Tyre width

Jan. 20th, 2016 12:03 am
jack: (bike)
[personal profile] jack
The tyres on my bike seem to be 35c and 38c width, if I read them right. Would a thinner tyre be better for cycling round Cambridge? I mostly go short distances 1 mile to 4 mile, but it would be nice if there wasn't unnecessary effort, and nice if it was possible to cycle to Shelford occasionally, which right now is possible but a bit too much of a trek to ever want to do it. Or should I be looking at a better bike instead?

Date: 2016-01-20 08:52 am (UTC)
emperor: (Default)
From: [personal profile] emperor
Narrower tyres can usually be inflated to higher pressures, and will offer less rolling resistance (I have 32C tyres, IIRC); but only a certain range of tyres will fit a particular rim (if you see what I mean).

Date: 2016-01-24 05:43 pm (UTC)
damerell: (cycling)
From: [personal profile] damerell
(C is not part of the width. It may be attached to eg "700" in "700x35C"; 700C is a rim diameter. The late great Sheldon Brown has a page explaining this; there is now a sane ISO system.)

Not particularly. The main factor informing rolling resistance is pressure - the higher the better. At a given pressure, a fat tyre has slightly lower rolling resistance. Unfortunately, the main factor informing rider comfort is also pressure - within reason, the lower the better. Hence a fat tyre means you have to compromise less. The risk of pinch flats is also much less on fat tyres, which is more of an issue with a more massive rider.

The reason everyone doesn't use fat tyres is threefold; as Emperor says, sometimes you just can't get to a desired pressure in a fat tyre (but this is not a given - the tandem uses 32mm tyres at 100psi). A fat tyre has higher air resistance but because power to overcome air resistance varies with the cube of speed this is not a significant effect unless you ride very quickly (like, one-testicled American speeds). A fat tyre (and a wide rim to mount it on) are heavier, which may be significant if you are gram-shaving (which we aren't) or believe exaggerated myths about rotating mass (which you shouldn't).

Another highly significant factor is tread. For road riding, tyres should be slick - a bicycle tyre cannot aquaplane at bicycle speeds. Tread pattern causes extra rolling resistance, and fat tyres are much more likely to have significant tread patterns - in particular, off-road knobblies are dog slow on asphalt.

Date: 2016-01-30 02:58 pm (UTC)
blue_mai: (Default)
From: [personal profile] blue_mai
I commented anonymously by mistake. that was me.

Active Recent Entries