Catastrophic uncontrollable oversteer
 

I had a little run in with a tire wall this weekend and I would really like to figure out what happened.

Things I know:
Unexpected and uncontrollable oversteer
Happened with steering pointed fairly straight on pavement
Started to oversteer while in WOT
I tried with all my might to steer into it asap
I probably lifted
There's a slight oil leak on one of the axle seals
It happened fast and I'm confused

Car details:
~200rwhp max
All mechanical steering/bearings/etc <1 year old
Poly bushings all around; Bilstien sports; 550/450 rates (I think...); not slammed
Stock 1992 sway bars
9" jongblooood with 225 rs3v2's (used but still have decent tread)
Kaaz 1.5 way rear differential; Assumed max 100% lockup settings
Basically no aero; just a ricer gv front lip.

Occurred in 3rd gear on a 5spd 4.1 rear end at ~4500 rpm
Here's a sweet mspaint diagram that's accurate to the 0.001" of what happened :giggle:
https://www.miataturbo.net/attachmen...ine=1457390341

Any input would be appreciated! The collective has probably solved this at one point or another...

550/450 and stock sways is the bulk of your issue. I would start by adding a big tubular FSB and about 200# to the front springs.

Who sold you those springrates?

If they are unvalved billies I would take rate out of the rears over adding more to the front.

You can take 125-150# out of the rear too, but you have to do something.

I probably sold them to myself haha. Really they are SM take-offs I believe and I never re-sprung them. They are indeed stock valved.

I should add that I have ~20 track events on this setup and this has actually happened once before (and I chalked that to cold tires). This was the first day on the turbo setup. It has generally felt pretty good, but I don't have much to compare it to.

That's actually better feedback from a money/time perspective. I was all hot and bothered to dismantle the diff, but from what I've felt/read the diff generally causes a little bit of understeer, which is why I'm confused.

The sage advice is greatly appreciated. It's a little unsettling to not trust your car on a big sweeper with high consequences.

A stiff rear end makes for lots of skidmarks.

SM is 700/325 with a big rear bar, so not SM takeoffs. With stock sways, those rear rates, and those tires you would want something between 900 and 1000lb front springs.

Buy some 325s for the rear, get a big front sway bar, and raise the car to at least 4.5" pinch weld heights.

Golden :rofl:

Here's the link where I bought these, the springs don't have markings so this is what I'm going on...:
https://www.miataturbo.net/miata-par...t-ready-79853/

Interesting about the SM rates; and great to hear that the setup is so odd. I think I'm at 5" or a little higher for the pinch welds, or whats left of them...
Much appreciation!

Those look real thick lol.

Its pretty easy to measure spring rate.

A stiff rear end could cause unexpected oversteer, wouldn't it, when you are expecting and managing power-on understeer?

I don't know your driving background, so ignore and tell me I'm wrong if this definitely doesn't apply to you, but

4500rpm on a 1.6 in 3rd coming on power exiting a sweeper... first time on turbo at track...rs3s...blaming diff and suspension...

Your suspension setup needs changes, no doubt, but my guess is that there's some driver error involved in this. If you don't acknowledge that, you're not going to solve the entire problem. You can't just expect to hammer 200ish torques down on a miata coming out of a sweeper at 60mph on street tires and expect it to stay planted.

I've seen newish drivers try and play too much detective on exactly what's causing their unexpected handling conditions when they needed to just focus a little more on their own inputs.

And yeah, work on that suspension, it's not ideal.

I've certainly made many errors at this track and have needed to be pulled out at least once before due to the sand. This is the only one that I don't understand. As mentioned earlier, I've done ~20 track *events on this specific track and I was pointed mostly straight at the time of the oversteer.
Car has a vvt swap, so 4500 rpm on that ;)
I was incrementally pushing the safer zones on the track; this was my third session. I'm a mellow early 30 something... not really on the edge of anything. It broke loose and surprised me.

Rear alignment bolts in good shape?
I had a worn lower rear bolt. The one at the front on the rear lower arm.

Just an idea. I have never been on a track so take it with a grain of salt.

The tires, although still showing tread, are old and have hardened. Buy some new tires and watch this problem go away. :2cents:

One other thing to look at is your rake. The first iteration of my bilstein/ebay/ground control setup had my rear end about .75" higher than the front at the pinch welds and it made the car really snap oversteery. Once I got proper sleeves and was able to lower the rear about half an inch, everything got a lot better.

I agree with the above assessment as to why the oversteer but you should also ask yourself what did you do when you hit the point of no return. Did you put two feet in? Normally that will lock the wheels and carry you into a trajectory the keeps you out of harms way.

I should say point of no return for me... I'm not great at saves, the car was dead when the dust settled so I didn't have the where for all to push the clutch in.

I have locked things up on other spin outs (probably too soon) and it made the situation worse.

I'm just a hobby driver and definitely have 0.1% of the experience of some of the commenters here. What do you guys do when you get caught off guard in an oversteer situation?

Just throwing this out there:

Track condition: any chance there was a fluid spill for your right side tires to get into?

Is it consistently oversteery, or is this a one-time occurrence? Do you have proper bump travel? If you hit a bump with the rear and your bump stops bottomed out, that could easily cause snap oversteer.

I cant find the thread, but I remember reading about a condition that is un-saveable no matter the car, or driver. Sudden, uncontrollable oversteer. Like once you realize what's happening, it's too late, and a human's reaction time isn't fast enough to input the proper correction.

The thread was on miataturbo, and someone had linked a video of a formula 1 car that had the condition.

Maybe this type of thing happened?

The magic begins at 2:24

Awesome! Thanks for digging that up.
It was kind of like that, except I was going slower and the pavement was smooth.
That video supports a lot of the info in this thread; it looks like he hits the bump stops hard and gets jostled on a harmonic.

