xShiFTx

iTrader: (5)

Hi guys, I figured I should start a thread here that will document the progress/problems with my autocross car. This car is a joint effort between my dad and I. We are doing it for fun but also trying to learn as much as we can. I am a junior in college majoring in Mechanical Engineering, but still have a lot to learn.

Here is a picture of the car.


We have already bought and installed a few things,
Poly bushings
Illumina shocks
16x8 XXR 513's
Hawk HP+ brake pads

Now I was going off the recommendation of a forum member that I would be able to use 225/50/16 tires on a 16x8 wheel and it would fit without rubbing.

This definitely wasn't the case, I was forced to roll the fenders to be able to turn even a little. The rears fit decently, but the fronts have been a nightmare.

After rolling the fenders I am still having some trouble with rubbing on the actual fender lip when I corner/brake/accelerate hard. The car was also raised approximately 1 inch with these new tires.
Here is a picture of the tire rubbing the fender before they were rolled.


So I have some questions about what would be the next best thing to do.

Some of my options:
1. Sell the wheels and tires and go with something that is easier to fit like 215's or 205's.

2. Cut into the fenders to allow for some clearance for the tire. If I were to do this I would probably also buy some coilovers and lower the car at least back to its stock ride height.

3. Buy coilovers and jack up the ride height a little more to make sure the tires have clearance.
(Whats the typical suspension travel for an autocross car? an inch or two?)

Am I really going to be able to tell a difference from raising the center of gravity an inch or two? Am I going to have trouble with any of the stock suspension components binding from the change in ride height? Are the tires going to screw up my gearing badly?

While I have autocrossed quite a bit, it was in a stock Ford Focus so I am out of my element here. Thanks in advance for any help on the subject.

Kentetsu

Well, I've been racing my '84GS in CSP for a few years now, but I kind of went a different direction than you did in regards to wheel size. I stuck with 13 wheels, but went wider at 8 inches.

The smaller wheels help to keep the center of gravity low. If you went with some Diamond Racing wheels at 13x10, then you could run the new Hoosier 255/13 tires for some serious grip! Or, do what I do and run 215 Sumitomos to keep the budget in line ($46.00 each).

With the 16s on there, I doubt that you'll be able to get down to a decent height without major modifications.

You could try seeking advice from Respeed by posting on their forum (dedicated suspension shop). www.re-speed.com Billy is very good at giving great advice, and he's seen just about everything out there.

If you would like to see how my car sits/handles on the 13 inch wheels and coilovers, check out the videos in my signature line.

Good luck with your project. I can't view the pics right now, but will take a look when I get home later.



.

finky

iTrader: (2)

I don'tknow if you run with SCCA (or a group with SCCAs ruleset) or not but you may want to look into the new Street Touring R class. You could run in that class and set up the car before you make the jump to CSP (which has more non reversable mods).
The GSL-SE can not run in the STS (old STS2) class due to the dif but this new class is open on dif rules. You will likely be midpack in both classes but can keep the car more streetable as you build in STR.
Just a heads up. If I was to move up classes with my ES car I would build to STR (unless I wanted to put my Hoosiers from my FD on my FC and beat up on Kentetsu in CSP ;-) -he is in my region- ).

xShiFTx

iTrader: (5)

I am not going to run r-comps, this year our club is implementing a pax modifier. The modifier will be only for cars that are running street tires in a non-street tire paxed class and will multiply the original pax number by 0.98 to try to level the playing field.

So with that said - The plan is to use a wheel size that has "good" street tires avaliable (think Kumho XS, Dunlop Starspecs, Bridgestone re-11's, Hankook rs3's). I haven't seen any hard data on the Sumitomo's but I would expect they perform significantly less than any of the above listed. Hopefully Billy sees this post and has some insight...

We had originally planned to build the car for STR but it turns out CSP is going to have a lot more local competition this year (including another rx7). Being streetable is the least of my worries because this car will be a track/autocross only car. We both have other cars as daily drivers.

mustanghammer

iTrader: (3)

I would sell what you have and get some 15x7 or 15x8 wheels. The Kumho XS and the Hankook RS3 come in 15" sizes that would fit on these wheels. They would also be more likely to fit under your fenders.

