'Bout right 40 all round I tried 35 and the tyres (Bronco Roughriders) started wearing more on the outsides than the insides. Try experimenting if your reeely particular, on my bike I increase the pressure of the front as it wears and decrease the rear as it wears, but then I do ride it a little hooliganish and want the best out of them, whereas with the 90 I wouldn't be able to tell the difference of nearly flat to about to explode!