Wheels for autocross...
 

I'm wanting to minus size my wheels due to the fact that I haven't been able to find good sticky tires for my stock 20's. Based on the following SCCA rules for street class can anyone help me with finding wheels that fit that criteria and also the widest tires that will fit? :thanks: :popcorn:

13.4 WHEELS
Any type wheel may be used provided it complies with the following:
A. It is the same width as standard and as installed it does not have an offset
more than ±7.00 mm (±0.275”) from a standard wheel for the car. The
resultant change in track dimensions is allowed.
B. Wheel (rim) diameter may be increased or decreased 1” from the standard
part.
Wheel spacers are permitted provided the resultant combination complies
with the offset requirements of this Section. On vehicles supplied with an
OE wheel spacer, the wheel spacer shall be considered as a part of the wheel.
Wheel studs, lug nuts, valve stems (including pressure-relief types), and/or
bolt length may be changed. Wheel bolts may be replaced with studs and nuts
but the number of fasteners may not be changed. Tire pressure monitoring
sensors may be removed.
Centerlock/Spline Drive/Knock-off type hubs may be converted to lug type
hubs provided the resultant combination complies with the offset requirements
of this Section.

The tire rules can be found here:
http://cdn.growassets.net/user_files...pdf?1484692275

When I autocrossed my 3rd Gen and 4th Gen Camaro's I used 245/45/16 BFG, Kumho, or Hoosier tires which were R compound in the F Stock of the time. Of course, the wheels were 16 X 8.
Your wheels are 20 X 8 front and 20 X 9 rear stock so you would need at least 245 size tires. I experimented with 255 Hoosiers and 265 Kumho tires but the 245 was quicker and less sloppy feeling in the slalom and in quick transition. Steady state cornering was about equal.
If you go to 19 in wheels, which I did since there was no other option last year, I think the Forgestar CF-5 or CF-5V in stock offsets is a good economical choice for autocrossing. I would say that on the 9in wide wheel, you could try the 275/35/19 in RE-71R and the 245/35/19 on the 8in front wheel. If you used your stock wheels, you could use the 245/35/20 and 255/40/20 sizes. I have no experience with these sizes other than the 275/35/19 on my 10" and 11" wide wheels for my 1LE. I liked that size other than the fact that the car was way loose for my taste, although my co-driver loved it.
There are other tires such as Hankook Ventus and Kumho Ecsta that might work as well. Nexen N Fera is another new tire that could be used. It appears to be well priced.

Hope this helps you in your decision.

Stock sizes are 245/275...he'll be fine going a size up generally speaking if he wants to stick with 20s. I would definitely not run a 255 out back.

According to TireRack right now, RE71R's come in 245/35R20 255/40R20 285/35R20 295/30R20. The current consensus is that it's the tire to have right now and after driving on them I'd tend to agree. Could slap on some 255/285s and call it a day.

If you're SUPER serious about running in FS, the non-1LE cars will have a hard time keeping up due to the wheel limitations. You might consider...if you're buying wheels and tires anyways...moving to STP/CAM-C to level the potential playing field.

If you're set on 19's in FS, you could move to RE71's as mentioned above. Could slo move to standard Rivals, which come in 255 and 285. RivalS/1.5 don't show anything in 19's on TireRack. RS4's seem to come in the appropriate range of sizes in 19, too.

Awesome, thanks for the input. All of that info gives me few things to think about. Also, I don't know how I overlooked the RE71R's in 20's.

Depending on how much you DD your car, between the different 20" tires that would fit 20x8 & 20x9, I recommend the 245s square.

1. Tire Rack measures that the 245s have more tread touching the ground than the 255s (9.1" vs 8.9").
2. Huge advantage is the lower tire diameter (26.8" vs 28") so you can put down power better.
3. They also have the XL rating with the stiffer 3-ply sidewall (SL on 255s have 2-ply)

Only issue with the 245 is that they are much shorter than stock (28.7") so your speedo won't be accurate for DD. Being able to put the power down out of slow corners is worth it though.

I'm testing 285/35/20 RE-71R vs 305/30/19 RE-71R and differences are significant. The reduced tire diameter of the 305s vs 285s (26.2" vs 27.9") is worth more than 0.5 seconds. Guessing the value of the additional rubber on the 305s (11.1" vs 10.4") is another 0.5 seconds.

If you do get another set of wheels and tires just for AX. I'd recommend skipping all of this and going straight to CAM and getting some off-the-shelf wheels + 305/30/19" RE-71R or 315/30/18" Rival S tires.

wheel weight also plays a significant role. What are the weights of the 20s vs. 19s?

The difference in weight is about 7 lbs a wheel. The 1LE Wheel + 285/35/20 tires weigh about 60 lbs.

With my car having a completely stock setup I've been finishing, on average, 2 seconds behind our fastest people so my question now is would it be worth it to move to stp/cam with stickier tires and possibly a full suspension upgrade?

STP and CAM will allow you to go wider with tires and wheels, but you're still working with the same 200-TW tire limitation. By one guideline (from an OE automotive engineer), going from 275 to 305 would probably buy you a second, maybe 1.5 seconds. How fast are the STP/CAM guys in your area?

How much of that 2 seconds between you and the fastest guys in FS is due to tire choice? to alignment settings? to brake pad choices?
etc.? (because I'm sure there's more that can legally be done within the Street Category ruleset).


Norm

Based on everyone's input here and more digging on my part this is what I'm thinking, I'm going to stay FS and if I'm interpreting the rules correctly I can't go with a square setup so assuming I can fit the RE71R 255/40-20 on the stock front 8" wheels and 285/35-20 on the stock 9" rear wheels I should be able to get quite a bit more grip that the stock P-zeros. Although Tire Rack says 9" and 10" which makes me wonder if they even fit at all. Any other suggestions? :iono:

If you are only 2 seconds off from your goal, then you should stay in FS.

You should go for 245/35/20 square on your 8" & 9" wheels. Those fit 8" - 9.5" wheels. Shorter tire diameter will be huge in terms of getting the power down.

The better rubber + lower diameter should get you those 2 seconds you are looking for.

This is assuming you have two set of wheels or you rarely DD your Camaro.

That makes much more sense than what I was thinking. I was trying to maximize tire width for both the 8" and 9" separately as opposed to what your suggesting. I can get another set of wheels but I usually only drive the car once a week. I don't trust the people I have to drive around on Hwy 98 here in NW Florida, especially during rush hour but that's another story. I'm a little confused on how the 245s have more tread touching than a 255. Do you have the link?

Stay in FS
 

Cheapest way is to stay in FS.
Do the following :
1. Get set of RE71s (either in 20") or get set in 19" (more money)if you get new rims take advantage of the 7mm offset allowance.
2. Get performance alignment , get as much caster and camber as you can up front.
3. If pads are over half worn, get a new set of pads with more initial bite.

If you move up to STP you will need to pick up 3 seconds of time to catch the front group. The above items should be around 1.50 seconds so with some extra seat time you will be nipping at the heels of the front runners in no time.

Can you go with 1LE sizes? It is stock and SCCA approved.