically remember rocky sections of trail where I braced for impact and never really felt the rocks, at least not what I was expecting to feel. Going back and forth from 29" to 26" was even more noticeable. I noticed how many fewer flat tires and dented rims I got after I switched to 29", despite running exactly the same tires and pressure. To hop in the way back machine, the old 24" rear wheels on Specialized Big Hits and Santa Cruz Super 8's were infamously bad for racing because they got sucked into every hole. Fact: smaller wheels hit bumps harder.
All of you guys who think rollover angle/angle of attack/angle of impact isn't affected by wheel size are tripping. A well-tuned mountain bike rider who's in...
All of you guys who think rollover angle/angle of attack/angle of impact isn't affected by wheel size are tripping. A well-tuned mountain bike rider who's in touch with their suspension is like the princess and the pea. You can feel the tiniest difference between a small root, a medium-sized root, and a small-ish but kinda medium-sized root through your feet, hands, and even your inner ear. Even if the difference in attack angle seems small between wheel sizes, it's still very noticeable when riding.
Going from 26" to 27.5" I specifically remember rocky sections of trail where I braced for impact and never really felt the rocks, at least not what I was expecting to feel. Going back and forth from 29" to 26" was even more noticeable. I noticed how many fewer flat tires and dented rims I got after I switched to 29", despite running exactly the same tires and pressure. To hop in the way back machine, the old 24" rear wheels on Specialized Big Hits and Santa Cruz Super 8's were infamously bad for racing because they got sucked into every hole. Fact: smaller wheels hit bumps harder.
Well, tripping is not allways a bad thing! Haha.
And yes, i agree completly with the feel of the ground and roots and all, but the reason being impact angle of the tires is up for debate. As Joe @ starling cycles explains, what you are feeling is the difference in gyroscopic stability. His theory is that the change in gyro-forces is greater then the angle of impact the wheel makes.
Though, it might be that a 1.4degree differance between 275 and 29 at a 2 inch root, is something that you feel and can attribute to this change. But it the mass in motion is greater, and makes a bigger variable between the two sizes.
I dont hold the answer, but it seems to me that we can not neglect these facts. And it is not the one over ther other that rocks the boat, but the combination. Though, one has a bigger change of factors then the other.
TBH I remember getting on the 27,5" bike and being blown away how little speed I lost on a flat, rooty section of a trail. And the effect was similar going to a 29er.
But I was thinking about the inertia effect of it all too. Have to put the XM1501/Aggressor combo back on the bike, it feels SO heavy and cumbersome since I've setup the 240s/EX511 32h Assegai combo last summer while I was without the bike and injured, so I got to properly ride it only in the fall and over winter. Now we're getting into summer conditions and conditions for more comparisons.
TBH I remember getting on the 27,5" bike and being blown away how little speed I lost on a flat, rooty section of a trail. And...
TBH I remember getting on the 27,5" bike and being blown away how little speed I lost on a flat, rooty section of a trail. And the effect was similar going to a 29er.
But I was thinking about the inertia effect of it all too. Have to put the XM1501/Aggressor combo back on the bike, it feels SO heavy and cumbersome since I've setup the 240s/EX511 32h Assegai combo last summer while I was without the bike and injured, so I got to properly ride it only in the fall and over winter. Now we're getting into summer conditions and conditions for more comparisons.
I definitely agree re. momentum over flat bumps. A couple years back I rode a loaner Nomad (27.5) from my local shop while my Sentinel (29) was getting some work done. The bikes felt like a reasonably similar speed on steeper terrain, but as soon as I entered a traversing section of my local trail that is fairly flat and rocky/bumpy it felt like someone threw an anchor off the back of the Nomad. I've never ridden a mullet bike properly, but I'd be really interested to feel out how much the bigger front wheel changes the performance on flatter ground.
As a mullet-rider (and previously had full 29s and full 27.5s), I'd say the roll-over is somewhat more than halfway in between full 29 and full 27.5. The added momentum from the larger front wheel is pretty noticeable, even on smooth pump tracks. Anecdotally, I can still catch up to a buddy on straight sections, smooth or rough, (riding similar bikes / tires, him on 27.5 and outweighing me by 30 lbs), but less rapidly than when I was on full 29. He's still a hair faster overall because he brakes less.
It would be cool if Vital did a quasi-scientific timed test like they did with tires a year or two ago. Ideally one bike capable of all 3 modes, same rider, same tires. Do timed runs down a straight smooth surface (like the road they used in the tire test) and average results. Do same thing but on a straight section of trail with a series of brake bumps.
So if I set my pressure in bars, your example doesn't work? How much pressure do I have then?
I'm not sure you're looking at the...
So if I set my pressure in bars, your example doesn't work? How much pressure do I have then?
