Myth: Wide Tires Need Wide Rims:

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romanmoser
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by romanmoser

Not more comfy at least on normal roads
More volume that's it
You can take bigger potholes and be more efficient on bads conditions roads tough

bm0p700f
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by bm0p700f

The larger air volume results in improved comfort even of the pressure are not lower.

The improved cornering grip comes from the tyres ability to absorb energy. The more energy a tyre can absorb through hysteria the more in grips in the bends. Side walls that are more vertical behave more like a spring than light bulb shaped tyres and presumably more energy is absorbed so improved grip. That would be the physical explanation. I dont know if anyone has been able to measure it though.

by Weenie


zefs
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by zefs

I don't think so, at the same pressures the larger tire is not more comfortable because of the extra material, that is what BRR mentions as well.

jlok
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by jlok

Same pressure say 85psi, 23mm wide vs 32mm wide tire on the same rim, anyone care to explain in maths why the 32mm is like a rock while it's much softer on the 23mm?
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Marin
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by Marin

jlok wrote:
Fri Jul 12, 2019 8:54 am
Same pressure say 85psi, 23mm wide vs 32mm wide tire on the same rim, anyone care to explain in maths why the 32mm is like a rock while it's much softer on the 23mm?
If you can read German: https://de.wikipedia.org/wiki/Kesselformel

The English version seems to be Barlow's formula. Basically, wall tension rises with the diameter.

This is also the reason for the "wider tires are faster" myth - they are simply harder at the same pressure and thus deform less. Obviously, they are also less comfortable at the same pressure, as you have found out.

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TonyM
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by TonyM

Marin wrote:
Fri Jul 12, 2019 11:00 am
jlok wrote:
Fri Jul 12, 2019 8:54 am
Same pressure say 85psi, 23mm wide vs 32mm wide tire on the same rim, anyone care to explain in maths why the 32mm is like a rock while it's much softer on the 23mm?
If you can read German: https://de.wikipedia.org/wiki/Kesselformel

The English version seems to be Barlow's formula. Basically, wall tension rises with the diameter.

This is also the reason for the "wider tires are faster" myth - they are simply harder at the same pressure and thus deform less. Obviously, they are also less comfortable at the same pressure, as you have found out.
@ jlok
@ Marin
Thanks for the question and for the answer! That helps! :thumbup:

Mr.Gib
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by Mr.Gib

Imaking20 wrote:
Wed Jul 10, 2019 11:40 pm
As far as engineering or physics to substantiate the perception - it seems like you're looking for quantification of something that is VERY personal and subjective. Respectfully, I'd say it appears you're looking for science to support something you prefer. Ride what you want, ride what you like, I just don't think it's necessary to reach for scientific-sounding answers when "I just like it" will suffice.
No, I'm just curious. It's the academic in me. My preference is irrelevant to the science. I do ride exactly what I want and will continue to do so regardless of data. Always have, always will. If my choices are slower, too bad. The good news is seems most of the guys are I ride with are slower also. :wink:

Imaking20 wrote:
Wed Jul 10, 2019 11:40 pm
It's totally fine to suggest wider tires and/or rims on grounds of comfort and handling (though I'd argue part of the difference in handling is also the increased trail that comes with larger tires).
The handling improvement that I notice is just improved traction on all surfaces which results in the ability to descend and corner faster. Nothing to do with steering feel. In fact I cannot feel any difference in steering between 28 and 30mm. Of course the difference is there and maybe it makes things better or maybe it makes things worse - depends on the exact situation I guess.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

bm0p700f
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by bm0p700f

Now your saying narrow tyres are more comfortable. Your leaving reality.

Take two tyre like the IRC formula pro rbcc 25mm and 28mm I run both at 80 psi because that feels right for me. The 28mm is definitely more comfortable.

Or the conti gp 5000 in 23mm and 32mm. You can run both at 70 psi. You cant be seriously telling me that the 23mm tyre is more comfortable I.e absorbs more buzz.

It's a bit like you started with you want a narrow tyre to be more comfortable at higher pressure and have dug out a fact to fit that premise.

Air volume matters for comfort. That's fact. Air pressure matters too as does casing flexibility which is related to air pressure as well as the material.

bm0p700f
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by bm0p700f

Theres a fundamental misunderstanding in this thread by some. Some are think comfort comes from the spring effect. Wrong it comes from hysteria/damping. Hystersis is the difference between the energy used to extend a material and the energy returned when it relaxes.

Springs bounce you about that's not comfortable. It is the ability to dampen the spring that's give rises to comfort. That means absorbing the energy of vertical motion caused by those lumps and bumps. That's what the casing if the tyre does in conjunction with the air volume. Increasing the air pressure does reduce the flexibility of the sidewalls and in turn reduces the amount if energy those sidewalls can absorb as the energy absorbed is linked to but not proportional the amount of deflection in the tyre. That is counteracted by the increasing the air volume while maintaining the same pressure, perhaps more so as experience shows.

