Ride Height and Suspension Settings for My 1977 911S

[evill]

This has been a 2+ year restoration. The car is done but needs final tweaking. My main gripe is the very heavy steering feel and to a lesser degree ride quality. I am looking for suggestions on ride height and suspension set up. The car will be used mainly for Street and a few DE events per year. Here are the details on my car.

The body is a 1977 911S. I added Carrera Rear Flares to it. These are butt welded and dead even side to side as measured from several locations. The suspension has been completely rebuilt. Torsion bars have been increased to 21mm and 28mm F&R. The bushings have been replaced with Weltmeister plastic. The struts are Bilstein Sports, new turbo tie rods were added and Weltmeister Steering Rack Spacers. The wheel bearings F&R, and ball joints are new. Weltmeister sway bars front and rear were added. Brakes were upgraded to Carrera calipers and rotors. Wheels are 7 and 8 by 15 Fuchs with 205/55/15 and 225/50/15 Yokohama AVS.

When I set the car up, I set ride height at the wheel well centers at 24.5-in front and 24-in rear. The measurements from the wheel centerlines to the torsion bar centerlines are 179mm front and 49mm rear, even on both sides. This is far off from the factory settings of 108mm front and 12mm rear. While the car looks good, I am convinced that it is way too low. At higher speeds or on rough roads I experience bump steer and then harshness when I believe the struts bottom out. The initial suspension is smooth, but gets hard quickly. BTW – the front strut spacers (thick steel washers) are removed.

The other day I raised the front and rear of the car 1-in higher with floor jacks. At Euro Spec, 25.5-in front and 25-in rear at the wheel wells, the wheel to torsion bar centers decrease to 154mm front and 21mm rear. These are still a way off from 108mm and 12mm. According to Bruce Anderson’s book, the rears can work well as low as 1.25-in, so I think the 21mm setting would be fine. I’m hoping that the increased ride height of 1-in in front will provide adequate strut travel. I realize that original tire diameter for this car was 25-in and my current set up is just under 24-in (23.8-in) but to get to the factory spec of 108mm in front, I would need to raise the front up another 1.6-in. (Rally Car?) When viewed from the front, the control arms angle upward a few degrees on the ball joint side. The tie rod ends also angle upward, hence the bump steer.

Now to my heavy steering. First I found that the Weltmeister spacers move the rack up to where the rubber bushing (under the steering shaft u-joints) binds. The inside of the rubber bushing has a groove in it; the shaft has a ring on it that rides in that groove. The rack spacers move the shaft up to where the ring and groove are not aligned. The rubber bushing nests into the clamp, so there is no adjustment to compensate for this change. I removed the clamp on the bushing and found the steering felt a bit easier. As an experiment, I added 1//4-in spacer under the bushing clamp to reduce friction against the shaft. I also checked the rack with the front end jacked up, it is smooth and easy with no binding. My alignment specs are Front: .7° Camber L/R, 6.1° Caster L, 6.2° Caster R, 0 toe. Rear: 1.4° Camber L/R and .03° toe. I am wondering if the caster is contributing to the heavy steering feel. I also have a Momo steering wheel which is a smaller diameter (350mm) than stock so that is a contributing factor as well as the wider front tires, 205mm vs. stock 185mm.

So my intention is to raise the suspension 1-in front and rear and remove the rack spacers and replace with adjustable tie rod ends if necessary. I want to reduce the heaviness of the steering. I like a firm planted feeling and I do not mind slightly heavy steering. Your thoughts and suggestions are welcomed.

Regards,
Ed

[evill]

BTW - I have been using the search feature, there are a lot of threads on this subject. I feel that raising the car 1-in is probably the best compromise for handling and looks. As for bump steer, I'm leaning towards the Elephant Racing Bolt On Bumpsteer Kit with the steering knuckle yoke. Can anyone provide feedback on this kit?

Ed

[911st]

My two cents.

911's run a lot of caster. This is what gives us stability and the heavy feeling in a corner when racing.

If you are talking about heaviness when parking that is friction and not having power steering.


Using smaller diameter wheels can be an advantage in that you can set the car somewhat low and still have decent front end geometry. That is, range of motion and still some neg camber gain under compression. I like the steering rack spacers if the front a arms are close to level or sloping down out to the wheels. I suspect if a car is not a full time track car it dose not need to be so low that for most people a bump steer kit should be needed. Stiffer springs restrict motion and should also reduce bump steer.


Another advantage to a lot of caster is it adds neg camber with a turn. As most unmodified 911's have difficulty achieving enough neg camber for the track, this is a plus.

I have wondered if one could get enough neg camber else where if dialing the caster back to say 3 deg would make a 911 less physical on the track. Another benefit if doing this is it would reduce the rate of camber change with a turn it might make tuning the front less sensitive to being set up as working best for long v small radius turns (think autoX v track sweepers.

I would not put a small steering wheel on a 911 that is truly going to see track duty. I prefer my full size stock and could not imagine using a small SW on the track with as physical as a stock wheel is. It basically takes two arms to mussel a stock SW in a full on corner with sticky tires.

[unclebilly]

-1.5 to -2° camber in the back.
.125" of toe in the front and 0° of camber.

