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Author Topic: Oversteer
Motor City Hamilton
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Thought I would add a thread for this since I'm having the opposite problem to the Understeer guy.

I am not new to racing, just new to the SM - 1st year. My car doesn't push anywhere. I'm pretty close to the JD set up guide - flat surface & scaled. The car is a little agressive for me as I'm making the switch from front drive Honda to rear drive Miata. I'm a little behind the car, so I want to make it a little more stable - less aggressive. I can always go back to aggressive once I catch up with the corner speeds.

I have lots of experience with race car suspension set ups, but NO experience with running on the bump stops. One change at a time, I was thinking about adding some rear toe in (at 1/16" now), then maybe soften the rear bar (in middle hole now), then maybe tire pressures (colds now front 33 and rear 32).

After reading the understeer thread, I'm thinking that I have a bump stop issue. I'm at 4 5/8" all the way around. I think my first change should be a slight raise of the rear?

Some evidence of the symptoms. I race at Waterford Hills, MI and Mid Ohio. Last weekend at Mid Ohio same symptoms in left turn 1, left kink up the hill to the carosel, right turn in 7? end of the back straight, right turn 12? entry to thunder valley and left turn 13 after thunder valley. The car gets really loose after turn in through mid corner. On the other hand, the car seems pretty neutral - almost perfect in all the lower speed tight stuff.

I think that I may have mis-diagnosed the problem. Your opinions please. Should I start with raising the rear ride height?

Thanks,
Keith

Jerry Cabe Verified Driver Made Donation to Website
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Keith,

I'm no where near experienced enough to give advice in the setup area, but I'll ask a question just to maybe help others comment. What tires were you running, and what were your hot pressures?

Jerry

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Just driving SM until the F-1 car is ready.

tony senese Verified Driver
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The first year I drove the miata, I spun at least once every race weekend for about a year. After driving a front wheel drive car for several years in HPDE I had to adjust.

The car rotates so nicely compared to any FWD car you have to learn to drive it. It isn't oversteering, you are! You are used to being able to pull your car through almost any turn without the rear wheels letting go at all. No matter what you do with your miata, it won't drive like that. The fast guys in miata's and lots of us slower guys have to learn to change our apex's and braking techniques to use this characteristic. I find to this day my biggest issue is over slowing on entry and then of course there is no way for the car to push, you're going way to slow. Then you compensate by getting hard on the gas before the apex with a little too much slip angle, and the car feels very loose.
Get someone who has driven a miata alot to go out with you and see if that helps.

--------------------
Tony Senese
SM#99
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Try to get it off the bump stops. Do you have the 99+ shock mounts? If not 4 5/8" is too low.

Do what I do - go to Bennett's paddock and pester the piss out of him with questions.

-Denny

Motor City Hamilton
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I do have the 99 hats.

Tony - good thoughts and I don't think I'm doing all of those bad behaviors. Even with front wheel drive I tried to be very smooth. I was pretty good in the rain too.

My first weekend in the Miata I was way off on the turn in as you describe. I was trail braking too long and scrubbing off too much speed. I have been really focused on being smooth, every session.

Let me try to describe how extreme the rotation is. If I turn the wheel from a 9 & 3 hands position to anywhere past a 10 & 4 position, the car will try getting sideways. Is that normal for you fast guys?

Tires - My hot pressures were 38 all around and my temps all looked great for in, mid and outside. My tires are still showing tread. I started at 4/32 and now have 13 sessions on them.

Matt Johnson Verified Driver
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Keith, step 1 is to figure out where you really are from a 'how much travel until each corner hits the jounce bumpers' standpoint. This is pretty easy to do with modeling clay stuck on the top of the shocks, gently lower the car onto it's tires (with some form of slip plates), then raise the car back up, remove and measure the clay.

Now you know your "real" ride heights - adjust from there. You will probably end up wanting to raise the rear a bit (this is a big hammer). Also check your rear outer lower control arm bolts - they stretch and you end up with power on compliance toe in, braking compliance toe out (yuck).

--------------------
Matt Johnson
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Motor City Hamilton
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Brand new suspension bolt all the way through.

I have about an inch of travel in the front and a little over 3/4" in the rear.

I really don't like measuring from the pinch welds anyway, but that seems like the popular thing to do. They can get bent and are rarely the same on each corner from the factory. I guess it can get you close.

