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Old 10-25-2011, 02:18 PM   #1
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Default WAY Too Much Oversteer, Help Me Sort it Out

Like the title says. I took my car to it's first autox on Saturday. Not my first, I usually run my 08 WRX with decent times for the car. Well I was looking forward to running the miata, to see what kind of times I could get. It was horrible, I was really disappointed. Throttle on oversteer, lift off oversteer, partial throttle oversteer. It was ridiculous. I was beginning to think that I couldn't drive worth a ****, so I grabbed an experienced old guy and threw him in behind the wheel. He was hardly able to control it either, "wow, this car is a handful" was his words.

The tires are really old Anzenzis that I was hoping to make last until winter.
RB hollow bar up front.
Stock rear sway, both with adj. end links.
G/C 500F 325R with Koni Sports on full stiff.
ES Bushings
12"F 12.5" rear ride height
90 4.3 open diff (4.1 torsen on the shelf, waiting for instal)
De-powered rack
Caster: 4.2
Camber: 2.5F 2.0R
Toe: zero F and R

I disconnected the rear sway, and put the spare tire and jack back in the trunk and it was a bit better for the afternoon session, but still a handful. Messing around with tire pressures made minor improvements also. The 2008 National champ (in an NC) suggested my rear springs were a bit to stiff compared to the fronts. Any other insights?
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Old 10-25-2011, 02:50 PM   #2
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To give you an idea of what I'm running-

FM sways F & R soft stiff front and middle rear setting
Ohlins DFV 12K F ; 8K R
10 clicks from full stiff FRONT , 7 clicks from full stiff REAR (yes, I run the rear on a stffer dampening setting)
949 adj. endlinks set to neutral when car is at rest.
3.9 Torsen diff
Alignment ????? Last time it was set 2 years ago it was -1.8F , -1.6R , spec caster and .1 total toe in on front 0* toe rear.
Running Kumho V170
Car is neutral to neutral-oversteer. I typically run pretty fast battling for first in class (SSM).

I'd be suspect of your tires first. Hard tires will **** everything up if you're expecting them to have more grip (I didn't run auto-x this year because my V710s have been through two full seasons and a couple of track days already...they're hard). The open diff also makes the car less stable- don't think it'll only give you one-wheel-wonders..it'll still throw the rear out. I'm surprised you didn't try to reduce the shock settings, as I've noticed big differences doing this. I would have dropped the rears down to half..if not full soft to see if getting it to squat more helped put weight down better.
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Old 10-25-2011, 03:15 PM   #3
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Replace tires and report back. I'd also have my rear shocks on full soft.
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Old 10-25-2011, 03:21 PM   #4
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Quote:
Originally Posted by dstn2bdoa View Post

The tires are really old Anzenzis that I was hoping to make last until winter.
RB hollow bar up front.
Stock rear sway, both with adj. end links.
G/C 500F 325R with Koni Sports on full stiff.
ES Bushings
12"F 12.5" rear ride height
90 4.3 open diff (4.1 torsen on the shelf, waiting for instal)
De-powered rack
Caster: 4.2
Camber: 2.5F 2.0R
Toe: zero F and R
Tires may be whored out
disconnect rear sway
put rear on soft
redo alignment cus it might be fucked

or

go drifting and DGAF
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Old 10-25-2011, 03:25 PM   #5
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Bald Anzenies make great AUTOX tires:

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Old 10-25-2011, 03:37 PM   #6
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Your spring rate might be a little high but I'm not looking it up for you. Go on fat cats website and plug your numbers in. You might also be on the bump stops in the rear which will make your spring rate like 1000lbs. Is there a reason your running full stiff all the way around like a ricer?
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Old 10-25-2011, 03:50 PM   #7
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His spreadsheet means little. It could say he has 70% FRC but obviously, he has major oversteer.

I've Autoxed on those shocls/GC rates before and the setup was pretty nuetral
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Old 10-25-2011, 04:21 PM   #8
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I ride stiff on the rear (heh heh) to compensate for the shorter suspension travel so I'm not beating the **** out of the bumpstops on rough city streets. For autoX, it's a different story and I lower rear dampening.
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Old 10-25-2011, 04:34 PM   #9
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I ride stiff everywhere I go. Full stiff, 24/7.
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Old 10-25-2011, 05:19 PM   #10
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Car is too low. You're deep into the bumpstops while cornering. The spring rates are dominated by the bumpstops. If you're deeper in the bumpstops in the rear than the front, you get oversteer. Especially power oversteer, which makes the rears squat and increases bumpstop rates even more.

To test this theory, raise the rear 1/4 " and report back.
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Old 10-25-2011, 05:30 PM   #11
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Alignment is less than a month old, probably 300 miles. FCM shock mounts and bumpstops, I doubt I'm on the stops.

Sav drove my car around on the streets for a bit after he tuned it, told me to go full stiff on the shocks. Who am I to argue with Sav?