[stlrj]

If you've ever driven a 911 at stock/factory or what we so often call "rally" height, you will notice the steering will be much lighter ( delightful, nimble, fun ) than that of a lowered 911. The reason is the increase in negative camber that results. More negative camber has a direct correlation to heavier steering as well as adding more push or plowing in those tight corners.

Keep in mind that lowering is more about looks ( I know there's a bit of "low rider" in all of us ) than what the engineers had intended when they designed it and that does include handling as well as feel.

[Bill Verburg]

Beautiful car!
I like a little more nose down, it could be just an artifact of the pic though

stock RoW tbar ctr to wheel ctr is 113mm front 7mm rear, if you go lower(higher # in front , lower # in rear) use a rack spacer or A arm bump steer kit, if the tie rods are horizontal at rest thats good.

front
0* toe, pressed
camber ~30' neg(or maybe a little more) depends on tires and how aggressive you drive
caster ~6*

rear
a little toe in
camber -1*(or maybe a little more)

[evill]

Thank you for the replies so far. I took the car out for a spirited drive yesterday. Found some curvy roads that I could drive at faster speeds, I found that the steering feels good and controlled at speeds, turn in is smooth with medium effort. I am going to swap in my stock steering wheel to see what type of difference the larger diameter makes to steering effort. Slow around town driving makes the steering feel heavy.

The ride height does need to come up to get the a arms and tie rods parallel or angled down towards the road surface. I will set ride height for best geometry, not looks.

As for rake, aside from wheel well measurements, I think I can put a protractor on the rocker area and confirm front rake of 1°. Is there a common place that is used to check rake?

Regards,
Ed

[911st]

Rake is an aftermarket concept. It might have some benifits other than cosmetic.

What are you going to use the car for or what are your goals.

If it is a street car lower camber values are ok. If it is inteneded for sporting purposes, you want as much camber as your car will give you and you can stand. Your suspention will not let you go to far.

I have my rear camber set at about -2.5. In the front I trimed my strut tops and with my low seting I was able to get almost -2 front camber but I am using my car for mostly track fun.

I would not get to hung up on the angle of the front A arms. If you can get them level or a little down sloped and still have the car look like you wish, great. That and the rack spacer should keep bump steer acceptable.

My car I have the center line of the a arm pivots .75" lower than the CL of the ball joint to put my front wheels at max neg camber at full track corning on my stock suspention car. My track is mostly smoth and bump steer dose not seem apparant to me though I am sure it is there.

I very much like what you have done.

[RoninLB]

I called it rake when I answered poster over on other BBS.

our 911's should be raked nose down 1%



the protractor on the rocker inside the door at the edge is a good measuring place

[911st]

Sorry I kind of opened the door on rake and dropped the ball.

I have my car raked and if your set up allows for it without inducing issues such as bump steer or dragging of the front out of drive ways it might contribute to a small amount of reduced lift at speeds. The design of the rear dose not create to much issue when being dropped except for possible bottoming. The front is a different situation and can suffer from lowering in other ways.

Also, there is nothing in any of the data out of Porsche I am aware of that addresses or indicates the use of "rake" in setting up a 911. The specs most quote as Euro have nothing to do with how the 911 was delivered in Europe. If we set them up to the specs of a 73 911S we would all think they were Rally Cars. Porsche did suggest a very low setting for racing on smooth surfaces like airport runways that was lower than "euro" but it was a squair setting. The worst that Porsche did was the 80's 911's where they actually had a bit of a minor nose up attitude.

I reviewed some of the Porsche data out of the early 70's for setting up a 911 for sport purpose and all there measurements put the car square to the ground.

Thus, I suspect the largest reason for rake is cosmetic for most of us and we even do so at the expense of good suspension geometry.

I also suspect some have found the front end bites a bit better with a lower front end. I believe that is because we are so neg camber changed and the 911 gains more effective neg camber the lower it goes to a point. The added neg camber should allow the front to work better in a corner.

As to tires if you wanted to run 225's front and rear it would help a little with the height issue in the front. For AutoX that is actually a better set up. On the track narrow body's have been running same size wheels front & rear for a long time. If I had 7&8/15's I would want to try the Toyo R888's in 225/235.

Not an expert on this, just what I have come to believe.

[RoninLB]

Originally Posted by 911st

sorry i kind of opened the door on rake and dropped the ball.
--------- not really. I bet many would be interested?


also, there is nothing in any of the data out of porsche i am aware of that addresses or indicates the use of "rake" in setting up a 911.
--------- is ba info good enough or do i have to keep digging?

the specs most quote as euro have nothing to do with how the 911 was delivered in europe.
--------- "euro" height is the common us term used for lowering the us saftey raised 911. It's used by many 911 tech writers.

i reviewed some of the porsche data out of the early 70's for setting up a 911 for sport purpose and all there measurements put the car square to the ground.
---------- news to me.
How about posting some of it if it's handy?

thus, i suspect the largest reason for rake is cosmetic for most of us and we even do so at the expense of good suspension geometry.
------- generally, but not based on suspension wear twist, "euro" height, 25" rear to fender and 25.5 measured to front fender will result in appx 1 deg nose down rake.

