Not sure I understand what you are asking.

They widened the fenders, added spacers to the front, different rear arms with different inner pick up point and stronger bearings. The sheet metal where the steering rack mounts is different. A few more lux options typically. An extra fuel pump. The 3.3T's had heaver rotors and bigger calipers that really did not add any weight as they were alloy v iron in most cases.

The answer pretty much covered the question, which I should have asked differently: "How did they make the suspension fit the wider body?" I suspected the trailing arms were different. I wondered about the front A arms, but I guess they are the same. This really doesn't make a substantial difference between the two models as far as suspension geometry. IMO.

Front suspension has anti-dive on a 930. Hubs are wider for the wider track.

Patrick,

It is different. Is it substantial. Maybe maybe not.

Basically the factory mods to the 930 seem to let it remain flatter under braking, acceleration, and cornering without resorting to stiffer springs.

The front mod is like having the spindle raised on the strut about a half an inch. Thus the A arm is at a better angle against side loads and dose not want to tuck under as easily. Same with braking loads, it dose not want to dive as easily. This can also make for a bit more camber gain in a corner.

As most know the rear has the inner link shortened, moved closer to the outer link, and raised. This has the same effect on side / cornering loads and the car should roll less. It also appears to make for a more substantial gain in camber such that the static camber setting can be less. This should help tire ware on the street as less static camber will be required. It should also improve braking as it will put the rear tires at a better angle to the track.

Then there is the widening of the track front and rear which may or my not be even more of an advantage.

If the wheel base goes from say 60 inches to say 64 inches this is probably a substantial improvement as the side load is at a better angle to the contact patch. Another way to look at it is it has the same effect of lowering the car with out having to do so and living with the negative geometry that comes with lowering the car. Or if you do lower it, it is a bigger advantage.

All this and we still have not even put on the wider tires that will fit under a turbo's flairs.

However, I believe that if you are going to run stiff race only spring rates this may become less important but I am not totally sure. This is because if you reduce suspention compliance you reduce lean and the need for as much static camber or the improved camber curve that comes with these mods.

I am not an expert and do not have the ability to express this in technical jargon so I hope you can follow my thoughts. I just seem to keep learning new things about these wonderful cars.

You cannot underestimate the difference that weight plays. Everytime I took weight off my 930, it felt different. Even taking 15 lbs off the car made it different...so that once you are done with the weight loss the car needs to be rebalanced or aligned and lowered.

The 930 has a different suspension than the 911 with front and rear antisquat geometry, the suspension is stiffer, the track is significantly wider, the engine hangs much further out the rear which causes a HUGE difference in weight balance. The engine plus intercooler plus turbo plus wastegate and plumbing is not only heavier but relatively speaking much further back when you look at the weight distribution on paper.

I cannot stress enough what a difference an extra 55 lbs of weight on the far back of the car makes. The 930 has completely different geometry just to keep the rear from oversteering in every corner.

The fact that a 930 feels planted is due to the suspension fighting off a ton of oversteer tendencies. In order to make a 930 handle sharper you must walk a line between removing understeer and not enhancing oversteer. It is a compromise that the 911 does not share.

By the way, Stephanie, I came up with a pretty good way to describe what I don't like about Bilstein sports in their stock form....they are like a Harley Hardtail. In other words they make your car stiff and handle great but when you hit a real sharp bump, you will feel like you have a solid suspension without any dampening. The car thuds over bumps and potholes in other words.

Most 911 front shocks in particular have a lot of rebound relative to the spring rate.

I wonder if this is another effort to arrest our over-steer potential as it has the effect of stiffening the front during turn initiation. This helps the rear wheels to do more work.

This is probably part of the reason some tuners might be suggesting to not run sport shocks in the front. Custom valving is of course a better solution. For autoX this might be a good place to look for turn in.

A lot of our front stiff feel seems to have to do with our great significant weight disparity.

With a car that has 50% more weight over the rear wheels you would think the rear spring rates would be a lot stiffer than the front's. However, that is not the case. The front's effective wheel rates are more like 10% higher than the rears. This is to balance body roll and shift traction to the rear in a corner.

