Why do 8th cars run fat front wheels ?

[andys]

Wondered this for a while, why do 10th scale off road run narrow wheels on the front, but 8 th scale run the same width all round ?

I remember from my early 10th scale off road racing days, people tried running wide wheels all round, but it was rubbish !

Surely 8th scale would benefit from slimmer front wheels ?

Also roll bars seem standard on an 8th car, but they are not run so much on 10th, especially front roll bars - why's that then ?