Road Cycling - Tire width, psi and rolling resistance

So seems like an older school of thought is that higher psi reduces rolling resistance along with a narrower tire.

Seems like the new school is wider tire and lower psi.

Test seem to show higher psi has a lower crr, and maybe wider tire?

I can see how a higher psi can cause fatigue and make the rider slower over all, but I'd rather limit discussion to just crr, as if this is true, you can just raise the psi till your at a comfortable level.

Fire away!
:crash:

.

Test seem to show higher psi has a lower crr,

and what tests would these be? Most of the data posted in these threads in recent years has shown the opposite.

Unless I'm reading these all wrong, some of the most linked, and referred to tests, such as this one.
http://www.biketechreview.com/tires/images/AFM_Bumpy_Data_BTR_rev1.pdf

or

http://www.rouesartisanales.com/article-1503651.html
The tubular test was tested at 2 air pressures

Unless I'm reading these all wrong, some of the most linked, and referred to tests, such as this one.
http://www.biketechreview.com/tires/images/AFM_Bumpy_Data_BTR_rev1.pdf

or

http://www.rouesartisanales.com/article-1503651.html
Both clinchers and tubulars show lower crr with the higher pressure tested.

I understand, however, that what's best on a smooth laboratory drum might not do so well on real world roads.

Every time that you hit a bump a tire that's pumped up very hard will bounce upward. The energy that's required to lift the bike upward has to come from you. A tire with less air pressure will conform to the smaller bumps and consequently bounce less and absorb less of the rider's energy.

That's why I referenced the first link specifically. My understanding of that test is that it was done on a bumpy roller, yet it still shows the same trends.

I'm just wondering if anyone has seen any better evidence of the lower psi = better crr effect, or if anyone has done some kind of road coast down testing?

So seems like an older school of thought is that higher psi reduces rolling resistance along with a narrower tire.

Seems like the new school is wider tire and lower psi.

Test seem to show higher psi has a lower crr, and maybe wider tire?

I can see how a higher psi can cause fatigue and make the rider slower over all, but I'd rather limit discussion to just crr, as if this is true, you can just raise the psi till your at a comfortable level.

Fire away!
:crash:

I'm sorry, what does "crr" mean?

Co-efficient of rolling resistance. Think of it like a number to tell you how much resistance your tires are giving you while rolling. High resistance means you need more power to roll the wheel.

A larger tire, AT THE SAME PRESSURE, has a lower rolling resistance.

Narrower tires generally run much higher pressures, and thusly have lower rolling resistance. However, if a 23mm tire and a 32 mm tire are both run at 90 PSI, the 32mm tire will have less rolling resistance as tire deformation regarding contact area with the ground will be less.

http://www.schwalbetires.com/images/e_img_1164_1.jpg

http://www.schwalbetires.com/images/e_img_1164_2.jpg

Following that logic we should be riding 32mm tire at very high psi. Or at least as high as we can tolerate.
As stated, you said a higher psi reduced rolling resistance.

Following that logic we should be riding 32mm tire at very high psi. Or at least as high as we can tolerate.
As stated, you said a higher psi reduced rolling resistance.

Horse>dead>stick.

It's not so simple.

Casing construction/deflection + Compounds + Rotational mass + Tire pressure = best OVERALL performance.

Improve on one and sacrifice on one or more of the others.

Bicycle Quarterly also came to the same conclusions - that wider tires w/ less PSI have better rolling resistance - least i think that's how it went.

as proof, the rider who did the 1200km PBP in 50 hours rides on 32's if i'm not mistaken..

Ok, so are there any racing type tires that are at least 25? Seems most racing type tires (I'm looking for tubulars by the way) are in the 20-23mm range.

Ok, so are there any racing type tires that are at least 25? Seems most racing type tires (I'm looking for tubulars by the way) are in the 20-23mm range.

Hmmm...I wonder why...

OK, I'm running 27's (nominal 28 Conti Gators) at mfg's max of 120 psi.