I've taken all of the great advice in here and ordered new springs/front sway/endlinks and tubing to extend my tophats while I'm at it.

I'll try and get some video at the next event and tinker with this corner for some analytics.

Edit: didn't notice the other responses.
It is possible that the track surface was compromised, but this has happened once before. Generally the car feels ok (to me, not much to compare to).
While n/a I was running the same lap times of comparably experienced drivers in sti's/c5's on 200tw tires so its not terrible until something like this happens. Note that our track is on the unforgiving side in general and favors a smaller wheelbase.

Edit2: This is the track being discussed for the curious, 1.7 mile, post turn 5 is where things went wrong:
https://www.miataturbo.net/attachmen...ine=1457467605

And this is a representative 3rd gear log showing my supercharger like boost curve (wastegate only)
https://www.miataturbo.net/attachmen...ine=1457467605

from what I know of kaaz diffs, transition from power to lift is abrupt and unforgiving, even at low speeds. if you lifted enough to unload the diff, it could upset the chassis a lot.

find a big, empty, unpatrolled parking lot and test it by driving in a circle under light power and just lift gently.

as an aside, you say you are no good at saves...

I recommend spending some time with Rfactor or Assetto Corsa and a decent wheel and pedals (logitech etc). I have encouraged a number of friends down this path and ALL have seen significant improvements in laptime, control and understanding of car dynamics and tuning etc...the seat time versus cost and muscle memory gain is well worth it in my opinion.

Of course its not like the real thing but it does provide a lot of the real thing at little to no cost.....

edit: and treat it like a REAL car, not a video game...

deleted

Catastrophic uncontrollable oversteer
 

No. Stickier tires would mask the problem until he was at higher speed and then the results would be more dramatic.

If the suspension is wrong the car won't work at their limits of adhesion with any tires.

I have been to that track multiple times. I think you probably lifted and it got you loose. The slowest corner on the track is right before where you say you had the problem, so you should have been accelerating hard and diving across that apex. You say you were straightening out when it happened, so a lift off seems most likely.

I was hoping someone who has driven there would drop in. This really is one of the simplest parts of the track...
One of the few things that I'm certain of is that I lost control under acceleration. I probably lifted as the oversteer got away from me though, and I'm not sure if that made it worse.

Too bad no video. I would tend to support Andrew's analysis. Regardless of how much power it has or your skill level, that is a severely mismatched suspension setup which is going to have the characteristic of abrupt oversteer.

Contributing factors are a differential that is known not to be very smooth. That means it's locking on decel is rather abrupt so it is not conducive to abrupt throttle lift mid turn on a car that is already loose. Then you have the additional power which means your rear tires were probably hotter than they normally are. Then you have possibly slow hands/shuffle steer where you did not make a quick/big enough correction soon as it started to yaw. But ultimately your suspension is not correct. Fix that first and then post some video.

I found that my car is SUPER loose (tail happy) on bad tires and perfectly neutral on sticky tires. No change other than wheels/tires.


Either way- OP's suspension sounds like it could use some adjusting.

Ok, if you say so, but the turn you lost it after is not a hard turn at all and is cambered in the direction you are going, so absolutely catastrophic oversteer is the only other rational explanation, brought on by your suspension set-up.

I really should pick up an action cam... I ski a lot and a chunk of that is in resorts; I need to get over my general distaste derived from the gopro clowns.
It would be funny to see my "awww geee Cletus I think I'm losin this here thing here" reaction time.
Thanks again for the help.


Chilicharger, any chance you're going to the event at ASR later this month?

Without video/data what you think you did is probably wrong. Humans don't remember things properly, you're remembering what you think you would have done. Not what you actually did.

Unfortunately not, work calls.:vash:

I did just buy a factory hardtop 06 specifically to make into a track car, though, so hopefully my schedule will line up at some point to take it to ASR or Motiva sometime this year. I will let you know.

I had my first track day with the new sway bar and rear springs.
Things seem to be much improved! I'm still taking it pretty easy but I managed to cut 1 second off my best lap time (pre-turbo and definitely not taking it easy).
I also got some time on the skid pad. I've never really done a donut so I'm not sure how exactly it was supposed to go, but it did seem to break loose in a fully predictable manner.

It seems the track maintenance guy decided to leave my exploded tire wall as I left it. You can also still see my skid marks. It looks like my mspaint diagram is fairly accurate.

https://www.miataturbo.net/attachmen...ine=1460005694

https://www.miataturbo.net/attachmen...ine=1460005694

https://www.miataturbo.net/attachmen...ine=1460005694

https://www.miataturbo.net/attachmen...ine=1460005694

https://www.miataturbo.net/attachmen...ine=1460005694

https://www.miataturbo.net/attachmen...ine=1460005694

Cat's given for tire wall destructive performance art. If I could give a second cat for listening, learning and being persistent, I would.

Back on the horse!

Tires are more effective as an attenuating device when strapped together in bundles. It is interesting that they are loose. Loose tires have the potential to launch cars airborne.

https://www.miataturbo.net/attachmen...ine=1460157635

My thoughts exactly. Between that, and no-one tidying up after they were scattered, I wonder about track standards, and what other shortcuts the owners/operators are taking. Do tracks over there have to be licenced, or is a case of throw down a bit of tar, and throw open the gates?

I think I would be looking for a new track, if any were available ...

I watched a mustang go under that same wall, tires bolted together, a couple years ago. That's The Bitch at Hallett

The track is in New Mexico. The poorest state. Don't expect anything fancy in New Mexico. The next closest track is Arroyo Seco outside of Las Cruces, NM. It is just an open field with some tar, basically.