Alignment question

[mikepellegrini]

I just did the balljoints and engine mounts in my 951. Because I had the control arms off, and dropped the crossmember, I had the car aligned after I was done.

It tracks well now at low and moderate speeds (and feels really solid - no more clunking on bumps!), but cornering at high speed (70-80 MPH) it seems like it's oversteering. Going around a corner fast, you come to a certain point when it seems like the front end is gonna take off (on a left hand corner, it feels like it wants to swerve left suddenly - it feels really unstable all of a sudden).

The front end is in good condition - no major wear or play in anything. And like I said, I just replaced the balljoints (the Rennbay kit).

I've done some reading and found that excessive toe could cause oversteer.

The alignment shop didn't change anything in back. As to the front camber, he said that what he got was as close as it could get (no more adjustment left). He didn't comment about the front toe.

Here's the specs from the alignment:



The front toe is way out of spec - I'm not sure why the alignment guy left it that way. I guess I'm just wondering if I should take the car back and have them put the toe in spec - and might that cure the oversteer (or whatever it is that's happening)?

[krystar]

yea that is wierd. even by his document, he returned the car out of spec....

[jkb58]

Originally Posted by mikepellegrini

but cornering at high speed (70-80 MPH) it seems like it's oversteering. Going around a corner fast, you come to a certain point when it seems like the front end is gonna take off (on a left hand corner, it feels like it wants to swerve left suddenly - it feels really unstable all of a sudden).

I've done some reading and found that excessive toe could cause oversteer.


The front toe is way out of spec - I'm not sure why the alignment guy left it that way. I guess I'm just wondering if I should take the car back and have them put the toe in spec - and might that cure the oversteer (or whatever it is that's happening)?

Oversteer is the back end stepping out, understeer is the front end plowing - Im not clear which your symptom of "front end taking off" is?

Front toe-out will cause tram-lining, the car will wander when trying to drive straight. But toe-out can actually improve turn-in, and therefore increase/induce oversteer.

Dramatic front toe-in may slightly increase understeer/decrease oversteer, but it should not be significant on the street.

Positive toe is toe-in. 3/32" per side is approx 0.22 deg. which is quite a bit of toe. I dont think I would recommend going much over 0.10 deg per side.


No more camber adjustment? Seems odd - typcially a 944 will easily get anywhere from +2/-2, and the later cars can get up to -3 on the front w/o modification.

[mikepellegrini]

Best I can describe it is when accellerating in a left turn at high speed (about 70 MPH on a freeway exit) you come to a point when the car feels like it suddenly wants to turn left - and you have to correct by easing the gas and turning the wheel to the right.

The tires aren't really close to losing traction when this happens. I can take the same corner in my NA at the same or higher speed and it feels completely stable.

It's kinda like the way a loose tie rod feels - where the car suddenly takes off in
the direction it wants. But it's not a tie rod - there's no play in the front end.

The car has new Michelin Pilot A/S tires on it - 17x40x245 front and 17x40x275 rear. So it's got great traction.

It's got the M474 sport package and I believe the Koni's are original.

I notice that on bumps, my left front tire rubs the fenderwells - but the right tire never does. There are no differences in either fenderwell. Maybe the left Koni is weak - not dampening the bumps properly? Might this also cause the veer to the left?

I don't know why the tech returned the car with the toe out of spec, but like I said, he did tell me the camber was all he could get out of it. He did say he had a hard time getting the steering wheel to center - maybe that's why he left the toe at 3/32. If that's the case, I would prefer to have the car in-spec with a off-center steering wheel - I can correct the steering wheel in less than 5 min myself.

The control arm bushings all look great and there's no evidence of ever having any front end damage.

I'm wondering if maybe I oughta get another tech to re-do it. Maybe I need to replace the struts?

[krystar]

...come again? you do 70pmh on exit ramp that turns left?

i think you're describing basic power-on oversteer... you're neutral at engine braking and holding throttle, but when power is applied, it oversteers. right?

[matthewb]

It could be the rear suspension steering the way they are designed to do...

[callmethewander]

while we're on the subject, is there a way to check or adjust the alignment yourself?

[Arizona_928]

It means your suposed to go faster

[jkb58]

What all has been changed since the car started feeling this way? Balljoints and engine mounts and the alignment, thats all, correct? Or were the new tires put on at the same time?

Dont replace anything else, until you get this sorted out. Unlikely that something else just happened to fail in the meantime - possible, but check all the changes first.

When you dropped the crossmember to replace the motor mounts, did you also remove the steering rack, or just disconnected the rack from the crossmember and let the rack dangle by the tie-rods and steering shaft? I suppose its worth double checking to make sure the rack is correctly centered and hasnt moved in the mounts/bushings after being reinstalled.

There is is a lot of adjustment in the tie-rods, so take a look at how even the threads are spaced side to side - that will tell you if one side is bottomed out or not. You cant run out of toe adjustment, and you shouldnt need to move the steering wheel by a spline.

I would take it back to the shop that did the work, describe what issues you are having and have them check the alignment and reduce the front toe-in. See if that helps. But because of some of the comments they apparently made about having problems getting toe-in and camber, I am a little suspect of their competence and/or effort on this. Are they a p-car shop? Not that you want to pay for an alignment twice, but is there another local p-car shop that you can take it to and have it checked out?

[mikepellegrini]

Originally Posted by krystar

...come again? you do 70pmh on exit ramp that turns left?

i think you're describing basic power-on oversteer... you're neutral at engine braking and holding throttle, but when power is applied, it oversteers. right?

