Rubber on the road does not create rolling resistance. *Flexing* of the tire to put rubber on the road does. If you have a 100psi tire supporting 100#, then the tire must flex enough to put 1 square inch of rubber on the road. A narrow tire must flex more than a wide tire in order to do that.

Agreed. Energy from the pedals goes into:
1. Mechanical friction.
2. Hysteresis losses in tire flexing.
3. Aerodynamic friction.
4. Bouncing the load vertically.

It's important to understand that it isn't the tire that supports, but the air within. The tire only serves to contain it. At equilibrium the axle weight will equal (roughly) the air pressure times the area of the contact patch. Assuming equal pressure, a narrow tire will have a long, narroy patch and a wider tire a short fat patch. Now draw a circle, and you'll see that a longer secant will cut deeper from the circumference than a short secant. That means more distortion of the tire, hence more loss to internal friction.

The thickness or thinness of the tread and the suppleness of the body, along with the shape of the wall also factor into this, but all things being equal a shorter (fatter) contact patch will roll easier than a long one.

No racing. Lots of fitness/recreational riding, frequent organized club/group rides, and several centuries and similar organized/charity events each summer. I'm looking at getting into some weekend and other short duration touring. My road bike is an old aluminum Trek 1500 that has been modified with triple and a long cage derailleur. I use it for training and group rides. My touring style bike is based on a cro-mo Trek 700 frameset, flatbar with all Deore and Deore LX components and a handbuilt set of 36-spoke touring wheels. This has been my distance bike for centuries and long fitness/pleasure rides. I've also got a rigid frame trail bike but it is irrelevant to this conversation as it is not built for speed and already has 40mm multi-surface tires on it.

I'm heading for 50 years old and even when I get down to my ideal weight, I won't be a small man as I carry a fair amount of upper body muscle, so I have no delusions about becoming a racer, nor do I have any desire to do so. That said, going fast is still fun and want to continue to improve my strength, speed and endurance.

Safety is also a concern as you can't go fast if you aren't confident about your tires doing what you need them to do. I wouldn't say the 23s on my road bike are all that uncomfortable, just less comfortable and less stable than my 25mm tires when it comes to less than perfect road surfaces.

All I'm really looking for is information on the performance changes I can expect if I move my 25mm tires to the road bike and go up a width or two with the same model of tire on the touring bike.

This is super helpful.
I'm probably in the same size bracket as you. I hit 230 or so during a brief period of inactivity in my mid-life, and am now back down to my "fit" 185-190 lbs, which is about as low as I go without getting scrawny.

I commute with panniers, etc, so my body weight + gear (bike not included) is typically 215-230, and way more when I make a grocery run.

My "light and fast" commuter was a classic sport/road bike, and I rode it with 32's, 28's and 25's. I preferred the 32's with my commuting loads, and found the 25's to be a bit overloaded for my taste, and not as fun. The 32's provided better comfort and more secure cornering with loads in the vicinity of your current riding weight, so that's my personal experience with it. I preferred my 25mm tires when it comes to less than perfect road surfaces. I preferred the 25's by far when riding unloaded (extended road rides), but bear in mind my body weight is lower.

I'd say, try some 28's for your sportier bike and 32's for your touring bike.

I finally found a rolling resistance test which compares various widths of tires and various models, all inflated to the maximum pressure written on the sidewall. It's here:
http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm
I don't know of another test like this.

The copyright on this test is 2002, so newer tires are not included, too bad. Nonetheless, one can clearly see the trendlines. Curiously, the tire tested with the least resistance at 20 mph is the 23c Vredestein Fortezza. My brevet tire of choice is the Fortezza Tricomp at the 140 lb. pressure that was tested.

I believe the OP is asking a question about rolling resistance, not advice on what might be the most comfortable tire for his (unknown) type of riding. As I said earlier, a much more useful way to get better riding comfort is to ride a more comfortable frame.

As for the contention that lower pressure is faster on a bumpy surface, here is a bumpy roller test:
http://www.biketechreview.com/tires_...a_BTR_rev1.pdf
As you can see, bumpy always has more resistance than smooth, though bumpy resistance decreases with increasing pressure, just like on a smooth roller. Jobst Brandt long ago pointed out that, while it is true that a tire encountering the front of a bump accelerates upward and is thus slowed, it is also true that the tire is just as likely to encounter the back side of a bump and be accelerated.

