affects of tyre width on speed

[PK99]

As a gereral rule, the wider the tyre the more rolling resistance it creates, as there is more rubber in contact with the road. So going down a size or two should speed your ride up a bit, but you will notice a bit more road vibration as there is less rubber. I run 25's on my bikes, except the tourer which has 28's and they are still pretty comfortable.

The amount of rubber in contact with the road is the same for a fat tyre or a slim tyre, at the same pressure.

200lb rider

100 pounds per sq inch pressure in tyre = 2 sq inches of contact patch

Fat tyre = low deformation = low energy loss = low rolling resistance

Slim tyre = large deformation = higher energy loss = higher rolling resistance

 

[asterix]

Racing, That's kinda what I was hinting at the pro's use 23mm, it kind of throws those lab tests out the window, I recckon they know what they are doing.

Pro racers never did like lab tests

 

[frank9755]

At the same pressure a wider tyre....

... is over-inflated!

ie a wider tyre is not designed to be run at the same pressure - it would have too little rubber in contact with the road and would give poor grip.

 

[GrasB]

According to lab tests if tyres are pumped up, the wider tyres will actually roll better but try telling that to Wiggins, Cavendish et al. I think they are on 23mm.

Firstly, 25c tyres have a higher front area so increased drag & they simply don't work aerodynamically on current deep V section rims but even if the rim is the right shape 23c tyres have a better drag co-efficent. More than that when you really start to push hard in the corners 23c tyres being smaller are more stable & so handle better. So while they have a lower rolling co-efficent, given the same tyre construction, they're a slower tyre when it comes to race day & further to that the fastest rolling race tyres don't come in wider widths.

 

[jig-sore]

and dont forget that a wider tyre has a larger circumference (the reason you have to re-set your computer) so will actually travel further per revolution

i run 700x40 tyres on one bike and 700x28 on the other. same tyre, different size. my commute times are much the same, in fact the wind speed makes more difference.

lets sum it up in 3 words.... its all bollocks !!!

you should worry more about comfort than speed, that is where you will notice the difference

 

[RecordAceFromNew]

... is over-inflated!

ie a wider tyre is not designed to be run at the same pressure - it would have too little rubber in contact with the road and would give poor grip.

Surely the contact area is essentially the same at the same pressure since area x pressure is weight?

However the contact areas are of different shapes - wider and shorter for a wider tyre, which leads to less side wall deformation, but larger frontal effect from road surface uneveness and air resistance etc., aside from it likely to be heavier.

 

[008]

OK, Here's my non scientific opinion... I changed from 28c to 23c on my Sirrus and they are noticeably faster (not loads but noticeable) but only slightly less comfortable. I had schwalbe stelvio plus and now bontrager racelite hardcase. The stelvio plus are more comfy than the bontys but the bontys are ever so slightly quicker imo! The bontys are a lot cheaper on the other hand.

 

[frank9755]

Surely the contact area is essentially the same at the same pressure since area x pressure is weight?

Yes, I agree with that.

But the point is that the bigger tyre is designed to have a bigger contact area when each is inflated to its respective correct pressure. ie it is designed to run at a lower pressure, to be more comfortable, and to have more grip.

 

[JonnyBlade]

I use 23c's and find the rides very comfortable. I find what sorts I'm wearing has more of an impact!!!!
Just ordered a couple of 18cs to try out, maybe see if it makes a difference to speed?

 

[asterix]

and dont forget that a wider tyre has a larger circumference (the reason you have to re-set your computer) so will actually travel further per revolution

i run 700x40 tyres on one bike and 700x28 on the other. same tyre, different size. my commute times are much the same, in fact the wind speed makes more difference.

lets sum it up in 3 words.... its all bollocks !!!

you should worry more about comfort than speed, that is where you will notice the difference

Yes, that is why I have gone back to wider tyres. Being uncomfortable over longer distances is in itself fatiguing and undoubtedly wider tyres are significantly more comfortable than narrow ones.

I just tried the narrow tyres to see what difference to speed it made and it was so marginal as to be meaningless.

 

[Norm]

With apologies to those who have seen me write this before, I was commuting 9 miles each way on a Secteur with 700x25 and a Tricross with 700x32. The times on each bike were pretty much exactly the same, I put it down to the extra comfort of the 32s meaning I could just ride without worrying about the road surface, whereas I was constantly dodging the cracks and holes and frequently slowing for the worst patches on 25s.

 

[GrasB]

Yes, that is why I have gone back to wider tyres. Being uncomfortable over longer distances is in itself fatiguing and undoubtedly wider tyres are significantly more comfortable than narrow ones.

Not always. Assuming tyres are properly inflated to a decent road pressure (10~15% static tyre droop) wider tyres give more cushioning on large single point deformations & on random mild surface deformation. However a thinner tyres will be far more comfortable over roads with significant random pitting. Now here's the fun bit at I weight about 77kg my bike about 8kg & at 15% droop I end up with the following tyre pressures on 650x23 Pro 3 Race tyres: 72.5psi front & 85psi rear. My conclusion is that most people have their tyre pressures way over pressure.

 

[asterix]

My tourer has 1.75" tyres at c.50psi. No 23c tyres could remotely compete with that in the comfort stakes, and the bike is not that slow either.

 

[GrasB]

That's the sort of size & pressure which can kick my hands off the handle bars on the deeply pitted sections of roads... far LESS comfortable than a 23c tyre ime.

I should say that the form of discomfort is very different on the wide tyres, the vibration on narrow tyres is fundamentally lateral vibration & in that motion the wider tyres are better. The thing is the wider tyres don't just 'bounce' up & down but they also bounce from side to side, where as the narrow tyres shimmy a bit if they catch the edge of & fall into the pit of the surface. The extra dimension of vibration that wider tyres give makes the tyre far less comfortable to ride on & also if catching things wrong can easily kick the handlebars to one side or another.

 

[threebikesmcginty]

I only cycle slowly anyway so the tyre width thing has never really bothered me although I use a range from 23 - 45 IIRC. As long as I enjoy the ride all is well.