Tyre Width

[Farky]

Is it true that thinner tyres do not necessarily mean less friction with the road? I have 21's and was going to go thinner (19's) but if it means more friction, I wont bother.

p.s. I currently pump them up to max psi which is 125

 

[HLaB]

I'm no expert but I think I read somewhere that you don't get much benefit once you go below 23mm. On that basis I doubt 21's to 19's would give you any benefit.

 

[Randochap]

There is very little relationship between tyre width and performance. In fact, contact patch can be very much the same for very wide tyres.

There are too many variables. The quality of the tyre casing is by far the biggest consideration. Pumping tyres up to silly high pressures on rough roads will actually slow you down, due to vibration, whereas a lower-pressure, wider tyre is actually an advantage under those conditions.

We don't ride on steel rollers, which is where most "rolling resistance" tests are performed.

I've explained this elsewhere, but I'll say it again: Conventional wisdom dies hard, along with over-inflated tyres.

Look into some of the latest, fast rolling wider tyres, like the new Continental Grand Prix 24mm and 25mm Schwalbe Ultremos. And don't pump them up to the max.

 

[cadseen]

stick to 23, minimum on the road, you may get an advantage for say 19-21 if your doing a time trial on a good surface (but would need to be a tubular) but thats about it.

 

[jimboalee]

Its the inflation pressure that determines contact area. That's why they call it "lb/sq in" or psi.

If you are 180 lb and your bike is 20lb, that is 200 lb. Assuming there is a 60/40 spread rear/front, and you have 100 psi in each tyre, there is 1.2 square inches in contact at the rear, and 0.8 square inches in contact up front.
Pump up to 120 psi, and the contact area reduces, and so does the coefficient of rolling resistance.

Imagine Track tubs at 150 psi. A 135lb lady rider on a 15lb bike - 0.5 sq in. each when she's stood up with her head over the stem.

I ride 23mm Gatorskins with 120 psi in the rear and 105 psi front.

 

[byegad]

There is certainly a big drag from a too soft tyre and pumping it up a bit noticably increases speed.
The tendancy is then to say, 'Well if a bit more pressure is good, a LOT of pressure must be better!'
This is actually wrong and above a certain pressure your rolling resistance on anything BUT a totally smooth road goes up. This is because if the tyres is JUST soft enough to deform over a small irregularity it will give back SOME of the energy absorbed by the deformation of the tyre over the irregularity.
A lot of people don't understand this but it can and has been proved.
On narrow tyres, 25mm or less I suspect that the pressure where you start to lose speed due to the amount energy last in vibration, rather than the 'give and take' on irragularities, is for most rider weights near the manufacturers upper pressure limit anyway. So the myth that harder is faster is reinforced.
Anecdotally. I changed from 25mm tyres to 35 some years back and promptly pumped the tyres up to maximum. I was appalled at how slow the bike felt. After a puncture where my roadside pump couldn't reinflate the rear tyre to maximum pressure I road home surprised at how fit I felt. After using my track pump to reinflate the repaired tyre the bike was slow again. So I tried reducing pressure with very pleasant results in speed.

 

[jimboalee]

Yes Byegad; difficult to believe.

After 20 years as a motorcar tester, ROCK HARD tyres give a better efficiency AND maximum speed than manufacturers recommended inflation pressures.
The downside is the vehicle loses contact area and can end up in the bushes.

Maybe the apparent 'slowness' of the 35mm tyres compared with the 25mm tyres was due to the increased moment of inertia and wider radius of gyration ?

 

[fossyant]

Go with 23's for all round performance - i.e. fast, light etc.

I used to TT on 18mm tubs, but tubs roll faster and are more comfy. I used to train on 21's for years, but moved to 23mm in the last few years as 21 and below give a harsh ride - 23mm slightly softer, but just as fast. If you want fast, light and comfy, then go for Mich Pro Race 2/3, Conti GP 4000, or Shwalbe Ultremo's.....

 

[asterix]

With roads like they are round here (York, at the moment), I wouldn't go under 23