I thought the bad tires just lowered my break away threshold. If I replaced my tires, wouldn't the car just be tail happy at 75mph instead of 45mph? If so, I'd rather figure this out prior to my first track day.
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Old 10-25-2011, 05:39 PM   #12
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Quote:
Originally Posted by jacob300zx View Post
Is there a reason your running full stiff all the way around like a ricer?
I drove the car a bunch in June after we built the drivetrain and it was bouncy, like there was way too little rebound in the car. The Konis are rebound-only adjustable so I told him to spin them up to full stiff and leave them there.

I did the same thing on the black car years ago - I thought I would turn the shocks down after a track day and almost binned the car on a highway onramp with a slight dip just after entry. Turned them right back up to full stiff and left them alone.

Dan, I suspect the tires are trashed. The rates are a little low in the front but not excessively low.
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Old 10-25-2011, 07:47 PM   #13
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Quote:
Originally Posted by dstn2bdoa View Post
I thought the bad tires just lowered my break away threshold. If I replaced my tires, wouldn't the car just be tail happy at 75mph instead of 45mph? If so, I'd rather figure this out prior to my first track day.
Your suspension seems pretty similar to mine, though I have a torsen. I will get oversteer if I goose the throttle too hard out of a corner at autox, where the tires basically never get up to temp and don't grip for ****. But I would not expect your car to be crazy tail-happy on track with decent semi-grippy tires once they get a little heat into them. My car is pretty neutral and pleasantly throttle-steerable on track, in fact I have gotten several comments from passengers on how well behaved it is. But on the few occasions a year that I do an autox it can feel like a handful. A little more effort is required to manage the faster transitions and lower grip.

If you want to replace your ragged out Azenis, go with RS3 or Kumho XS or Star Specs or one of the newer tires that has done well in GRM's tests. I think I remember someone posting on this forum (Emilio maybe?) that comparing RS3 to NT01 lap times on the same car, the RS3 didn't give up a whole lot considering they are "street tires." The RS3 seems to do okay with autox too, I see a bunch of them at local events. My RS2s, in addition to wearing like the 200 treadwear rocks they are, also have a bunch of HPDE days on them and are certainly heat cycled to death. So I know how you feel autocrossing on shitty tires. Get new ones.
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Old 10-25-2011, 09:40 PM   #14
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Take off the rear bar. I have a comparable f/r spring ratio on my car and it's undrivable at autocross with the rear bar.
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Old 10-25-2011, 11:02 PM   #15
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There is no reason that car should be so tail happy. I've autoxed on 450/350, spec bars, and 205 azenis and spanked *** with 230whp and a torsen t2r. You have something wonky and I am guessing its in the rear. Was the driver who drove your car the kind of guy that slides his car? Your other car is awd? You might just be a big *****
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Old 10-25-2011, 11:50 PM   #16
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Tires.

what tire pressures did you run?
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Old 10-26-2011, 12:07 AM   #17
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I think I run a nugget of toe in in the back. That might help too.
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Old 10-26-2011, 12:19 AM   #18
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Quote:
Originally Posted by dstn2bdoa View Post
Camber: 2.5F 2.0R
Your springrate spread seems reasonable, but these alignment numbers are interesting.

In the turbo car, I always ran more negative camber in the rear than the front, (in the red car I was at -1.5F, -2.0R) and from what I've read, this is typical for both autocrossers and "spirited" street drivers. Makes for a very predictable car- neutral throttle into a corner produces a little understeer, which you can correct for with throttle.

Most of the folks I have seen running more negative camber up front are from the trackday crowd.

As an experiment, you might dial the front back a little- just eyeball it and see what happens. It'll **** up your camber and toe, but just mark the original settings with a paint pen so you can go back to them if you want. Turn the adjusters through about 1/3 of their range and see if you like the result.
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Old 10-26-2011, 12:36 AM   #19
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Ahem!

Quote:
Originally Posted by JasonC SBB View Post
Car is too low. You're deep into the bumpstops while cornering. The spring rates are dominated by the bumpstops. If you're deeper in the bumpstops in the rear than the front, you get oversteer. Especially power oversteer, which makes the rears squat and increases bumpstop rates even more.

To test this theory, raise the rear 1/4 " and report back.
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Old 10-26-2011, 06:32 AM   #20
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Quote:
Originally Posted by Joe Perez View Post
Your springrate spread seems reasonable, but these alignment numbers are interesting.

In the turbo car, I always ran more negative camber in the rear than the front, (in the red car I was at -1.5F, -2.0R) and from what I've read, this is typical for both autocrossers and "spirited" street drivers. Makes for a very predictable car- neutral throttle into a corner produces a little understeer, which you can correct for with throttle.

Most of the folks I have seen running more negative camber up front are from the trackday crowd.

As an experiment, you might dial the front back a little- just eyeball it and see what happens. It'll **** up your camber and toe, but just mark the original settings with a paint pen so you can go back to them if you want. Turn the adjusters through about 1/3 of their range and see if you like the result.
I'm not sure who told you that you should run more camber in the rear of a Miata for AutoX...but NEVER listen to that person again....EVER. I run over 3 degrees upfront and around 2 in the rear. My FIRST thought was that he was on the bump stops, but if he has ISC top hats that's not the case. My second thought was shitty tires and that for sure is the case and my third thought was take off the rear bar and throw it in the trashcan. If you put new tires on it and it is still loose try adding a slight amount of rear toe IN.
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