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Old 10-08-05, 03:40 PM   #1
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Rolling resistance

hi guys,
does anyone know much about rolling resistance. If so what do you know about the effects of different tyres, tyre pressures and bearings on this area. Also, does anyone know of any accurate research that has been conducted.

Thanks!
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Old 10-08-05, 04:11 PM   #2
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It's minimal, the majority of the drag is from wind-resistance. Just lowering your head by 2" makes a bigger difference than any variation in tyre types & pressures. Here's some info:

Jobst Brandt - Tire Rolling Resitance
Analytic Cycling - Tire Rolling Resistance
Journal Applied Physiology - Hour Record Case Study.pdf
Jim Martin - Aerodynamics of Cycling
Bret L. Breslin, Ph.D - The Cycling Thesis
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Old 10-08-05, 05:06 PM   #3
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Higher tire pressures doesn't mean less rolling resistance and neither do smaller tires.
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Old 10-09-05, 10:06 PM   #4
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What's basically happening is the energy is expended deforming the tire, and it's lost in the form of heat and noise (mostly heat). A wider tire generally deforms a greater mass of tire and higher pressure resists the deformation, so those two factors do influence your rolling resistance. While I haven't ever quantified it, I would swear that I feel far more effect from having my tires at the proper pressure than I do from lowering my head. The second link that Danno posted has a nice graph showing tires under different conditions experiencing significantly less rolling resistance as pressure increases.
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Old 10-09-05, 10:30 PM   #5
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Back in the 70's, when Schwinn was actually an American bicycle maker, and not a sticker on a Chino-crap bike, they did some interesting tire research. Around 1970, the sort of cyclist who would buy a top level bike used sew-up tires, rather than clinchers. Schwinn research was directed at designing clinchers that could compete in weight and rolling resistance with sew-up tires.

And, the result of their research was evidence that modifying the rubber that was in contact with the road could reduce rolling resistance by 50%. By 1980, Specialized was working with its Asian suppliers (with National's Panaracer likely be a major player) to design clinchers that had even lower rolling resistance.

If you look through back issues of "Bicycling" from the mid-80's, you see advertisements for tires where the tire featured in the ad would be compared with Brands "A", "B" and "X". Often, there were dramatic differences in rolling resistance between tires of identical size, but of differing designs.

In the past year or two, I don't recall seeing any tire ads that discuss rolling resistance. I suspect that tire companies have figured out that their customers have only two real "obsessions": the race crowd, with their obsession with light weight. The commuting/touring/recreational crowd with their obsession with avoiding flat tires.

In 2005, it doesn't seem as though anyone is out buying tires based upon manufacturer's claims about rolling resistance. Out on the road, any difference between brands RR performance is not obvious enough to merit consideration..



I
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Old 10-10-05, 08:10 AM   #6
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Quote:
Originally Posted by alanbikehouston
And, the result of their research was evidence that modifying the rubber that was in contact with the road could reduce rolling resistance by 50%.

you see advertisements for tires where the tire in the ad would be compared with Brands "A", "B" and "X". Often, there were dramatic differences in rolling resistance between tires of identical size, but of differing designs.
I think that you have to be careful with that type of data. I don't doubt they are factual, I just question the relevence. I don't know what the measurement of rolling resistance is, I assume it's grams or something like that. Suppose tire A has 10 grams of rolling resistance and tire B has only 5 grams. You could factually say that tire B has half the rolling resistance of tire A and yet the 5 grams of difference is so tiny that it's irrelevant.

If you want to go faster, work on your position on the bike. Compared to the energy required to push your torso through the air everything else is small potatoes.
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Old 10-10-05, 12:22 PM   #7
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Quote:
Originally Posted by DannoXYZ
It's minimal, the majority of the drag is from wind-resistance. Just lowering your head by 2" makes a bigger difference than any variation in tyre types & pressures. Here's some info:
I'd be more specific. Varying tires on a road bike (like going from a 700x23 to a 700x25) won't make a huge difference, so, yes, lowering your head will have a larger effect. But go from a road bike to a mountainbike with 2.3" knobbies, and I'll guarantee you can tuck all you want and won't match the speed of a road bike.
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Old 10-10-05, 01:03 PM   #8
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Yes, there is a difference, I'm not denying that. I'm talking about quantitative numbers. I was talking more about variation in tyres on the same bike. If we want to compare knobbies with road-bikes on the big extreme, then we need to compare extremes in positioning as well. The results of a coasting test down a hill may end up looking something like this:

TOP-SPEED DOWN HILL, UPRIGHT POSITION
700x23c: 35mph
2.3" knobbies: 31mph

TOP-SPEED DOWN HILL, TUCKED POSITION
700x23c: 45mph
2.3" knobbies: 42mph

The faster you go, the less and less rolling-resistance makes a difference. It goes up linearly with speed, so if you go twice as fast, you may end up with twice the rolling-resistance. However, wind-resistance and drag goes up to the square (^2) function of speed, so wind-resistance is 4x as great when you go twice as fast.