Am I bad ? Or is it "my bad"?

;)

Hmmm...I wonder why...

So do I...
Lets look at your last post


Casing construction/deflection + Compounds + Rotational mass + Tire pressure = best OVERALL performance.

What part of the above cannot be scaled to a 25mm tire from a 23? Maybe a bit in construction. I'm sure the compounds used can be the same, rotational mass? hardly is gonna matter, tire pressure? Thats what this discussion is all about.

This theory is great and all but one only needs to look at what the pros ride to see what's "fastest". If a wider tire at higher pressure was faster, you bet your ass that's what they'd be riding. But they're not.

Of course they're going much faster than snails pace most rec cyclists go like botto for example.

I don't think we even need to look at what the pros ride. Just trying different sizes of tires yourself is pretty revealing. Personally, I don't buy the fatter tire idea at all. Even "just a recreational cyclist" can tell the difference. Plus, I find there's a difference in handling too. I also don't buy the idea that only wider is comfortable. Quality of the casing definitely affects it. I don't care what the tests show or what the marketing is. I don't use a cyclocomputer, so I don't have speed measurements, but I can guarantee you that a high-quality 23mm tires feels a heck of a lot snappier than a 32mm tire (and more than a 28, but 25 might be a toss-up).

Contradicting common sense with little scientific evidence to get attention seems to be one of the newer tricks in the book.

The wider tire thing is utter BS. The lower psi thing is BS as well in regards to crr. Trying to factor in rider comfort is just accounting for a variable outside the problem.

Can anyone in support of a lower tire pressure having a lower crr think of any reason that that might be true?

I mean, take it to the extremes, what's going to roll faster, a tire with 50 psi or a tire with 150 psi? I sure hope there's no doubt about that one.

Hmmm...I wonder why...

There's a huge difference in cornering and handling with wider tires.

Following that logic we should be riding 32mm tire at very high psi. Or at least as high as we can tolerate.
As stated, you said a higher psi reduced rolling resistance.

32mm tires won't run pressures to make them equivalent to, say, 23mm. The volumes are too large...to get that PSI would require a much wider (and therefore heavier) rim, and a very robust bead. There's a huge difference between 90 psi and 120 psi.

It's the at equal pressure parts that seems to throw people. The argument only really matters if you are running the narrow tire at low pressures.

If you are running your narrower tire really low for a particular reason, at that point you should look into a wider tire that will max out at the pressure you're running. Otherwise, it's technically an apples/oranges comparison.

I commute to work on a Giant Rainier that has been modified to ride like a road bike as much as possible without completely ripping it apart (trekking bars, 11-26 cassette, trekking crankset, road saddle...). With regard to the wheels, I have been experimenting with tires on my hilly 15 mile commute. I rode 2" Forte VersTracs for a long time because my old commute was off-road (and more fun). I recently switched to 1.5" Michelin TransWorld City for about a month. I can hardly tell the difference. Last night I slapped the VersTracs back on, and to me at least, I was absolutely flying up the hills on my commute.

The only common factor I can see between the two is that run them both at max psi (2" at 65 psi, 1.5" at 87-90 psi). Logically, the 2" tire should be much slower than the 1.5" tire due to weight and rotational mass, but it is not slower. Not trying to invoke heresy, but this is my experience. FWIW, the VersaTrac (2" tire) is knobby, but with a center bead that makes for one smooth ride.

Contradicting common sense with little scientific evidence to get attention seems to be one of the newer tricks in the book.

Are you kidding? It's an age-old art. Then again, it's funny how many idiotic cycling myths get perpetuated by "common sense".


The wider tire thing is utter BS. The lower psi thing is BS as well in regards to crr. Trying to factor in rider comfort is just accounting for a variable outside the problem.

Do you find yourself rocking back and forth as you repeat this mantra? There seems to be honest evidence that a wider tire, even at lower pressure, has less rolling resistance. There are many other factors to take into account, but I don't see why you immediately discount the data.

