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Old 04-29-2019, 03:28 PM   #1
Melon
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Melon's Autocross Thread

So, I finally got some good seat time in the car, but I noticed a few issues, and wanted to get some input from the more experienced E30 drivers.

Background:
Front and rear - toe Neutral alignment
M3 control arm bushings
H&R Sport springs
H&R sways (Front set to med, Rear set to soft)
Bilstein B8 shocks
Apex ARC-8 wheels, 215/45/17 Falken Azenis

25mm MC

M20 w/ 272 cam
Running the car in STX
( Yes, I know about the cam, no one cares locally, and I'll forfeit my points if I were to win the class. )

I installed a Massive brake setup, 300x22, with HT10 pads. I still have all the ABS items installed, but it's non functional.

These are the issues. There seems to be too much front brake bias, so I ordered parts to delete the stock proportioning valve, and install a Wilwood adjustable piece for the rear. When I was heading into a corner at speed it always felt like there could be more, and the fronts locked up really easily, and I couldn't get the car to rotate at all. Next event, I'll set the rear bar to stiff, and with the proportioning valve removed, hopefully I'll have better brake bias, and a little more loose rear end.

At the last events I couldn't get it to dance at all behind me, felt like a FWD car more than a neutral RWD car.

Anyway, that's my plan, would appreciate any input.

First run video:

https://www.youtube.com/watch?v=EfSnxYseZZc
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Old 04-30-2019, 09:12 AM   #2
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Just a couple random thoughts:

- H&R Sports are really soft and understeer prone

- Stiffer rear bar may help some

- M3 CABs reduce low speed steering response

- The 25mm MC increases pedal effort and moves brake bias forward versus the stock MC

I would talk directly with Lee at Massive about your concerns with the brake bias. I don't know how his front brake kit changes things. He should be able to offer good advice on setting that up properly.

In general, not much can be learned from that out of the car video you posted. However, it looks like a really low speed run. From the sound of it, you are at the bottom of 2nd gear? I don't think you'll be able to do much to get the car to "dance" at those speeds, unless you are ultra aggressive with your inputs.

Your steering inputs look way late. You can start your inputs much earlier to set yourself up closer to the cones, and be thinking about the next 1-2 cones well in advance. In most cases you should be using the cone you are currently at to set up for what is coming next, rather than reacting to the next cone once you make it there.

Don't forget to experiment a lot with tire pressures, they can make a huge difference in how the car feels and performs.
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Old 04-30-2019, 09:19 AM   #3
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That video was a slow ass run, and yeah, it was more of a "Here it is!" type of thing, nothing to really be analyzed. In car would be much better for that.

I was running the fronts at 28psi, and the rears at 30psi.
I agree, more experimentation can dial that in.

Thanks for your notes on the suspension, I'll keep that in mind.
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Old 04-30-2019, 09:25 AM   #4
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You can probably increase the tire pressures quite a bit, since autocross is too slow and too short to build up heat in the tires, they are not going to raise the pressures much at all. I'd try different pressures up to 36+psi, that will help free up the car.
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Old 04-30-2019, 09:31 AM   #5
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Right on.
I had no issues with the front getting loose, mainly the rear.
Id like to be able to rotate under braking.

I'll message Lee about the brakes.
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Old 05-01-2019, 06:55 PM   #6
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Hi Alan

As DigitalWave mentioned, going from the original 22/17mm MC to any other MC with equal size pistons (including your 25/25) will automatically move bias forward by a huge amount. The OEM pressure valve was designed to tame the rear hydraulic pressure. Ditch it. Had you kept the original MC, and with your combo of 300mm rotors and 1.25" pistons, you'd have ended with a bias exactly as stock. Well, within 1 or 2 %. To compensate for the larger rotors, I suggested to reduce piston size compared to stock. But it is the equal size MC that makes the difference now. Go ditch that bias valve now

260mm discs --- 300mm = 15% bigger (the more precise calculation requires to measure the diameter at the center of the brake pad )

BMW calipers w/ 48mm piston = 1809sq.mm piston area

Wilwood calipers w/ 1.25" pistons = 1583sq.mm piston area= 13% smaller than stock.

And as a last note, use the same pads at the front and the rear for stock bias...


And if you like your car more tail happy, then increase rear spring rate. On my e30 M3, rear spring rate was 50% more than front. Then I went to 55%. With stock sway bars, or no sway bars at all if you want to put the power down sooner...
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Last edited by Massive Lee; 05-02-2019 at 04:45 AM.
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Old 05-02-2019, 04:59 AM   #7
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Lee, Thanks for breaking it down even further for me, outside of our PM's.
I really appreciate it, I've learned a lot. This is the first time I've installed a BBK and altered factory brake biasing, so for me, I'm in uncharted waters.

I even had a stock sized MC on and switched it before I finished the brakes.

I did look up larger master cylinders on R3v
"You'll like the harder pedal feel" they said. Believe them I did.

I'm not interested in re-springing the car, that's additional costs, and going to race springs introduces alignment issues I purposely avoided. However, I didn't even think about disconnecting the sway bar altogether, I'll try that.

Ultimately the E30 will be a casual AutoX car, There's a V6 Mustang in STX that's got me by 1.5s, and I can't keep losing to him.

The C5 is going to get some suspension work over the summer, that's my main machine. Me and a good friend with a C5Z are constantly going at it. I'll bring that out and mop the floor with the Mustang. Muahahaha.
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Old 05-02-2019, 07:07 AM   #8
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Increasing rear tires pressure has sevral positif effects if you want to add some oversteer.
1- Being stiffer, it is therefore less compliant (stiffer sidewalls) and offers less grab on the ground. Also you can increase pressure to reduce the contact patch by making the patch slightly "rounder".

I hear you when you mention that you wish you could rotate the car by simply lifting the throttle. My e30 M3 was like that. As an instructor I was demonstrating how to rotate a well set-up car with throttle-on and throttle-off. And personally I prefer a car that oversteers than one that understeers.
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Old 05-02-2019, 07:25 AM   #9
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Quote:
Originally Posted by Massive Lee View Post
Increasing rear tires pressure has sevral positif effects if you want to add some oversteer.
1- Being stiffer, it is therefore less compliant (stiffer sidewalls) and offers less grab on the ground. Also you can increase pressure to reduce the contact patch by making the patch slightly "rounder".

I hear you when you mention that you wish you could rotate the car by simply lifting the throttle. My e30 M3 was like that. As an instructor I was demonstrating how to rotate a well set-up car with throttle-on and throttle-off. And personally I prefer a car that oversteers than one that understeers.
Same, for AutoX, I prefer a little bit of a waggly tail.

In my Corvette and when I had my NC Miata, I'm able to rotate the rear under braking, and that's great for tight maneuvers and being able to back sight a pointer cone. The Corvette I can make the ass dance with the throttle too, I won't get that with a nearly stock M20, but it does have enough power to help correct understeer, which is nice to be able to floor it almost anywhere on course.

I'm mainly after the rotation under braking. At the last event I didn't feel the rears biting at all, and I lost some time.
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Old 05-02-2019, 06:50 PM   #10
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Try playing with the front bar as well as the rear.
It probably doesn't have enough effect to fix much,
but first try soft, then stiff, then unhooked.

Just for grins.

Springs may be required.

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