NYC993

OP,
what about tire pressures?

My guess is too much tire upfront with much softer springs. Try to stiffen front ARB and run slightly more tire pressure than in the rear.

i run 225 front 275 rear NT01s. Front RS bar is middle hole, rear full hard. With newly rebuild LSD I have very little oversteer, I would actually like to add more. I have street HR coilovers, and while a bit too soft, the car tracks very well. Just came from Shenandoah and car was fantastic on the little technical track.

MSR Racer

Not enough rubber in the rear. Those car understeer everywhere usually. I raced a 993.

rlm328

Your sway bar set up stiff in front soft in the rear is to induce oversteer. Correct one of them or both by going to full neutral on both to see what the car does and then adjust just one of them.

This will cost you nothing and you can adjust it at the track.

jstyer

This is not right. Read any vehicle dynamics textbook in the world, or just go adjust your car, you'll find out pretty quickly.

Edit: Didn't mean to sound too harsh. But you could also look at that simple VD chart you posted earlier!

rlm328

Go read the chart I sent you.

jdistefa

Put 400lb fronts on.

FYI I run at 0.8 F:R like Bill.

And yes, put 285s on the rear.

stownsen914

Stiffer on front bar and softer on rear bar is standard to induce understeer, not oversteer. I didn't see anything on the chart you linked to indicate otherwise. Is there something out of the ordinary that you are suggesting re: swaybar adjustments?

Bill Verburg

W/ MCS shocks you can run much more spring on the street than w/ old school shocks. The secret is in the valving and adjustability

Typically you'd run,
600/800 or 600/750. The former will have a bit less understeer. This will still be fine for limited street use.

Again an effective lsd helps a lot, an asymmetric 40/60 or so would be great.

If I could get the tires I'd want 245/35 & 285/30 on 8.5 /10(or 10.5), but since I like NT01 I have to run 235/40 & 275/30 but 225/40 & 265/30 RE71 are almost as good on 8/10. The NT01 will last longer than RE 71, grip levels are comparable. Direzza * spec isn't far behind(I have all 3 on my cars now)

not sure what some of this means
I use 100% monoball and would recommend the same for any mostly track car. I used to use RS spec all around except for the rear toe arm which was mono-ball. This was fine except for 2 things, 1- rear camber was limited and 2- the adjusting eccentrics would walk, this made the handling unpredictable. The solution was turnbuckle arms w/ locks for all the rear suspension except the rear A arm which is RSR mit mono-ball

lastly RSR inner tie rods for the steering are a big plus

morsini

Listen to what bill is saying, but my opinion is 600/800 in going to be a little harsh for street use. Get some real rubber, have the car setup by someone that knows and understands 993s.

dan212

^^^^^^^ THIS ^^^^^^^^^^^

mark kibort

not only this, but as i understand it , the 993 was the first to use something similar to the 928 suspension in the rear (weisach = autotoe in). if so , alignment settings can be critical, but generally, it will cause the car to push more if set correctly. it really sounds like tire pressure and tire brand/type and quality.

many cars will perform very loose, if the tire pressure on the track is anywhere near the 40psi range hot. i always refernce a story of a bunch of guys i was helping at a track event (NSX's) and all of them had 2 things in common. all had offs in one session and all had 40psi pressure in the rear tires (these cars have very little front tires too) anyway, adjusting back down to near 30psi cold was something that helped all of the drivers.

i know from many years of experience, just changing the rear tires can make a night and day difference if the rears are even the slightest bit old, worn, or heat cycled to a point where their grip is compromised.

jstyer

Bill, I originally had 515/700 on the car, but even with the MCS shocks, it was just too brutal on Houston's (3rd world country quality) roads. Loved it as soon as I got outside of downtown, and I definitely miss the response on track.

Here's a further explanation of what I mean as far as suspension:
- I bought new rear control arms, but immediately replaced the rubber rear bushing with a 25% higher durometer.
- Ditto for the camber and KT links.
- solid monoball rear toe link.
- solid aluminum rear suspension sub-frame mounts.
- polyurethane rear sway bar bushings.
- polyurethane front control arm bushings
- RSR front tie rods

This car still sees 3-5K street miles per year, so the intention was to create a compromise between full solid rear end, and the softer stock rubber. The rear end feels very connected compared to a stock 993, but there's very little increase in NVH. Obviously the car is not perfect yet (that's why I'm here!), but so far I'm happy with my solid/rubber mix.

So far I've had good luck with the camber and KT eccentrics not walking, even in one nasty spin I had. Though I do check my witness marks after each track day. I've heard the worst stories with the rear toe arm which largely influenced my decision to go with a solid toe link.

Bill Verburg

mechanically that's a decent setup, both in components and setup so just address the tire issue & the spring issue & again an effective asymmetric lsd would help a lot

245/35 & 285/30 is best but you almost have to be using Hoosiers to get those sizes, 245/35 or /40 & 275/35 next best & widely available in several tire lines or 225/40 & 265/35 next best. What you use will depend on the tire line you want to use.

The street/track conundrum wrt the spring rates. If stiffer is out the only choice is a more balanced lighter setup, look for ~150# to 200# Δ, you are @224 f/r Δ now so I'd want closer to 150#. Do you have a dual spring setup? If not that should also take some of the sting out of stiff mains, the cost is dual set points. Unfortunately the softer the springs the more roll, the more roll the more roll steer

RS sways should be neutral for most tracks w/ this set up but for track days maybe go up a step or 2 equally f/r. This will help limit roll steer some but also reduces grip a bit. Roll steer and KT steer are both present w/ rubber KT arm and A arm bushes. For track days you really want to limit both.

Lastly Be sure that the KT is the same measure L/R not necessarily going to be the same eccentric setting l/r and in the range 2 - 4 on the Motorsport gauge, 2 will make for a quicker rear response 4 slower, you want the fastest reacting rear that you feel comfortable w/. Back in the day factory recommendation for max rear caster(KT) was 3° 30', I'm unsure whether that is 3.5 on the msp gauge or not.

Tire pressures are also critical I find that both NT01 & RE71 like ~ 34-35 hot max the further above that the greasier they feel.

Difool

A bit OT, but are you running separate set of track wheels? RE71R will will be stickier than NT01 but wear out twice as quick. They also can get a bit greasy in 85 degree plus weather. They are better for street driving ... until you wear them out quickly, and any tire without tread depth will be a menace to you and others if you get caught in the rain. NT01 really shouldn't be driven in the rain.

Regarding your OP, have you been watching your hot temps closely? I don't know anything about Direzzas, but if you are over inflating or getting higher pressures after warming up you can get behavior like that. Similar if the tires are old or bad. May not be the issue but changing tire pressure is super easy to try out. For reference I ran several tire brands (AD08R, RE71R) at 32 hot. I talked to people that swore by much higher temps, but it really didn't work for me.

Bill Verburg

after using both in temps to upper 90s, I find little difference between them. I agree that 71s will wear out more quickly but I believe the reason is that they come w/ what used to be shaved tread depth when new, there's just less rubber to ear away.

I agree 01s aren't a rain tire, but then neither is 71