What part of the above cannot be scaled to a 25mm tire from a 23? Maybe a bit in construction. I'm sure the compounds used can be the same, rotational mass? hardly is gonna matter, tire pressure? Thats what this discussion is all about.

You want to throw out rotational mass? :rolleyes:

Between a 23 and 25 the casing construction (and thereby contact patch and casing deflection) will be virtually identical.

Compounding: the same.

Tire pressure: ditto. Although the 25 may be rated for a slightly lower pressure with the safety margins built into these ratings you could certainly run both the 23 and 25 at identical pressures.

The extra volume of a 25 over a 23 will give you some pinch flat protection but the only real difference will be mass which will be in the neighbourhood of 5% - 10%.

If you are talking about optimal tire pressure for a given size tire then that is another thing to consider.

Each tire will have its own optimal range. This is mostly a function of casing construction. Harder is certainly not faster as casing deflection is affected and, beyond a certain point, this will actually increase rolling resistance. Softer may be faster under certain conditions but too soft will also affect casing deflection.

If you are seeing guys riding wider tires at lower pressures maybe it has less to do with speed and more to due with the fact that road racers are getting older, on average, and our old backs can't take the pounding of a 23 at 120psi like they used to.

Wider tyres have more wind resistance and weight but roll better. On chip-seal roads, go wider. On smooth roads, go narrower.

Hi Bob, I'm not sure how maybe 25g of rotational mass would matter very much on a discussion of crr of tires. Would you be a bit slower accelerating? Yes, not by much.

I guess to make the question more specific. Given tires supposedly identical makes of tires (yes I've seen that even though 2 tires have the same name the construction can be different)

Lets say the avg person using 20mm has an optimal psi of 100psi, the 22 has 110psi. Which is going to roll faster? Or would the optimal rolling resistance be achieved for the 22 at 100psi? Or would it actually be the 20 at something like 130?

Still hoping to see some more data or good evidence of either.

A larger tire, AT THE SAME PRESSURE, has a lower rolling resistance.

Narrower tires generally run much higher pressures, and thusly have lower rolling resistance. However, if a 23mm tire and a 32 mm tire are both run at 90 PSI, the 32mm tire will have less rolling resistance as tire deformation regarding contact area with the ground will be less.

http://www.schwalbetires.com/images/e_img_1164_1.jpg

http://www.schwalbetires.com/images/e_img_1164_2.jpg


Due to the gas laws, a larger tire will support a larger mass at a lower pressure. Look at your car tires. Typical PSI for these is in the 30s, the same as an MTB tire. So yeah, when you make a tire super skinny, it requires higher pressure. The bigger the tire, the less pressure needed for similar rolling resistances.

Contradicting common sense with little scientific evidence to get attention seems to be one of the newer tricks in the book.

The wider tire thing is utter BS. The lower psi thing is BS as well in regards to crr. Trying to factor in rider comfort is just accounting for a variable outside the problem.

Contradicting scientific evidence with so called "common sense" is the oldest trick in the book. Crack open a physics book and you will see that friction is independent of surface area and higher volume makes up for high pressures.

Hi Bob, I'm not sure how maybe 25g of rotational mass would matter very much on a discussion of crr of tires. Would you be a bit slower accelerating? Yes, not by much.

25g will matter to which tire is faster. You want to talk about rolling resistance ONLY or do you want to talk about which is faster. Pick one because they are not always the same thing. You're trying to reduce a very complicated discussion to the point where it just doesn't make sense.


I guess to make the question more specific. Given tires supposedly identical makes of tires (yes I've seen that even though 2 tires have the same name the construction can be different)

I'm not sure what you are trying to say here. Also, tires with the same name will have the same construction. The casing is just wider.


Lets say the avg person using 20mm has an optimal psi of 100psi, the 22 has 110psi. Which is going to roll faster? Or would the optimal rolling resistance be achieved for the 22 at 100psi? Or would it actually be the 20 at something like 130?

