Alignment results/specs.

[911st]

Just got back from having my alignment done after replacing my bushings.

Car is limited use 86 Carrera w 7&8/16's, no spoilers, and LSD that I mostly want to DE and do Sunday drives.

Front:
-1.25 camber, +6.75 Caster, 0 toe

Rear:
-2.5 camber, + 3/32 toe

Front fender height is rightt at 26". I have rack spacers but still felt my tie rod ends were not close to level. May bring down a little w corner balance. I may dial in a bit of toe in latter depending on how stable it is. Wanted 2 deg neg but only could get 1.25 deg even after extensive cleaning and detailing of the factory holes. Less neg camber should benefit stopping.

Rear fender height is rightt at 25". I may raise the rear to 25.25" with the corner balance. Would put me right at 1.5" difference from wheel center and spring center to the ground which is what Bruce Anderson says is the best for the rear.

I do not think I will be able to get 1deg forward rake. My end up about .5deg as I want the front to work correctly.

Any thoughts or considerations?

[911st]

Just got a chance to drive it a bit.

Front seems a little light on the freeway in that it is willing to change direction easer than before the alignment. I still have most of the Caster from before but we took it to zero toe. I kind of liked to high speed confidence of a heaver feel so may try dialing back in a little toe.

Boy this thing can stop and go around a corner fast. It has been about 5 years since my sport purpose 72 911S and I do not remember it holding this well and it ws on R1's (Dunlop Star Specs on the Carrera)

[JP911]

I found that dropping the front ride height a little (trying to induce the recommended rake) helped to plant the front end a little better. I actually experimented with it during a track day. That "light" feeling in the front is NO FUN on the track. If you have a helper, you should try and have the ride heights checked with you sitting in the driver's seat. This may help to get the car a little more balanced on the road. FWIW, I actually have my front end toed out by 1/8 (total) and the rear is 1/16 toed in (total).

[911st]

Jon,

Do you think 3/32 rear toe is to much? I wonder what factory rear toe spec is in inchs? I wonder if the guy was lazy or did that to hit my neg camber goals.

I am trying to think my way through the front end height but maybe I should just do what everyone else is doing.

If my calculations are right, we lower the rear .75" under ROW specs and the front a big 1.75". It seems Porsche did not put "rake" into the cars.

Down at that level we do pick up some neg camber at rest which should be good thing.

However get an upward angle on the tie rods. Now under compression we also end up w a dynamic increase in toe out. I added the 11mm (<.5") spacers under the steering rack which will help a this issue a bit.

We also push the 'roll center' down which may make the front want to sway more than it would at the stock height. I also wonder about having all that side load on the a arms that may be trying to push the a arms down and compress the front end.

Having said all that, to in my opinion "to low" front end seems to be what the track guys run so who am I to argue.

Jon, your expereance trumps my guesses.

It sounds like you played w this and could tell the difference at the track with the front up or down. Could it have been a differace in feel or did the front just hold better? It seems like we should have a much higher tire to weight ratio in the front compaired to the rear.

I can not seem to see how pushing the front down or dialing in rake to the car may help help keep the front planted.

Thx.

[911st]

I am concerned now about the rear toe.

If he gave me 3/32's that is .09".

Factory spec is 10min +/- 10 min.

If I figured correctly 10 min is .04 inch or 0 to .08" is spec.

Guess I have to go back.

[Flieger]

Do you think the "too low" front end may be more responsive because the added roll makes it more consistant with the rear? It makes both of the roll centers low, rather than just the rear. The added roll is similar to having less rebound damping, keeping the front inside tire on the ground longer during transitions and giving more grip and a more responsive front end.

Just my theory...

[911st]

Flieger,

I am out of my skill level here and relying on my natural feeling for materials and physical properties.

I think, because of the design of the front and rear suspension, lowering the rear dose not change the roll center very much and w the lower CG may actually improve sway.

The front because it is a strut design w a very short a-arm when lowered, lowers the roll center very quickly and of more concern to me, may put the side load on the A-arm on the side of its hinge to force down the outside suspention.

