Reply to "Extreme Rear Suspension Compression"

I had 325/25R20 tires on the back of 6018, 12mm offset.

The outer edges of tires were flush with the edges of the fenders, required rolling the back half of the fender edges on both sides.

After rolling the fenders I disconnected the shocks and raised the tires within the wheel houses with a floor jack, the tires rubbed up inside the wheel houses on the inner edge & outer edge simultaneously, therefore I am under the impression 12 mm offset centered the tires very well within the wheel houses in terms of clearance.

However, like you, I would have preferred if the outer edges of tires were set inside the fender just a bit, say 1/4". So if I were doing it again I would use 18mm offset instead of 12mm offset. This may cause some muffler rubbing issues that will need a little "massaging" for clearance. If you have an ANSA exhaust the "possible" problem areas are going to be the outer corners of the mufflers nearest the tires. On the positive side increasing offset may also negate the need to roll the fender edges.

With the tires jacked-up until they hit the wheel houses the suspension did not contact the tail pipes. Those 20" tires were 26.4" diameter. Your 19" tires are 26.67" diameter, so there should be 1/8" more clearance between the suspension and tailpipes when the tires contact the wheel houses.

I did indeed have tire rub marks up inside the wheel houses, indicating the suspension compressed enough for that to happen from time to time. But nothing ever hit anything other than the tires rubbing. The rear springs on 6018 are supposed to be about the same as those on a GT5, which is around 500 pounds per inch.

Also keep in mind the advice of Dennis Quella passed-on by David Nunn to add enough "rubber bumper" to the shocks to prevent them from ever compressing to the point of the tires actually rubbing the wheel houses ... or the suspension hitting the tailpipes. That's good advice.

Those are my experiences with a tire of identical width and similar diameter.