It's a ramp from one freeway to another. It's a slight uphill grade and a relatively easy corner.

In my NA I can accellerate (moderately - not crazy fast) through the corner ending up at about 75-80 when I exit onto the other freeway. In the 951, most of the way through the corner, the front end suddenly wants to go left. It's not losing traction - it just wants to go left.

[mikepellegrini]

[QUOTE=jkb58;4533651] What all has been changed since the car started feeling this way? Balljoints and engine mounts and the alignment, thats all, correct? Or were the new tires put on at the same time?

Dont replace anything else, until you get this sorted out. Unlikely that something else just happened to fail in the meantime - possible, but check all the changes first.
[QUOTE]

It did this before I did anything to the front end. I was hoping the alignment would solve the problem.

When I did the engine mounts, I left the rack connected to the crossmember, so nothing changed there.

I put the new tires on a couple months ago and can't honestly say if the car had the problem before that. The first time I noticed it, I had just put the new tires on and was pushing it pretty good.

The shop where I took the car is supposed to be one of the better P-car shops in the area - recommended by a guy who is a local PCA technical instructor who is also a master P tech (owns his own import repair shop - and also races Porsches - he just doesn't do alignments in his shop).

I took the car in on a Saturday - I'm thinking the knowledgable guy may only work M-F or something.

[stewhatch]

This might sound stupid, but sometimes the simplest reasons are overlooked: have you checked your tire pressures? I experienced something similar and when I adjusted all FOUR tire pressures per the factory manual, my problem disappeared and the car handled perfectly. I spent a few $$ on an alignment I never really needed to cure my issue. It's a cheap and easy fix if that is the problem. The tires looked fine, but were all over the place pressure-wise. Just a thought - it might very well not be the problem but you never know.

[mikepellegrini]

Originally Posted by stewhatch

This might sound stupid, but sometimes the simplest reasons are overlooked: have you checked your tire pressures?

I'll give that a try. I've never checked the pressure - the tires are brand new. But ya never know...

[jkb58]

Originally Posted by mikepellegrini

It did this before I did anything to the front end. I was hoping the alignment would solve the problem.

I put the new tires on a couple months ago and can't honestly say if the car had the problem before that. The first time I noticed it, I had just put the new tires on and was pushing it pretty good.

Are the new tires a different brand/model and or size than the previous tires?

Different tires have different sidewall construction and rubber compounds and can react/handle quite different on the same car.

I had a set of Pirelli P-Zeros that were extremely sensitive to toe (they wanted a lot of toe-in) and tram-lined severly at anything above 70 mph, where previous toyos and subsequent bridgestones do not have any problems with the existing alignment.

Your new tires may be overly sensitive to too much toe-in and may benefit from more neutral toe settings. As mentioned above, your old alignment toe spec had huge toe-in and even the new alignment still retains quite a significant toe-in stance.

[mikepellegrini]

The new tires are Michelin Sport Pilot A/S - 245x40x17 front and 275x40x17 in back. The old tires were the same size but were good Dunlops in front and cheap Falken's in back.

The Dunlops had a lot of tread, but the rear tires were almost done. I woulda just bought two new Dunlops for the back but they didn't have that size/model tire anymore. So instead, I went with the four new Michelins.

I'll talk to the alignment place and see what they say. I'd like to see them put the toe in spec at least, and see what happens. Like I said, I have no idea why they didn't put it in spec in the first place.

[962porsche]

the tow setting is the most important in determining how a car will handle . a very small change will have a large effect on the way a car handles most of the car are set with tow in or zero tow . the basic reason is the forces that act on the front tires tend to cause towing out . cars for the most part come with rubber bushing and as you know they will flex . road drag and braking force the tires back and out . making for tow out ! this even gets greater as speeds increase and when you start using the brakes harder with also even more road drag . when you have tow out there is a small amount of slip angle on the front tires .becouse of these slip angles the car will try to steer its self becouse each tire wants to go in deferent directions . anything that makes the slip angle change (bumps, turning and so on ) will unbalance the car . as soon as one slip angle is reduced the slip angle of the other tire takes over and the car want to steer its self . so in other words have the car at zero tow or tow in . with the 944 and becouse of its suspension coming from a vw they like to get alittle shack in the steering wheel at speed in my shop we do just a little tow in about 1/16 total . over the past 16 years i have owned my shop we have never had a come back with that set up . i got that setup from when i worked for porsche N.A.and the 944s first came out that was the service bulletin from porsche QU germany .

[mikepellegrini]

I talked to the tech who aligned the car this morning and explained the problems I had.

He told me that on cars low to the ground with really wide tires (they're 245x17x40) they usually give it a little extra toe to improve handling and make it so the car didn't follow bumps and what not. And that's why he set the toe at 3/32 each side, not between 1/32 to 1/16 (which is the spec).

He told me if I wanted, he'd put the car in-spec at 1/16 each side. I'll pick it up after work

He said there was nothing he could do for the camber - the eccentric bolts were maxed out where he had it now.

[mikepellegrini]

I got them to re-do the toe - the guy set it at 1/16 for both sides and it made all the difference in the world. It feels completely stable now in corners at high speed. Way different. Spec is between 1/32 and 1/16.

He was able to get a little more camber on the right side - -0.45, but the left is farther out - at -0.92 (before it was -0.90). Spec is between -0.59 and -0.09. So the right is in spec but the left is not.

He set the toe on the rear wheels to 1/16 as well.