The best setup for a CSP RX7 is going to be 13's and frankly you aren't going to save that much money running extreme summer tires vs full DOT R comps. So if you are buying wheels anyway....get some 13's And yes.....a lower center of gravity is important and a short 13 will get you closer to the ground.

s1mpsons

iTrader: (5)

As much as I love ST* classes, the FB belongs in CSP over STR. The FB would be way over powered by a Porsche Boxster or S2000. There are a couple of areas to address in *SP:

1) Tire: These are numero uno. If you have a ST* index for *SP cars, and your going to give that a shot, I can tell you I had great success at nationals on Dunlop Z1s (3rd of 46 in STU). The tire is predictable and will grip until it tells you no more. Gives lots of tire feedback. If you decide you want to take CSP more seriously go with short wheels and wide Hoosier A6s. As wide as possible. Adjust your roll stiffness, camber and fenders to make it work.
2) Alignment: Dial in your negative camber so that tire temperature difference from inside to outside is -10*F (inside should be slightly hotter). Make sure the car is reacting the way you want it to. Front toe-out will make for a sharper turn-in, rear toe-in will generally neutralize turn-in oversteer while rear toe-out will generally induce turn-in oversteer. Most of this applies to any class I suppose.
3) Roll Stiffness: I can't advise on rates, as I am not familiar with FB wheel rates, but stiffer is generally better (especially as you break into the r-compound territory). Big front bar is par in autox. Stiff coilovers are par in ST* and *SP classes. Get yourself a set.
4) Shocks: Do your research and you'll find a wide range of info. Generally the autox guys stick to Koni or Bilstein to stay affordable and go nuts with Ohlins, Penske, Moton, JRZ, and the like. Everyone says stay clear of Chinese manufactured shocks/coilovers. Its up to you what you want to try and whee you budget falls.

Good luck out there. Hope the build goes well. And remember, LOOK AHEAD. In the end, it's 80% driver anyway.

xShiFTx

iTrader: (5)

Looking at 255/40/13 Hoosier A6's they are $207 a pop. The 225/45/15 RS3's are $115..

Also, I understand that a low center of gravity is important I was just curious if the extra inch is going to be extremely noticeable? I have never really had the opportunity to play with ride heights and such.

I like the idea of dropping to a 15x8 and using the rs-3's though. This would allow me to maintain the stock diameter. The downside to this is that I am stuck to being able to run only one kind of tire.

Keep the comments/suggestions coming guys.. It is much appreciated!

finky

iTrader: (2)

You could try JBRacingtires.net to see if you can get a good deal on some 13" rubber. Used racing tires are a good way to get into them until you get really competitive and justify the cost of new. Only thing is once you go on race tires you will beg, borrow, and steal to get another set.

Hey Kentetsu, do you have any info on RJs GSL-SE build? Maybe it could help this guy out.


xShiFTx, I don't know if you guys do events right in Abq or what region you run in, but do you do any events closer to Roswell? My dad lives down in Roswell (with the aliens) and I have been trying to get him to take his Vette out to an autocross since he moved down there.
I just looked at the schedule and it looks like you guys lost your National Tour race in Farmington, NM.

xShiFTx

iTrader: (5)

Most of our events happen out in Farmington, then a few in Santa Fe, and possibly one or two here in the middle of Albuquerque. Get him to come out! We'd love to have him!

I did not attend our National Tour due to some tests for school lying on days before/after but wasn't it one of the lowest turn out National events of last year?

jdmsuper7

iTrader: (1)

Sell those wheels. If you are really set on running street tires go with the suggested 15" sizes. Besides raising the car, the 16"s are going to murder your gearing on an already torque-challenged car.

If you are just going out there to have fun, don't get too stressed out about your setup. Just get a good performance alignment like S1mpsons suggested and a set of tires that fits.

s1mpsons

iTrader: (5)

Could you do me a favor and say Hi to Wiggy for me. He's the big guy out there driving anything he can get his hands on.

Kentetsu

RJ sold his car to a forum member. A search for posts by Mikeric should bring up everything done to the car since then (turbo now).

xShiFTx

iTrader: (5)

I'd prefer to run street tires because this is only my seconds season and I am still learning a lot. Chances are I am going to go to the 15x8's with the 225/45/15 RS-3's and just run the doors off of it this season.

Will do! Wiggy rocks!

mustanghammer

iTrader: (3)

Keep in mind that tires like the RS-3 need to be shaved in order to perform at their best. That adds $15 to their cost. The DOT R Comps you are comparing them to are great tires but typically any DOT R comp will out perform a 140 treadwear tire in an autocross. When you compare a shaved RS-3 to a Kumho V710 215/50x13 at $161 the cost difference is not that extreme. However the performance difference can be. Another 13 tire to consider would be the Hankook Z214 in 225/24x13.