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quote:
Originally posted by Matt Johnson:
Keith, step 1 is to figure out where you really are from a 'how much travel until each corner hits the jounce bumpers' standpoint. This is pretty easy to do with modeling clay stuck on the top of the shocks, gently lower the car onto it's tires (with some form of slip plates), then raise the car back up, remove and measure the clay.

Matt - Could you please elaborate on this method.
Slow newbie here.

--------------------
Muda Motorsports
"We're all here 'cause we're not all there."

Matt Johnson Verified Driver
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Keith, that is exactly why I don't do anything with the pinch flanges other than lift the car...

I suspect that you are playing in the 'rear jounce bumpers hit, but fronts don't' kind of ride height setup there. I (by no means one of the fastest guys around) shoot for about .50 inch clearance between the shock tops and main flat surface of the jounce bumpers (i.e. I ignore the nubs) both front and rear. I will then adjust the car as I see fit at the track, but usually not much.

Muda,
To elaborate; the body stamping and assembly process is notoriously bad for tolerances in things that the customers don't see (fender height vs. wheel, pinch flange to ground, etc. Then the cars go out in the real world and get beat up...

The industry method of measuring ride heights is generally the vertical diference between inner and outer control arm pivots. On a racecar that uses it's jounce bumpers as a handling tuning tool, I think it makes more sense (and doesn't loose acuracy) to directly measure free travel to jounce bumper engagment.

It is tough to get a measuring stick in between the spring coils while the car is sitting on the ground, so I raise the car up in the air and put something deformable in the area I want to measure (in this case modeling clay on the top of the shock cans). Then lower the car back onto it's wheels with slip plates (or folded garbage bags on a smooth, clean, level surface) to let the suspension settle. This should be done at race weights (fuel and driver masses in place), and needs to be done gently so that the suspension goes to it't race ride height without over shooting.

Then, lift the car back up and pull the clay out carefully, measure with a set of calipers, and figure out what if anything you want to change...

Hope this helps.

--------------------
Matt Johnson
1990 SM #73 - yet another red miata.

38BFAST Verified Driver
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Keith, you are fast enough!

--------------------
Ralph Provitz
#38
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"I see", said the blind man.

Thanks Matt!

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Motor City Hamilton
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quote:
Originally posted by 38BFAST:
Keith, you are fast enough!

Ralph - I have two remaining Waterford Hills weekends this season to catch up to you. I'd like to finish one with you in sight. I'd be happy with you crossing the finish line as I'm coming out of swamp. That would be about 3 seconds behind - like 0.25 seconds a lap off your pace. I think that would be getting up to speed quickly in this car?

By the way, I'm signing up for both SM and ITA next weekend. I need the seat time.

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quote:
Originally posted by Motor City Hamilton:
quote:
Originally posted by 38BFAST:
Keith, you are fast enough!

Ralph - I have two remaining Waterford Hills weekends this season to catch up to you. I'd like to finish one with you in sight. I'd be happy with you crossing the finish line as I'm coming out of swamp. That would be about 3 seconds behind - like 0.25 seconds a lap off your pace. I think that would be getting up to speed quickly in this car?

By the way, I'm signing up for both SM and ITA next weekend. I need the seat time.

Be carfull in ITA. It can get crazy and Jeff is on a mission. Hope to see you at the pointy end of SM. Well, as long as it is behind me [Big Grin]

Oh back to your original question. I wish I could get my car loose on turn in. For the most part I am always fighting push. The 1.8s have a front bar designed for a Corvette. I would love to have the 1.6 ajustable bar.

--------------------
Ralph Provitz
#38
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Motor City Hamilton
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Ye'ah. I figured that the car was close to right and that I am causing some of this. I think I'm going to start by raising the rear a little to get off the bump stops. I was trying to think if I noticed a "snap loose" condition at mid corner. I'm trying to be really smooth, so it's not really a snap. It does seem though that when I really got through the entry of Mid-O turns 1, 7 and 13 at a good entry speed that the loose condition started (or got worse) at the car's weight set onto the outside tires. Bump stops?

I'll start with raising the rear at home, then re-camber, toe and scale to get to my Mid-O settings. That'll leave me with some simple at-track changes (swaybar, rear toe in, etc.).

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You do have to be smooth because the SM shocks are way under valved. It was the first thing I noticed when I got into SM.

--------------------
Ralph Provitz
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Motor City Hamilton
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New measurements from the car after the race weekend, back on my flat setup surface in my garage with driver weight in the car.