With this the front is going to feel very harsh relative to the rear as it has less mass to off set the forces working against it in bump. Kind of like the difference in shooting a light weight gun compared to one with more mass. Less kick is transfered.

At least this is what I believe so far.

Fun stuff.

Maybe try your 911 wheels and tires on your 930. See if that makes a difference.

You'll get used to it... and then, you'll ask why the 911 don't handle like a 930.

DDDD, there was a thread in the tech forum which wandered off topic but the upshot was that the 930 rear suspension geometry actually has less anti-squat than the 911. It has more anti-roll than the 911, however. The front 930 still has anti-dive relative to the 911 but no significant change in anti-roll.

935 had anti-roll at both ends, anti-dive at front, and anti-dive and anti-lift at rear. That is the benefit or relocated pickups in a way only possible with coil-over springs.

Dear DDDD,
Thank you for sharing your knowledge with us!
Sincerely, W. Greg

Flieger.

I thought both the front and the rear picked up additional 'anti-roll' (among other things).

The rear's from the inner link being raised 10mm and shorting the distance between the inner and outer rear arm attachment points.

The front's from raising what is basically the back link of the A arm to the strut 13mm. I thought this would have much of the same effect in that it puts the arm at more of a downward angle to side loads.

It would seem this would have the same effect on roll as raising the spindle on the strut an equal amount but without inducing more bump steer if the steering arm attachment is not modified.

Again I know there are other effects. Just wondering about the 'anti-roll' at this point.

Am I misinterpreting this?

Thank you for the help.

The anti-roll depends on the suspension geometry. The front uses a strut and A-arm. The rear is a semi-trailing arm.

If you want a higher instant center for the strut/A-arm suspension, you need to make the strut more vertical or, the better way, make the A-arm angle down towards the wheel. The only way to do this without raising the ride height is to raise the spindle on the strut. This lowers the center of mass (ride height effect) and raises the instant center for more anti-roll effect.

As far as I know, the 930 did not have raised spindles from the factory.

+1 for weight distribution being a defining factor. A suggestion for a cheap test:

Put your spare tire and heavy battery back up front (and anything else easy to bolt down) and fill up the tank. Weight ahead of the front axle makes an even bigger difference than removing weight from the rear... If you're feeling adventurous remove the rear wing and/ or heavy rear muffler. Go for a spin and see if it feels better- it won't solve all your issues, but I suspect you might find it a step in the right direction.

I'm running close to your target tire sizes, and while I think they are good, I think they will make your car feel less like your 911, not more...

Flieger,

Thank you for all you have helped me on my learning journey so far.

How do I try to express this.

Seems there should be two ways to increase and make the A-arm angle down toward the wheel.

One is to lower the outer attachment point as dose raising the axel on the strut.

The other is to raise the inner attachment point as done with the 930.

Both increase the A-arm angle and should reduce anti-roll should they not?



Another way to look at it might be to first try to think of the A arm as two links that attach the strut to the chassis instead of as a solid plate (like the EPR 935 style system).

One from the front inner attachment point to the ball joint and the other from the steering rack cross member to the ball joint.

I suspect the front link's angle has more to do with anti squat and not much effect on roll.

It would seem the cross member to ball joint link, being in a more direct line with cornering load, would seem to be the relevant link as to anti-roll.


Am I making any sense?

The wheel/hub/splindle is mounted on the strut and is always at a fixed angle to it. Therefore, it is the angle of the strut that matters. What positions the strut is the A-arm. That is why it is not a swing axle (basically an A-arm with the wheel rigidly mounted, no ball joint).

If you raise both pivots of the A-arm, then you will certainly achieve the result you think. The car will still be lower and the A-arm will have a downward angle to the wheel.

The 930 had the front lowered and the back raised.

I suppose that since you have the ball joint located right at the end of the A-arm axis near the rear pickup point, then the rear pickup elevation does add a little anti-roll.

I suspect that the main reason the A-arm axis was inclined was the anti-dive. Raising spindles would likely provide a better ratio of mm change to anti-dive effect.

