# affects of tyre width on speed



## tubbylee (9 Mar 2011)

im thinking of changing the tyres on my sirrus elite from 28c to 23c,the tyres i have are specialised all condition tyres and have never let me down.im competing in a duathlon in a months time and ive been told by collegues 23c would make a big difference on my speed is this true,i would be looking to use a similar type of puncture resistant tyre,as a flat in the middle of the race would be of no benefit.any advice would be appechiated thankyou


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## Rouge Penguin (10 Mar 2011)

The biggest difference would be comfort. I run 25s and wouldn't bother going to 23.


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## Rouge Penguin (10 Mar 2011)

Let me quantify that. I wouldnt because of one event, it wouldn't outweigh the rest of the longer rides. Work on your average speeds to be quicker.


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## Paulus (10 Mar 2011)

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.


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## BSRU (10 Mar 2011)

Paulus said:


> 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.



Wasn't there some research lately that suggested bigger tyres had lower rolling resistance due not deforming as much as thinner tyres. Thinner tyres were better aerodynamically, i.e. less wind resistance.


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## gbb (10 Mar 2011)

Reading Zinns Art of Roadbike Maintenance the other day opened my eyes to this issue. He stated that tyre width doesn't neccessarily make that much difference to speed, its the side wall, more importantly the strength of that side wall, that makes the difference. His opinion was that many 25mm tyres would be just as good as 23mm's. 
Mind, the difference from 28 to 23 must have an impact...surely ?


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## Rob3rt (10 Mar 2011)

Someone posted a scientific study on here somewhere not long ago that basically claimed to debunk the tyre width's effect on rolling resistance (whether results are noteworthy or not I dont know). Thus increased emphasis should be paid to the deflection of the tyre and thus tyre pressure, compound and sidewall strength rule the day.


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## frank9755 (10 Mar 2011)

Narrower tyres are faster not mainly because they are narrower but because they can be run at higher pressures. Higher pressure means less deformation of the sidewall and associated energy loss.

As others mention, there are other factors involved such as the type of compound and how it deforms. Tyres with better puncture resistance are generally slower. For example, Marathon Plus tyres are noticeably slower than ordinary Marathons of the same size. 

If you are racing then 23s would be sensible. They will be faster than 28s (not because they are narrower but because you will run them at c120psi rather than c100 so they will deform less). Then you have to decide what trade-off you want to make between a fast compound and puncture resistance. 

Here's a good summary of options!


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## HLaB (10 Mar 2011)

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.

On a persosal note my Kinesis used to have a 23 front/ 25 rear combo; when the 25 wore out the 23 was moved to the rear and a new 23 went on the front I've noticed little if any difference. I also changed the 28's for 25's on the Sirrus I found that made a more noticeable difference without too harsh a ride but how much of it was to do with me getting fitter and other mods (new wheels, drop bars & carbon seatpost) I couldn't quantify. Probably others will have other opinions but I think 25mm are the best compromise for comfort/speed.


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## PpPete (10 Mar 2011)

Rather depends whether you want one set of tyres for day to day use, and a different set for racing....

Single set for everything - I'd definitely go for 25s rather than 23s.


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## asterix (10 Mar 2011)

My bike had 23s and I have replaced them with 28s. I'll be using it for a sportive event in May that will be 100 miles and I want a bit more comfort. There is a time cut-off but I don't think the tyres are going make any difference to whether I make it or not. When I used the 23s on the Spring into the Dales ride the road surfaces gave me a lot of grief.. The hills I could manage.

I really think the only difference is slight extra weight and wind resistance.


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## frank9755 (10 Mar 2011)

HLaB said:


> 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.
> 
> On a persosal note my Kinesis used to have a 23 front/ 25 rear combo; when the 25 wore out the 23 was moved to the rear and a new 23 went on the front I've noticed little if any difference. I also changed the 28's for 25's on the Sirrus I found that made a more noticeable difference without too harsh a ride but how much of it was to do with me getting fitter and other mods (new wheels, drop bars & carbon seatpost) I couldn't quantify. Probably others will have other opinions but I think 25mm are the best compromise for comfort/speed.




Yes, but the point is that you can pump 23s up to a higher pressure. It's the pressure, not the width which makes them roll faster. The giveaway line in the article - which they don't bother to explain - is 'all other things being equal' - but they're not equal because 23s will be at higher pressure!

The OP wants the fastest tyres for racing. If he wasn't racing it wouldn't be worth bothering to change. Like you I use 25s on my commuting bike, for audax, sportives, etc, but on my time trial bike, where I will sacrifice comfort for speed, I have some very fast compound 23s at high pressure. My touring bike has 32s and my pub bike has 37s.

Sheldon's logic was that if you are going to have different sized tyres, you get optimal results from having the fat one with the lower pressure on the front, not on the back: lower rolling resistance from the one that bears most weight and a softer ride from the one under your handlebars.