Ride height at straight parts of the pinch welds. LF & LR 4 7/16" or 11.3 cm
RF & RR 4 1/2" or 11.5 cm

Ride height at the sub-frame
(for front used the bottom or head of the subframe bolt right behind the rear pivot of the front lower arm)
(for rear used the bottom/head of the subframe bolt in front of the front pivot of the lower arm)
LF 9cm LR 11.2cm RF 8.7cm RR 11.1cm

Shock travel
LF 1.2cm or 31/64"
LR 1.2cm or 31/64"
RF 0.7cm or 9/32"
RR 1.1cm or 7/16"

Conclusions:
The car is too low and I'm riding on the bump stops alot.
The pinch welds on my car are nowhere close to even. I even marked them at relatively straight parts. Compare the pinch weld numbers to the sub-frame and shock travel measurements. The pinch welds indicate that the right side of the car is higher than the left. The other two measurements both show that the left is higher than the right. I think I'm going to start measuring from the subframe bolts. No rake is actually 9cm front and 11.2cm rear.

How much shock travel do people tend to run? I've heard no less than 3/4" and I've also heard no less than 1".

[ 08-18-2008, 03:30 PM: Message edited by: Motor City Hamilton ]

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I put my car up on a digital frame machine and then marked the pich flange to a z plane off of the cars datum points. I back checked to the shock to bumpstop and it is very close.

--------------------
Ralph Provitz
#38
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Pat
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Ralph, I've always been suspicious about the accuracy of the pinch weld measure. Just to be clear, are you saying that your checks concluded that the pinch welds DO get you close enough?

Kieth, not a driver, but have some limited experience and do scale and set-up miata.

Similar situation, driver complained of loose in, and proved it by looping it in T8, and almost in t1 a couple times. I tried something far more easy. Dropped rear tire psi by 2 lbs. and raised front by 2 lbs. Driver Happy, and 1/2 second faster on avg.

If you wanted to try ride hieghts, I would start by raising entire car a couple turns, if your sure you were at 50% cross.

J.D.'s set-up guide clearly says lower is not better, also in another post, if you started with 4/32 tread depth, I've read several posts that indicate that you have a ways to go before those toyos (assumption) are prime. Drago has posted as much as 2 seconds difference between 4/32 and 2/32.! While one might think this is not a factor in overall balance, if not rotating between every session, fronts are getting to prime rubber more quickly than rears (I think- could be wrong)

J.D.'s set-up guide also clearly says, dont listen to paddock experts.!!!!! [Big Grin] so feel free to pick these thoughts apart.! and let me know how any changes helped or hurt. Just throwin it out there, here to learn.

B(Kuch) Kucera 45 Verified Driver
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I will say the same thing,4/32 3/32 and even 2/32 are slow.I alway's get my new tires shaved to 2/32 to start with.With a new set of 2/32 tires on the car,the car will be slow at Mid-O.

Mid-O is a smooth track and will take some time to wear the tires in.Now Nelson Ledges will get those 2/32 tires in shape after one weekend.With 2/32 tires at Mid-O I'm 1.5sec slower then with a set of prime tires.When I say prime I mean when the tires are at there quickest.

The best tire performance at Mid-O with Toyo's are when you can barely see any tire grooves at all.In my car with new tires I play with my tire pressures after every time out to help performance (handling)until the tires reach there prime.If you notice alot of the fast guy's have a set of qualifying tires and a set of racing tires.Also pay attention to there lap times,during the race their not as fast as qualifying (most of the time).

I don't run my pressures that high,I keep them slightly lower.For some reason my car likes the lower psi,doesn't feel that lose with the lower pressures.

Bottom line is,all cars and drivers are diff.so you have to set it up for you and the way you drive.This means seat time,and test and tune,or fun day's and alot of adjustments to find what fits you best.Remember to right all your adjustments down and how it felt before you change anything so you can go back if you have to.

--------------------
Bob
!KUCH!

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I'll agree with Pat & Bob about the tread depth, but I'll add that I found that Mid-O is more sensitive than other tracks. The session I got my pole time last year was on corded tires. Unfortunately, that meant I had to go out on "sticker" 2/32nds tires for the next session. I was nearly a sec slower while most went faster.

