Join Date: Jul 2003
Location: Norfolk, England
Bikes: Orbea Enol roadie, Fly Micromachine BMX, Fort Track fixed
With regards to the tyres, front tyres are generally wider, because it offers more grip during cornering (ditto if it's a knobby), but rear tyres are narrower (and smoother) because they have a smaller rolling resistance so they slow you down less.
As for the crank, if it's a three piece, did you put the correct spacer between the bearings? There are two widths, only a millimeter or two's difference, but it is ctritical you get the right one, otherwise you'll be putting undue strees on the bearings which will kill them real quick. If it's a one piece or has open cage bearings, you may have just tightened the cones too much. I would also suggest you put in a few spacers to move the arms away from your brakes.