J Henry

Had a front wheel alignment performad at my OPC as front tyres were scrubbing out on the inside & they didn't know what settings to use. They asked me if I wanted it set up for handling & naturally I said yes. Car is 1990 C4 fitted with turbo lowered suspension, 17 inch Cup wheels with 205/45 front & 255 /40 rears. The car now understeers considerably more than it used to & the steering is very heavy when trying to turn into the corners.
My question is this. With these suspension mods & wheels & tyres should the alignment be set to the factory specs as per my handbook? Or will these alterations mean I should use different settings?
Many Thanks

horst

Actually, you should have a FOUR wheel alignment done. I have a 90C4, lowered, with 17"cups, and is lowered 1-1/2". I have the same rear tires, but 215-45 fronts. A 21 mm rear sway bar helps a LOT. The specifications I use is as follows:
Left front Camber =-1.0, caster =3.9, toe= 0.01 right front camber=-1.0, caster= 3.9, toe =-0.01; cross camber-0.0, cross caster=-0.1; left rear camber=-1.0, toe-0.03; right rear camber=-1.1, toe 0.07 total toe=0.04, thrust angle=-0.05 . With this combination, my car rides & handles fantastically. Try it, you will be happy.You may need to be sure that the shop you use has the proper computer equipment and understands Porsche. The " factory settings" are merely a crude guide, and assume only stock suspension, wheel & tire size.

Christer

your fronts should be 205/50 not 205/45.

Ade - C4 91

Horst - your rear toe looks a little wrong, it's negative on left side and positive on the right (or is that a typo).

To answer the original question, a lot of people try to achieve 91-93 RS settings with lowered 964's, which are approx -1deg camber and about -0'10" toe front/rear, with about 3.6 to 3.9 deg caster (all off the top of my head - so don't use as gospel). Horsts settings are pretty close to that by the looks. The ride height is important, as is corner weight/balancing. It would be interesting to know what setting they gave you - did you get a print out?

Ade.

horst

Not a typo. the expected range is -0.08 to 0.08, either side. Actually all these values are what I believe to be preliminary. It was suggested, and it makes sense to me, that since I had just gotten through lowering the car, and going to 17" wheels, new tires, etc, that things should be given a bit of time to "settle" and then re-check. We will revisit the rear toe at that time. I guess mabey next month... you have a sharp eye!

Kevin Asbridge

Horst,
I have aften wondered about "thrust angle". It is a measurement that appears on some alignment machines and not others-what is it and can it be used to bias the car to the left or right?

My settings are currently:

Left Front +11minutes toe, 3deg 34minutes caster, -11minutes camber
Right Front +13minutes toe, 3deg40minutes caster, -9minutes camber

Left Rear +11minutes toe, -1deg 39minutes camber
Right Rear +10minutes toe, -1deg 52minutes camber

Thrust line 0deg 0minutes

Ade - C4 91

horst - you're right, things certainly take a while to settle with new suspension, I've been through two full alignments (with Roock Coil-overs) in 3 months and the things still keep moving around, mostly with toe.

It's amazing how little it takes to get it all out of wack on a 964, they are quite unforgiving to minor changes. Tyres also have a major impact, significantly more so that on a 993 (so i'm told), as does temperature.

Ade

Bill Gregory

The factory specs are in the 964 faq here

Adrian

Dear J Henry,
You shoul dinstall 225/45s on the front. The 205/45 is the wrong tyre in 17 inch size for the front as well. 225 on the front will reduce the understeer. You also need to look at your rear sway bar. Standard is 18 mm and you should install a 21mm (best) or 22 mm. What size sway bar is on the front?
What does Turbo lowered suspension mean? The Turbos in standard form had the same ride height as the normally aspirated 964s except the Turbo S, Turbo 3.6 (ROW) and Turbo 3.6S. What did you have installed?
Ciao,
Adrian
964C4

horst

Kevin: please excuse me for being a bit thick. I do not understand "minutes" Is that a european designation? Re; "thrust angle" visualize a line drawn down the center of the car, front to back. Thrust angle is the deviation right or left that the rear is tracking. As I recal, a minus figure would mean that the rear is wanting to track to the right, positive to the left. If you have a 0, then you are dead on. In my case it is -.05, meaning that the rear is tracking very slightly to the right. The specified range for this is -0.17 to +0.17

Kevin Asbridge

Horst,
I am sorry we still measure distance in chains and furlongs here in the north of england

Here in the land of warm beer and crap food, angular measurements are usually expressed as degrees and minutes, there are 60 minutes to 1 degree and 360 degrees in a circle (obviously), we also use radians but this is a measure used exclusively by engineers and academics and is not in common parlance.

Thanks for the clarification, I take it you cannot detect any bias to left or right with your current settings? My car has a tendency to follow left cambers slightly more than right, hence the question,

horst

This sounds like something in the front end- could be camber is incorrect on one side or toe improper. As I indicated, I was super pleased with the shop that worked on mine last. The fellow asked me (for the first time that I was ever asked) if I wanted the car set up to correct itself for a crowned road, or for flat roads. I strongly suggest you find a shop that has a computerized 4- wheel alignment rig.

Kevin Asbridge

Horst,
Any idea on how they correct for crowned roads?

My car has been set up on a computerised rig by a very competent guy but here in the UK the concept of correcting for crowned roads is not commonly understood, I would be interested in knowing which parameter is adjusted to achieve this since I could then adjust out my slight bias.

The car has been checked a couple of times now and we have been through all the usual stuff, new tyres all round, pressures etc

Thanks in advance,

horst

To adjust for crowned or flat roads, you need to play with the front wheel caster. On my car, since I wanted to adjust for flat, my caster is set at 3.9 degrees, both wheels. If I wanted to adjust for crowned roads, I would set caster at 3.9 deg, left, and 4.2 degrees right. Since you guys insist on driving on the wrong side of the road, in your case reverse these settings

J Henry

Thanks to all who have responded. I will try to answer your comments. First some info on my vehicle.
Horst, I would normally get a 4 wheel alignment done but tyres are almost due for replacement & am just trying to get a little more life from the fronts.
Christer, my apologies, I do in fact have 205/50 on the front.
Adrian, Some corrected & additional information for you to help in the diagnosis. Suspension mods were done to the car before I bought it. The mechanic told me that when the car was lowered they didn't just put lowered springs on, but used the modified arms? to ensure the geometry was correct at the lowered height. Current wheels are 17inch x 7 inchx55 offset on front & 17 inch x 9 inch x 55 offset on rear (205/50 & 255/40 Continental Conti Sport). The ride height is as follows. Vertical measurement from the ground through the centre line of the wheel to the guard is 635mm front & 625mm rear.
I doubt whether I can fit 225's to the front as when I first got the car the 205's used to foul the lip of the front guard over bumps. Guard edges have been rolled & the adjusting rods behind the plastic wheel arch covers adjusted for clearance. This cured the problem but there isn't much physical clearance there.Am taking the car into the OPC on Tuesday to have new spark plug leads fitted to try & cure my previous PDAS/ABS light problem so will get them to check the diameter of the anti roll bars then
Thanks to all again & will report back soon,
John