SCCA STX E30 Build/Introduction

[Jean]

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

[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.

[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?]

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.

[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?]

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.

[bmwguy325is]

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

[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.

[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!

[race2win]

Thanks everyone for the comments & suggestions. In regards to the Fat Cat Bilstiens, they will be rebound adjustable, definitely need that otherwise I wouldn't consider it. The Miata I drove to E-Stock wins last year at the San Diego National Tour & the 1st round of the Nor Pac Divisional has Fat Cat adjustable Bilstiens on it, they were fantastic...much better than the Konis I had on my personal E-Stock Miata the year before. The adjustment knobs are at the top of the shock like a Koni which is nice, & each quarter-turn can have a noticeable affect on handling. Fat Cat's success in Miatas is hands-down proven, with too many Tour & Pro wins to count, & quite a few National Championships...I'm very confident Shaikh can put together a competitive BMW package. Plus, they are autocrossers & know what is neccesary to run up front, & rebuilds or upgrades are easy.

I have heard nothing but great things in regards to AST, & I must admit I am drooling over the new 4150/4250's as well (especially with aluminum bodies). However, what is mainly holding me back is high cost (I'm guessing $2500-3000 for 4150s, & that's without camber plates), but also the "one-size-fits-all" valving, & at least for me, more difficulty getting support & rebuilds if needed. My target for shocks/springs in this car is no more than $2K, & that hopefully will include camber plates. This is for many reasons, but mainly to show that a simple cost-effective set-up can be competitive. In my career I have always done very well with simple shock packages, I want to continue that trend here. As I have said earlier in this thread, I want to provide an easy-to-duplcate set-up that other E30 owners can use on their cars. As good as AST, Motons, Penskes, etc. are, there just aren't going to be many E30 owners spending $3-5K on shocks for their $3-5K car.

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.

I will admit to not being very knowledgable on the engineering of suspension design & all the geometry such as wheel rate, etc., so I could be way off base. I will be talking with both Fat Cat & Ground Control in the coming weeks to come up with a game plan, in the mean time keep the comments & suggestions coming!!

[e30bulldog]

race2win:

Looks like you have a good build on your hands. I am currently driving a 88 325is in STX. I am also using a GC setup with koni D/A's... and I love them. I drove my car for years in a similar for that yours is in now. I had big sways all around (25/22), the rear bar does great when you have soft sport springs under the car.

I have driven cars with the fatcat motorsports suspension (miata of coarse) and I really did like it, my only beef with it is there is no adjustment. Even a car with just single adjustables is worth it to me.

I have recently bought a set of hankook rs3's, they are phenomenal...unless its cold and then they are useless...hehe. I have also use the dunlop direzza, and the toyo r1r, all good tires but they don't have the grip of the rs3.


Good luck with your build, I honestly thing a e30 is not enough to compete nationally in STX but I commend you for trying, these cars can amaze you from time to time.

here's a pic of my car from a few years ago

[Bimmerman325i]

I have AST 4100s on my Manwagon, and I would put them on an E30 in a heartbeat. Each click makes a very noticeable difference in feel to the driver, which is (imo) worth the price differential over GC or TCK. I have TCK DAs on my M3, and they are great shocks...but they require more clicks or turns (comp / rebound) to have a noticeable effect. I'm drooling over the AST 4250s that just got announced, they will be epic TT killers.

I can't speak to Bilstein-based kits, but for a competitive autocross build I would not waste my time with anything that is not adjustable, and adjustable to where you can feel the difference between a few adjustments (like GC/TCK/AST/$$$$$). If the shocks used in the Fat Cat kit are PSS9-esque, that could be good, but if they're converted Billy sports without any adjustment, I wouldn't do that unless there are other cars with the same setup you can drive to test. Probably still wouldn't, if you're doing a serious all-out build.

[Jean]

race2win - if you go that route, I would love to hear more about it.

My current bilsten sports were sent to bilstein for a re-valve job, they have been used with 550front/675rears IIRC and netted me and my co-driver 1st and 3rd place last year in SM class locally. This is with a cabrio front bar, no rear bar, dot r-tires and gc plates.

The valving is not easy for daily driving though, very rough over potholes or under hard braking if it's bumpy. I may have to re-visit this again or swap to another insert.

[110stx]

I've driven an e30///M3 that was setup on GC coilovers with Koni SAs, GC camber plates, etc. It was great. Conant has since gone with AST 5200s.

But when I began setting up my car, I went with ASTs. I have AST 5100s and Vorschlag stuff.

It is great stuff.

The car was (until very recently) my daily driver too, 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.

My only complaint -- and it's really my fault for pushing the ASTs through winter weather in KC -- is that the rebound adjusters (at the bottom of the struts) seized up about midway through the 2011 season.

I don't change the adjustments much, but when I want to, I want to ...

I'll be getting the struts rebuilt for 2012 season and won't be pushing the car through the snow any more, so hopefully that won't be a problem going forward.

d.hitchcock

[race2win]

Winter Update, Time For Shocks & Springs

Hey everyone, been a little while since the last update, my crazy work schedule & the holiday season have prevented any progress with the car.

So, I'm just about ready to pull the trigger on a shock/spring/coil-over set-up, so I thought I would see what the E30 community consensus was. Initially I was deciding between AST, TC Kline & a custom Koni/Ground Control set-up, & now I'm adding another possibility to the mix...a custom adjustable Bilstien/Ground Control set-up. Any real world autocross or track experience out there with any of those set-ups?

Here is what I am leaning towards...The owner of Fat Cat Motorsports, who is a Bilstien guru in the Miata community, says he should be able to build me an adjustable set of custom monotube Bilstiens. So I am thinking of going that route with a Ground Control coil over set up with custom spring rates to match my set-up. The benefits of this set-up would be dealing with semi-local companies to me that have proven competition motorsports success & great support, plus it would be a semi-low cost alternative to ASTs etc.

Assuming I go this route, what is the consensus on spring rates? My goal is to make the car transition very well, so I'm initially thinking of very stiff spring rates & no rear bar. Anyone with suggestions on spring rates? What kind of difference front to rear should be used with no rear bar?

Other than the suspension, still planning to go through the brakes, header & custom exhaust, fog light deletes, race seats, light weight battery, & then test a 17" wheel/tire package