ok Im aware that on 4wd you need to match your front and rear rolling radius as close as possible to avoid burning out the viscous coupling.

But what is the acceptable tolerance when youve got different width rims front and rear??

at moment ive got 225/40/R18 on front, 255/35/R18 at back and the difference is 0.3 % difference... that i definitely think is ok as there would be varience in front rear split turning and over varying surfaces within that tolerance when driving anyway.

but im planning on putting 11" rears on so want to get the right rolling radius.

11" = 279.4mm

closest tyre width is either 275/35/R18 or 285/30/R18 width tyres giving a difference of 2 % and 1.7% respectively.

Is about 2% acceptable???

Also with those sizes would i be better off with the 275's because a higher profile is less different to the fronts.

 

1 decimal place is your limit really.