SCCA STX E30 Build/Introduction

[Jean]

I went with my rates after speaking with Ground Control, actually my initial rates for a slightly softer and this is my 2nd config (after the engine swap), but I am also on dot-r tires vs street tires.

Good luck and keep us posted!

[110stx]

650/800 will make for an e30 that rotates QUICK!

Too fast for me, even with a big front bar and no rear bar ...

And overall maybe a tad too much spring for the car ... IMHO.

[bmwguy325is]

I run 525s and 750s and the IE bars. car turns in great.

[GotCone?]

So, back to spring rates...so it appears most people are running more rate in the rear when not using a rear bar. That being said, my initial thought is going with something like 650-ish in the front & maybe 800 in back?? Again, I want the car to transition great, so I am basing my numbers off what the ST & STS cars run.

You can't base anything off any other cars in the ST/STS classes unless they share a similar suspension geometry to the E30. Mac Strut front, semi trailing arm rear. Even worse, if you are comparing rates to FWD hondas and the like.

However, I don't think 650f/800r would be a bad place to start at all. Especially if you run a big front swaybar and no rear bar. It's not too far out of line on what I'd recommend assuming your run on grippy concrete. It's a bit much for asphalt probably.

with ASTs and 550/630 lb-in springs. No big deal there. I just stayed out of the big potholes and the car was fine.

Using my 'differential' calculations that I like to use when trying to calculate rotation/balance. Doug you're at a 16% differential at 550/630. I tend to like at minimum 20% on E30s for autocross. This is assuming an upgraded front bar and no rear swaybar. 650/800 is at 23% so is still within the realm. This setup would be even better if one were running wider and slightly taller overall wheel/tire package.

My $0.02

Doug I've only driven your E30 at MCC, I'd love to try it out at LAP sometime.

[race2win]

You can't base anything off any other cars in the ST/STS classes unless they share a similar suspension geometry to the E30. Mac Strut front, semi trailing arm rear. Even worse, if you are comparing rates to FWD hondas and the like.

100% agree with you. Let me clarify... I mention the other ST* classes to reference very high spring rates on street tires. When I first competed in STS2 in 2005-2006, I ran 550/300 on my 90 Miata...the theory was softer rates than CSP due to less tire grip. Now, with the current crop of street tires providing so much grip, Miatas & Civics are running much stiffer spring rates. The other reason I mention them is that both ST Civics & the STS Miatas transition VERY well with these stiff springs. I want my E30 to turn right NOW & get through transistions quick...again, trying to set the car up around it's strengths (light & narrow). Yes, a lot of that has to do with the suspension geometry, double wishbones, etc on the ST/STS cars. But it would seem odd to me that a heavier car would run less spring rate...regardless of suspension design. That being said, assuming a 25XX curb weight, I think around 600-650# up front & around 750-800# in back should be a good place to start.

As I said before though, I am no suspension guru, so I may be off base. Definitely some thoughts to run by the experts at Fat Cat & Ground Control.

However, I don't think 650f/800r would be a bad place to start at all. Especially if you run a big front swaybar and no rear bar. It's not too far out of line on what I'd recommend assuming your run on grippy concrete. It's a bit much for asphalt probably.

Around here, most SCCA events will be on asphalt, but I will be running some events on concrete as well...it's just not very grippy concrete. My ultimate goal is to make it to Lincoln in 2012 though...

Using my 'differential' calculations that I like to use when trying to calculate rotation/balance. Doug you're at a 16% differential at 550/630. I tend to like at minimum 20% on E30s for autocross. This is assuming an upgraded front bar and no rear swaybar. 650/800 is at 23% so is still within the realm. This setup would be even better if one were running wider and slightly taller overall wheel/tire package.

I do plan to experiment with a 17" wheel/tire package, so this may be a good point if I end up sticking with it. On shorter courses where the temps are above 70*, I still think the 225/15 RS3s on 15x8s will be the fast E30 set-up, but a 235/40-17 Dunlop Star Spec could be a great all-around choice & help with gearing on longer courses.

[GotCone?]

you are choosing a great place to start rate wise.

I have been spoiled having Lincoln 45 minutes from my house that I haven't had to do any short/small courses unless I head out to one of our other sites or out of town.

Back when we ran in topeka, I had two sets of wheels/tires just for gearing purposes. So good call there.