As far as diameter difference, it could make a difference depending on the rear end gear that you have. For example, there is a 7% difference in diameter between the RS-3 and the 215/50 Kumho. You can use that percentage to predict the gears that you will use on course. It may work out better to have taller tire. You have to run the numbers. In my opinion you want to keep gear changes to a minimum when you are on course.

If you stick with the 15" wheel another tire to consider would be the Nitto NT-01. It comes in the 225/45x15 size and it more of race tire than the RS-3. We have used them in club racing and in CSP on an RX7 and they worked better as an autocross tire. They should be shaved for optimum performance. www.discounttire.com carries them for a great price.

s1mpsons

iTrader: (5)

I don't necessarily think that shaving a st tire helps any. The STU national champion ran full tread dunlops and beat me on my shaved tires (and all the other 46 drivers most of whom
showed up on shaved tires).

mustanghammer

iTrader: (3)

To shave or not to shave depends on the tire and I would consult with the manufacturer. Maybe the manufacturer told the champion not to shave the tires. Never know until you ask.

I have club raced on Kumho V700's shaved and unshaved and the difference is significant. It also makes a difference on the Nitto NT-01 and Toyo RA-1....those tires are faster shaved.

Wearing a tire down to optimum depth by racing on it is not the same as shaving. Racing a tire creates heat cycles that age the compound so that by the time you get to 4/32's the rubber that is left is not as sticky. So you are left with a tire that started slow because of tread squirm and then wasn't that much better at the end of it's life.

Super82

iTrader: (1)

As has been said, 16" wheels and FB's don't mix. Atleast not for racing. 15"s will open up a bunch more performance tire choices that will actually fit. 225/45s would be great. Watch your wheel weight as well, that makes a difference. Sportmaxx wheels aren't known for being light. Personally I run the stock 13x5.5's with a cantellievered 20x8 Hoosier slick.

The FB is allowed in STR, but I really fail to see it being competitive. STR doesn't allow many mods that would pick up the power for the FB, and without some more power the FB doesn't have a chance in the class. In reality the FB really seems to be made for CSP, 90% of the fun mods most people do to their FB puts it in CSP. That being said the miata has remained the top dog in CSP on a national level.

Get some good rubber under there and race. There is nothing that tells you what really needs to be done to your car better than the track. After a few races you'll probably have a better idea of what mods would help out most. Even so, in autocross more parts does not equal faster times, unfortunately, so you really don't need to spend a bunch of money quite yet. If you don't have much money to spend I'd recommend getting some weight out of the car, as GSL-SEs are a bit heavy. Also, a test tube for the cat can be made pretty cheaply if you have access to a welder.

justint5387

iTrader: (1)

I would run STR if you are staying with street tires. Your wallet will thank you for it.

Kentetsu

Hey Justin. How are you liking the 255 Hoosiers? Any trouble fitting a 10" wheel?

I was considering running that same setup, but for financial reasons I won't be attempting any National level racing this year, so it has been postponed for another year...

justint5387

iTrader: (1)

If i do it again, I would just run 13x9. The 255 will work fine on a 9 inch wheel. 9 inch wheel will still stick out of the fender, so a set of fender flares will make it look better.

Super82

iTrader: (1)

Any pics? How much do they stick out? Are we talking full-board redneck truck tire level of sticking out?

The 255 A6's look like a hot setup for our cars, but I'm still happy with the good old Hoosier road racing slicks. They are lighter and come in many sizes. Also they can be picked up for dirt cheap used. I got mine with about 80% tread on them for $75 for the set.

jdmsuper7

iTrader: (1)

They are also illegal for CSP if anyone wanted to protest you.

Super82

iTrader: (1)

What? I've never heard that. Are only radial slicks like V710's and A6's legal for CSP?

Thanks for the heads up dude. My club doesn't care, but I'm one of the only ones in CSP that races regularily. The other guys all drive Miatas and are nationally competitive...I believe they are on road racing slicks too. Sorry for putting out bad info.

jdmsuper7

iTrader: (1)

Need to be DOT approved tires like the 710s or A6s for SP classes. I think true slicks bump you into Prepared classes. If you aren't winning, nobody is going to care.
National miata guys will make the 255/40?/13 or the 275/35/15 A6s work like you wouldn't believe.

xShiFTx

iTrader: (5)

Anyone have any suggestions on some lightweight 15x8's? I'm having trouble finding anything with the right bolt pattern and those XXR's are heavy.

Also was kicking around the idea of putting adapters to go to 4x100 bolt pattern and then use a higher offset wheel. This would open up wheel choices immensely. Something like a cheap/light Miata wheel. Thoughts?