SCCA STR Autocross Carrera Build

[Driven97]

I'll be using Euromeister fake Fuchs, 17" variety.



Well, took the car out of the garage for a quick squeak check. The side skirts are off, it's dirty, and totally not aligned, but it drives again. Definitely stiffer, a little louder, and the 150k mile shocks cannot handle the torsion rates. Height "looks" pretty good in the rear, but I have to raise the front to get correct geometry back. It also seems that my car can get a lot more camber on the right rear than the left rear, is this common?

It's taken me 10 days so far to do the suspension. Good thing I pay myself by the hour. In beer.

[Randy W]

Originally Posted by 5:04

I had 23/30's on my car and when I auto-x'ed it pushed like a son of *****. If I were to set the car up for Auto-X I'd either go stiffer in the rear or softer in the front and then balance it with sways.

Also agree that 23/30 is less than ideal for autocross. Neither is 21/31 or 22/33 IMO. 21/29 or 22/30 would be a better choice for a Carrera on an autox course. You need to get the car to rotate easily, and you also need some compliance. The right shocks are even more important than torsion bars, as you are usually dealing with parking lot surfaces and abrupt transitions. I would also go with the lowest aspect 15-inch sticky street tire you can find to help with your car's tall 2nd gear (2225-45/15 Hankook Ventus R-S3 wouid work).

[Driven97]

Well, you guys have me doubting my choices so far. Perhaps I should have asked on this board first. Ah well, live and learn.

I did a string alignment last weekend. Decided to go a little aggressive with zero rear toe since the consensus is that I'll be pushy with my setup. I'm not going to touch front camber until I verify that the tires will fit in the fenders - it is now set with the camber plates maxed out (negative.)



So far I'm impressed with all of the products. The car actually rides quieter, and my wife thinks it's more comfortable than before. Go figure. My old bushings must have been in much worse shape than they looked. But really, even though spring rate more than doubled, it's not nearly as stiff as I expected. The shocks are inadequate - the car does "bounce" (what's faster than a bounce but slower than a vibrate? A jiggle?) Can't wait to get them revalved.

The rear seems to have settled a bit, so when I corner balance I think I'll raise it up. Then just shocks and tires left to do before I unleash the car on the cones.

[Driven97]

No massive update, but the car has been all back together for a while, going for a nice exercise a few times a week since the roads have been pretty dry here.



And some nice Dunlop Z2 tires showed up today:



These are the 225/45-17 for the front. I'm still undecided on the rears, but am leaning towards the 245/40-17 for better balance and improved gearing over the 255s. Comments?

[rennch]

I did extensive autocrossing with my RSR, and going back to 15's (from 17's) made a HUGE improvement in my times. Consider doing some 7 & 9 Group 4 wheels, perhaps?

[Driven97]

Tire selection. Nothing wider than 225s in 140tw+ in 15".

[ben parrish]

Matt, I'd listen to Michael...been in a car with him on the autocross and he is quick...even with the limited choice 15's.

[DG624]

The advantage of using 15 X 7, 8 is you get a lower car without changing the suspension...almost 1" lower and quicker acceleration. AutoX is about accelerating from tight turns. I was thinking of going to 16s but the tire size does not allow any smaller diameter for lowering the car. I was wondering if 15 X 8 and 9 would work with a non turbo car?

[Driven97]

I'm not convinced. The M coupe, 350z, and Z4 are all also rans in the class. It's dominated by the Miata and S2000. Power doesn't mean anything if you can't put it down. Grip is everything.

I would gladly run 255s on 15" wheels if they existed, but the smallest diameter to get them in is 17". I'm not giving up that grip advantage, especially when the 911 has a torque advantage over the top two cars already.

[DG624]

Numbers are misleading until you race. I can beat Miatas but S2000 are hard to beat. Grip is nothing without minimizing body lean and fast times depend on a very responsive car that can break and accelerate. A good alignment can really tell you what your base is before you change costly parts. Also make sure you don't have any rust on the front end that weakens stiffness. I was not willing to spend big bucks until I had an idea of the handling. Tell me if the bigger tires work. You can also buy used tires for half price (SCCA Sports Car Mag).

[Driven97]

Minor update -Avoiding the Porsche Tax

I'm not too keen on paying $200 for a strut tower brace when they are available on ebay for every other car for $20 or less. So I decided to adapt my own. I bought a Honda Accord brace for $8 including shipping. Took some scrap aluminum square tube, and made my own side brackets. Let's just say there is a reason I don't work in a machine shop:


Two issues I ran into:
The Honda Accord brace was about 6" shorter than what would be perfect, so my brackets had to extend the extra distance.
The strut tops aren't flat. What a pain. My solution was to chamfer the ends of the plates and let them bend to shape as I tightened them. Worked like a charm, but the brackets ended up pointing down slightly. Ah well.

End result:


Once I cut the carpet it'll hide my shoddy aluminum fabrication. Tensioned it nice and tight with preload. Not perfect, but certainly not $192 worse than the off the shelf option.

[Elombard]

I think it will flex under a load that woudl flex the chassis there. You may be adding weight. I would re design or ditch it. I do applaud your efforts - better looking than some of my fabbed pieces ;-)

[rennch]

Hey Ben!!! Nice to see you here, buddy! How's the car?

Originally Posted by ben parrish

Matt, I'd listen to Michael...been in a car with him on the autocross and he is quick...even with the limited choice 15's.

[Driven97]

Well, looks like BraidUSA has listened to you all and is running 205 / 225 - 15 combo.

Me, I'm hard headed as all getup and just got my 225 / 255 - 17 combo installed.

We'll be competing at the same events, so looks like this will be a great experiment!

Just in case you are all right I have my OEM 15s in a nice stack in the corner of my garage...



The racing season is upon us. Just a few things left to do before the first event - still need a corner balance and a catalytic install.

Stay tuned for the first results of all that hard work.

[Craig_D]

Hey Matt, is your front bumper shortened? I mean...recessed? I've been wanting to do that mod and it looks like yours is recessed.

[Driven97]

Originally Posted by Craig_D

Hey Matt, is your front bumper shortened? I mean...recessed? I've been wanting to do that mod and it looks like yours is recessed.

I hope not, it's not an allowed modification. Looks normal to me, maybe the lighting and cell phone camera combined to make a weird effect?

[Mehoff]

Originally Posted by Driven97

Well, looks like BraidUSA has listened to you all and is running 205 / 225 - 15 combo.

Me, I'm hard headed as all getup and just got my 225 / 255 - 17 combo installed.

Ha! Hard headed is right....255 is WAY too much tire for an AutoX car. Hell, it's almost too much tire for a track car with a stock drivetrain (factory weight).

[Driven97]

Originally Posted by Mehoff

Ha! Hard headed is right....255 is WAY too much tire for an AutoX car. Hell, it's almost too much tire for a track car with a stock drivetrain (factory weight).

Come beat me and I'll listen to you.

[RonDent]

Was that the sound of a glove being thrown down?

[neilschelly]

Originally Posted by Mehoff

Ha! Hard headed is right....255 is WAY too much tire for an AutoX car. Hell, it's almost too much tire for a track car with a stock drivetrain (factory weight).

I'd expect an autocross car to have more use of wider tires than a track car. I don't recall seeing too many Miatas on 255s or 275s on a track, but they sure do love them on an autocross course. I ran my Impreza autocross car (same weight as a Carrera 3.2) on 255s, and I was the odd one out when everyone else was running them on 275s.
-N