Different ET on gtir

I acquired some BBS Rs's pair of 8 wide and et43 and pair of 9 wide et40. Any thoughts why it's a bad idea?

Idont think the 9'' will fit with a poor offset as the back edge of the wheel will touch the suspension strut (even with coilovers fitted so you would have to use really large spacers.

If you look at the photos of the orange car i put up for sale, that has 9'' wide tsw rims but the offset is very low on them which means theres no contact with the struts, flip side is you will need very wide arches to accomodate them

The other thing to take into consideration is the larger the wheel offset means you have a lot more loading on the wheel bearings especially when cornering hard, this also makes the steering much more twitchy in a straight line and the slightest input to steering wheel relates to much more movement at the road wheel.
Hope that helps a bit

When you say pair you do you mean two or a set of four.? This could also read where you want to use different wheels on front to rear like a 2wd drag car ?

theres 4 of them, they are three piece splits. I was thinking 8" et43 on front and 9" et40 rear. I just know from somewhere that you not supposed to use different with wheels on 4x4 setups.

You can use different sized wheels as long as the rolling radius is the same which you can get round by running different profile tyres, you can work it out if your half good at maths

For example the Gtr has 11" rears & 10" front wheels with 315.30.20 rear and 285.35.20 front

Also if your running a plated diff it isnt a real problem, its viscous type diffs that are the issue as one diff is in theory being dragged due to different rotational speed which causes the viscous type fluid to thicken then  overheat.

Got 'ya, i do run nismo in dif have one for rear but haven't installed it. Doesn't different with put different load on axels as there is different area of contact from rubber touching the tarmac?

No not really its the rolling radius that really matters (rpm per axle) so as said you can get round that by running different profile tyres