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Ride height / rates for a 2nd gen

Old 09-14-10, 12:54 PM
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Ride height / rates for a 2nd gen

Hope this is an autocross-friendly environment.

I built a 2nd gen GTUs for SCCA autocross this year. After struggling most of the year with various problems (self-induced, mostly), I got the car working "pretty well" and managed a very close 3rd place finish at the ProSolo Finale, and coned away 3rd or 4th at Nationals in a very competitive STS class.

The shock / spring package I have is something Ground Control put together for me. It's shortened Koni single adjustable front struts and rear shocks, with 2.5" coilover springs. I'm running 450lb front springs and 300lb rears. I run a 1.125" ST front bar on soft, no rear bar. Camber is -3.5 front with zero toe. Rear is -2.0 camber and 1/8" toe-in.

Ride heights are about 12 1/4" front and 12 3/4" rear. With the front this low, the outer ball joints are about an inch higher than the inner pivots, meaning the car is well into the positive-camber gain arena.

The car drives .. not badly. It's very good in transitions - very stable, but it rotates. On corner entry it tends to be loose, especially with any trail braking. On corner exit, it's pushy. Very pushy. I know this is typically a characteristic of very low front roll centers.

I would like to try raising the whole car, as it theoretically should allow me to run less static negative camber all around. The issue is the shocks are so short they are nearly topped out, static. I have only about 0.5" of front droop available.

Is this typical for how 2nd gens are set up for racing? Are there other shocks out there that are worth trying? Should I just live with the low roll centers (I can't legally fix them, other than raising the car)?

Thanks for any input. Attached is a shot of the car in a steady-state corner. By the way - in STS we are restricted to a 225mm wide street tire on a 7.5" wide rim.
Attached Thumbnails Ride height / rates for a 2nd gen-img_0638.jpg  
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Old 09-15-10, 02:39 AM
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do you have any strut bars in the front or back?
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Old 09-15-10, 03:47 AM
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Where are you measuring ride height to?
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Old 09-15-10, 05:57 AM
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No strut bars - though I'm not sure why it matters.

Ride height measured from the top of the wheel arch to the wheel center.
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Old 09-15-10, 09:03 AM
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You want to loosen the car up on exit, put the stock rear bar back in. We run the stock sway bars all around with about the sam spring rates. I think our ride height is close to yours.

Most racing setups include a full coilover conversion such that ride heights are fully adjustable without affecting the shock travel.
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Old 09-15-10, 09:48 AM
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Originally Posted by SoloII///M View Post
I would like to try raising the whole car, as it theoretically should allow me to run less static negative camber all around. The issue is the shocks are so short they are nearly topped out, static. I have only about 0.5" of front droop available.

Is this typical for how 2nd gens are set up for racing? Are there other shocks out there that are worth trying? Should I just live with the low roll centers (I can't legally fix them, other than raising the car)?

Thanks for any input. Attached is a shot of the car in a steady-state corner. By the way - in STS we are restricted to a 225mm wide street tire on a 7.5" wide rim.
you're right to measure it from wheel center to something else, my car is lower to the ground than my friends, but he's tucking 17's and im totally stock, if we measure from the wheel to the fender i'm like a truck....

anyways, i forget your exact hardware. i'm assuming that the rear strut is a rear strut and its ok, but the front is an insert that's all the way up.

if yes, then can you space up the insert in the strut housing?
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Old 09-15-10, 06:24 PM
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Typically I don't run the rear bar and that's how I ran the car at the Pro Finale. But I did put it back on for nationals and that's how I ran it both days. It didn't make much of a difference.

The front strut is indeed an insert, a custom valved 8641-1547 koni. I guess I could space it up in the housing - hadn't really thought about that.

As I said above, GC purposely built the front struts so that they would limit the droop travel. I'm not knowledgeable enough to understand why they want to limit the droop, but that's what they told me.

