[NomadTW]

you can have different sized wheels front/back
w/o any modification if you keep the outside diam of the tire the same...

but if you want big fat tires in the back, you can change the front diff ration to a higher ratio to counteract the difference in roation speed from front to back so that the shafts are spinning at the same speed

w/ enuf money it could be done completely reliably