So at lower-speeds, rolling-resistance makes the biggest difference. Such as pushing a baby-stroller and seeing how long it'll coast before coming to a stop. Tyres would make a great difference at these 2-3mph speeds. However, as you pick up more and more speed, the less and less rolling-resistance makes a difference as wind-drag increases so much more.
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Old 10-10-05, 03:08 PM   #9
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Quote:
Originally Posted by DannoXYZ
TOP-SPEED DOWN HILL, UPRIGHT POSITION
700x23c: 35mph
2.3" knobbies: 31mph

TOP-SPEED DOWN HILL, TUCKED POSITION
700x23c: 45mph
2.3" knobbies: 42mph
I'm very surprised. I've often told people not to worry so much about rolling resistance and to work onltheir position on the bike, but even I would have expected the difference in coasting speeds between 700 X 23c road tires and 2.3" knobbies to be greater than that.
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Old 10-10-05, 03:24 PM   #10
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The differences are actually greater than that on the slight downhills and rollers of between 20-30mph where most people spend their times. I'm just trying to equalize as many outside variables as possible to focus on just rolling-resistance of the tyres. I presented some extreme examples of very steep hills with perfect side-by-side starts and coasting only.

In actual use, you usually see greater differences because you typically start downhills faster on road-bikes than MTB/beach-cruisers, so you end up with even faster top-speeds. And road-bikes have taller gearing so the roadie can have more human-power added to his downhill speed than the MTB/beach-cruiser which mainly relies on gravity. Then there's the aerodynamics of the bikes themselves. Would be best to have a cross/touring bike that can take both 700c and 26" wheels to make the controls easier to manage.

There are just so many variables, and most of them are more significant than rolling-resistance, that's all I'm trying to point out.

Interesting parallel between Brandt's comparison of tyre construction that roughly follows the evolution of auto-tyres from bias-ply to radial construction. The benefits in reduction in total carcass-flex, heat-buildup and rolling-resistance have been documented for decades and radial tyres are the norm in cars and more recently motorcycles. His comparison of same-model tyres in different widths seems to born this out as well with the Avocet 20/30 tyres having less rolling-resistance in the wider 28c size than the narower 25c version. All four of which outperformed the narrowest tyre, the Michelin Hilite Comp in 20c width.

Last edited by DannoXYZ; 10-10-05 at 03:34 PM.
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Old 10-10-05, 08:49 PM   #11
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Quote:
Originally Posted by Retro Grouch
I'm very surprised. I've often told people not to worry so much about rolling resistance and to work onltheir position on the bike, but even I would have expected the difference in coasting speeds between 700 X 23c road tires and 2.3" knobbies to be greater than that.
Don't be surprised. That wasn't actual data, just speculation:
Quote:
Originally Posted by DannoXYZ
The results of a coasting test down a hill may end up looking something like this:
Though in his defense, he did call that "quantitative."

Last edited by Layton; 10-11-05 at 11:35 AM.
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Old 10-10-05, 09:05 PM   #12
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Quote:
Originally Posted by operator
Higher tire pressures doesn't mean less rolling resistance
In general, that's incorrect.

Without going into the physics of it, it's instructive to consider that tires running at lower pressures run hotter due to the friction generated by the deformation of the rubber. Heat is energy, energy which is essentially being generated by your legs and isn't helping you go any faster.

Take a guy who's running at 70psi and have him go to 120, and he's not going to slow down, unless it's a ride quality issue, or some other outside factor.
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Old 10-10-05, 09:25 PM   #13
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I have 2.3's and 1.95's I switch back and forth on my MTB for
different situations and there is absolutely no doubt the narrower
tires roll better and are easier to pedal.
Also, tucking down will get you 2 or so mph.
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Old 10-10-05, 09:53 PM   #14
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Quote:
Originally Posted by alanbikehouston
snip...In the past year or two, I don't recall seeing any tire ads that discuss rolling resistance. I suspect that tire companies have figured out that their customers have only two real "obsessions": the race crowd, with their obsession with light weight. The commuting/touring/recreational crowd with their obsession with avoiding flat tires.

In 2005, it doesn't seem as though anyone is out buying tires based upon manufacturer's claims about rolling resistance. Out on the road, any difference between brands RR performance is not obvious enough to merit consideration..
Probably there is not a significant difference between brands anymore. It's possible there was no difference to begin with, but more likely, other companies recognized that less rolling resistance was a selling point and developed their own improvements in tire compounds and designs to match, and no one's improved on it significantly since then.
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Old 10-11-05, 06:42 AM   #15
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Quote:
Originally Posted by operator
Higher tire pressures doesn't mean less rolling resistance
Quote:
Originally Posted by Layton
In general, that's incorrect.