Thicker sidewalls should absorb more buzz but that in turn contributes to the lack of feel you get from heavier dead tyres. These thick casing are also less flexible so there is less hystersis. Thin walled tyres are flexible and show more of hystersis and therefore absorb more energy per gram of material. That's also why they provide more grip.

Aluminium does not absorb much of the energy transmitted by road buzz. Relative to what the tyre does so thinking about how the amount of material in the rim as zef has is dead end. It's barely relevant especially since wider rims are not always heavier than narrower ones. Wider rims get ther radial lateral and twisting/torsional stiffness more from there shape. Narrower rims were either box or v section and needed thicker walls to provide some lateral stiffness hense why many older narrow v rims were tank like.

That's my understanding of the physics of tyres.

alcatraz
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by alcatraz

What about comparing a 23c and 32c at a high pressure like 100psi. Is the 32c really more comfortable?

It'd be nice to somehow get air volume and tire deformation separated in the analyses.

Is there a study that analyzes what tire compression rate is most efficient at reducing impedance/rr losses? I've seen the number 15% thrown around. Is it accurate?

Marin
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by Marin

bm0p700f wrote:
Sun Jul 14, 2019 10:07 am
gp 5000 in 23mm and 32mm. You can run both at 70 psi. You cant be seriously telling me that the 23mm tyre is more comfortable I.e absorbs more buzz.
The Physics cleary says that the 28 provides less suspension at 70 psi than the 23. Try it.

Obviously, you can and will run the 28 at a lower pressure because you have 5mm more travel before it bottoms out.

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TonyM
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by TonyM


bm0p700f wrote:
Aluminium does not absorb much of the energy transmitted by road buzz.
Then carbon rims would be more comfortable than aluminum rims?

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pdlpsher1
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by pdlpsher1

Marin wrote:
Mon Jul 15, 2019 11:17 am
bm0p700f wrote:
Sun Jul 14, 2019 10:07 am
gp 5000 in 23mm and 32mm. You can run both at 70 psi. You cant be seriously telling me that the 23mm tyre is more comfortable I.e absorbs more buzz.
The Physics cleary says that the 28 provides less suspension at 70 psi than the 23. Try it.

Obviously, you can and will run the 28 at a lower pressure because you have 5mm more travel before it bottoms out.
What defines comfort is the tire's casing tension not psi. At the same psi the wider tire will have a higher casing tension because there's more surface area for the air pressure to act on. This is the reason why a wider tire needs lower psi to maintain the same comfort as a narrower tire. A wider tire can have an edge on comfort simply because you can run them at a lower psi and still not have pinch flats. Narrower tires needs a minimum psi to avoid pinch flats.

Try pumping up a MTB tire to 100psi and see what happens. The extreme tension in the casing will likely blow the bead off the rim or split the casing in half.

So yeah the GP5K in 32mm at 70psi will be way harsher than the GP5K 23mm at the same pressure due to the significantly higher casing tension in the 32mm.

spud
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by spud

bm0p700f wrote:
Sun Jul 14, 2019 11:08 am
Theres a fundamental misunderstanding in this thread by some. Some are think comfort comes from the spring effect. Wrong it comes from hysteria/damping. Hystersis is the difference between the energy used to extend a material and the energy returned when it relaxes.


Thicker sidewalls should absorb more buzz but that in turn contributes to the lack of feel you get from heavier dead tyres. These thick casing are also less flexible so there is less hystersis. Thin walled tyres are flexible and show more of hystersis and therefore absorb more energy per gram of material. That's also why they provide more grip.


That's my understanding of the physics of tyres.
Not disagreeing with the macro conclusions of wider vs narrower in terms of comfort. But there are two aspects to comfort - ability to deal with road buzz, and ability to deal with big hits (loosly defined). We tend to remember the rougher stuff, and wider definitely deals with it better. But for low amplitude vibration, narrower on same pressure will be more comfortable.

confort comes from both the spring factor and dampening factor. I couldn't give you a breakdown, but the lower spring rate contributes to less vertical displacement of the rider going over a bump. The damping contributes to less macro oscilation, and less micro (tire tread bouncing at road interface). Heavier tires with thicker casings have more damping than light tires, which also contributes to their rolling drag, which is obviously higher than light weight tires assuming comparable rubber compound.

by Weenie


Mr.Gib
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by Mr.Gib

spud wrote:
Tue Jul 16, 2019 8:27 pm
But for low amplitude vibration, narrower on same pressure will be more comfortable.
Isn't this irrelevant though? Why would you run "narrower on same pressure" or more properly why would you pump up a larger tire to the same pressure as a narrower one? The whole point of the larger tire is so that you can run it at a lower pressure and get the benefit of improved comfort and traction.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

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