I'd love to see someone try 17" wheels with 24.5-25" diameter tires in STX on an E30 in Lincoln. I think it could bring it closer to the E36s.

[e30bulldog]

speaking of 17's toyo is making a 245/35/17.... that is really short and I would love to see someone run it on an e30.

[GotCone?]

I think the E30 is too heavy to keep from over heating those Toyos after 2 runs. But I'd love to be proven wrong. That diameter won't really change the gearing -vs- the 225/50-15, which I think will hurt the car on the faster national courses, but it has all the prospect of being wider... if you can legally fit it. Put that on at least a 17x8.5.

[Jean]

Do STX rules allow it? I am in SM, so STX rules are foreign to me lol

[race2win]

Do STX rules allow it? I am in SM, so STX rules are foreign to me lol

You can run up to 265 width tires on up to 9" wide wheels in STX on 2wd cars. The limiting factor on an E30 is the small fenders, STX rules only allow rolling of the inner fender lip, but no change to outer contour is allowed. That being said, 265s on 17x9s won't fit, 235-245 on 8's or maybe 8.5's will be the limit I think.

speaking of 17's toyo is making a 245/35/17.... that is really short and I would love to see someone run it on an e30.

Yes, this tire could be a solid choice in the right situation, but it's wide so I'm not sure it can squeeze in there. At 23.8" diameter, it's only .8 taller than the 225/45-15 RS3s I run now...which would be perfect gearing-wise. But like GotCone? mentions, they would most likely over-heat very quickly in all but the coldest conditions on an E30. Assuming they would fit, they would be a great wet tire though.

The set-up I plan to try is 235/40-17 Dunlop Star Specs on 17x8s. That tire is about .7" wider than my RS3s & should fit, I'm just not sure about the height as they are 24.4" which is almost an inch & a half taller. It will definitely extend 2nd gear...to 62 MPH, which will be about 4 MPH faster than the 15" RS3s. The other benefit to the Dunlops is that they are better in cold & wet conditions, without giving up too much in dry and/or hot conditions. RS3s are hands-down the best tire when it's warm, but they NEED heat to work well & are virtually useless in conditions below 50* and/or wet.

The biggest negative I see to running a 17" wheel/tire package is weight...at minimum it will add 5-6 lbs of un-sprung weight to each corner, I'm just not sure the slight gain in width is worth the weight penalty. So, I still see myself on the 225/45-15 RS3s in most situations.

Now, if they ever come out with a 245/45-15...

[e30bulldog]

I hear you on that I wish they would make some wider street tires for a 15" wheel. I did use the toyo R1r for about a half a season, I didn't have much trouble overheating them until I had a co-driver on a hot Mississippi summer day.

[CrazyB]

Great to see more Bay area e30s running, I am in DSP but caught a few of your runs last year the car looked great out there :)

[GotCone?]

FWIW... I ran 225/50-16x8 +20mm w/o rolling and there was zero rubbing issues.



The car was pretty flat






Would require more camber and or other tweaks to fit wider, but the height isn't an issue if you set things up right.

[race2win]

Wow, that's a tall tire! Those are listed at 24.9", which is a half inch taller than the 235/40-17, but the 17s are a half inch wider so the right camber & ride height settings will be important. I wish there was a better 16" option than 225/50...225/40 would be ideal, or maybe a 245/40-16 :)

I'm confident the 17s will fit, the negatives are higher unsprung weight & running a potentially higher ride height for them to clear...two things that can potentially slow a car down through tight transitions. I'm still on the fence whether it would be a benefit or not...

[GotCone?]

You should have a decent sampling of Street touring competitors in your area. See if you can't get some worn down scrubs or something from someone. 235/40-17 or 245/40-17.

XXR has some new wheels that should be a good fit. They are cheap, so it's minimal outlay to give it a try and should be easy wheels to resell later.

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XXR 530

17x8.25", 4x100, +25mm
$115 each = $460 set
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XXR 527

17x8.25", 4x100, +25mm
$115 each = $460 set
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They look like great options to try. Otherwise Rota has a 17x8.5 D2, but it's a lot more $$ for an experiment.

I think it can be made to work and will really help the E30 on a national level.

I'd love to help someone in a region near mine give it a try and get the setup dialed in *cough* Doug H.*cough*

Thanks - Jon