I'm not sure you're looking at the whole picture when you're saying I shouldn't argue basic physics. I'm not. I'm just advising against going too basic. And don't worry, I'm well aware of what pressure does and the like. Don't believe me? Go through my post history, I think I don't need to type out my qualifications?
As for 'could vary construction and rim width', well... Yeah, you could. But the issue here is also that YOU vary it. By varying the tyre width, which by default varies the effective rim width, carcas shape, etc.
Don't get me wrong, all other variables staying the same does mean different pressure, different patch size. But like you said, all other variables staying the same. Different sized tyres is a changed variable, which is my point from the beginning, from the first mention of this (sub)topic.
Anywho, regarding wheel sizes, I've just been thinking a bit, a smaller wheel size is like a smaller side radius ona carving ski, X amount of lean angle will cause more 'turning' than on a larger wheel size, like you sorto of mentioned. But the thing is that a leaned over wheel rotating sort of 'falls down' as it turns - the smaller the diameter, the further it has to 'fall' to get into contact with the ground. Thus making a tighter radius.
Sure, diameter differences aren't that large between wheels when it comes to roll over differences, but this difference is increased (effectively) when leaned over.
If we really want to be scientific, maybe we should use SI units and be talking in kPa...
In all seriousness though, I don't mean to disrespect you. I've read and enjoyed a lot of your thought provoking posts and analysis.
Doesn't mean I won't argue with you though! On the contrary. I'm more likely to argue with someone I respect.
From your reply above I don't think we are actually too far apart on the pressure vs contact patch topic.
I think your ski side radius analogy is a good one. A smaller wheel will behave like a smaller radius/deeper sidecut.
Teamrobot, I'm not arguing the difference in feel over trail bumps between 29 and 27.5. Just the reason for it.
The effect is real, but the mechanism probably isn't what the "conventional wisdom" about 29" wheels says it is.
Maybe there are some further benefits to be had by poking a bit further at it and understanding the reasons behind it a bit better.
I'm surprised we haven't seen/heard of someone experimenting with these geometry concepts yet in a more rigorous way. It would only take a few folks with welders who were bored in lockdown (or a big company with R&D money) to more systematically test this. At a minimum, you could build a rigid or hardtail frame with a concentric BB, sliding dropouts or multiple dropout holes at different heights/lengths/angles (aside: angled sliding/flip-chip dropouts would move two things at once, and seems like a good idea for a bike designed around full 29 and mullet) and a headtube with a reach adjust headset. Then, test times as stated above on straights, bumps, high/low speed, berms, flat corners, etc and compare times.
This actually sounds like something a YouTuber would do, but I wonder if anyone at the big companies has ever tried this to see where they actually want the geometry to be instead of just following industry trends. Minaar mentioned a few years ago that he thought his bike should be longer but that people need time to adapt/accept the change, but do the bike companies know where the limit is? Or maybe the limit does not exist.
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will...
Of course you could vary the tyre construction and rim width to change the shape of the contact patch and yes, different shape contact patches will feel different. A much stiffer casing would probably reduce the contact patch slightly.
If you leave all the other variables alone, contact patch size is directly correlated to tyre pressure. Tyre pressure in pounds per square inch. Vertical load in pounds. contact area supporting this load in square inches.
Please don't try to argue against basic physics.
The difference in feel between 29 and 27.5" tyres is not well understood by most people and the reasons for the differences that most people state are wrong. It's not about angle of attack or a bigger contact patch.
The blog post by Joe from Starling linked earlier in this thread by SB14 explains this really well.
Back to the main topic, I would love to see some research into the gyro effects and turning arcs of different diameter wheels on cornering.
My anecdotal evidence is that mullets do corner better. I love my new mullet bike (thanks Joe, the Twist is fantastic!)
It would be awesome to have a full understanding of why.
Please don't try to argue against basic physics.
Not arguing with physics but are you sure we are taking all the variables in consideration ? For instance, common practice is to measure tire pressure unloaded right ? Additionally we can agree that for the same tire section, the total air volume will be bigger for a 29 wheel than for a 27.5 wheel. If my physics is not too rusty, air pressure increase exponentially in a given volume and the bigger the volume the more displacement will be needed to end-up at the same pressure. So considering that initial pressure, loading and tire section are kept constant, in order to reach the same loaded pressure the 29er will have to displace more volume (contact patch) more than the smaller wheels. Effect that would be exacerbated by the bigger tire area likely to stretch under pressure increasing even more the space available for the air to spread.
If we really want to be scientific, maybe we should use SI units and be talking in kPa...
In all seriousness though, I don't mean to...
If we really want to be scientific, maybe we should use SI units and be talking in kPa...