Incidentally, not having anti-dive is not so bad. If your suspension is firm, not Formula 1 hard, then you can trail brake the car a little to load the front tires on a 911, then when you are still braking maybe 20% force, get off the brakes quite quickly. The suspension will stay loaded because the springs and dampers have not had time to react, but the braking force will be gone instantly, so that means the tires have extra cornering capacity since they are not braking or accelerating but they have more load on them. You can rotate the car in a rally or autocross like this. If you hade a very high spring rate and were not overdamped, or if you had lots of anti-dive, then the load on the front tires would vanish at the same time as the brake force, so you would have less time to do your turn-in.

So lowering the front attachment point relative to the rear reduces squat potential.

And, raising the the ball joint to cross member attachment point may reduce roll potential.

But to what magnitude?

I think if we look at it Porsche changed the front to rear attachment points inclination and the ball joint to cross member inclination about the same 4 to 5 deg's.

Thus, I am guessing the mods to the front improved anti dive and anti roll to about the same magnitude. I am not strong at math and I am only guessing at the lengths of the A arm so I could be wrong.

I wonder if we look at the back of the car's rear arm inner and outer attachment point improvement if it to is in the 4 to 5 deg range?

Just a guess.

Fun stuff!

It improves anti-dive on the front suspension. Squat is only effected by drive wheels. Anti-dive is only on braking wheels. Not sure if this was just a typo.

You may be on to something with anti-roll and anti-squat both being improved significantly. Both the front view and side view instant center is determined by both a line 90 degrees to the strut top and a line through the A-arm (or the A-arm axis). Therefore, if caster is equal to camber, then a degree away from level for the A-arm angle to ball joint moves the FVIC as much as a degree away from level for the A-arm axis moves the SVIC.

http://forums.pelicanparts.com/uploa...1290399142.jpg
http://forums.pelicanparts.com/uploa...1290399162.jpg

Anti-roll changes much more throughout the range of suspension travel than does anti-dive, however. This is due to the angle of the A-arm being directly linked (mathematically) with a relatively short link to the wheel's vertical displacement. The A-arm axis does not change angle with suspension displacement, though each degree of pitch changes the caster angle as the strut compresses.

Flieger,

Lots of factors that keep popping up. Still a fun puzzle.

So, if the A arm is at an angle less than 90 deg to the strut, is there some anti roll effect?

If the A arm is at a right angle to the strut in a corner is anti roll neutral?

If the A arm is at an angle greater than 90 deg to the strut in a corner, is there n increase in roll?



Another question, if we lower a car and shorten the distance from the contact patch to the strut top attachment dose that effect the forces at the ball joint pushing against the A arm?

And, does lowering the ball joint relative to the tire contact patch (in effect moving the fulcrum) reduce the side forces at the ball joint?

If so this may make for less anti dive than raising the inner attachment point depending on the angle of the A arm to the strut body.

Boy I wish I had taken some engineering in collage.

The side load moment is taken within the spindle and strut, not the ball joint. The side load itself is independent of its distance from the ball joint/A-arm. Only the total 3D angle really matters in this case in how that force is distributed through the A-arm.

The caster and A-arm angles both interact to locate th wheel and FVIC, so it does not do very much for you to look at the A-arm relative to the strut without taking into account the strut relative to car. But yes, having the A-arm 90 degrees or more to the strut makes for lots of body roll.

You should just look at it as: find the height and compare to the center of mass, then find the body roll. It gets confusing when you define "neutral roll" etc. :)

OK, I was starting to see that with a strut system there is not really any side load at the axle. Every thing between the tire contact point and the strut top acts as one lever.

This lever pushes and transfers side loads to the ball joint connection and then through the A arm.

The angle of the A arm to the strut can have a neutral, jacking, or compressive force that can have the impact of increasing or decreasing the effective wheel spring rate. Get this right and we get a mild jacking that makes for an anti roll effect.


Then if we look at what I think is the center of mass relative to the tire contact point, this determines the amount of body roll potential. That relative to wheel spring rates then determines actual body roll.

If so, it would seem if we then widen the wheel base which has the effect of lengthening the lever between the center of mass and tire contact, this should reduce actual body roll potential even more.

Interesting.