am i right in understanding that the rolling radius/circumferance is the only figure that needs to be constant all round on a 4wd. i.e on the rear of my car i'll have 245/35/17's, but on the front i can have 215/40/17's? if that being the case, could i use 7.5j wheels on the front and 8j onthe rear, with the above tyres withought damaging my transfer box/differentials?

got rolling radius figures from here
http://www.falkentyres.co.uk/fk451.asp?cookiecheck=yes&