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## HLaB (10 Mar 2011)

frank9755 said:


> Yes, but the point is that you can pump 23s up to a higher pressure. It's the pressure, not the width which makes them roll faster. The giveaway line in the article - which they don't bother to explain - is 'all other things being equal' - but they're not equal because 23s will be at higher pressure!
> 
> The OP wants the fastest tyres for racing. If he wasn't racing it wouldn't be worth bothering to change. Like you I use 25s on my commuting bike, for audax, sportives, etc, but on my time trial bike, where I will sacrifice comfort for speed, I have some very fast compound 23s at high pressure. My touring bike has 32s and my pub bike has 37s.
> 
> Sheldon's logic was that if you are going to have different sized tyres, you get optimal results from having the fat one with the lower pressure on the front, not on the back: lower rolling resistance from the one that bears most weight and a softer ride from the one under your handlebars.




Aggreed, I don't give too much weight behind lab tests  

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.  

I cant remember the full in and outs of Sheldon's article but iirc it was quite balanced between the pro and cons of each method on tyre sizing (I think the pro's of the wider tyre on the back were more important to me and I doubt mere mortals would perceive the difference; I certainly can't). Just to muddy the water conti brought out their force/attack system (24mm rear/ 22mm front)


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## John the Monkey (10 Mar 2011)

I went from 32c to 42c on the Long Haul Trucker (and 90psi to 60psi) and didn't see my commuting averages change at all.


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## PK99 (10 Mar 2011)

HLaB said:


> Aggreed, I don't give too much weight behind lab tests
> 
> 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.





there are other issues at play in addition to rolling resistance: rotating mass - the lighter the better - and aerodynamic drag - no point i having aero wheels if the tyre itself creates drag

At the same pressure a wider tyre has lower rolling resistance, but this is outweighed by the greater rotating mass and, most significantly, greater drag


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## PK99 (10 Mar 2011)

Paulus said:


> 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


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## asterix (10 Mar 2011)

> 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


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## frank9755 (10 Mar 2011)

PK99 said:


> 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.


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## GrasB (10 Mar 2011)

HLaB said:


> 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.


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## jig-sore (10 Mar 2011)

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


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## RecordAceFromNew (10 Mar 2011)

frank9755 said:


> ... 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.


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## 008 (10 Mar 2011)

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.


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## frank9755 (10 Mar 2011)

RecordAceFromNew said:


> 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.


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## JonnyBlade (10 Mar 2011)

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?


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## asterix (11 Mar 2011)

jig-sore said:


> 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.
> 
> ...




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.


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## Norm (11 Mar 2011)

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.


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## GrasB (11 Mar 2011)

asterix said:


> 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.


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## asterix (11 Mar 2011)

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.


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## GrasB (11 Mar 2011)

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.


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## threebikesmcginty (11 Mar 2011)

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.


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## tbtb (11 Mar 2011)

If the OP is thinking of new tyres for speed, first thing to check is that he has the first essential: a (floor, ideally) pump with a good big pressure guage on it. £15 well spent, lets you put current tyres at their exact max and at various other pressures, to find what works best _for you_. Different terrain, different rider, different best tyre. 

Grab a set of 23s cheap, sure. Might be wise to google your rim first, have a look at the manufacturer's webpage. Not guaranteed that the rim will be happy with a 23.


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## Banjo (11 Mar 2011)

I think the tyre weight has more effect than the size. I use very heavy Michelin City Pilots 32c on my commuter bike in Winter as they are incredibly tough. When I change to the same size but much lighter Bontrager racelight 32c summer tires it feels like a new bike much faster and more responsive.

As soon as its daylight on my commute both ways I change to the bontragers and its a relief.


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## Chris S (12 Mar 2011)

I'd have thought tyre pressure would have had more effect on speed - mine were way under and I've just pumped them up. The bike is noticeably faster.


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## tbtb (12 Mar 2011)

Chris S said:


> I'd have thought tyre pressure would have had more effect on speed


Narrow tyres have higher max pressures.


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## rualexander (12 Mar 2011)

Another thing that affects this subject is the road surface, if it is very smooth tarmac then narrower tyres will be best as they are lighter weight, but if the road surface is the harsh 'knobbly' kind of tarmac then wider tyres will roll better. 
In both cases you want to have tyres with supple sidewalls to minimise rolling resistance.
In my view, lighter weight to reduce rotating mass and supple sidewalls to cope with the 'knobblyness' of the surface will make the most difference rather than purely looking at tyre cross section.


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## RecordAceFromNew (13 Mar 2011)

tbtb said:


> Narrow tyres have higher max pressures.



+1 and actually narrower tyres should be run at higher pressure. As can be deduced from the respective shapes of the contact areas - else one will get pinch flats and/or rim damage more easily than with wider tyres. The relationship is essentially inverse proportional - e.g. halving the width needs doubling the pressure.


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## HLaB (13 Mar 2011)

tbtb said:


> Narrow tyres have higher max pressures.




Whilst I'd agree with you there are some minor exceptions my 25mm Vitoria Rubinos are rated to a max of 130psi where as my 23mm conti Gran Prix is only rated to 120psi max (not that it makes much noticeable difference at that level)


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