24mm vs 22mm

[mustang1]

No - I don't think you're getting this at all. That isn't what I said. If you inflate 23s to 100psi, you can also inflate 25s to 100psi and potentially roll better and with more comfort. Come on mate, seriously..


You asked this question before, and I answered it before.

Sorry! Someone has posted a link for jobst Brandt which I'm reviewing...

 

[boydj]

I have my 25mm tyres at 80 psi after reading
http://velonews.competitor.com/2012...esistance-than-their-narrower-brethren_209268
http://velonews.competitor.com/2012...ech-faq-again-bigger-tires-roll-faster_209888
http://velonews.competitor.com/2014...essure-width-affect-rolling-resistance_355085

 

[Mark2802]

I've also read that a tyre at higher pressure will effectively 'bounce' over gravel, stones etc. This apparently reduces direct contact with the road, so energy is lost.
A tyre with lower pressure will 'roll' over imperfections keeping good contact with the road, transferring more energy through the road surface thus increasing performance and speed. There must be a lower limit though or we'd all be riding on 10psi

 

[Yellow Saddle]

I've also read that a tyre at higher pressure will effectively 'bounce' over gravel, stones etc. This apparently reduces direct contact with the road, so energy is lost.
A tyre with lower pressure will 'roll' over imperfections keeping good contact with the road, transferring more energy through the road surface thus increasing performance and speed. There must be a lower limit though or we'd all be riding on 10psi

This is pseudo science.

In the first scenario, bouncing so that the tyre loses contact with the surface is obviously a scenario where you will do fresh air wheel spinning and yes, energy is lost. But this is not a real scenario and you'll never ride like that, not even in MTB. In other words, a made-up scenario that says or proves nothing.

In the second scenario, it is all nonsense. There is no such thing as transferring energy through the road surface etc.

Rolling resistance is under discussion and it stems from compressing rubber which then springs back with less energy than what was put in.

 

[Yellow Saddle]

I have my 25mm tyres at 80 psi after reading
http://velonews.competitor.com/2012...esistance-than-their-narrower-brethren_209268
http://velonews.competitor.com/2012...ech-faq-again-bigger-tires-roll-faster_209888
http://velonews.competitor.com/2014...essure-width-affect-rolling-resistance_355085

I read the first one and then gave up, Mr Zinn doesn't understand the concept of the co-efficient of friction and has some vague concepts of "internal friction" combined with hysteresis. I'm afraid what he wrote there is not helping the understanding of rolling resistance.

 

[bpsmith]

This is pseudo science.

In the first scenario, bouncing so that the tyre loses contact with the surface is obviously a scenario where you will do fresh air wheel spinning and yes, energy is lost. But this is not a real scenario and you'll never ride like that, not even in MTB. In other words, a made-up scenario that says or proves nothing.

In the second scenario, it is all nonsense. There is no such thing as transferring energy through the road surface etc.

Rolling resistance is under discussion and it stems from compressing rubber which then springs back with less energy than what was put in.

Actually, the discussion is whether 24mm is better than 22mm. RR is just part of it and @Mark2802 makes another point which is definitely part of the equation and which is often tagged along with RR on many articles on this. He shouldn't be shot down because you only want to discuss RR.

The whole point is that you can get the same RR but at different tyre pressures. The lower tyre pressure on the larger tyre gives you a smoother ride from a comfort point of view, along with the tyre not bouncing over tougher road surfaces and slowing you down.

People are arguing with your point on RR, and why you would ride a narrower tyre at a lower pressure, as you have glossed over the gains of lower pressure with the same RR.

 

[Mark2802]

I was not inferring that when riding over uneven road surface you take off and free wheel through the air. The bike 'apparently' bounces around minutely and becomes unsteady compared to a super smooth ride. This in turn affects momentum and fluidity in the pedal stroke. A wider, lower pressure tyre will 'give' absorbing and dissipating more road buzz keeping the bike steadier.
It's what I read is all so don't shoot the messenger. This and other things I read are the reason, as well as increased comfort that I changed from 23mm to 25mm tyres and for me, it works!

 

[Mark2802]

I was not inferring that when riding over uneven road surface you take off and free wheel through the air. The bike 'apparently' bounces around minutely and becomes unsteady compared to a super smooth ride. This in turn affects momentum and fluidity in the pedal stroke. A wider, lower pressure tyre will 'give' absorbing and dissipating more road buzz keeping the bike steadier.
It's what I read is all so don't shoot the messenger. This and other things I read are the reason, as well as increased comfort that I changed from 23mm to 25mm tyres and for me, it works!