.
.

[Bill Verburg]

Rake is all about aero, nose down reduces flow under the car and raises the tail further into cleaner air, it's all good.

All race Porsche race cars are raked, if you have the race manuals you can see that they are not set up like street cars and are lower than street cars too.

[stlrj]

Originally Posted by Bill Verburg

Rake is all about aero, nose down reduces flow under the car and raises the tail further into cleaner air, it's all good.

All race Porsche race cars are raked, if you have the race manuals you can see that they are not set up like street cars and are lower than street cars too.

Humm...

But street cars are more about coefficient of drag for better mileage and stability at speed. That's why you will notice that the Porsche factory spent a lot of effort designing their cars ( 864s, 993s and 996s ) without any rake with special attention to smoothing the undercarriage with aero panels for better better air flow under the cars resulting in higher top speed, stability and mileage...all good!

Don't be fooled by the "boy racer" race car mentality since much of what they do is also more about looks and relies heavily upon copycat pseudo-technology that can always be explained simply as "goes to reason" and "everybody's doing it so it must be right" or "if I want to remain competitive (fit in), I better do what everyone else is doing, besides, it looks cool".

[Bill Verburg]

Originally Posted by stlrj

Humm...

But street cars are more about coefficient of drag for better mileage and stability at speed. That's why you will notice that the Porsche factory spent a lot of effort designing their cars ( 864s, 993s and 996s ) without any rake with special attention to smoothing the undercarriage with aero panels for better better air flow under the cars resulting in higher top speed, stability and mileage...all good!

Don't be fooled by the "boy racer" race car mentality since much of what they do is also more about looks and relies heavily upon unproven copycat pseudo-technology that can always be explained simply as "goes to reason" and "everybody's doing it so it must be right" or "if I want to remain competitive (fit in), I better do what everyone else is doing, besides, it looks cool".

You cannot compare the aero of street to race, street cars are compromised in many ways due to the wide variety of expected use, a race car on the otherhand is optimized for a narrower purpose

The #1 compromise is ride height and suspension travel to provide ground clearance for any conceiveable road obstacle or transition. A lower car w/ less wheel travel can very succesfully be correctly set up at the cost of comfort and clearance, particularly in the nose.

[stlrj]

Originally Posted by Bill Verburg

You cannot compare the aero of street to race, street cars are compromised in many ways due to the wide variety of expected use, a race car on the otherhand is optimized for a narrower purpose.

Maybe you are unable compare the two, but I can since they are all related, considering all the race heritage that is built into every production Porsche ( good engineering too, I might add ). That's why we have this board ( freedom of speech etc. ) to discuss these, plus a wide variety of other car related issues.

Originally Posted by evill

The car will be used mainly for Street and a few DE events per year.

My response was geared more towards the original poster who would be using his car mainly for the street and only a few DE per year.

[Paulporsche]

I think your car's rake is good. Most have too much for my taste. When the rake is correct, the rubber strip between the front bumper and wheelwell, and the one from the rear bumper to the well look parallel to the road surface.

[stlrj]

I hope we don't get too hung up on this rake issue, but I have to agree that most have way too much for my taste too. Keeping it subtle would be a good description.

[Paulporsche]

Good point. I should point out that my car is for street use. It's been a while since my track days. And my comments refer only to the aesthetics of the issue.

[911st]

Rake looks good on a 911 and I worked to get rake into mine.

It it can have some benefits (areo and net camber). Some question the net effect of the areo if the car is not set pretty low and has an effective front spoiler.

It is just my opinion but I suspect that if one goes much beyond the "euro" style of 25.5" in general at the front fender ( with normal diameter tires, and on stock springs) --one may start to have increased issue with bump steer, bottoming of suspension, and less camber gain with cornering & possibly even camber loss at some point (camber curve).

Lowering to Euro Style is much more aggressive on the front than the rear. The camber curve on the rear is liner however the fronts is a curve with less camber gain under compression the lower the front. I forget the numbers but euro it is like a 1" lower rear than stock and like 2.5" lower in front.

If most of us stooped at the 25.5 & 25 fender heights (stock wheel height) and added the rack spacers we would probably not be looking at any significant issue.

However, many now are going to 25/25 or lower. It looks cool but the benefit from lower center of gravity, net neg camber, or areo is not probably going to help potental as much as the potential for the effect of the negatives that may arise.

The info I referenced above was from the factory 1972 Sports Purposes catalog that Porsche put out that included all the 911ST, 911S lt wt, & 914-6 GT stuff. I no longer have the info but when I looked at there suggestions depending on class, for the 911 it was all square not raked.

With stiffer springs one might go lower than Euro Style w/o issue. If going lower than euro raising the spindle on the strut would be good to consider.

How dose this apply to Ed's car. I think he is running 23" tall front wheels and stiffer springs. If I were him I would set 24.5-24" at the fender lip as a genneral limit as to how low I would go. If he can get the front a arms close to level to the ground even better. That sets the front.

Now, do we set up the rear for 'rake" or do we set the rear square for a lower center of gravety?

Fun stuff.

[RoninLB]