Tyre size

[cdfeto]

Hi,
I'd like to find my wheel (tyre) diameter to set up a speedometer.
The front wheel has a 2.75-17 tyre on at the moment, and although I could just measure the diameter (would require some big verniers or a couple of squares, which I don't have handy at the moment) I was hoping I could just get the diameter from a conversion or calculation.

Any help would be great, cheers.

[bogan]

Hi,
I'd like to find my wheel (tyre) diameter to set up a speedometer.
The front wheel has a 2.75-17 tyre on at the moment, and although I could just measure the diameter (would require some big verniers or a couple of squares, which I don't have handy at the moment) I was hoping I could just get the diameter from a conversion or calculation.

Any help would be great, cheers.

put a mark on the tyre, mark where that points hits the ground, average over 3 or 4 rotations if you have a tape measure big enough

[Latte]

Bogan's advice will give you the circumference (which is what most cycle computers use) if you really do need the diameter divide the circumference by pi (3.14xxx)