I've been doing the same competitive (aren't they all!?) group ride every Sunday for the past 15 years. We aren't exactly newbies. We all run 23c tires. We don't pinch flat. The last brevet I was on with Chris Ragsdale, he was riding a Cervelo with 23c tires. All the top brevet finishers ride carbon bikes with 23c tires, except for Heine, who rides the tires he sells. My tandem riding friends who hold the Seattle-Spokane (S2S) tandem record set it on 23c Vredestein Tricomps. If it were true that wider, low pressure tires were faster, either from lower rolling resistance or lower fatigue, one would think competitive riders would have noticed. In 2011, Ragsdale rode PBP (1200km) in 44:36, even though he made the mistake of following other riders on a 40 km navigational error near the finish. He was about 9 hours faster than Heine. Ragsdale rode a Kestrel on PBP. Judging by his kit, they were a sponsor. I can't vouch for the exact size of his tires, but they look like 23c in the photos.

I confess I'm a huge Ragsdale fan. I've ridden with him and he is the finest riding companion one could have as well as a wonderful human being. I wish him luck on his solo RAAM attempt.

Jut to make things interesting, I'll point out that it's the tension in the sidewalls at the top of the wheel that supports the weight. Here're a couple of references:

http://books.google.com/books?id=ViI...ewalls&f=false

http://www.millersville.edu/physics/.../059/index.php

This is true (the nature of the OP's question), but the OP did mention that the HP 23's were not suiting him. So, this being the case, it seems you're recommending that he stick with 23's at high pressure and get a new frame.

There are other factors, I believe, that pros and aspiring racers are running 23's as a norm - weight being one. The narrower tires will have less rotational mass and will accelerate more easily, etc. Plus, many race-spec tires are not available in widths wider than 23.
The physics have been analyzed, and a significant enough number of the results have shown that for a given pressure, the rolling resistance (driven by deformation) is actually lower with a wider tire.
Other factors such as wind resistance, availability and rotational mass help build the case for narrower tires for those concerned with these things.

I quite frankly do not believe that the incremental rotational mass and wind resistance is going to make a difference in the context of this post - larger rider, non-racing, discomfort with higher pressure, etc.

So, to the OP, as you can see the whole rolling resistance topic is a can of worms. Hopefully you can glean enough from the many perspectives here to form your own opinion on what will suit you best for your needs.

Cheers,
Michael

This is the important point: The contact patch size is equal to the load on the tire divided by the tire pressure.*

So two different tires with the same load and same pressure have the same size contact patch.

This is what many people miss. A fat tire and a skinny tire that are both inflated to 100 psi have the same size contact patch. And since the fat tire is wider, it needs to deform less of the circle to make the same size area. (This would really be a good place for a picture. Oh well....).

Cheers,
Charles

* For a normally inflated tire. Clearly, if the air pressure is 0, the contact patch is not infinitely large. :)

To the OP, if you can get wider tires that run at the same pressure at your narrow tires, you will lose nothing as far as rolling resistance. What you may find with the wider tire is that you prefer to lower the air pressure depending on your weight to make your ride more comfortable (which you can't do with a skinnier tire) and you may even gain in speed if the high pressure is causing you to bounce on crappy roads.

In summary: Go big. :D

Cheers,
Charles

It has to do with the mechanism that causes rolling resistance - it is not from the rubber rubbing against the road, but from the deflection of the tire as it rotates under load. Rolling resistance is primarily caused by energy lost in the casing and tread as the bottom of the tire constantly flattens out then rebounds while the wheel rotates. A larger tire (all other things being equal) has less deflection than a narrower one, and so if you compare two tires - a fat one and a skinny one with no other differences, there will be less rolling resistance from the fat one.

In reality, all other things are not equal - fatter tires are generally run at lower pressures than skinny ones, and the same unltra-light thin casing racing tires avaialbe in 23 and 25mm wide are usually not available in 32 or 35mm versions... the wider tires are usually flat resistant and/or have a thicker tread. Also, narrower tires have less aerodynamic resistance and are lighter, so there are trade offs. In reality, as mentioned above, the rolling resistance is a pretty minor drag compared to aerodynamic resistance and gravity pulling you down as you climb a hill, so a narrower tire will have a net benifit of being 'faster' even though it is possible to have lower rolling resistance.

These are interesting discussions, and I'm always interested to see the data that each camp brings out to support their hypothesis, but in the end, I'm pretty agnostic as to which tire has the absolute lowest RR. At least until I have the power-to-weight ratio to be competitive (and assuming I want to compete in something), I'm happy to use a tire that's a size or two too big for the comfort. (Heck, my riding group must not be very competitive if I can hang out at the front with 26x1.75 Paselas. :p)

I think the OP might be pleasantly surprised if he were to try a set of quality 700x25s. The RR shouldn't go up significantly, and he'd be able to drop his pressures a little without raising his risk of pinch flats.

The size of the contact patch is equal to the weight the tire is carrying divided by the tire pressure.

So if you have a skinny and an fat tire at the same pressure, they have the same size contact patch. This is what most people miss.

Now think of how the tire deforms to make the contact patch. The wide tire is wider, so it needs flatten less of the circle to get its patch. The narrow tire, however, need to deform more of the circle to get the same size patch. So the narrow tire deforms itself more than the wide tire. And this is why the narrow tire has more rolling resistance than the wide tire (assuming the same material and air pressure).