By lowering the rear .75" we do not effect things much but the1.75" drop in the front that is of design that will be effected a lot by such change seem like a dramatic amount.

My confidence in these thoughts comes and goes.

Again, I am not sure I have a full grasp of the concept or vocab but the same forces you site about a lower roll center reducing dampening needs is the same force that has increased and is trying to push down the hinge on the on outside front a arm, making for more roll ,and lifting the inside wheel.

Here is a thought, lowered front end increases the rate of positive toe gain and the inside wheel pulls the car faster at first into a corner.

Just a thought.

If this is the case, ultimate cornering may be lessened when weight shifts to the outside wheel do to the increased body roll.
-----

After the alignment I noticed two things, first the front feels lighter (height unchanged) and second, at freeway speed it wants to turn quicker w the start of a lane change. I suspect it is the rear toe creating a little steering effect.

Could it be? My camber caster has not changed that much but I do not know what the delta was on the front & rear toe.

[Flieger]

I thought you said that you lessened the front toe to 0. This would be pretty sharp and quick to react to steering input. I think that the factory specifies a little toe-in for street cars. The front end would definately feel like it wants to hunt more if this is the case. Not sure, though.

I was saying that the lower roll center would have a similar effect to softer dampers on a standard suspension. To control the lower car you need stiffer sways and dampers as you say.

[911st]

Agree on the toe.

Still not sure if I have to much on the back for a street/track car but suspect I do.

Appreciate the help and sounding board.

[Todd Simpson]

I believe the benefit of rake is solely aero. Get the front end down and keep the air from getting under the car.

I used to run 3/32 on the rear of my track car. I thought it was a little too much at the time, but once I got it on the track it was fast and neutral so I left it that way. (I do my own alignments) Are you using rubber inner trailing arm mounts or monoballs?

Over the winter I reduced the rear toe down to 1/32, measured at the rim edge of 16" wheels. I've only driven it one day at the track so far and it was great. I reduced the toe because I was wearing the outer edges of my rear tires, despite having over 3 degrees of negative camber.

I still run some front toe in and I'm gradually moving that towards 0 toe. Caster is maxed (high steering effort) and once I matched caster side to side the on center feel improved greatly.

My gut tells me tire condition and pressures play more of a role than this really deep geometric theory you're getting into. I'd say set the car up in the ballpark of the accepted numbers (you're already there) and drive it. If you're then getting into tire temps at the track you can begin to dial in a specific setting for your car.

[911st]

Tod,

Excellent points, thx.

I am all stock on the bushings and suspension except turbo tie rods, rack spacer, Hd/Sport shocks and almost R tires.

Thus, could have rear toe change w transition from full accel to full braking toward toe out. Could make the rear jump if I was at zero I suspect.

Zero rear toe w rear of wheels pulled togeather would be interesting.

Was it on street driving that the rear wore to out-sides? If so might be able to use rear toe to even ware on rear, though at a faster rate.

Wonder if no toe might help tire temps on the straights. Not concerned to much w rear slip angles.

Do not think much would be lost w being and average of 3/4 inch higher than others unless I lost a lot of neg camber.

One board member I respect seemed to discount the areo which was after as I have no spoilers though I can add one in the front. I suspect a reverse rake could be a bad thing for areo.

I think less thinking and more driving but all the will help me understand the dynamics and what can be done.

I used to have a 72 911S track car that used to get a bit squirmy at times like over a rise or w braking. It had stiff bushings and springs and had not clue what to do or if normal.

[Todd Simpson]

Here's a very good thread on rake. Certainly some knowledgeable guys weighing in on the benefits.

Setup - rake question.

The wear on the outer edge of my rear tires came from the track, and I agree with your assertion that less toe would mean less heat in the tires. My rears were right on target in terms of temp but the fronts were a little cold.

This is the benefit of doing your own alignments...you can play with this stuff a little at a time. It can be done cheaply too, with strings. The most expensive tool you really need is the $150 deco wheel weight checker. The rest is levels, a good ruler and some patience.