32 mm Vs 35mm Tire

[Yellow Saddle]

Heine's main point is about suspension losses, which he claims are much more significant (i.e. more watts of lost power) than rolling resistance and air drag (presumably on a sufficiently-rough road surface). He describes the drastic increase in drag and slowdown felt when riding over rumble strips, which I'm sure most of us have also experienced.

Heine's musings over clinchers or tubulars is, again, not specifically about rolling resistance, but about their impact on suspension losses, which is affected by how flexible their sidewalls are and their usable range of inflation pressures. This affects how well they absorb bumps and isolate the sprung mass of the rider and bicycle. It is mainly in the body of the rider where the suspension losses happen - jiggling of the rider's flesh is powered by vibrations transmitted up from the road surface.

Brandt is either discussing rolling resistance in a very narrow technical sense, or considers that suspension losses are insignificant but offers no estimation of just how insignificant. Heine, on the other hand, has considered both. Brandt would be correct if real roads were as smooth as the steel drums used in rolling resistance tests, which is rarely the case.

No mystery here, wider tyres are tested at lower pressures because they cannot be inflated to pressures as high as narrower tyres - this is a limitation of the tyres, not the test procedure or equipment. Within the same brand & model, wider tyres usually have lower maximum inflation pressures than narrower ones, due to the mechanical limitations of the bead/rim interface.

In any case, the premise behind the 15% tyre drop method is that wider tyres should be inflated to a lower pressure than narrower tyres to reduce suspension losses (which results in higher speed) for a given level of snakebite resistance, so it's not even a limitation.

Heine does not work for a bike or tyre manufacturer and does not have access to laboratory equipment - roll-down tests on a real road are all he can do and he has described their drawbacks, so I won't knock him for that.

Tyre manufacturers don't publish suspension loss tests, I can speculate this is because:
1. There is no standard for a jiggling, vibrating human body, therefore test results would not be comparable
2. There is no standard for how rough a road surface is, therefore test results would not be comparable
3. If suspension losses are much larger than rolling resistance losses, then that would make the differences between different tyres seem insignificantly tiny, which does not help sell that brand of tyre. Much like factoring in rider weight makes the weight savings of a more expensive, lighter bike seem insignificantly tiny.

Which is why Heine tested at the same temperature.

Before I take this further, I want to understand suspension losses. Are you talking about a combination of tyre compliance as well as all the other losses in everything except the tyre?

 

[snailracer]

Before I take this further, I want to understand suspension losses. Are you talking about a combination of tyre compliance as well as all the other losses in everything except the tyre?

Suspension losses exclude losses in the tyre and any air drag. It would mostly be due to friction of the rider's jiggling body and luggage, maybe a little in the dampers of the suspension system if the bike is equipped with them.
If the tyre is perfectly compliant (i.e. transmits no vibration) or the road is perfectly smooth, then suspension losses will be zero, while rolling resistance losses in the tyre would still be present.

 

[Yellow Saddle]

Suspension losses exclude losses in the tyre and any air drag. It would mostly be due to friction of the rider's jiggling body and luggage, maybe a little in the dampers of the suspension system if the bike is equipped with them.
If the tyre is perfectly compliant (i.e. transmits no vibration) or the road is perfectly smooth, then suspension losses will be zero, while rolling resistance losses in the tyre would still exist.

Thanks. I've re-read the article and see the paragraph on that now. I should have picked it up earlier.

This is a strange experiment and it is ambiguous about what he wants to measure or prove.
Since suspension losses are apparently a result of vibration induced into the bike and rider, a simple test would be to attach the same wheel with different tyres at different pressures to an accelerometer and vibrate them and measure output vibrations at the axle.

To get any meaningful result you have to separate rolling resistance and suspension losses and then assemble them at the end in combinations to see what combo gives the best result.

His findings are flawed:
1. Rolling resistance is higher than aero drag. This requires a speed component and ideally, a graph. Aero drag goes up by the square of the speed and very quickly overtakes RR.
2. On the steel drum story, Brandt et al have quantified the RR for various widths and pressure. His "finding" is like rediscovering gravity. RR is a baseline constant and increases as road roughness increases. It is therefore irrelevant to talk about real roads. It confuses the issue and makes people think that some tyres will, irrespective of having a higher RR than others on a steel drum, perform better than those same ones on "real roads". This is not realistic.
3. "Supple casing" is a vague term. He should have introduced hysteresis of the tyre and tube combination. You can have a rayon or silk casing of 220 TPI that's very supple and slap a 10mm slab of soft rubber on it and fit that to a puncture proof 10kg tube. The result will not be a low RR device. The concept of hysteresis does away with all the nonsense.

Sorry my Heine, but no cigar for you this time.

 

[snailracer]

...This is a strange experiment and it is ambiguous about what he wants to measure or prove...

I agree that Heine's article is all over the shop, but then it is written for cycling enthusiasts, by a cycling enthusiast, it is not a self-contained scientific paper aimed at scientists or engineers. That thread about tyres has been going on for literally years, it would be tedious for their regular readers if every new article reiterated every detail of previous testing carried out over that time.

...Since suspension losses are apparently a result of vibration induced into the bike and rider, a simple test would be to attach the same wheel with different tyres at different pressures to an accelerometer and vibrate them and measure output vibrations at the axle.

To get any meaningful result you have to separate rolling resistance and suspension losses and then assemble them at the end in combinations to see what combo gives the best result...

That is how a professional engineer with access to the relevent equipment would probably do it, but he would still need a industry-standard set of input vibrations modelled on an industry-standard real road, and an industry-standard human body model to convert the axle vibrations to energy dissipated in that body. As far as I know, those standards don't exist.

