Wider lower pressure tyres are faster! (Warning friday content)

Mycroft H

Couple of interesting (and possibly controversial) points from a blog I read.

A quick snippet

Our research had profound implications:

Tire resistance is much more important than previously thought. For most riders, changing the tires is by far the biggest improvement they can make to their bikes’ performance. (Aero wheels will improve your bicycle’s speed by less than 2%, whereas tires can make a 20% difference.)

On steel drums, wider tires were slower because they had to run at relatively low pressures. Once we had shown that the high pressures served little benefit, it became clear that on real roads, wider tires are faster, period.

The secret to a fast tire is a supple casing. Compared to the casing, all other tire factors are relatively unimportant… In the past, many considered a high pressure rating as a sign of a “good, fast” tire. In fact, tires with high pressure ratings tend to need sturdier casings that make the tire slower.

Now, the author is known as a fan of the fat 35+mm 650b tyre size (Older TT machines and some audax/brevet bikes) and he makes a couple of interesting points. The main one, is that we should all abandon the skinny tyre size and have fat lower pressure tyres on our bikes.

Now, my experience on the matter is that I am struggling to notice the difference between my bike when fitted with 25mm tyres and 32mm (same rims). This is totally anecdotal, but I've not noticed a perceptible difference between the two performance wise. One is more comfortable. However, as I said this is totally anecdotal and is not the norm across the range I would guess.

Any one else have an opinion on the matter?

Lumen

Fat tyres might roll better for the same pressure, but nobody in their right mind runs 35mm tyres at 110psi or 23mm tyres at 70psi.

My subjective experience is that there are some exceptionally light and rare 28mm tyres that are almost as fast as 23mm tyres, but most 28mm tyres are slower, and most 32mm+ tyres are significantly slower.

Aside from rolling resistance, fatter tyres are significantly less aerodynamic, and this matters a lot at higher speeds.

Efficient cycling is about the sum of the parts. Taken separately, various practical changes (fatter tyres, heavier wheels, heavier frame, more relaxed geometry, dynamo hub, hub gear) don't make a massive difference, but if you stick them all together you get a very slow bike.

ednwireland

my vittoria diamante pro's are 220tpi think they roll much nicer than 127 tpi tyres (schwalbe ultremos), purely subjective opinion

barrabus

http://velonews.competitor.com/2012/05/news/giro-tech-rise-of-the-25c-tire_218011

Lumen

barrabus wrote: »

http://velonews.competitor.com/2012/05/news/giro-tech-rise-of-the-25c-tire_218011

“We never put more than 8 bar (116psi) in them, except for some of the Spanish guys, they really love high pressure. I don’t know why, but they do. So to make them happy I have to put more in. We run about 1 bar (15 psi) lower in the wider tires than in 23c tires.”

That suggests that 130psi is a common pressure for 23mm tyres. Don't fancy that on Irish roads!

AstraMonti

Lumen wrote: »

Aside from rolling resistance, fatter tyres are significantly less aerodynamic, and this matters a lot at higher speeds.

Why wider rims are more aero then? For exampe Hed is almost 29mm wide.

Lumen

AstraMonti wrote: »

Why wider rims are more aero then? For exampe Hed is almost 29mm wide.

A wide tyre on a narrow rim is draggy.

reallyunique

Why does the cross-section of the tyre significantly affect drag? The frame and rider should be orders of magnitude larger than the tyres in this respect.
Certainly the air thrown forward by the tyres as they rotate will contribute a great deal to the overall coefficient of drag but I don't see that increasing its contribution much as tyre width increases.
Is there any research on this?

Lumen

reallyunique wrote: »

Why does the cross-section of the tyre significantly affect drag? The frame and rider should be orders of magnitude larger than the tyres in this respect.
Certainly the air thrown forward by the tyres as they rotate will contribute a great deal to the overall coefficient of drag but I don't see that increasing its contribution much as tyre width increases.
Is there any research on this?

In terms of orders of magnitude, the difference between an excellent and terrible front wheel at 50kph is about 15W. That speed requires over 400W, even with a perfect aerodynamic position on a state of the art TT bike.

So thats 15/400, or less than 4%.

On the other hand, in competition 4% is an enormous amount and there is no reason to choose a slow wheel when a faster one is available.

Those numbers are all with 23mm or narrower tyres.

http://www.rouesartisanales.com/article-15505311.html