knfeparty

I think you can tell from my signature that I have experience in this area of dialing out bad handling on skinny street tires. Word to the wise- it isn't a modern pushy car (I learned to drive on a 325) and it is probably mostly your fault. Learning how to drive the car on street tires made me very competitive once I stepped up to race tires, though.

Mongo

I have no spare in the back of mine and have NEVER encountered a problem with terminal/unpredictable oversteer.

M758

Add some fuel. Maybe 5-6 gallons or put the spare tire back in. Alternatively you can lower the rear ride height a bit to get the same effect. I when autocrossing my stock 83 944 I was suffering with corner exit oversteer(I could not get the power down) and some extra weight in the back made all the difference in world. In other events I was fine with out the spare and on low fuel. It was very course dependant.

M758

39 rear is too high even for street tires.


I'd do tire pressures first (36 psi all the way round first)

M758

If you have instability and oversteer underbraking I would consider that toe. Not enough toe in to control the back end. No what is interesting is a little corner ENTRY oversteer is nice in autocorss. Corner exit oversteer will cost you time and you need to soften or lower the rear. Lowering tire pressures will help the tire bite the road better as well.

Van

To the OP: can you clarify if the back end is coming loose on acceleration or on deceleration?

You do say that stepping on the gas doesn’t help – assuming that you have an open diff, the inside rear wheel probably spins. But I wonder what’s happening (the transition) before you accelerate. For example, if you’re in a turn, and have a bit of body roll, you’re unloading your inside rear tire.

Perhaps you need stiffer sway bars. Or larger rear torsion bars. Or a different alignment. Or wider rear tires…

There usually isn’t an easy answer, because all of these things work together.

xsboost90

i have found from autox and DE events that very small adjustments w/ ride height or weight make big differences. Had some oversteer at putnam park, raised the front like 1/4-1/2" and it was gone. Autox if i got some understeer i'd pull the tire, mostly ran w/ it in though. Sometimes you need even tire pressures, sometimes alittle more up front, or whatever. Oversteer/understeer- learn it, live it , love it.

Techno Duck

Regarding what Van is mentioning, if the oversteer is on deceleration that is because of the weight transfer. You can manipulate this with braking and starting your turn entry at the same time. Also known as trail braking...it can be very useful to rotate the car around quickly. I was doing this by accident for about 3-4 auto-x's before i started to get comfortable with using it to my advantage.

N_Halbert

As you can see the views are all over the place on tire pressure. 39 rear to high, 38-39 just right. It all depends upon what tires you are running and your mileage will vary from one to another. With street tires you may have to run higher pressures if they have soft side walls or lower if they are stiff. It is a matter keeping the tire flat and not rolling over. Too soft and you end up running on the edge. Chalking the edge before a run will show you if they are too soft.

I am running on street tire, Toyo T1R, vs my normal RA1s. It's a whole lot of fun. Typical I will start cold at 35 all round. Once warm, the T1's would continue to go up in pressure if at less than 40 psi at the start of the run but would remain at 40 if left at 40. They were flexing more a the lower pressure and continued to heat up and get greasy.

You need to work with your car. The combination of spring, shock, torsen bars and tires are unique to it. You need to establish a base point from which to work and write it down. From there start with the suspension settings then tune with tire pressures.

Assuming they did dial in 1/16 to 1/8 toe on the rear, I would start with the tire pressures at 35 all round and not allow more than a 2lb front to rear difference. Then take the shocks up to about 3/4 and the rear down a click or two. Then see how it behaves.

You don't mention if the sway bars are adjustable. If they are keep shocks at current settings , tires at 35 and stiffen the front. 26.8mm front, 18mm rear swaybars are not bad but may be contributing. The M030 paired a 30 with a 19. With a stock suspension set to hard makes the car tail happy, mid is a good balance.

How long had you been autoX-ing before upgrading? Driving style can also induce oversteer. You say you have trouble getting the power down. Now is the tail coming around or are you stuffing the car into the corner lifting the opposite rear? Smooth is fast.

heavy fuel

Yes smooth is fast, my technique is needing gross improvement. Probably i'm in too fast, lifting the rear and not ever recovering. i'm very gentle on the power, the rear is loose before power gets applied.

my tires are Yoko ES100 in 225/50/15, 280 treadwear. the sidewalls look to be pretty stiff, rolling over to the edge of the tread judging by the wear marks.

the alignment was 1/16 toe in the rear, so should be ok. non-adjustable swaybars, probably worn out bushings not allowing them to work correctly.

sounds like the remedy is more experience, stiffen shock in front, even out tire pressures, and more experience. oh, and more experience.

M758

I advise 36 psi cold for all corners. I ran 225/50R15 ES100's on my 83 stock autocross car using 36 psi cold.
If the rear is loose before power is applied it sounds like it is lose on corner entry. My advice is to even up the tire pressures and make sure you brake in a straight line. If the rear steps out at turn in make the turn in more gradual and be ready to get on the gas to settle the back end. When I was autocrossing my 83 I could get the back end to come around as needed to and then use the gas to settle the car. It was perfect for fast laps, but did take skill to get right. Sounds like the rear tire pressures are a bit too high and your turn in technique needs improving. I think If I drove that car I would love it.