The pages in the service manual that cover alignment and ride height are pretty much the same for all model years. Whether the ride height should be different for Euro vs. US models is another matter, as the Service manual I have only covers the US models.

MY SWAG is that the ride height specs are probably all about the same. YMMV.

 

Ed,
The height at front was L/R = 171/174 mm
As Wally correctly said, that’s a complicated issue, not only depending of the steering tie rods are horizontal.
But the best prove is to ask you to check yourself on your car – Maybe my car is special, but I doubt! – The 928 is special, and that’s one the reason we have this (stupid) car – Much easier to buy a Toyota!

Wally,
Yes, I had the looking bolt in
Believe me, at least at my car, 2/3 of the failure comes from the right wheel

As I said before, I have not finished the evaluation, but a part of the problem is that the steering rack is placed too low – I have now reduced the ‘failure’ (the change of toe) to approximately 40% of what it was before, by lifting the steering rack app. 5 mm (Eliminated the rubber bushes) – As I said before, I have not finished the evaluation job, but I will do

Tim
Toe: When a set of wheels is set so that the leading edge are pointing slightly towards each other they have toe-in = + (positive) toe - and visa versa with toe-out
Camber: Is the angle of the wheel relative to the vertical, as viewed from the front or rear - Like Ford = + (positive)- Like formula 1 = - (negative)
Caster: Caster is the angle to which the top of the steering pivot axis is tilted as viewed from the side – Rearwards = + (positive) Forwards = - (negative)

 

Erik:
Mine has been right for over two years, which is why my tires are wearing so well. The height is set at about 160mm up front and about 170mm in the rear. YMMV.

It sounds like something is not right with your setup. Either the rack and/or its bushings, or one of the tie rod pivots is loose.

Lastly, the minimum toe out only occurs as I mentioned in a previous post. That's when the tie rods are extneded outward (pushing the rear of the hubs) the farthest from the rack. YMMV.

 

Ed,
Don’t get me wrong, I have no tire wear, and absolute no problem with my alignment, that’s is adjusted 100% according to the Porsche spec. and the car is running wonderful - Only I have together with a professional garage owner been wondering about the question: ‘Do not lift the car before adjusting’ – Most cars can be lifted without problems – Therefore we decided to evaluate the problem.
Again Ed, believe what I said, or make your own test, just to convincing yourself!

 

O.K...it's Tuesday...what's the report?

Tim Delarm
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

 

Little eager arn't you?

Well, here's some information for the board to chew on. I can't figure it out.

Before I went to take it to the shop, I figured, hay, why not check it one last time. If the tire is wearing, and/or the camber is off, I have a few more feathers in my cap. Right?

Here's the results of that inspection. The frount tires are wearing evenly, and regulary accrost the tread. The inner shoulder does NOT look worn. Heck, except for looking dirty, the tires look new!!!! The tires do not run hot. Even though I drive like a bat out of hell. I just checked my recoards, and I have almost 3,000 on them.

Also, checked it with a level on a unusaly flat slab of concret. The concrete easily puts the bubble in the lines. Because of the wind, I could not use a plumb line. Cup IIs are heck to deal with though. You have to make a spacer before you can put a level up to them. And even then fight with the fenders. Best I can tell the tops are pointing inward a good bit less than a degree. If my measurements are even close, between 0 and .9 It depends on exactly which set of measurments I go by. I know it's a wide range, but I'm not working with profeshional grade equipment.

The tires have no toe in, or toe out as far as I can tell.

I know for a fact the car was lifted, and then set back down. I know for a fact the tech did NOT use the pull down cables. I know for a fact the tires are NOT wearing and if the alignment is off, it's not far. I don't get it.

Eighter my car is special, I'm crazy, or I'm the luckest son of a gun you ever saw. The latter is quite posible actualy....

 

Sounds like we need to revisit ride height measuring. I submit that any method which references the ground is WRONG!

Why?

Because tire diameters can vary drastically. Big tires will yield high ride heights when suspension is set properly and small tires, the opposite.

What needs to be measured is strut length or something intrinsic to the suspension only, eliminating the tire variable.

Am I wrong??

 

Probably true, but what are you going to measure?

If your running larger rims, you should have lower profile tires. The over all dia should be nearly the same. At most a mm or two off. You'd get more diffrence from tire wear than from diffrent wheel/tire combos. I figure I'm going to wear at least 3mm of each side of the tire, before I get rid of mine. Thats a 6mm diffrnece between new and old tires. A bigger deal than the diffrence in properly set up wheel/tire combos.