I guess I'm hoping to understand why everyone runs the cars so low. Maybe it's fine, but it just doesn't seem right to me. The roll center drops faster than the Cg with a strut, and forces you to run a lot of negative camber unless the car is as stiff as a brick.

And I still don't understand the strut bar question.
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Old 09-15-10, 10:31 PM
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Generalities: Most cars come with way more droop travel than is useful. Limiting droop travel is a cheap way to use the chassis as a swaybar. Left hand turn, weight on right wheel, if the left wheel can't extend more than 1/2" then you're either going to lift it, or use it to limit the travel...

I've seen lots of instances in lots of cars where people run lower than the "good" trim height. Some guys are successful despite this, but most are much happier making the car work in the designed range. That said a lot of strut cars do exactly what you say -- become go-karts with so much roll stiffness that you take the suspension out of the picture. My understand is that this is common practice with the Porsches...
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Old 09-16-10, 11:53 AM
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Have you tried dial out some camber in the front at your current ride height? We run about 3deg neg with almost perfect tire wear characteristics in the front. Seems like the car handles quite well. It will rotate at will on entry or exit.

Maybe take out some rear toe in?
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Old 09-16-10, 01:19 PM
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I plan to dial out some of the negative camber up front. It may be slightly excessive.

I already re-aligned the car and took out some of the rear camber (and as a result, some of the rear toe-in). Only issue now is that I'm at the limit of the stock toe eccentrics. With around -1.8 negative in the rear, I can only get about 1/16" total toe-in at the rear.

We'll see how this affects corner entry. Again, the car was nice and neutral on entry (in fact, sometimes a bit TOO neutral)... it was just corner exit where it was tight.
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Old 09-16-10, 01:35 PM
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Yeah 1.8-2.0 rear neg seemed about optimal for us. Any less and the car was super loose on entry.
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Old 09-16-10, 02:23 PM
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Originally Posted by SoloII///M View Post
The front strut is indeed an insert, a custom valved 8641-1547 koni. I guess I could space it up in the housing - hadn't really thought about that.
my buddy just bought a hatchi, and he put the standard fanboi suspension on it (cut strut housings w the tokico HTS shocks) and with the car so high the shocks are topped out, its almost as high as he needs it.

he does um we'll say hill climbs, and its bumpy...

one solution is the put the HTS cartridge in a longer uncut stock housing with a spacer at the bottom...

just kind of thinking out loud, as it needs testing.

or maybe you could space the camber plate down? my friends FC with a similar setup has a similar problem, although right now the spring is too short, its basically all the way up to get to the lofty heights you are at
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Old 09-16-10, 02:53 PM
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What's a hatchi?

I had thought about spacing the front camber plate down as well... it would accomplish the same thing.

I guess I'll have to experiment. It seems to me that the higher ride height would work better, but nobody who races these things runs them up there so I must be missing something.
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Old 09-17-10, 12:32 AM
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Hachi Roku - Eight Six - Corolla AE86.

Riz.
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Old 09-17-10, 04:47 AM
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So back to the original question - what do you guys who race your FCs run for ride height, measured from the wheel center to the top of the fender, front and rear?
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Old 09-17-10, 11:58 AM
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Check this recent thread about ride height:

http://www.improvedtouring.com/forum...ad.php?t=28225

Now this is for track not autox so setup may be different for you.
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Old 09-17-10, 02:41 PM
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I'll take a measurement when i get home tonight.
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Old 09-17-10, 03:53 PM
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my STOCK low mileage original 87 GXL is 13.75" F and 14.5" R from the center of the wheel to the fender.
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Old 09-25-10, 08:15 PM
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Do yu run long enough to take tire temp into consideration? If the camber is right for the track, the temps will be even across the face. But you knew this.

Yes, start with putting the rear bar back on. The ST, RB and Eibach tuned kits all have higher rates on springs and thicker bars front and rear. It is a balance act, and you have no rear bar at all.
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