Tyre performance

doozerie

The topic of tyre widths and tyre pressure seems to be getting more air time recently, or at least that's the impression I'm left with as I've been stumbling across more online articles and discussions on it recently even though some of the research cited is a year old or more. It's an interesting topic, and if you believe some of the claims it's worth exploring for the potentially significant "free" performance benefits it offers.

There is a lot of information available, some of it purely anecdotal and some of it very much based on scientific study (Zipp have a lot to say on it, for example, backed by what seems like a lot of research). Some of the information is so sciencey that it melts my brain, but this Bicycle Quarterly: Performance of Tires article from June 2012 is very accessible and is also more willing than many to nail its colours to the mast with the following claims:

Our research had profound implications:

1. 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.)

2. 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.

3. 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.

Whether you accept those claims at face value or not there is certainly some interesting stuff in there that at least challenges some commonly held ideas about what contributes to greater speed on a bike.

07Lapierre

Eh.. Whats a "tire"?

Seaneh

doozerie wrote: »

The topic of tyre widths and tyre pressure seems to be getting more air time recently, or at least that's the impression I'm left with as I've been stumbling across more online articles and discussions on it recently even though some of the research cited is a year old or more. It's an interesting topic, and if you believe some of the claims it's worth exploring for the potentially significant "free" performance benefits it offers.

There is a lot of information available, some of it purely anecdotal and some of it very much based on scientific study (Zipp have a lot to say on it, for example, backed by what seems like a lot of research). Some of the information is so sciencey that it melts my brain, but this Bicycle Quarterly: Performance of Tires article from June 2012 is very accessible and is also more willing than many to nail its colours to the mast with the following claims:



Whether you accept those claims at face value or not there is certainly some interesting stuff in there that at least challenges some commonly held ideas about what contributes to greater speed on a bike.

So according to this the 32m tyres I have on my bike at the moment are faster than the 23m's I had on my last bike?

Not a fecking chance!

petethedrummer

Seaneh wrote: »

So according to this the 32m tyres I have on my bike at the moment are faster than the 23m's I had on my last bike?

Not a fecking chance!

nope!

Jan Heine, Editor, Bicycle Quarterly says:
June 13, 2012 at 4:28 pm
It probably depends on the size of your bumps, too. We haven’t tested identical tires in different widths beyond 25 mm, because at the time, there weren’t any available. We now are working on this, to see whether, for example, a 32 mm Grand Bois is significantly faster than a 29 or a 26 mm, all with the same casing and tread.

or maybe

Jan Heine, Editor, Bicycle Quarterly says:
June 19, 2012 at 7:45 pm
The trend from 20 to 23 to 25 mm is so linear that it’s obvious that there isn’t a plateau anywhere near 25 mm. We also tested some truly wide tires, up to 42 mm, and found that they certainly aren’t slower than the narrower ones. So assuming you have a somewhat normal road bike, the widest tires you can fit will be more comfortable and either faster or no slower than narrower tires.

Of course, if you ride a mountain bike, then this advice should be qualified a bit. And as I said, we have been doing more tests, so hopefully, we’ll have more results and more definite answers to these questions soon.

doozerie

Seaneh wrote:

So according to this the 32m tyres I have on my bike at the moment are faster than the 23m's I had on my last bike?

That depends. For one thing, across two different bikes then I can't imagine it's possible to compare so it's not possible to say one way or the other that bike A with 32mm tyre is faster (or slower) than bike B with 23mm tyres simply because of the tyres.

What the article does state though is that they found that wider tyres (up to 25mm) on the same bike rolled faster. But they also mention that tyre pressure plays a part, a view supported by stuff I've read from other sources. So a 25mm tyre with "excessive" pressure may be worse than a 23mm tyre with appropriate pressure. So there is more than one variable. From stuff I've read from Zipp on the topic, they optimise their rim design for 23mm tyres, so there is another variable again, the rim.

I've read more recent stuff where people speculated that the rolling benefits of wider tyres start to lose out to aerodynamic cost at about 28mm width, but I haven't found anything to verify that figure of 28mm. So the aerodynamic cost of wider tyres is yet another variable, and this may vary per frameset too due to different design (a frameset built to take 32mm tyres probably incurs more aerodynamic drag than one built to take a max of 23mm tyres).

Plus the construction of the tyre and its weight all play a part, so one brand or model of tyre in 25mm might not be comparable to another in 23mm either. Etc.

Seaneh wrote:

Not a fecking chance!

It's that thinking that the article, and others like it, challenges. Why do you believe that 23mm tyres are faster than 32mm tyres, even on the same bike? They might well prove to be, but the article puts the case very well that it's a mistake to assume 23mm are faster just because they are narrower.

This and other articles also suggest that it's a mistake to assume that inflating a tyre to higher pressure will improve it's rolling resistance too, quite the contrary beyond a certain point in fact. That too challenges the accepted practice of many.

petethedrummer

Was it Laurent Fignon who first went to 22/23mm tyres from the traditional 19mm? Apparently his team demolished everyone downhill, till the rest switched.

Lumen

It's a conspiracy to make us gravitate towards stupid fat 650b tyres on stupid fat aero wheels with stupid disc brakes and stupid stiff forks.

bbolger

Inrng has a pretty good post on the topic from a couple weeks ago:

http://inrng.com/2013/04/reinventing-the-wheel-25mm/