Originally Posted by
Marc sierra
A 2wd will need a stronger diff than a 4x4 as only 66% of the torque is going to the rear on a 4x4. That is also the reason why a 2wd has a 7.5" and a 4x4 has 7" as standard. The tyres will spin at the same torque, as that is just the grip limit of the tyres, for which it doesn't make a difference whether it's 2wd or 4x4.
Good explanation, like that.
Why don't 2wd break boxes like 4wd though? Is the 2wd box stronger as same sized housing contains more strength as doesn't need room for transfer?
Tyres will spin at same torque, yes but if a 400 bhp / 400 ftlb car was 4wd the rear diff only sees 66% of the gross power / torque. 2 wd gets all the torque so the gross engine output on a 4wd can be higher before rears spin. Plus a 2wd has 2 tyres contact patch, a good 4wd with lsd (front and rear) has 4 contact patches to distribute the power.
Putting it another way the 2wd has more torque to deal with on 2 tyres, the 4wd rear only has 66% of the same torque therefore a 2wd will be more willing to spin the rear wheels than an exactly the same powered 4wd twin lsd car will spin the rears. So a 400 bhp car will spinnthe power away where a 4wd is more likely to have 100% traction; albeit spread across 4 tyres.
I am not arguing with you by the way, I am here to learn.