Again, I don't have a clue as to what you are trying to talk about here - rolling resistance or which is faster?

You can't establish and optimal pressure as a general rule because it is specific to each model of tire. This is because of the other factors I pointed out earlier.



Still hoping to see some more data or good evidence of either.

Use the search function. This topic has been discussed to death on this forum. Do some reading. You might find whatever it is you are trying to figure out there.

I have done tons of reading, and what I've read does not make sense as everything posted contradicts itself.

Do you have any data or is the answer to everything you go do some reading?

Well, here's my reading.
Most discussions imply rotational mass is over rated according to all the physics formulas. So I will repeat 25g might help you accelerate a tiny weeny bit faster, but is hardly a contributor to which wheel is going to be faster. Otherwise Tufos would be the fastest tire around. That is the only thing you have suggested to make a difference.

I wish to talk about RR, since I don't think 25g in acceleration is going to matter. If you wanna talk about the combo, go ahead, but cite your data please.

If we can't establish an optimal pressure and general rule, and if we have no specific data for each tire than any discussion about tires is useless because we don't know what to test for.

And yes I have done a search. I've asked about specific examples in the original post for which no one has provided data to the contrary.

So as it stands, higher PSI is going to be faster.

The Bicycle Quarterly tests indicated that tire pressure had a very small effect on rolling resistance of most tires within a normal range of pressures. A 23mm tire at 105psi rolled fastest but lowering the pressure to 85psi increased rolling resistance less than 2%. A 28mm tire rolled fastest at 85psi and increasing the pressure did not decrease rolling resistance, but lowering it to 55 psi did increase resistance a little and lowering it to 35psi increased it a lot.

What made a bigger difference in rolling resistance was tire construction, tread thickness, tread pattern, tire age (older is faster), and tire temperature (hot is faster). The editor (mentioned above) used older, thinner, tires for PBP; had more flats, but still had an outstanding time.

I have done tons of reading, and what I've read does not make sense as everything posted contradicts itself.

This is quite possibly true.


Do you have any data or is the answer to everything you go do some reading?

Yes, I have data done by Continental AG, a few years ago. If you can't understand what I am trying to tell you, however, the data would be useless.


Well, here's my reading.
Most discussions imply rotational mass is over rated according to all the physics formulas. So I will repeat 25g might help you accelerate a tiny weeny bit faster, but is hardly a contributor to which wheel is going to be faster. Otherwise Tufos would be the fastest tire around. That is the only thing you have suggested to make a difference.

I was responding to your desire to compare a 23c and a 25c tire. My point was that any potential difference in RR of identical model tires, at the same pressure and under the same conditions just might be nullified by the difference in mass.

Just a point. No data.


I wish to talk about RR, since I don't think 25g in acceleration is going to matter. If you wanna talk about the combo, go ahead, but cite your data please.

See above.


If we can't establish an optimal pressure and general rule, and if we have no specific data for each tire than any discussion about tires is useless because we don't know what to test for.

A higher PSI will be faster, for a given tire, until you reach the point where the casing can no longer deflect effectively and then rolling resistance will increase.

This tipping point is different for every model of tire so how can you establish a general rule. If you can't understand this there is nothing left to discuss.

There is also no general rule because there are far too many variables involved.

Why would we not know what to test for? I thought you wanted to test rolling resistance?


And yes I have done a search. I've asked about specific examples in the original post for which no one has provided data to the contrary.

Look harder. Data and links abound.


So as it stands, higher PSI is going to be faster.

Incorrect.

Good night.

Look, some companies and websites want to sell in a niche market, and they contradict what every experienced road cyclist knows to be true. Don't read, ride. Ride the actual tires and then come back and tell us which feels like it's easiest to push.

Thanks Mkarl.

