Was wondering what to do with my track wheel situation.

I got a set of 17 x 9 +45 Enkei RPF1s thinking they would be a slightly wider rim than my set of 17 x 8.5 +40 RPF1s. I do not have to run any spacers with the 8.5s and they clear the 300ZX BBK with ease. I thought at worst case I would have to run a 5 mm spacer with the 9" rims, not a big deal. Turns out Enkei makes a different fitment even though the specifications are similar.

Regardless I had to do this to clear my 300ZX BBK.



In comparison to the rear with no spacers what so ever.



5 mm hubcentric & studcentric spacer and a H&R 15 mm hubcentric spacer to get good fitment. The rim and tire only stick out of the fender by 5~6 mm, I would of thought they would stick out alot more.

I can roll the fenders to get more tire clearence when I lower it some more. However my main concern is it safe to run that big of a spacer on a track wheel? The ARP wheel studs are close to being maxed out and the safety tech told me thats about the most he would allow for a track car.

I ran on the road course for about 120 miles of driving and did not experience any major problems in regards to the wheels or spacers. I liked the wider track this new combination offered as it gave a little more understeer on corner entry but more front grip at the apex and leaving the corner. So much so I was able to get the rear of the car to rotate around a couple of turns if I setup the car right. I even had to apply some countersteer to get the car pointing straight when I did not expect any oversteer to show up.

However the initial turn in made the steering feel much more heavy and less responsive, not something I would run on auto-x.

I like this setup as I can rotate the tires front to back as the wheels are the same. It would be cool if I could get a 17 x 9 +22 for the fronts but then I would not be able to rotate tires so easily.

 

I'd feel better if it was a single 20mm spacers instead of two spacers.

 

Two spacers stacked is bad juju and would fail tech at many (maybe most) places if they know they are there.

I would guess that the steering feel issue is most likely secondary scrub radius issues.
Long story short I think you have found the area of diminishing returns on wheel fitment.

If your 8.5s will stuff a lot of rubber under the fender and do so without the need for spacers I think I would run those and be happy in knowing that my car would be well balanced and that I would not need to change wheel bearings once a month.

 

^^ fully agree with what he said. And yes the farther out your offset brings the tire, the more it's going to affect your scrub radius and make the steering feel slower, in most cases.