be careful if u fit 14mm hex wheels - the driveshafts are under a lot more stress with them fitted - i broke one as soon as i fitted mine, where the hex pin hole is... very very frustrating. also the gearing would be a bit much for the standard motor i feel, or at least it would with the ofna brick pins i have fitted to mine.

but if u wanna try it - the 1mm spacer should work well enough if u can get it real tight round the 12mm hex. i have heard of people just chucking a tmaxx hex on the cen shafts - sounds dodgy to me, but they reckon u get away with it...