Cheers,
Charles

The "maximum pressure written on the sidewall" has nothing to do with optimum pressure for a given load, nor is there an equal relationship with that number across all manufacturers. The max pressure number written on sidewalls is the result of a test to see at what maximum pressure a tire (actually group of tires) will remain seated on a given rim (there is no test rim standard BTW), divided by two. http://www.bccclub.org/documents/Tireinflation.pdf see third paragraph of MAXIMUM INFLATION PRESSURE. Sorry, that table of rolling resistance testing is flawed.



Except you're omitting the effect rim width has on contact patch shape & area, and assuming the tire is static.

I'm too lazy to go and find the quote, but someone said it best about having the right amount of air for a given condition. On a perfectly smooth track 18mm tires cranked up to 150psi make sense. Obviously you would never use those for mountain biking. I've seen cyclocross racers run their tubulars at 25psi or less. There's an ideal width and pressure for every application, and finding that balance for your riding style is for you to figure out. I have 22mm tubulars on my race bike and they're very fast but I would never want that on a commuter.

Sorry, but this is total BS. The chosen tire width and pressure has a HUGE influence on the comfort of the bike. If I put 23s on my commuter and inflated them to the maximum inflation pressure as you suggest (which is not logical whatsoever...) the ride would be harsh and punishing. But with 28mm tires inflated to a reasonable pressure (about 90psi) the bike is reasonably quick and still comfortable. With 38mm tires at around 60psi I can ride down stairs on the thing.

I realize that if you run a tire at higher pressure than the manufacturer recommends, you do so at your own risk, but does this mean that it is reasonably safe to run a tire at say 125% of its rated top pressure? Being a clyde I've often run tires 5-10 psi above their rating in order to stay at a roughly 15% drop, but this seems to indicate a lot more leeway than that. I understand that with wide tires running extremely high pressures puts a lot of stress on the rims so that would have to be considered as well.

What is a "safe" pressure is a result, not a prediction. How well the tire seats on any one rim might not be the same as the next rim. Feel free to experiment with "some" over pressure but even a under pressured tire can blow off if the fit is not correct. Andy.

This rolling resistance debate is and probably always will be silly.

I don't know. There's nothing wrong with trying to find a better way. But I agree that folks take it to extremes.

Then again this is Bike Forums, and I can't see that this is any sillier than some of the other debates that seem to inflame so much passion.

Chain lube, wheel building, frame material, buying on the net vs. LBS (haven't heard so much of that one lately), and so on.

Maybe one of those folks who knows how to post a survey thread, can put one up and let us vote for what we think is the silliest topic.

This is a small effect on the tire patch area, but a much larger effect on the tire patch shape. Assuming a reasonable pressure, of course (as a tire with no pressure doesn't have infinite contact patch area) and at that point, it's the tire as much as the rim.

I've been experimenting with my bikes. Fatter tyres are comfier and slower. Except on really bad roads. On bad roads, fatter tyres can be faster as well as comfier.

When accelerating, or braking, or when going really fast - fatter tyres are even more slow than thinner ones.


For bad roads in my country, I'm still not sure whether 23 or 35 tyres are faster. So many bumps that fatter ones can sometimes be ridden faster, more comfortably. I'll experiment with 25 and 28 ones, to try and find "the sweet spot".

My experience has been that overpressure is more like to crack the rim sidewalls outward, than to harm the tire.

For anyone who hasn't looked at the article, there is a nifty list of pro teams tire and inflation pressures. And what Shimagnolo is pointing out that Carbonfibreboy got wrong is that they are generally using much lower pressures with the 25-30 mm wide tubulars... some inflated as low as the mid 50s psi. Only one or trwo was above 80 psi!

The lesson to be learned here is that rolling resistance is just not as important as many make it out to be, especially when compared to drag from other sources like aerodynamics.
I recall reading somewhere that tubulars often have higher RR than top quality racing clinchers, but are still widely (universally?) used in the pro peleton because of the other advantages they give (smoother ride, more traction, etc).

Interesting. Is there a similar article about what tires and pressures teams use for TDF?

What would be the point?

None of are riding the TDF, none have fulltime team support, none are being paid to use sponsors equipment, and all of are paying for our own equipment.

We all weigh different amounts, and ride different ways, under different conditions. There's plenty of info available, and many links to it in this thread. The data's there, so it's up to each of to consider it, form our own opinions and apply it to our specific needs.

Tire selection, width and pressure are like chain lube, regardless of any science, people have their own preconceived notions and will believe what they believe, and act accordingly. Some, like me might even sit on the fence and ride 25mm tires for sport road and 50mm tires for commuting, with pressures chosen accordingly.