Bob -I've never said I don't understand what your saying, that's what you've been saying. You state a higher psi will be faster up till a tipping point. In the test quoted the tipping point was not reached till maybe around 150psi. So what is incorrect that higher psi is going to be faster?
As most recommendations I've seen seem to be about 100-110psi depending on rider weight.

Longfemur, would love to go out and test everything in the world and decide what I think is best, but I know of no one personally that can afford to do that. So the best I can do is read about product differences and try and decide what is best.

The nice thing about cycling is that, while it certainly can get very expensive, there is no change you can make to a bike that makes more difference than tires, and it's not that expensive to buy a pair of tires. Seriously, this is something you have to experience for yourself. The internet is full of rationalized BS from people who don't really know what they're talking about.

Buy a set, try them, and if you end up preferring the slower tires, just hang the good ones in the garage in case you have a change of heart later.

Lots of BS on the internet... Everyone should read, and use their brain.

Tires are expensive! Avg price for a gd tubular seems to be about 90. That makes a pair 180!! I can afford to test maybe 2 sets, but after that, I'll have to sell my left nut! (Which probably wouldn't go for much anyways)

Hows the weather down in Ottawa lately? Is it crazy like in Toronto? Sunny and than hail the next minute?

In my experience, the bigger the tire, ceteris paribus, the slower. Bigger means more rolling weight, wind resistance, energy absorbing. A 28c gatorskin is fairly petite for that size and can be pumped up to a high 120 psi. Even so, a 28 will be slower--although more comfortable--than an, e.g., 23 or 25 gatorskin. That's why all of the dedicated "race" bikes pretty much only accommodate 23s whereas the comfort oriented bikes usually come with 25s and can take 28s and higher without dragging on the brake housings.

The Bicycle Quarterly tests indicated that tire pressure had a very small effect on rolling resistance of most tires within a normal range of pressures. A 23mm tire at 105psi rolled fastest but lowering the pressure to 85psi increased rolling resistance less than 2%.

Now we're getting somewhere.

So what happens if you inflate the same tire to 125psi? Did they test that?

My other question has to do with test surface. If my understanding is correct I'd imagine that the optimum air pressure would decrease as the test surface gets progressively bumpier.

The 21mm Clement Criterium tubular tires rolled slightly slower (1.4%) at 130psi then they did at 105psi.

In general the tubular tires did better than similar sized clincher tires.

The 28mm Clement C. del Mundo tubular tires were 5.5% faster at at 105psi then the 21mm Clement Criterium at 105psi. Lowering the pressure to 85psi gained another slight 1.5% gain in speed.

CCrack open a physics book and you will see that friction is independent of surface area and higher volume makes up for high pressures.

Then why don't any world speed record setting bikes use huge fat tires?

There ya go, what we knew all along: nice tubies are fastest.

After about ten miles per hour rolling resistance gets overtaken by aerodynamics. So all the foremost mentioned is moot. Unless you guys roll around at 8mph.

Contradicting common sense with little scientific evidence to get attention seems to be one of the newer tricks in the book.

The wider tire thing is utter BS. The lower psi thing is BS as well in regards to crr. Trying to factor in rider comfort is just accounting for a variable outside the problem.

A+ to this. Any tire needs to be inflated at the pressure recommended by the manufacturer for the weight (bike plus rider) that it carries. The rolling resistance is higher if the tire contact surface is greater (let's not get down to the atomic level analysis). Wide tires are generally slower than narrow ones. The exception may be when you get down to 23 tire size; if you go lower, based on my experience, 20 c tire is slower on an average quality road, probably due to bouncing off.
saying that wider tire has lower rolling resistance at the same pressure is simply misleading - what is the rolling resistance of 2 tires of different size at their recommended (or optimal) pressures? I will leave discussion about the comfort to others.

The rolling resistance is higher if the tire contact surface is greater.

I don't think that's true.