In all seriousness though, I don't mean to disrespect you. I've read and enjoyed a lot of your thought provoking posts and analysis.
Doesn't mean I won't argue with you though! On the contrary. I'm more likely to argue with someone I respect.
From your reply above I don't think we are actually too far apart on the pressure vs contact patch topic.
I think your ski side radius analogy is a good one. A smaller wheel will behave like a smaller radius/deeper sidecut.
Teamrobot, I'm not arguing the difference in feel over trail bumps between 29 and 27.5. Just the reason for it.
The effect is real, but the mechanism probably isn't what the "conventional wisdom" about 29" wheels says it is.
Maybe there are some further benefits to be had by poking a bit further at it and understanding the reasons behind it a bit better.
We're not, I just think you missed the original point of someone else, where a 4,0 and a 2,4 inch wide tyre at the same pressure was mentioned. I based all my writing off that, as the tyre size, on the same rim or on a proportionally wider rim, should cause a difference just due to different carcass stiffness characteristics (even if it's 'the same' carcass, marketing wise), due to the shape of it and the resulting support from the sidewalls, etc.
Remember the marketing stuff on wider rims and bigger tyres, how they give you more support. Now think about a car tyre in a corner, which will have more 'sideways stiffness', which will be more wallowy, a slightly stretched tyre (too narrow for the given rim) or a tyre that is just the right width or maybe a bit too wide even? And this is regardless of the pressures run (well, if they are the same actually), as the geometry itself will define a lot of that.
But like I said, tyre X, rim Y, more pressure, less contact patch, that part is clear and logical.
Or just compare seated cornering (COG up high) with cornering while standing, bike/body separation, weight on the pedals, COG low.
NotMeAtAll: "Its the same principle of supermotard bikes going circles around super sport motorbikes in a corner."
By that logic ADVs should be going circles around motards.
https://www.vitalmtb.com/videos/features/Matt-Walker-Charlie-Hatton-and…
Regarding the former turning radius i mentioned, it does not apply to this mixed wheel convo but of course wheel base/ turning radius effect tight switchbacks and slow tech riding. I havent found the change to make anything unrideable but it certainly does effect line choice.
My initial feeling of the change in behaviour on flat supported corners (Finale Ligure) was also similar to yours.
Thing is, you don't run them at the same pressure. You can run the 4" tyre at about half the pressure so you get double the contact patch.
Wheel diameter doesn't change the size of the contact patch either, but it changes the shape. A larger diameter will give you a longer, skinnier contact patch.
I'm sure that the casing also plays a role, as the tire isn't a uniform piece of rubber and may influence things somewhat
If you leave all the other variables alone, contact patch size is directly correlated to tyre pressure. Tyre pressure in pounds per square inch. Vertical load in pounds. contact area supporting this load in square inches.
Please don't try to argue against basic physics.
The difference in feel between 29 and 27.5" tyres is not well understood by most people and the reasons for the differences that most people state are wrong. It's not about angle of attack or a bigger contact patch.
The blog post by Joe from Starling linked earlier in this thread by SB14 explains this really well.
Back to the main topic, I would love to see some research into the gyro effects and turning arcs of different diameter wheels on cornering.
My anecdotal evidence is that mullets do corner better. I love my new mullet bike (thanks Joe, the Twist is fantastic!)
It would be awesome to have a full understanding of why.
I would have to say that the mullet does most things better compared to the full 29er setup based on my first impressions. Acceleration, general maneuverability, leaning the bike over, and it gives you a bit of extra clearance on jump landings. EXCEPT on the fast and chunky stuff it gets knocked around more which seems logical to me and potentially worth it in the end.
The mullet really rewards a bit more lean angle. Loads of grip and great transition between corners.
Tied together in a system like a bicycle they will be forced to carve a similar radius so if the smaller rear wheel follows the line of the front it will have to scrub a bit. This is one of the mechanisms put forward for the more lively cornering of a mullet.
The smaller wheel will turn more revolutions so have a higher angular velocity, but will still have less gyro effect than the bigger, heavier wheel and this might also help make it easier to lean over and turn.
A bit like the Yamaha R1 engine that spins reverse to conventional to counter the gyro effect of the wheel and reduce stability of the bike to make it more agile.
Lots of hypotheses getting around. It definitely needs a bit of scientific exploration to quantify all these effects.
I'm not sure you're looking at the whole picture when you're saying I shouldn't argue basic physics. I'm not. I'm just advising against going too basic. And don't worry, I'm well aware of what pressure does and the like. Don't believe me? Go through my post history, I think I don't need to type out my qualifications?
As for 'could vary construction and rim width', well... Yeah, you could. But the issue here is also that YOU vary it. By varying the tyre width, which by default varies the effective rim width, carcas shape, etc.
