Will the overall width between the fattest part of the walls on any given tyre be 1/2in greater on a 6J than a 5.5J?

Depends on the tyre size,and for suspension clearance,offset of the wheel.

Obviously the unstressed tread will always be perfectly centre to the wheel,so if the rim is wider,the band is pulled further but the tread isnt - so the mid sidewall moves out half the distance of the rim.

If this question is for suspension clearance,remember a 6in et38 wheel's inner rim is a quarter inch closer to the suspension leg than a 5.5in et38 wheel's inner rim. And tyre wall deflection is reduced with stretch.

As I thought - ta muchly.

hI

it is a recognised fact that for every 1/2" of rim diffeerence the overall tyre width alters by 5mm as identified by ETRTO and others.

Bet x