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There's a vintage DIY alignment thread on RL that shows the laser fixtures I made. The lasers are long out of production, but the revival here poked me to look for some currently-available options. The first pass generated a lot of plastic-lens laser pointers, with some pretty significant beam bloom. I stopped there.
The fixtures clamp to the rim face at four points, lasers point perpendicular to that face. Point the beam at the ground 43" behind wheel center on both sides, and the same distance in front. Measure the distance between the two marks in front, adjust to be 3/8 to 1/2 inch closer the the distance between the two rear marks. Set up camber and caster first, set toe, back through camber and caster again just to verify no shift, and then verify toe numbers. Car needs to be settled, and be at the ride height you desire before you start. The rack needs to be centered (use the correct tapered bolt...), and the wheels need to be centered in the car. If you plan to align the rear, do it first so you can use the lasers to center the front wheels. Using the 43"x2 distance means that the 3/8 to 1/2" delta equals the 15 to 20 minutes (one quarter to one third of a degree) total toe that the WSM recommends. Whatever laser you choose, mark the results on the floor consistently. try for the center of the beam obviously, but if there's consumer-laser beam-bloom you may decide to try and find an inner or outer beam edge instead. Whatever you choose, use the same on all four measurement points. There's a lot of rolling and repositioning the car after each adjustment. Be ready to spend some time getting everything right at the same time.
I'm in the process of redoing my suspension (TT was out and the original gray Boge were still in the 86.5....Sean R shamed me into buying new shocks on FB...he was right...they looked good, but I guess you have to replace them every 34 years or so?!??!)
I've got an alignment shop that does chassis setups and corner balancing for autocross (corvettes mainly) with a Hunter Machine. The owner is familiar with and has owned some 928's and worked on them, but wants all the intel I can share. The specialist is willing to let me help and they will spend as much time as needed on the car he said. When I bought the car it had the telltale signs of being aligned wrong with the worn inner fronts. I have some time and may even take it to the local shop that aligned it before for a "close enough not to ruin my tires" dial-in ahead of time, this shop has a newer "hanging machine" and got it really close. The owner is a racer and "juttered the car" to death and compesated for sag, he tried real hard but knows I want it done on the right equipment.
86.5, stock springs (2 Blue tics on them), new Koni D 1086 and 1085 internal adjustable (not the external *****), new tie rods, and front-wheel bearings were done last year, all other bushings pass the pry bar/wiggle test IMO. Car has 40K on it (was driven 100-500 miles a year by the previous owner).
So far I've dialed in the shocks to 1 turn in the front (from 1.6 total revolutions from the FULL FIRM) and 1.5 on the rears from 2.5 revolutions from the full firm) per a 928 vendors website as a starting point. It's riding on the stock 16 Square wheels with 225 Continental DWS tires.
QUESTIONS:
I've cleaned and installed the stock adjustment collars (fronts were bonded in). What is a good starting point for ride height from top thread? The rears were about 30 MM from top thread and the fronts almost level with the top when I removed them. I know this has to be set for the aligment, just looking to save some time pulling and adjusting.
I've got this bar from my MOTOR MOUNT/OIL PAN repairs and it looks like it will work as the PULLDOWN TOOL for the front they show in the manual and as discussed in other threads. https://smile.amazon.com/dp/B01BRB0R..._MdxUEbBTX0VVE thoughts?
Are the 1 full turn front and 1.5 turns rear a good starting point? That puts them middle/upper middle...and I assume it won't affect the alignment if adjusted later. I have the KONI's and stock springs and don't race the car, but went with what was recommended. I've read lots on spring and shock combo threads and stayed away from some set-ups because of what was recommended NOT TO GET also. My driving is mainly street and I want firm but reasonable compliance, I have the long wrench to adjust them without removal on the way if the base settings are off, but a starting point would be good info to have.
All the adjusters and essentrics were moved last year and seem in good shape.
I'm planning on sending the WSM pages in advance and some of the thread notes too. Any other suggestions for "getting it close" or "double-check this?"
If I need to start a fresh thead let me know...but I felt this fell into the conversation.
I am from the school of thought that says there is only one way to set the ride height and that is to measure the settled height from the measuring points. Beyond that if you want the corner balancing spot on you have to load the car to the starting point of your choice- there are recommendations in the WSM. The accuracy of the springs will determine whether corner balance adjustments need to be made . The rear springs can be adjusted with the wheels on the deck, the front ones seemed nigh on impossible when I tried with the on the deck- up in the air no problem but then you have the ride it, settle it remeasure it syndrone..
