Singlespeed Urban MTB Gearing

[Brian73]

I'm building up a singlespeed urban mtb similar to the Carrera Subway Zero

Fitted with rigid forks, 26 inch wheels, 18T freewheel, 120mm rear spacing and 68mm BB

It's going to be used for pavement, gravel and grass, with climbs of no more than 10%

Was thinking of a 42T chainset as the best compromise.

Most track chainsets are 165mm cranks, I'm more used to 170/175mm, what would be best?

Thanks.

[iandriver]

Have you used a gear inch calculator before? http://www.sheldonbrown.com/gloss_g.html
Do you have a geared similar bike?

[barrym]

Sheldon also has useful advice on single speed. If I remember correctly he recommends 2:1 for 26" wheels as a starting point, so in your case 36:18. Take a look.