18x9.5 w/ 275/35-18 on all four corners?

[TCorzett]

I've been beating my head against what wheels/tires I will be able to run for Auto-X and HPDE/Track Days. After pouring over the boards I thought I had a plan, but I keep second-guessing myself. :hmm:

I would like to run a 275/35-18 on a 18x9.5 wheel... on all four corners.

The wheels/tires will not be used on the street, and at most there will be two people in the front of the car. I am ~1" lower than stock, and I anticipate some suspension compression under hard turning... so I don't want to rub (too much) and damage a set of tires. Potential fitment issue include Pedders Supercar Coilovers (larger shock body than the Xa's) and a Baer BBK (the OEM Sport 19" fit).

My first thought/plan was to use a +45mm offset and a 5mm spacer on the front. This would mimic the setup others are using with 275/35-19, but with a little extra room by using the 18" wheels/tires.

Now, I'm thinking about what I could do to eliminate the need for a spacer on the front. I am looking into a +34mm offset on all four corners... which should work well on the front, but will it work on the rear? Most of what I've read said a +40mm wouldn't work on the rear, but that was for 19" wheels/tires. :huh:

What are people's thoughts on this? :confused:

After all these numbers I need to go let my head cool-off! :stretcher:

-Todd...

[dklau33]

I think an 18x9.5 +34 in the rear with 275's would stick out too far. Falken has RT7-M in 18x9 +40 and TSW has Nurburgring in 18x9.5 +40 that I was looking into to do 275's all around.

[TCorzett]

Based on some measurements I found on the other board I worked-up this:


http://www.unitonestudios.com/_Other/G8/G8%20Wheels%20v1.jpg

Based on this, a 9.5" wheel would need a +45mm offset to have approximately 0.125" clearance from the inside of the OEM fender lip in the rear. This diagram is for the wheel only, so if there is any overhang from the tire it would be getting too close to the fender without cutting/rolling.

I'm really leaning towards going with the initial idea of a +45 with a 5mm spacer in the front. I might need to roll/cut the rear if rubbing becomes an issue. I could go with a +40, but it looks like that would require rolling/cutting in the rear.

-Todd...

[Slizzo]

If you want all the same rims, get it with a +45mm offset like Andy did and run 5mm spacers on the front.

[BATOYGIO]

If you want all the same rims, get it with a +45mm offset like Andy did and run 5mm spacers on the front.

Does that mean you mounted up your 20x9.5 set and it didn't fit? Any details on that? Im looking to do something similar with all four same wheels....

[TCorzett]

If you want all the same rims, get it with a +45mm offset like Andy did and run 5mm spacers on the front.
That is most than likely what I will be doing... it's hard when a very reputable wheel manufacturer says that a +34mm 9.5 will fit on all four corners.

-Todd...

[hulkss]

I you want your steering scrub radius correct for performance, you need 48mm offset up front with a 9" wide wheel. In back a 57 offset is ideal for a 9.5" wide wheel. I know this combination fits OK with 19" wheels and 255/40 and 285/35 tires. With 19" wheels you can get big brakes for track day.

[TCorzett]

I you want your steering scrub radius correct for performance, you need 48mm offset up front with a 9" wide wheel. In back a 57 offset is ideal for a 9.5" wide wheel. I know this combination fits OK with 19" wheels and 255/40 and 285/35 tires.
I'll do some research into this scrub radius stuff. I want to run a non-staggered setup so that I can rotate tires when I move to a slick.


With 19" wheels you can get big brakes for track day.
The BBK I have fits under 18" wheels... also, there are FAR more tire compounds available for 18" wheels compared to 19" ones.

-Todd...

[Slizzo]

Does that mean you mounted up your 20x9.5 set and it didn't fit? Any details on that? Im looking to do something similar with all four same wheels....

Haven't put them on yet. I'm confident that fronts will be OK no problem, rears may rub on larger bumps with weight (I'm not lowered, and not rolled).

[BATOYGIO]

Haven't put them on yet. I'm confident that fronts will be OK no problem, rears may rub on larger bumps with weight (I'm not lowered, and not rolled).

Ok cool. Interested in the results. If your combo works with no rubbing (even if rolling is needed) that would be perfect.

[Slizzo]

Ok cool. Interested in the results. If your combo works with no rubbing (even if rolling is needed) that would be perfect.


Yeah, honestly I want to get the rears milled down by 5mm (adjusting offset to a +45) for peace of mind. But I will post pics and impressions once my tires come in (285/30/20 Hankooks are on backorder at TireRack right now unfortunately).