Regarding ride height different folks will suggest different numbers. I reckon 170mm front and 163 rear is optimal for stock suspension setup. I ran a bit lower but then I have the stiffer Eibach springs.
335 wide rear tires call for small rear end camber, the wheels as straight up as possible. Åke
Actually, the car would benefit quite a bit, in handling, with more negative camber....but the tires would wear on the inside edge. Not because of the increased negative camber, but because of the increased leverage on the front rear bushing with super wide tires.....changing toe.
People overlook the fact that all of the front of the rear control arm bushings (which control toe under all conditions but especially when cornering) have the same part number and thus the same hardness of rubber. Yes, all the bushings are the same, from the very first 928 with little narrow tires through the last 928 with radically higher rubber contact, in the rear.
And then, stuff on an absurdly wide 335 and the "leverage" on that poor "soft" bushing goes way, way up....increasing the rear toe changes....everywhere.
The result is increased inboard tire wear which has to be compensated either by stiffer rubber in the front bushing, or by reducing the rear camber. No stiffer rubber available? Cure the actual problem by taking away camber.
sorry for my "stupid" question.... as i changed to a '90 GT suspension on my '82 i measured now toe in at 45' total. ( with laser set ) after getting it "visual" right....
The spec's on the left are for the S4 types... but is 15'+5' toe in for 1 wheel or for both in total ?
Actually, the car would benefit quite a bit, in handling, with more negative camber....but the tires would wear on the inside edge. Not because of the increased negative camber, but because of the increased leverage on the front rear bushing with super wide tires.....changing toe.
People overlook the fact that all of the front of the rear control arm bushings (which control toe under all conditions but especially when cornering) have the same part number and thus the same hardness of rubber. Yes, all the bushings are the same, from the very first 928 with little narrow tires through the last 928 with radically higher rubber contact, in the rear.
And then, stuff on an absurdly wide 335 and the "leverage" on that poor "soft" bushing goes way, way up....increasing the rear toe changes....everywhere.
The result is increased inboard tire wear which has to be compensated either by stiffer rubber in the front bushing, or by reducing the rear camber. No stiffer rubber available? Cure the actual problem by taking away camber.
With the alignment I have the 335 rear tires wear fairly evenly across the width. The problem with the Pirelli tires is soft rubber that wears down very quickly. If I'm lucky I can drive about 10,000 km or 6000-7000 miles with a set of rear tires. I do not race so I do not need maximum grip. Now I have bought Michelin rear tires to see if they last longer. Only Pirelli and Michelin make this size of tires.
Åke
I treat the toe-in spec as total toe, because there no place that says otherwise.
Greg mentions that the rear toe and camber numbers really need to consider wheel width and total net offset. Those affect the net spring rates and damping too. But staying focused on the front settings, one needs to consider the same things. Usually much easier to think about when discussing the fronts because the wheel offset is stamped on the wheel itself. Unless you have spacers added, which I think we are smart enough to avoid. The toe settings are needed to compensate for wear and bushing deflection when driving, making the static setting a best-guesstimation. The factory numbers are a great starting point, but assume new-spec parts. Do the age-hardened bushings compensate for wear in the tie rods and ends? Maybe some. Should we increase the toe settings slightly for wheels with less offset? Probably, but maybe just to the limits of the factory toe range, so -20' (one third of one degree) total toe would be a good setting.
The suspension is a bit more tolerant of a larger static total-toe-in number than it is a neutral or slightly toe'd-out setting when it comes to tire wear. OTOH, a neutral static toe gives a slight toe'd-out dynamic, something that offers a more solid initial turn-in feel especially with sticky (read:race) tires. The outer front tire sidewall is already "loaded" for a turn so it feels a little less floaty as you add steering lock. Not great for tire life but adds a little more precision feel to the transition from straight to turn.
The rear "rocker bar" or "kinematic bushing" at the front of the rear control arms has been, interestingly enough, the same through all of the different years/models. Porsche never changed the hardness of the rubber to compensate for the increased leverage the bigger, wider, more offset rear tires exerted. The result is that the GTS model cars had more "toe change" than the very first cars had.
Wider tires/stickier rubber exasperate this problem, to a huge extent. The result is very poor rear tire wear, with wide/sticky rear tires, since the tires are constantly going from toe-in to toe-out....literally "scrubbing" the rubber off every time the vehicle accelerates or slows down.
And as those bushing wear, things get really nasty, with even more movement allowed. The bushing will deflect more. Generally, it is simple to see the aluminum part of the bushing pushed back into the control arm so far that the rubber part will be very concave, instead of perpendicular to the control arm, at rest.