...His findings are flawed:
1. Rolling resistance is higher than aero drag. This requires a speed component and ideally, a graph. Aero drag goes up by the square of the speed and very quickly overtakes RR...

He is talking about the small aero drag of wheels only, not the whole rider/bicycle system.

...2. On the steel drum story, Brandt et al have quantified the RR for various widths and pressure. His "finding" is like rediscovering gravity. RR is a baseline constant and increases as road roughness increases...

Rolling resistance covers the energy dissipated within the tyre itself, and Heine does not claim that this changes as the road roughness increases. As far as I know, rolling resistance measurements are only ever done on a smooth steel drum, so it is unknown whether rolling resistance changes with roughness - it probably doesn't, to first-order approximation. Heine's point is that road roughness increases suspension losses, and that is completely ignored by the established rolling resistance test setup because there is no source of vibrations and no hysteretic "rider body" being vibrated in the test fixture. Rolling resistance testing doesn't cover aero losses either, but you don't seem to have issue with that.

...It is therefore irrelevant to talk about real roads. It confuses the issue and makes people think that some tyres will, irrespective of having a higher RR than others on a steel drum, perform better than those same ones on "real roads". This is not realistic...

I actually believe that a high RR tyre can go faster than a low RR tyre on a real road, IF it can be inflated to a pressure that results in lower total combined rolling resistance and suspension losses. If that confuses people, then too bad, it's not Heine's problem if truth is complicated.

As the OP asked, if you have 2 similar tyres, but one wider than the other, then usually the narrower tyre will have lower RR losses because it will be inflated to a higher pressure than the wider tyre. The pressure is assumed to be sufficiently higher to overcome any minor effects of contact patch shape. However, the narrower tyre, inflated to a higher pressure than the wider tyre, will transmit more vibration to the rider and increase suspension losses.

Narrower tyres are usually inflated to a higher pressure than wider tyres for the following reasons:
- They have a higher maximum pressure rating
- They have a higher minimum pressure rating
- There is less tyre separating the rim from the ground, therefore more pressure is needed for equivalent protection against snakebite.

...3. "Supple casing" is a vague term. He should have introduced hysteresis of the tyre and tube combination. You can have a rayon or silk casing of 220 TPI that's very supple and slap a 10mm slab of soft rubber on it and fit that to a puncture proof 10kg tube. The result will not be a low RR device. The concept of hysteresis does away with all the nonsense...

Heine doesn't need to go into detail about supple casings and hysteresis because, while these are big factors in rolling resistance, they have only minor effect on suspension losses because compliance is dominated by inflation pressure.

In principle, you could make tyres and tubes from materials with zero hysteretic losses (and therefore zero RR) but you will still have suspension losses.

 

[Yellow Saddle]

I agree that Heine's article is all over the shop, but then it is written for cycling enthusiasts, by a cycling enthusiast, it is not a self-contained scientific paper aimed at scientists or engineers. That thread about tyres has been going on for literally years, it would be tedious for their regular readers if every new article reiterated every detail of previous testing carried out over that time.

That is how a professional engineer with access to the relevent equipment would probably do it, but he would still need a industry-standard set of input vibrations modelled on an industry-standard real road, and an industry-standard human body model to convert the axle vibrations to energy dissipated in that body. As far as I know, those standards don't exist.

He is talking about the small aero drag of wheels only, not the whole rider/bicycle system.

Rolling resistance covers the energy dissipated within the tyre itself, and Heine does not claim that this changes as the road roughness increases. As far as I know, rolling resistance measurements are only ever done on a smooth steel drum, so it is unknown whether rolling resistance changes with roughness - it probably doesn't, to first-order approximation. Heine's point is that road roughness increases suspension losses, and that is completely ignored by the established rolling resistance test setup because there is no hysteretic "rider body" being vibrated in the test fixture. Rolling resistance testing doesn't cover aero losses either, but you don't seem to have issue with that.

I actually believe that a high RR tyre can go faster than a low RR tyre on a real road, IF it can be inflated to a pressure that results in lower total combined rolling resistance and suspension losses. If that confuses people, then too bad, it's not Heine's problem if truth is complicated.

As the OP asked, if you have 2 similar tyres, but one wider than the other, then usually the narrower tyre will have lower RR losses because it will be inflated to a higher pressure than the wider tyre. The pressure is assumed to be sufficiently higher to overcome any minor effects of contact patch shape. However, the narrower tyre, inflated to a higher pressure than the wider tyre, will transmit more vibration to the rider and increase suspension losses.

Narrower tyres are usually inflated to a higher pressure than wider tyres for the following reasons:
- They have a higher maximum pressure rating
- They have a higher minimum pressure rating
- There is less tyre separating the rim from the ground, therefore more pressure is needed for equivalent protection against snakebite.

Heine doesn't need to go into detail about supple casings and hysteresis because, while these are big factors in rolling resistance, they have only minor effect on suspension losses because compliance is dominated by inflation pressure.

In principle, you could make tyres and tubes from materials with zero hysteretic losses (and therefore zero RR) but you will still have suspension losses.

Thanks for taking the time to respond so comprehensively. I now gasp the concept.

If anyone else is confused, just suck in your gut, tense all your muscles and lose some body fat. That will make you loose less energy to suspension losses....but necessarily faster. Gravity was not included in the experiments.

 

[snailracer]

Thanks for taking the time to respond so comprehensively. I now gasp the concept.

If anyone else is confused, just such in your gut, tense all your muscles and lose some body fat. That will make you loose less energy to suspension losses....but necessarily faster. Gravity was not included in the experiments.

Or you could fit a saddle with springs