Without going into the physics of it, it's instructive to consider that tires running at lower pressures run hotter due to the friction generated by the deformation of the rubber. Heat is energy, energy which is essentially being generated by your legs and isn't helping you go any faster.

Take a guy who's running at 70psi and have him go to 120, and he's not going to slow down, unless it's a ride quality issue, or some other outside factor.
If you look at the test data, it pretty much shows on a single tyre-model, higher-pressure always results in lower rolling-resistance. However, the difference between 100-150psi is quite minimal. I think what Operator was getting at is that it's not a hard and fast rule. For example, some tyres at 90psi have less rolling resistance than others at 120psi. So you can't make the "higher-pressure = less rolling-resistance" assumption across different tyre-models. Then throw in the width where wider tyres have less rolling-resistance, but higher wind-drag and it muddies the water even more.
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Old 10-11-05, 11:46 AM   #16
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Quote:
Originally Posted by DannoXYZ
If you look at the test data, it pretty much shows on a single tyre-model, higher-pressure always results in lower rolling-resistance.
Thanks for restating what I said.
Quote:
Originally Posted by DannoXYZ
I think what Operator was getting at is that it's not a hard and fast rule.
"...higher-pressure always results in lower rolling-resistance." Sounds hard and fast.
Quote:
Originally Posted by DannoXYZ
For example, some tyres at 90psi have less rolling resistance than others at 120psi. So you can't make the "higher-pressure = less rolling-resistance" assumption across different tyre-models.
I never made that assumption, as is obvious from my post. You quoted my post - but did you even read it? And if that's what Operator was getting at, then he should have actually done so.
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Old 10-11-05, 09:16 PM   #17
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Quote:
Originally Posted by DannoXYZ
Then throw in the width where wider tyres have less rolling-resistance, but higher wind-drag and it muddies the water even more.
I'm almost positive wider tires generally have slightly higher rolling resistance than narrower...all other factors being controlled, of course. The same load would cause more deflection over the wider span, so there should be more energy loss, so you've got both deformation and drag working against you with fat tires.
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Old 10-11-05, 11:53 PM   #18
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Since no one is looking at the test-data, I'll post it here:


First, note that for ALL tyres of any construction and model, the higher the pressure, the lower the rolling-resistance, for that tyre only. So yes, you can say that running at 120psi on a VittoriaCX will have less rolling-resistance than 90psi. Same thing with 120psi on a Michelin HiLite vs. the same tire at 90psi. However, trying to compare between different tyres is difficult, because an Avocet30 @ 70psi has the same rolling resistance as the Specialized Touring at 130psi.

Then we can narrow down the variables by looking at a single tyre-model only. The Avocet20 in 25mm width is the exact same construction as the 28mm version. Same thing with the Avocet30 in 25 and 28mm widths. Comparing the Avocet20 in 25mm width vs. the 28mm width shows the wider 28mm one has lower rolling-resistance at the same pressure. Same thing with the Avocet30 where the wider 28mm has lower rolling-resistance than the 25mm one at the same pressure. Why?

The reason has to do with the shape of the contact patch. The contact-patch surface-area at the same pressure will be the same for both 25mm and 28mm tyres. This surface area is dictated by the equation:

ContactPatch = Load / PSI

So both narrow and wide tyres have the same contact-patch surface-area with the same load and same tyre-pressure. Let's take the case of a 150lb rider running 100psi tyres. We can compute the contact-patch as:

ContactPatch = 150 lbs / 100 lbs/sq.in. = 1.50 SqIn contact area

However the shape of that contact patch will look different between a wide vs. narrow tyre:



The wider tyre will have a wider shorter contact path while the narrower one will have a narrow, longer contact path. Note that the surface-area of both contact-patches is the same square-inches because we're holding load and pressure constant.

The main difference is in the longitudinal deformation of the casing. The wider short contact patch of the wide-tyre deforms a smaller amount of the circumference of the casing than the longer/narrow contact-patch of the narrow tyre. The greater deformation generates for more carcass-flexing and more heat generated.

This is exactly the same phenomenon with car tyres. Wider tyres can carry more load because at teh same pressure, it takes more load to deform the same amount of circumference. For the same load, the lower deformation gives better grip because the contact patch squirms less. Wider tyres also last longer due to the lower heat-buildup. But... they do weigh more and have more aerodynamic drag. So bodywork is crucial to make a car aerodynamic around the tyres.

Last edited by DannoXYZ; 10-12-05 at 11:24 PM.
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