Autocross/18x8 wheels/what tires?

[rmz290]

I've done some searching and not really come to a resolution on this.

I got a screaming deal locally on 4x 18x8 +51 OZ Superleggara which weight 17.6 pounds. They came with 235/40 StarSpecs that are close to end of life. I don't like these as they are larger in diameter than stock and throw off the gearing and make the car feel slow. I bought the wheels for the weight/price and appearance. I had looked at 17x8 rpf1's just could not find any in my price range. I did my first autocross on stock tires and wheels yesterday and loved it, but really need a better tire.

I will use these 18" wheels for mostly autocross, maybe a track day per year and some street driving. What size tire should I put on them? What have other people had success with on here on 18's? I'm looking at 215/40-18's and 245/35-18's. I know, drastic range but these seem to be the two closest to stock diameter.

A few questions?
-What would be the better performing size? 245's seem like a lot of tire for the car but autocrossers seems to try to pack the most tire in possible.
-Will 245's clear or will I need spacers? 235/40's are a few mm away currently from the stock springs.
-245's on 8" wide wheels?

I know almost everyone is leaning towards 17's but I think with 18 inch wheels this light depending on the weight of the tire I should still be slightly lighter than the stock wheel/tire package.

[Vracer111]

The thing is you really want to get the unsprung weight down as much as possible, dropping 4lbs a corner from stock wheel/tire weight makes a very noticeable difference in feel and handling of the FR-S, feels sharper and really smooths the ride out. The problem with tracking/autocrossing 18" wheels on the FR-S is tire selection...much better tire selection that stays within stock tire diameter, and less expensive as well for 17" wheels. Those 18" with those tires are noticeable heavier than the stock setup too...looking at ~43lbs a corner verses ~40lbs a corner.

Id recommend keeping the 18"s for daily if you like them and 17"s for autocross/track...especially with a +51mm offset. A +45mm to +35mm offset for an 8" wide wheel would be better. With the right 215/45-17 stock sized tire on a 17x8 wheel it will be much lighter than stock while raising the performance envelope to where it should be to have fun on track/autocrossing. If you are going for an autocross Regional or National championship it would be a different story and width would be more important than weight, but if not going for the championship don't worry about wider than stock tires and have more fun than the guys fighting wider tires...

[rmz290]

Originally Posted by Vracer111

The thing is you really want to get the unsprung weight down as much as possible, dropping 4lbs a corner from stock wheel/tire weight makes a very noticeable difference in feel and handling of the FR-S, feels sharper and really smooths the ride out. The problem with tracking/autocrossing 18" wheels on the FR-S is tire selection...much better tire selection that stays within stock tire diameter, and less expensive as well. Those 18" with those tires are noticeable heavier than the stock setup too...looking at ~43lbs a corner verses ~40lbs a corner.

Id recommend keeping the 18"s for daily if you like them and 17"s for autocross/track...especially with a +51mm offset. A +45mm to +35mm offset for an 8" wide wheel would be better. With the right 215/45-17 stock sized tire on a 17x8 wheel it will be much lighter than stock while raising the performance envelope to where it should be to have fun on track/autocrossing. If you are going for an autocross Regional or National championship it would be a different story and width would be more important than weight, but if not going for the championship don't worry about wider than stock tires and have more fun than the guys fighting wider tires...

I think the 18" wheels I have at 17.6 pounds with 245's at 21/22 pounds should end up a pound or two less than stock. With that setup I almost wonder if the polar moment of inertia would be better than middle weight 17's as well. As far as the offset goes I will just get whatever spacer I need to clear. I'd rather have the wheels as in as much as possible than poking out.

It really I think comes down to a 245 on a 8" wide wheel or 215. Not much of a fan of the stretched look but concerned if there will be a noticeable difference in rolling resistance and acceleration with the wider tire. Assuming diameter is within .5% and weight is equal to or less than stock.

The only other option slightly bigger in diameter is a 225/40.

[Vracer111]

If you were talking about 17" wheels then yes I could see potentially finding some 245 width tires that weigh 22lbs... most 235/40 18" tires that you'd want seem to come in at ~25 lbs...or you'll be spending nearly $1000 on a set of Max performance level 22lb Michelin PSS... You really want one the following tires: BFG g-Force Rival, Bridgestone Potenza RE-11, Dunlop Direzza ZII, Hankook RS-3, Kumho Ecsta XS, Toyo Proxies R1R...and of those, the Kumho Ecsta XS is the only one available in any tire size you specified (only available in 245/35-18 @ 25lbs)... hence I'd recommend to go with 17's...I'd much rather spend ~$500 on 17" tires than $900+ on 18" tires...

A 17x8" wheel with +36mm offset is still easily within the wheel well plane at the top. Pictures below of 215/45-17 Ecsta XS tires mounted on +36mm 17x8 wheels (Kosei K4R's) - combo comes in at over 4 lbs a corner lighter than stock:



225/40-17 size would maybe be more ideal in width for autocrossing and fit fine as well, but it comes with a few lbs more weight penalty. I don't autocross much anymore, mainly street with some track days thrown in...so I value improved ride/suspension efficiency of less unsprung weight over a little bit extra mechanical grip of heavier and wider tires.

Course layout may have an effect on tire size as well - faster, flowing courses or more technical and tighter courses would probably each favor different tire diameter setups. Best to know what kind of courses your area likes to run and choose tire sizes accordingly.

I did have a blast for quite a few years coming in midpack over the entire field (around 200-250 entries) with my fully functional as an everyday useful truck 98 Toyota Tacoma extended cab, even vying for second and sometimes first place in STF class.

[fatoni]

i think you need to be a little more specific with your goals. right now its looking that the bfg rival seems to be the new hotness and from what ive seen. its living up to its hype. i dont know how it deals with poor weather though so consider that as i live in socal. i also think that the concern for unsprung weight is exaggerated. a while back grm did a test and it showed that a miata was just as fast (actually faster) on a wheel that weighed 4 lbs more per corner on an autox course.

while it may not be faster, lighter feels better. for most applications, wider is going to be faster well past what seems reasonable. be honest with yourself, do you want to be fast and maybe impair your learning process or be slow but have fun and develop as a driver? im in a similar situation with my miata. i dont know if i should go with the lighter 15x8 wheel on 205s or the heavier, but both faster and cheaper, 15x9 wrapped in 225s.

[EAGLE5]

How about 245 on a 17x8? What offset then? Still +35? I thought it would also fit at +45.

[rmz290]

I had some time so I mapped out the different tire options I was considering to try to get some more direction on what to choose.

I'm leaning towards the Kumho XS right now but still have some more searching to do. My goal is to have something the performs well at autocross but is also fun. The course I will typically run is on a set of runways so higher speed. The last course was slower than usual and I was just about bouncing off the rev limiter in second gear at the higher speed sections. I think a slightly larger tire may help this, especially when corner speeds are even higher due to a wider stickier tire. I think the current 235/40's on the car now are too tall but something in between those and stock would likely be about right.

It looks like with the 18x8 superleggara's and 225's the wheel tire combination will still be slightly under stock. Again, I'm there to have fun so giving up a pound or two due to the 18's isn't a big deal since they were so inexpensive.