Porsche has had no stock of these bushings, for years.
I finally got Mark Anderson to have his suspension rebuilding company make some of these bushings...and I believe he has two prototypes that will be installed and tested, shortly.
Hopefully, I will be able to encourage that company to make some bushings with stiffer rubber, for use on cars with increased tire width/stickier rubber....something that is desperately needed.
Low mileage GTS rocker bar bushing. Note that the rubber is still perpendicular to the control arm and has no deflection. Note that the edge of the rubber is still in contact with the control arm, not lifted off.
A bit tough to see the deflection, from this picture. Rocker bar bushing "pushed" into control arm 2mm-3mm. Note how the edge of the rubber that contacts the control arm is "lifted" off of the control arm, from the deflection. Completely worn out.
My apologies to Barry- i miss read his question in post 37.
I put great emphasis on getting the settings equal both sides and I know exactly what I want each side. The total front toe specified is 15 +/- 5 so in other words a range of between 10 minutes and 20 minutes of total toe. On a stock car I would probably go for 10 minutes each side. In my case, with wider front wheels I go for the minimum setting of 5 minutes each side - this helps turn in and also makes the steering a little lighter thus helps offset the extra effort needed as a result of the wider tyres I use. I have tried setting front toe at zero both sides but I found it too twitchy even for my likes but I suspect it is probably optimal for track work with wider wheels. On the Hunter there is no excuse for getting the front toe set to anything other than the spot on value required.
If you go for total toe and do not have both sides evenly balanced the steering wheel will take a natural offset when driving in a straight line- does no harm but such drives me up the wall!
no need for apologies Fred, so with the 245 tires in front i should aim for around 10...15 total toe in.
Changing to a '90GT suspension on my '82 i kept the steering rack on the '82 ( not using the '90GT one ) , so i had to shorten the rods each side by 10 mm according the WSM which is almost at max for the threads on it....will have to see if i can screw the rods still a little bit further in to get less toe in. ( now total 45' )
no need for apologies Fred, so with the 245 tires in front i should aim for around 10...15 total toe in.
Changing to a '90GT suspension on my '82 i kept the steering rack on the '82 ( not using the '90GT one ) , so i had to shorten the rods each side by 10 mm according the WSM which is almost at max for the threads on it....will have to see if i can screw the rods still a little bit further in to get less toe in. ( now total 45' )
Barry,
I would think with a total toe of 15 minutes [7.5 each side] you will be a happy camper. There is a point where less toe-in gets to feel "twitchy" when driving in a straight line and in my experience that happens when toe-in is a tad less than the 10 minutes total toe [5 each side] I typically run with. Historically I ran with 265's up front but at the moment I now run 255's and both produce a heavy feel to the steering input but lots of feedback as to how they are gripping [or are not at the limit].
Regarding your situation it is well known that more toe-in is a better proposition than too little toe or worse, a toe-out condition but I have no idea at what point too much toe-in scrubs the front rubber but with 45 minutes total toe I would feel "concerned". You should have no issue with straight line stability but I suspect you will find some reluctance to turn in. At the end of the day stability and maneuverability are at odds with each other- to change direction you need instability- something of a paradox and the trick is to find the optimal compromise. I would opine that if you cannot get the total toe down to 20 minutes then you need to do something about it.
Modern "sticky rubber" is more grippy compared to rubber of the day when these cars were designed and as more lateral grip is applied more camber is needed. I aim for 1.5 degrees on the fronts [less on the rears] and with 245's I suspect minus 1.25 degrees might be optimal for you up front. I also use the 928 Motorsports lower frame brace and I have a custom upper frame brace to help keep things straight- the stock upper brace is woefully weak. I also run with the greater caster specified for later models so that also induces a bit more load on the steering wheel.
Given your background and experience I suspect you will iterate to a solution that suits your driving style.
just tried and there is more then enough thread on the rods to get it right . I had still 2 mm thread each side to play with.
Now surprized how sensitive it is ! i shorten both rods exactly 1 mm ( feeler gauge between rod end and counter nut ) and became 20' toe out instead of 45' toe in !
So the final will be to return the rods 1/2 mm , that should be around the desired 10...20' toe in.
all "if" my ( cheap) laser set works correctly... but i check it twice and got comparable readings. ( between settings i drive the car a bit to settle the wheels... )
i also use the 928MS lower frame brace ....do you mount it tension free or with some tension , pull or push ?
Regarding camber i would assume we may give it a bit push ?
Last edited by belgiumbarry; 09-09-2020 at 09:14 AM.
05-08-2020, 05:20 PM
