[apex]

So the new tires are on - my olds wore out very quickly on the inside. I didn't ask for a print out after my last alignment and I think I paid the price - the rear camber was WAY off - over 3 degrees negative.

The new shop seems quite knowledgeable and highly organized - they have all the right porsche tools (another one I checked didn't) and seem to know their way around the car.

So Flash's advice from his ALIGNMENT post coupled with my racing guru's incredulous reaction to the factory-spec zero-degree front camber inspired me to 'go custom' with a little bit of increased front negative camber and see how that feels. Right now the fronts are right on -.80 degrees.

However, the shop could not get the rear camber dialed in - without causing the rear ride height to change. So the got it as close as they could and left the rears at about -2.2. They were reluctant to start raising and lowering the car to get the camber right.

Can someone walk me through how rear ride height is coupled to the camber setting? Ha. This is my golden opportunity to get to know the back of my car a little better.

PS - I've always thought that my car had been lowered in the back - I love the way it looks - but have never checked by measuring. Might be time to do that.

Partial Post: Please Login or Register to read the full post.

[flash]

unfortunately the rear geometry is complicated, because the arms are triangular in mounting and yes, the ride height affects the camber - you can see this by merely having somebody push down on the rear of the car - as they do that, watch the rear tires - they will squat inward at the top - the lower the car, the more negative camber - there is a point where you will max out and not be able to reduce the camber any farther

ride height should be the first thing set though, and any decent alignment shop knows this - it's also the hardest thing to set, which is why a lot of them shy away from it - it requires a couple of special tools too

when you set it, do so with the driver weight in the driver seat, and the car loaded as it is driven, and about 1/2 tank of gas - also make sure that you have the correct pressures in the tires

THEN you move on to camber specs and toe specs in the rear

THEN you move on to the front of the car, setting castor first, then camber, then toe

something to realize about the ride height is that the lower the rear is, the more load is placed on it - it is about 200lbs per inch - if you are in a hardtop, which is already 66lbs rear biased, then you are potentially dramatically upsetting the balance of the car by having the rear low - the best way to set ride height is with corner scales, but a tape measure can get you pretty close - a level on the door sill will also tell you where it is

Partial Post: Please Login or Register to read the full post.

[apex]

Thanks for your reply - that's helpful.

The shop did insist on doing rear first, then front - ha - at least they have that right.

Sounds like I should revisit them and have them check the ride height as you say.

How will the rear tires wear with negative camber of just over 2 degrees? How would you say handling is affected?

Partial Post: Please Login or Register to read the full post.

[flash]

good deal - that's good to know

2 degrees isn't the end of the world - it's a lot, but not all that uncommon - how it affects things really depends on a lot of things

at 2 degrees, they will wear more quickly than if they had 1 degree - how fast depends on things like speed, tire compound, inflation, weather, etc

handling will respond well, but depending on the rest of the setup, could actually get dicey at the edge of the envelope,as the car rolls, and you lose inside tire contact patch area - i have about that much rear camber now (hoping to reduce it to about 1.2 when i finish the camber kit) - the only thing keeping the back planted on mine is the setup of the car and the fact that i have a very sticky 285/35-18 back there

i'd get back in there and set it up as soon as is feasible - it sounds like the shop you are using wanted to do that anyway, but didn't know the car that well - if you run into problems, feel free to contact me

Partial Post: Please Login or Register to read the full post.

[apex]

thanks - one question I forgot earlier - are there any "camber kits" out there to extend the range and allow lower-slung, properly cambered back ends?

Partial Post: Please Login or Register to read the full post.

[flash]

lol - no - that's exactly why i'm working on it - if there was one already out there, i'd just buy it - i certainly don't need another new project - i already have the design in mind though, and should get to it in the next couple of weeks

Partial Post: Please Login or Register to read the full post.

[apex]

Update - it seems torsion bars have sagged a bit on my car over the last 18 years - hard to tell exactly but perhaps as much as 1" relative to the front. Currently the eccentric bolts are set about the middle so presumably there is enough adjustment left in ride height to turn camber in approximately a little less than one degree. (Target is 1.5, currently sitting at 2.2).

The shop has been very accommodating and has agreed to charge me only 1hr labor to re-set the ride height and re-do the alignment - which they'll do tomorrow morning.

Questions:

yeah - I know - I should just get a four-corner coil-over kit and be done with this... [img]style_emoticons/<#EMO_DIR#>/dry.gif[/img]

1. Can anyone give me a feel for how much camber will move for a given change in rear ride height? I've got half the trailing arm adjustment left - enough? I don't want to raise the car too much - any issues with setting the ride height this way - or better to re-index the bars?

and a general question

2. I don't think the back is all that low. I should post a pic but the tops of the tires are just about even with the fender rim. I've seen 968's lower than mine. If camber is limited by ride height, how does one keep (camber) alignment correct with a lowered car?

Thanks!

Partial Post: Please Login or Register to read the full post.

[flash]

1. there is about 3/4" of ride height adjustment via the eccentrics on the trailing arms - if you are half way now, you can expect it to go up about 3/8" - i would avoid reindexing, but if you decide to go that route, i would replace the torsion bars with fresh ones of whatever rate you wanted

i would expect to see about 1/4 to 1/2 degree of camber change at the rear, and about 1/10 to 1/4 degree at the front, for that much rear ride height change

2. no matter how much you might like the "look", the rear should not be lower than the front - that will upset the balance of the car and affect both braking and handling

as for keeping camber correct on a lowered car, you can't - but, with cars that don't have chassis stiffening and really large swaybars, a bit more camber is a common practice, and a trade-off many are wiling to make -

however, that is exactly why i am working on a camber kit for this car - i no longer need that much camber, and am not willing to make the compromises

Partial Post: Please Login or Register to read the full post.

[danderson]

I have noticed that my right rear tire has worn far more on the inside than the left. This is over about 10,000 miles, so I know that the camber is not far off but I would like to adjust it. The wear is very smooth with no feathering so I do not believe I have a toe issue. In looking at the workshop manual, it indicates that the bolts on the trailing arm behind the anti-roll bar mounts are the one(s) for adjusting the camber. They are supposed to be eccentric bolts. I cannot see that as of yet, but looking at their orientation, I do not see how they could affect the camber unless it is the result of the complexity of the geometry. Would some one offer their thoughts on this? Thank you very much.

Dwight Anderson

94 red and pink coupe

Partial Post: Please Login or Register to read the full post.

[gcb729]

How much would lowering the front ride height help out in the rear camber issue? It seems the height correction would not push you to the mobility limit of the front ball joints and to my eye setting the height a bit lower produces a desirable stance.

Partial Post: Please Login or Register to read the full post.

[danderson]

I actually have no idea. I did not realize front ride height is adjustable. I would consider a bit of lowering were it possible(other than changing springs). I may not know enough in all of this.

Dwight Anderson

Partial Post: Please Login or Register to read the full post.

[gcb729]

It takes new lowering springs or an adjustable spring perch.

Partial Post: Please Login or Register to read the full post.