 

[bpsmith]

I challenge anyone with 120psi inflated tyres not to notice a loss in momentum when riding over rougher tarmac, compared to ultra smooth tarnac. It is so obvious when it happens. Cattle grids show this off nicely.

 

[Yellow Saddle]

I challenge anyone with 120psi inflated tyres not to notice a loss in momentum when riding over rougher tarmac, compared to ultra smooth tarnac. It is so obvious when it happens. Cattle grids show this off nicely.

Momentum is defined as the function of mass times velocity and our forward momentum is linear. Riding over a cattle grid has no effect on that momentum. The reason you slow down is primarily because you stop pedaling and a very small component of hysteresis losses in the tyre. Remember, rolling resistance is measured in grams - five grams or so. A cattle grid has, say, ten beams which lets say, each increases the rolling resistance by a factor of four. This shows how small the increase of RR is going over a grid.

 

[Yellow Saddle]

I was not inferring that when riding over uneven road surface you take off and free wheel through the air. The bike 'apparently' bounces around minutely and becomes unsteady compared to a super smooth ride. This in turn affects momentum and fluidity in the pedal stroke. A wider, lower pressure tyre will 'give' absorbing and dissipating more road buzz keeping the bike steadier.
It's what I read is all so don't shoot the messenger. This and other things I read are the reason, as well as increased comfort that I changed from 23mm to 25mm tyres and for me, it works!

OK, if we are not considering "air" losses in pedaling effort, the only other explanation for energy losses is as explained to BP above. A rougher surface will increase hysteresis in the rubber and this is small. As you say, loss of momentum is probably due to less pedaling effort because shaking around like that hurts and you instinctively know that going slower will hurt less. On a wider tyre the relative increase in RR will be in line with the overall RR of the tyre but the reason you feel you don't lose momentum with fatter tyres is because you keep on pedaling.

 

[Cyclist33]

I was not inferring that when riding over uneven road surface you take off and free wheel through the air. The bike 'apparently' bounces around minutely and becomes unsteady compared to a super smooth ride. This in turn affects momentum and fluidity in the pedal stroke. A wider, lower pressure tyre will 'give' absorbing and dissipating more road buzz keeping the bike steadier.
It's what I read is all so don't shoot the messenger. This and other things I read are the reason, as well as increased comfort that I changed from 23mm to 25mm tyres and for me, it works!

At what point did @Yellow Saddle "shoot the messenger"? You posted something you'd read and he challenged that - not you. I can't see anywhere where he said "you're an idiot" or made it personal in any way.

 

[bpsmith]

Momentum is defined as the function of mass times velocity and our forward momentum is linear. Riding over a cattle grid has no effect on that momentum. The reason you slow down is primarily because you stop pedaling and a very small component of hysteresis losses in the tyre. Remember, rolling resistance is measured in grams - five grams or so. A cattle grid has, say, ten beams which lets say, each increases the rolling resistance by a factor of four. This shows how small the increase of RR is going over a grid.

I don't stop pedalling over Cattle Grids!

 

[bpsmith]

OK, if we are not considering "air" losses in pedaling effort, the only other explanation for energy losses is as explained to BP above. A rougher surface will increase hysteresis in the rubber and this is small. As you say, loss of momentum is probably due to less pedaling effort because shaking around like that hurts and you instinctively know that going slower will hurt less. On a wider tyre the relative increase in RR will be in line with the overall RR of the tyre but the reason you feel you don't lose momentum with fatter tyres is because you keep on pedaling.

Similarly, I don't stop pedalling over rougher tarmac.

Perhaps I used the wrong terminology, but I am slower over rougher tarmac than smooth tarmac and am also slower on rougher tarmac with the same tyres pumped to a higher pressure.

The point being, without trying to argue the wrong use of terminology, wider tyres allow the use of lower pressures which absorbs the shock more and loses less speed.

You can argue how minimal it is, but I can clearly feel it and see it on my Garmin at the time.

 

[bpsmith]

At what point did @Yellow Saddle "shoot the messenger"? You posted something you'd read and he challenged that - not you. I can't see anywhere where he said "you're an idiot" or made it personal in any way.

He doesn't ever actually say you're an idiot, but words it to make you feel that way. Every gain is supposedly "proven" to be negligible, yet many experience a difference. It's a repeating pattern for lots of posts on here.