Keith, your situation is probably similar to mine. We both came from Hondas and Hoosiers. My Honda was a lot stiffer sprung then yours, but the Miata is quite a bit softer than either. The Toyos are quite a bit less responsive than the small Hoosiers we ran too. I found that I had to significantly slow my steering inputs down and be a lot smoother with the steering and throttle to go faster. There was far more time in altering my driving than any set-up change that I have made.

Ed.

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Edwin Ho
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If you want to know if you are hitting the bumpstops but a tiny zip tie around the shock rod. Put it really tight against the shock body, then go out for a session. The zip tie will move up and stay in place if you got it tight enough.

MEAT

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Keith, I see you run a 94. Bear in mind, the higher unsprung weight from the larger brakes. Also I find that the rear brakes have a bit too much bias, which will make it more difficult to trail brake. Pad selection will help here. You'll have to compensate when trail braking.

From what has been written, IMO, you have too little suspension travel. Start with 3/4 inch in the front, and an 1/8 inch (or zero) of rake to set the rear. Full soft on the rear bar. Depending on the smoothness of the track, you can go lower.

As to driving, I have found it very rewarding to get the car to "set" smoothly. Bouncing hard on to the bump rubber leads to confusion and variable handling in mid corner, with corresponding slow exit speeds.

--------------------
-Tosh Desai
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Motor City Hamilton
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Thanks for all of the advice. My car's pinch welds are nowhere close from side to side and corner to corner. I do have the zip tie trick already installed. Always had those on the sprint car and other oval teams that I have worked for. The car was definately too low and I was way deep into the bump stops in all of the left handers at Mid-O. Those are kind of important corners.

I set the car up for this past weekend with 3/4" of travel on all four corners and cross weights at 50/50. I checked travel by setting the car ( bounce it then role back and forth) then moving my zip ties to sit against the shock bodies. Raised one side of the car, then measured the distance from bump stop to bottom edge of the zip tie. For the other side, you need to re-bounce the car, role it and move the zip tie into position. Jack up that side, then measure. That's the most accurate way I found to set shock travel to 3/4". Next I measured the pinch welds for reference to everyone elses's set ups (mine are each different). Then I looked for a more consistent, harder to bend place to measure from. I chose the subframe at the chassis bolt (front is from the back sub frame bolt and rear is from forward subframe bolt). I now have a reference that I can measure in milimeters and know that my shock travel will be in-line. Well, in-line at least until something on the car gets bent.

Ed and others who have suggested it, yes, there is a big learning curve moving from front drive on Hoosiers to SM on Toyos. I want to get the car driveable, then I'm not changing it for the rest of the season. If the car is consistent, I'll learn faster.

Raced at Waterford Hills this past weekend (Ralph and Ed will know this track well). Basically take Mid-Ohio's technical 2.5 mile track, make it two lanes wide and take 1 mile out of it. Fourteen corners of narrow fun. The car was really good. My times dropped a full second between Friday's practice day and Sunday's race day. I checked mylaps.com and 90% of my laps are within 0.5 sec of each other. I need to work on that other 10% of mistakes and or traffic. Also need to improve by one more sec a lap. The fast group (Allen Faitel and Ralph Provitz) are one sec up. I finished 6th in our 17 car field, so I'm getting there. And, I think I know which corners they're beating me in (swamp and turn one)

Thanks again for everyone's help. Heading to Mid-Ohio for the September 6&7 double regional. Any of you who like to talk racing line, please stop by the obnoxious green car and chat. I could use some advice through madness (which turn do you give up)?

Motor City Hamilton
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Also, hate the brakes on my 1994. The rears will lock up first. I didn't have power brakes in the Honda, so I've been working on being smooth. Are there different pads anyone would recommend for the 94? I'm on Carbotech's right now. A little less rear bias would be cool.

Front XP10
Rear XP8

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Check the parking brake adjusters, make sure the rears are free and have a low threshold for replacing the proportioning valve.

--------------------
Do I turn my 99 Hard S into a killerfast SM or seek a donor?

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quote:
Originally posted by Pat:
Ralph, I've always been suspicious about the accuracy of the pinch weld measure. Just to be clear, are you saying that your checks concluded that the pinch welds DO get you close enough?


It all depends on the car. Like I said I put mine up on a digital frame machine to check mine out. I then marked on the pinch weld 4 points that were flat in the X axis.

Mine were out a total of 1/4 on the lowest corner.

--------------------
Ralph Provitz
#38
2008 WHRRI SM Champion
2008 WHRRI Top 10 Overall
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