At a given air pressure the size of the contact patch will be about the same. The shape of the contact patch, however is dependant on tire width. A very narrow tire will have a long narrow contact patch. That means the tire has to deform more where it meets the flat road surface. The energy that it takes to continuously deform the tire as it rolls is a major contributor to rolling resistance.

Thanks Mkarl.

Bob -I've never said I don't understand what your saying, that's what you've been saying. You state a higher psi will be faster up till a tipping point. In the test quoted the tipping point was not reached till maybe around 150psi. So what is incorrect that higher psi is going to be faster?
As most recommendations I've seen seem to be about 100-110psi depending on rider weight.

Longfemur, would love to go out and test everything in the world and decide what I think is best, but I know of no one personally that can afford to do that. So the best I can do is read about product differences and try and decide what is best.

Like I keep saying, each tire will have a different tipping point so it is impossible to establish a general rule for all tires under all conditions. There are too many variables.

And again, does decreased rolling resistance mean the tire will also be faster? Maybe. But under what conditions? Crit? RR? Uphill TT? Triathlon? Kilo? Hot? Cold? Wet? Dry? Chipseal? Ashphalt? Teak? Crosswind? Headwind? Sprinting? Climbing? Accelerating out of a corner? Do I need to keep going?

Over and out.

I don't think that's true.

At a given air pressure the size of the contact patch will be about the same. The shape of the contact patch, however is dependant on tire width. A very narrow tire will have a long narrow contact patch. That means the tire has to deform more where it meets the flat road surface. The energy that it takes to continuously deform the tire as it rolls is a major contributor to rolling resistance.

True, but the pressure is not the same, it is different and not given. Narrow tire is has higher recommended pressure than the wider one just to keep the patch size smaller while the shape is almost the same in either case. Try a simple test - make an imprint of 23 and 28 c tires under the same load with recommended pressures (different for each) and check the size of the patches.
Not to go in details, just think of car tires - the pressure must be just right, not high, not low, to minimize the fuel (energy) consumption. Similar logic applies to all tires.

I don't think that's true.

At a given air pressure the size of the contact patch will be about the same. The shape of the contact patch, however is dependant on tire width. A very narrow tire will have a long narrow contact patch. That means the tire has to deform more where it meets the flat road surface. The energy that it takes to continuously deform the tire as it rolls is a major contributor to rolling resistance.

Agreed.

In any event the empirical evidence is more persuasive then philosophic argument. Fact findings are not put aside by claims that they contradict common sense.

I doubt any of us would even notice the difference in rolling resistance out there on the bike, honestly.

Agreed and closed - over 2 years using 20 c and 23 c tires I did not notice any gain or loss in speed whatsoever. As comfort is not a topic here, I would not mention it (although safety and comfort are second and 3rd reason I'm riding on 23 c tire. The first one is $$$$).

Like I keep saying, each tire will have a different tipping point so it is impossible to establish a general rule for all tires under all conditions. There are too many variables.

And again, does decreased rolling resistance mean the tire will also be faster? Maybe. But under what conditions? Crit? RR? Uphill TT? Triathlon? Kilo? Hot? Cold? Wet? Dry? Chipseal? Ashphalt? Teak? Crosswind? Headwind? Sprinting? Climbing? Accelerating out of a corner? Do I need to keep going?

Over and out.

Now you're just being mean. The OP seems to be interested in better understanding rolling resistance and the factors that affect it for different tires. While it's fine for you to correct oversimplifications, the OP and all of us would appreciate it if you would stop heading off discussion with "Its too complicated for you to understand." You seem to have access to meaningful data and experience in this arena. Can you give us a few specific findings or experiences that would be pertinent to the subject matter? Is there a range that these tipping points can be found based off of tire quality/compound/maker/width? I would guess that this tipping point is often above the max psi listed on the tire? How did this testing done with Continental affect their tire development program? In your experience, is it often the best policy to run tires near the max pressure listed on the sidewall? Is this one of the reasons why tire manufactures choose the max pressure they do? Or is it just strength based?