As such, since the over all dia should be the same, the ride height should be the same, assumeing that the tires are not excessivly worn.

Result, referenceing the ground is OK.

Course with my 83, that doesn't matter much. Only way I can rest the ride height is to pull the shocks apart and add spacers. Unless the ride heigh is way off, thats not happening.

 

The allowable ride height range can accomodate various tire/wheel combinations. However, the measurements in the Service Manual are based on using OEM wheels and tires (with full tread and pressurized to the amount recommended in the owner's manual).

If one replaced their OEM wheels/tires (which let's say were 225/50-16) to 225/45-17, the overall diameter of this new setup would be about 0.1 inches taller than the original OEM setup. Thus, the ride height would be nearly identical to the OEM ride height. Going to 18" wheels would have a larger effect, but a tech could still find the height (within the range of allowable heights) that would cause the tie-rods to be in perfect line with the steering rack. YMMV.

 

Ed and other interested,
Wally’s answer lead me to a search for ‘Bump steer’ and I found a good explanation – Please see: <a href="http://www.racerpartswholesale.com/longtech3.htm" target="_blank">http://www.racerpartswholesale.com/longtech3.htm</a> -Especially the last item F. 'Diagram' gives us the answer we are looking for.
This diagram will help me to finalize my evaluation and correction of the bump steer on my car – As I said before, I already reduced it to 40% of what it was before, by lifting the whole steering rack approximately 5 mm (Eliminating the height of the rubber/steel bushes – I.e. the steering rack is forced to front cross beam), and that lead me to the postulate: ‘Maybe the Porsche engineers forgot the height of this bushes when they did there excellent design’ – Maybe that’s only my car – Only by testing individually we can find the whole answer.

 

erik,
is your rack 'fixed' to the crossmember so it cannot move? i thought they needed to 'float' a little, hence the rubber bushes? without this movement it may fail prematurely??

ive just had my car re-aligned with some improvement in feel, however the caster is still out; left 4deg 06, right 4deg 49. is this critical?

also with respect to toe, do negative numbers mean toe in?

 

Negative #s usually means toe-in. BTW, it's acceptable for the rear tires to have a bit of toe-in.

Erik:
I don't buy into your argument at all. The two 928s I have owned since 1990 have not had alignment or bump-steer problems. The ride heights for each was set a bit low, but still within the range permitted. Except for the one time I didn't know better (and allowed a non-928 tech to align the car) the tires have lasted nearly 20k miles. My steering rack bushings are in place and doing what they are supposed to do. If you have removed yours, then I would expect a shortened life for that rack. YMMV.

 

It is possible that Porsche actually intended for the toe to change. The toe change during roll might increase understeer, or something similar.

 

Dear all 928 owners,
I wrote a comprehensive article regarding ‘Do it yourself wheel alignment - Porsche 928’.

Here I tell how to make a quality alignment with inexpensive tools – All a result of my, one year long, research in this field.

The article is scheduled to be published in the spring issue of the new magazine ‘928 FORUM’

I.e. if you did not order your subscription for this great magazine, you hereby have an idea for a good Christmas gift.

I wish you all a Merry Christmas

<img src="graemlins/yltype.gif" border="0" alt="[typing]" /> <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

Nick,
Yes for time being – as a test – the rack is pressed to the cross-member, i.e. the rubber bushes are still there but eliminated
On most cars you do not have these rubber bushes, and they must be placed there for comfort reason only – But of course without these, the steering response is more efficient, especially when making slalom-like responses.
Your caster should be between + 3.5 a + 4.0 degree, but your figures are not critical,on the other hand why not adjust them to the factory specification? (If you cannot do it with the excentric, you can place shims under the upper A arm).
More caster tends to straiten the wheel when the vehicle is travelling forwards, and thus is used to enhance the trait-line stability.
Positive toe is Toe-in and negative toe is Toe-out

Ed,
You did not read the article regarding bump steer
But OK buy my ide or not, the fact is, we are all fighting with the toe question due to this bump steer tendency, therefore I try to reduce this.
What will shorten the lifetime for the steering rack is certainly if the car is extremely low – i.e. the tie rods not in line with the rack - I am not worried about the ‘missing’ rubber bushes.
Some people are looking for more power, I feel I have power enough, but want optimal driving properties especially during high speed driving in Germany (In Denmark I am not allowed)

Wally,
Yes maybe Porsche made this by purpose, it could be interesting to find out – Who can answer this question?