Don't get me wrong, all other variables staying the same does mean different pressure, different patch size. But like you said, all other variables staying the same. Different sized tyres is a changed variable, which is my point from the beginning, from the first mention of this (sub)topic.
Anywho, regarding wheel sizes, I've just been thinking a bit, a smaller wheel size is like a smaller side radius ona carving ski, X amount of lean angle will cause more 'turning' than on a larger wheel size, like you sorto of mentioned. But the thing is that a leaned over wheel rotating sort of 'falls down' as it turns - the smaller the diameter, the further it has to 'fall' to get into contact with the ground. Thus making a tighter radius.
Sure, diameter differences aren't that large between wheels when it comes to roll over differences, but this difference is increased (effectively) when leaned over.
Going from 26" to 27.5" I specifically remember rocky sections of trail where I braced for impact and never really felt the rocks, at least not what I was expecting to feel. Going back and forth from 29" to 26" was even more noticeable. I noticed how many fewer flat tires and dented rims I got after I switched to 29", despite running exactly the same tires and pressure. To hop in the way back machine, the old 24" rear wheels on Specialized Big Hits and Santa Cruz Super 8's were infamously bad for racing because they got sucked into every hole. Fact: smaller wheels hit bumps harder.
And yes, i agree completly with the feel of the ground and roots and all, but the reason being impact angle of the tires is up for debate. As Joe @ starling cycles explains, what you are feeling is the difference in gyroscopic stability. His theory is that the change in gyro-forces is greater then the angle of impact the wheel makes.
Though, it might be that a 1.4degree differance between 275 and 29 at a 2 inch root, is something that you feel and can attribute to this change. But it the mass in motion is greater, and makes a bigger variable between the two sizes.
I dont hold the answer, but it seems to me that we can not neglect these facts. And it is not the one over ther other that rocks the boat, but the combination. Though, one has a bigger change of factors then the other.
But I was thinking about the inertia effect of it all too. Have to put the XM1501/Aggressor combo back on the bike, it feels SO heavy and cumbersome since I've setup the 240s/EX511 32h Assegai combo last summer while I was without the bike and injured, so I got to properly ride it only in the fall and over winter. Now we're getting into summer conditions and conditions for more comparisons.
It would be cool if Vital did a quasi-scientific timed test like they did with tires a year or two ago. Ideally one bike capable of all 3 modes, same rider, same tires. Do timed runs down a straight smooth surface (like the road they used in the tire test) and average results. Do same thing but on a straight section of trail with a series of brake bumps.
In all seriousness though, I don't mean to disrespect you. I've read and enjoyed a lot of your thought provoking posts and analysis.
Doesn't mean I won't argue with you though! On the contrary. I'm more likely to argue with someone I respect.
From your reply above I don't think we are actually too far apart on the pressure vs contact patch topic.
I think your ski side radius analogy is a good one. A smaller wheel will behave like a smaller radius/deeper sidecut.
Teamrobot, I'm not arguing the difference in feel over trail bumps between 29 and 27.5. Just the reason for it.
The effect is real, but the mechanism probably isn't what the "conventional wisdom" about 29" wheels says it is.
Maybe there are some further benefits to be had by poking a bit further at it and understanding the reasons behind it a bit better.
This actually sounds like something a YouTuber would do, but I wonder if anyone at the big companies has ever tried this to see where they actually want the geometry to be instead of just following industry trends. Minaar mentioned a few years ago that he thought his bike should be longer but that people need time to adapt/accept the change, but do the bike companies know where the limit is? Or maybe the limit does not exist.
Not arguing with physics but are you sure we are taking all the variables in consideration ? For instance, common practice is to measure tire pressure unloaded right ? Additionally we can agree that for the same tire section, the total air volume will be bigger for a 29 wheel than for a 27.5 wheel. If my physics is not too rusty, air pressure increase exponentially in a given volume and the bigger the volume the more displacement will be needed to end-up at the same pressure. So considering that initial pressure, loading and tire section are kept constant, in order to reach the same loaded pressure the 29er will have to displace more volume (contact patch) more than the smaller wheels. Effect that would be exacerbated by the bigger tire area likely to stretch under pressure increasing even more the space available for the air to spread.
Remember the marketing stuff on wider rims and bigger tyres, how they give you more support. Now think about a car tyre in a corner, which will have more 'sideways stiffness', which will be more wallowy, a slightly stretched tyre (too narrow for the given rim) or a tyre that is just the right width or maybe a bit too wide even? And this is regardless of the pressures run (well, if they are the same actually), as the geometry itself will define a lot of that.
But like I said, tyre X, rim Y, more pressure, less contact patch, that part is clear and logical.
Post a reply to: BB-height, cornering and why mullet bikes might turn better.