"Wide tires do not roll slower at lower pressures. In fact, testing indicated that a wide tire at lower pressures rolls faster than a narrow tire at high pressures, if all other factors remain the same. Even narrow tires can be ridden at comfortable pressures with only very small concessions to performance.
Perhaps the most important result of the test is that tire pressure does not significantly affect rolling resistance. Wide tires in particular do not need high pressures to roll fast. But because many current wide tires are designed to handle high pressure, they have strong casings that lack suppleness. This results in higher rolling resistance than necessary."
- Road Bike Rider Newsletter (2006), based on Vol 5 No. 1 issue from Bicycle Quarterly http://www.bicyclequarterly.com. The test included nine 700C tires, seven 650B tires and two tubulars. The protocol and results were reviewed by industry experts.
Courtesy : Velo Chimp
Posts
I can't imagine racing on big 25C tires that are running at 80psi.
ReplyDeleteWow that surprises me. I always thought that fatter tyres had more resistance.
ReplyDeletehmmm....now I am going to need to find a new excuse as to why I go so slow.
Years ago I had inside info that Cyril Guimard (at the time Bernard Hinault's DS) instructed his team mechanics to inflate the tubs up to 110 psi, not beyond. His idea was that the lower psi resulted in a more comfortable ride with no compromise of rolling resistance, with the result of a fresher rider at the end of the day. Looks like he knew something....
ReplyDeleteGentleriders :
ReplyDeleteHere's the dirty little secret. The claims made in the first statement of the post are not outrageous, although it would be nice to know exactly what factors they kept SAME. But the protocol should be, I believe, a basic smooth metal drum test.
A wider tire at a lower pressure absorbs road shock more due to the higher surface of area and contact patch. It literally gobbles up the road irregularities without any change in speed.
A ridiculously high pressure thin tire does the opposite. Because of a low contact patch and lesser surface area, it will just bounce over the irregularities and actually sap away some of the power input to the pedals. That means small decelerations in speed and that put over a long period of time add up to a considerable amount. Basically, what is means is that you're wasting energy while losing speed every now and then, as well as sacrificing comfort which basically decreases your overall output unless you can somehow stand the punishment on your crotch.
This is why riders at the Paris Roubaix are wiser. They oump their tires to 80-90 psi, not more. Do they lose speed, not really.
The other case they are making for here is the fact that wider tires are meant to be run at somewhat lower pressures than your typical road racing tires. By increasing or decreasing the pressure by a few PSI's, you're really not going to affect the rolling resistance that much, in fact, that value is in terms of little grams of force.
Very high pressure tires also take something away from cornering grip in wet weather. Try it.
Anyway, compare grams (think ridiculous carbon bottle cage) side to side with a few pounds of fat that you can take off from your body.
The bottom line here is : Thinking of speed just in terms of TIRE PRESSURE is stupid.
There is a pronounced inverse relationship between vehicle weight and rolling resistance, as well as dependence on the quality of tires, TPI, blah blah.
There is conventional folklore.
Then there is Analytic Cycling. Pull up the the Rolling Resistance page any time you want, put in the numbers and start believing real things :)
Btw, just a thought : We're all riding pneumatic tires, not solid rubber tires of olden days. Pneumatic tires are designed to compress and account for road surface variations. If you suddenly pump your tires up to ridiculous amounts, think of what you're losing.
ReplyDeleteI really respect and miss the issues of Bicycle Quarterly. They had some very sound technical articles.
ReplyDeleteYeah, they're one of the best publications out there. Some of the bike magazines these days really upset me, which explains why I dont bother subscribing.
ReplyDeleteCheck out the
past issues of Bike Quarterly,
including topics covered. I think you can still order back issues.
A copy-paste from their site -
ReplyDeleteQ: Most bike magazines like everything their advertisers sell. How about you?
A: Most bicycle magazines are financed through advertising. Contrasting this, more than 90% of Bicycle Quarterly's revenues come from readers' subscriptions. So we can afford to tell you what we think, even if it offends our advertisers. In fact, advertisers who make good products, appreciate our honest reviews: If we like something, it really is very good.
This is why tubeless makes so much sense. Low pressure, but not risk of snakebites. Great cornering grip. No increase in rolling resistance.
ReplyDeleteBTW - I have the new Dura Ace 7850SL wheels with Hutchinson Fusion Tubeless tires and they are sublime. I've sold all my tubulars except for a nice set of Mavic Cosmic Carbone Pros with Vittoria CXs.
Anon - The only disadvantages being - you need lots of arm strength to install them, and deal with messy sealants. Theoretically the rolling resistance must be somewhat lower but I have to give it to someone for noticing the subtle difference. At high speeds, aero drag overshadows everything else.
ReplyDeleteAnon @ 10:46,
ReplyDeleteHow many miles would you say you got in those tires and did you have flats upto this point. I also wonder if they're like those latex inner tubes that lose a tenth of the total pressure every night, before you have to fill them up again? Tubeless might be good for mountain biking but I havent tried.
The tires were difficult to mount dry. However, a little soapy water on the beads and it was a snap.
ReplyDeleteTrue, I can't tell a difference in rolling resistance, but so long as they are not SLOWER, I find the other advantages are significant.
I agree that at speed aero means everyhing. But, the tubeless are great for my training, group rides, rides in the mountains with lots of hard cornering, etc.
I've never flatted them and they lose about 10psi per night.