Just wondering if there is a way to tell if it's not correct from handling. I blistered the inside edge of a set of rear tires and my mechanic said that incorrect rear toe can do that. The Racing and Drivers Ed Forum guys said my tire pressures were probably too high by all of 5 lbs. But I just thought I'd ask about the kinematic toe in order to cover all the bases. Thanks,

Greg H.

 

Keep in mind that "incorrect rear toe" is different from "kinematic toe" AFAIK. "Toe" is a static setting. OTOH, kinematic toe setting has to do with how the toe changes as the suspension compresses. So I don't think your wrench was referring to kinematic toe. In which case he might be right; you should have your alignment checked. How much neg camber are you running?

Excessive pressure wouldn't cause the inside edge to blister, I don't think.

 

This is what was said in the "993 Suspension Explained" by Jim Pasha:

" ...It's the angle of the lower control arms, side-to-side. The goal is to have the control arms level when the car is at rest, regardless of ride height. This ensures the suspension will deflect equally under load. If the difference from side side to too much, the car will have a tendency to steer under acceleration. In addition, it will increase tire wear and may cause premature ball joint failure due to the excessive thrust loading. The Kinematic adjustment is set with a pair of protractors (Porsche tool)"

 

Hi Greg,

While I personally have not felt ill-handling due to kinematic toe gone awry, I recall others saying that it feels squirrely and unstable in turns, almost as if the car doesn't want to track properly when bent in a corner, especially with bumps as the suspension rises/falls.

The inside edge will typically wear faster as a consequence of the negative camber set in the car. Of course, the more neg camber you have, the more aggressive the wear on the inner edge (for a street-driven car, that is). But if you have one tire wearing considerably more than the other, then indeed have the alignment re-checked. Incorrect static toe at rear usually wears both rear tires, though, so it is more likely camber.

As for tire pressure, if you are in the range of "acceptable," you're not going to get vastly uneven tire wear. It does sound like something is amiss in the alignment department. Does the car feel darty or loose, or does it track solidly where you point it?

Edward

 

well, my car's kinematic toe was off when I first got my car, so I think I can help.

The best way that I could describe it would be that it felt as if the throttle and the tail of the car were connected. If you accelerated, the tail had a tendency to push out and lifting the throttle, it would come back into shape. It was very unsettling.

Also, I had no unusual tire wear doing this fiasco, just felt too much motion in the tail.

Sounds to me that its a general alignment issue or tire pressure problem.

Hope this helps,

Jeff N

 

I thought I corded one tire. The alignment shop said it looked more like I blistered both rear tires and then one started coming apart, so the problem was on both sides.

The descriptions of a mis-set kinematic toe was exactly what I was looking for. I think I can eliminate that problem. I'm no expert by any means, but I thought the car handled pretty well. It definitely was not coming back in if I lifted, as Jeff said, cause I spun the first time I did that. Seriously, I thought the rear was fairly predictable.

I'm running -1.5 negative camber in the rear. The reason I asked about the kinematic toe is that I had the car aligned before the track event and then again, at a different shop, after. I have to assume they at least set the static toe, but I know that the kinematic sometimes doesn't get done. Anyway, I'm going to Thunderhill on the 21st and I'm going to try dropping the pressure from 40 to 35 and see what happens. Thanks for all your input,

Greg H.

 

That's very little camber. I run 2.5 all around and wear has been even.

 

Greg, I am assuming you mean 40 psi when the tires are hot, and not starting at 40 psi before going out on the track. If you were running at 40 psi cold during a DE then when hot you could have easily had 48 psi, which is WAAAAAYYYYYYY too high.

Start with your tires at 35 psi cold all around and then immediately check your pressures when you come in from a session. Bleed off the pressure until all four tires read 40 psi when HOT. Go out for another session and do the exact same thing with the tire pressure when you come in. By the third session you will have the correct pressure. After the car sits overnight, check your cold tire pressures and write them down. This is where you should start next time you go to the track.

 

Just wondering, do the rear subframe to body rubber bushings ever wear out / need replacing.
And what are the symptoms of having worn bushings?

Mika

 

Daniel - I was referring to hot pressures. I was doing exactly as you suggested, bleeding to 40 hot. I'm going to try starting at 32 cold and bleeding down to 35 or 36 hot.

Jauder - What pressures were you running on your Dunlops? From what I've seen others post I aggree that I am not running a lot of negative camber. I was really expecting to wear the outside edges.

Greg H.

 

Mika,Usually they don't wear out, they wear if oil,(leaks from above) gets to them,you will hear a thud everytime you over rough uneven surfaces, kind of a loose shock mount.,cheers,Sonny.

 

Thanks Sonny !
I guess mine just needs adjustment of kinematic toe then.
Rear end feels a bit loose and unsettled when changing lane or entering corner.

Mika

 

Mine was out once and it made right turns a lot of fun. Absolutely no problems with push.

 

After installing my H&R springs, I took my '95 to Prestige Motors, the dealer in Denver, CO. They could not adjust the K-toe on my car because they told me the adjustment were maxed out. Additionally, they said the 10" turbo twists on the rear made it impossible to mount the K-toe level tool. I was told this was a result of the lowered car. So, my K-toe is maxed out. I've done a couple track days and have put about 4000 miles on my tires and have not noted any ill-handling and or irregular tire wear. Wish me luck,

Lee

 

If the car is lowered quite a bit, alignment folks tend to max out the kinematic toe (Perhaps an urban ledgend?).

When my car was not so low, I had the car's rear alignment butchered my a monkey with a wrench. I then took the car to the track...on high speed deceleration (Turn 8 at Willow Springs International Raceway in Cali), the rear end was unsettled, squirrelly...some side to side motion that I did not appreciate.

Soon thereafter, I took my car into ANDIAL for an alignment..the kinematic toe was way off...it was re-set correctly, and the problems went away. I didn't leave the car running with the bad set up long enough to experience poor tire wear.