Swapping between different offset wheels - How much difference is too much?

[longsh07]

Have posted in the other cars section because this doesn't directly relate to a 350 however could apply to any car.

 

I'm looking to get a spare set of alloys for my FN2 Type R so I can swap between winter/track day tyres easily but dont want to have to get the car realigned every time.

I plan to step down from an 18" to a 17" wheel, same width (7.5") but I'm a little concerned about how a different offset can affect things like scrub radius and alignment settings.

 

The question is, how much difference in offset is too much difference?

For example, Going from an 18x7.5 ET55 to a 17x7.5 ET53 is obviously not going to have a major (if any!) effect on alignment because its only 2mm difference.

However, would going from ET55 to ET45 be too big of a step?

 

10mm doesn't sound a lot but when you consider the accuracy of these laser alignment machines these days surely that difference could throw everything out?

With that said, in the real world would there be any noticeable extra wear on the tyres with a 10mm difference?

[Jay Kay]

I'm not sure offset changes the alignment, just how far in or out the wheel sits. Too much change however will ruin the drive and potentially cause the car to tramline all over the place.

[longsh07]

I probably didn't explain it very well to be honest.

I know it wont change the alignment settings themselves however I was struggling to work out (much like adding spacers) if big offset changes are going to require an alignment to bring things back into spec (camber?) or if all its doing it affecting the scrub radius of the tyre.

[longsh07]

Ended up kind of answering my own question. Offset directly affects scrub radius, as does camber by altering the centre line angle of the wheel.

So swapping wheels should be fine as long as the camber was not adjusted but it will affect handling.

The question of how much change only relates to scrub radius and will subjective per car.