Geometry Settings help needed!

PJS917 · Mar 12, 2009

My car is booked in next week for a geometry set up. I had the car sorted by Chris Franklin at CofG last year, but after changing various bits on the front suspension over the winter the car needs setting up again. I have unfortunately not got the settings that Chris set the car too, but the car has always under steered a little to much anyway so I want to reduce that. I actually think I may want to go to a fairly aggressive set up as my car is used for hill climbs and I want the car to change direction quickly. Tyre wear is not really an issue.

So the question is, does anyone have a definitive list of geometry settings and how the car feels with the settings in place?

My car is running 968 torsion bars and KW suspension, if that has any bearing on things?

944 man · Mar 12, 2009

Id be interested too. I have Jim Pascha's settings if theyre any use (front: 3/4°, 1/16" toe-in, 3° castor or as close as you can get and equal on both sides - rear: 1°, 1/16" toe-in)?

appletonn · Mar 12, 2009

OK, here's mine:

Front -2.7 deg camber & 2.4 castor with 12" toe in (I guess that is minutes not inches!)

Rear - 1.8 deg camber & 22" toe in

Need to check those toe figures - assume they are minutes of toe per side, but not sure so will double check

On track, car turns in well with very little understeer and is very adjustable in corners on lifting off/reapplying throttle, seeming to pivot around you - not too nervous on road though.

Mine is, however, a road car first and track car second so probably not 'pointy' enough for Peter's competition needs!

Peter Empson · Mar 12, 2009

I'm running the track settings JZ developed and love it, but they don't give the details out (trade secret) so haven't the faintest what the figures are I'm afraid...

It's a pretty aggresive setup and wears tyres heavily on the road as there's a lot of negative camber. It is at the expense of some straight ahead stability but it has great turn in.

Neil Haughey · Mar 12, 2009

Mine is as follows and the camber is set to get even wear on the Hankooks on the car at the moment (very stiff construction compared to pilot cups and R888 apparently).

Camber: front 2.5 degrees, rear 1.5ish degrees
Toe: front 0, rear 10 minutes per side toe in
Castor: As much as you can get until the adjuster is just pushing the pivot point upwards rather then adding more castor.

IMHO you will need more camber on track with many of the tyres around.

The one thing I experimented with a lot was front toe, I found that I didn't like the various -ve effects of going away from 0, go one way and the car follows every rut in the road go the other way and the car falls into corners.

Big Dave · Mar 12, 2009

Neil.
In your last paragraph. You say the car " falls into corners", By that do you mean it feels like it wants to oversteer into the corner.??? What toe setting was that with..???

Pete. The settings i have on the 68 are,,
Front
Castor.3.30,,,, Camber -2.16 ,,,, Toe in total of 0deg 16mins.
Rear.
Camber -2.03 ,,,,, Toe in total 0deg 22mins.

BUT im contemplating "tweeking" these...
Any "constructive" comments on the above will be greatly recieved...[

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zcacogp · Mar 12, 2009

Peter,

I take it from your post that you are not going back to Chris at CofG .. can you not ask him what settings he used?

The usual advice for a roadgoing 944 is to take the extreme variation of the most aggressive set of settings listed. I think that's the '89 models, and the precise details can be found in the factory manuals (which can be downloaded from Rick Cannell's site.) Having said that, I appreciate that you are talking about not just road use, so may want to just use these as a starting point.

Oli.

PJS917 · Mar 13, 2009

Oli, I know Chris set my car to the Jim Pascha settings 944 man has kindly listed above. The car is great on the road with these but tends to under steer a little too much.

Thanks to everyone that has contributed so far. It is giving me plenty to go on.

edh · Mar 13, 2009

Looks to me like you might need some more front camber

This may end up as quite a useful reference thread - geo settings is a common question.

There are lots of other things you can do to change the balance of the car - I find that relatively small variations in tyre pressures & damper settings make a considerable difference on my car. It's also worth trying the same tyre width all round. You also need to factor in driving style - how do you brake coming in to bends? - do you come off before turning in, or turn in & gradually lift off to keep the weight on the front tyres?

Hilux · Mar 13, 2009

You can also help dial out/reduce understeer with flatter cornering by uprated ARB`s or installing adjustable ones.

ARB`s are often forgotten in these discussions and if suspension is being uprated then the ARB`s need to be considered in tandem as one change affects others greatly. They play a huge role in keeping the car cornering flatter ie: reducing weight transfer (and understeer)

EDH is absolutely correct for your braking point and how hard you brake or how you brake determines the cars stance into a corner.

Sometimes stamping on the brakes and then easeing off as you turn in so as to` set` the cars stance/balance into tight corners works (at least it does for me on ocassion)

Remember also tyres gain heat and gain pressure so the optimum hot pressures can be exceeded (hence understeer) if you havent determined what the heat gain is and allow for it by reducing cold pressures first (thats what I do anyway as the last time I said this I was flamed a bit [8|])

If you dont agree then talk to people who use slicks/super sticky tyres and in particular motorbike racers whose tyres heat up enormously.

Neil Haughey · Mar 14, 2009

No Paul you are right, I was seeing a 10 psi increase over 20 minutes with the tyres already hot. If you go out with stone cold tyres in the mid 20's it will only take a couple of laps to get them up operating temperature by which time I bet they will be in the mid 30's.

BigDave, the falling into a corner feeling is not so much oversteer as steering which is non-linear turning into corners. Basically the car starts to turn in then turns much sharper I think this may have been with more then a 10 minutes of toe-in, and likely depends on the tyres used.

Another point I remembered is that my rear toe measurement of 10 minutes was before dropping the rear end down an inch. Probably more like 20 minutes by now. One thing for sure though, my rear camber and toe by mark one eyeball looks identical to the PCGB 944 S2 race car I was looking at today at EMC.

One thing I am convinced by though is that you can skin this cat many ways as long as the settings are balanced on the car.

appletonn · Mar 31, 2009

Just by way of an update to the settings I originally listed, following the fitment of Peter's old Racers Edge top mounts, I have had the toe changed on the car to try and further sharpen up the front end 'bite' when turning into corners - now running at 5" out, rather than in - that's minutes NOT inches btw!

Car is keener to turn in but not really any more nervous when tracking straight on camber roads - apparently on braking (exaggerated by my car being lowered) the movement of the trackrod ends as the suspension compresses will serve to pull both wheels closer to parallel under braking, enhancing stability.

Have to say, under heavy braking today, the car felt superb so very happy.

Latest tweeks have reignited my enjoyment of the car.

Neil Haughey · Apr 1, 2009

A small amount of toe out is no bad thing, the benefits in theory are like you say given that the car has a front mounted rack. ISTR the only negative I can recall from to much toe out was the steering getting very heavy. I don't think you can go to wrong with any settings up front that are close to 0 though 5" is not much.

Hilux · Apr 1, 2009

the car falls into corners.

Oversteer.

Car is keener to turn in but not really any more nervous when tracking straight on camber roads - apparently on braking (exaggerated by my car being lowered) the movement of the trackrod ends as the suspension compresses will serve to pull both wheels closer to parallel under braking, enhancing stability

Again with better (adjustable) ARB`s tuned to the suspension, the strain (exagerated movement distance) particularly on a fully loaded nose dive or a fully loaded outside wheel on the front lower A arm swivel pin is much reduced as the car weight transfer is better controlled. Ask Peter about this, he had a `moment` last year [

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I`ve not done the exercise however the lowering of the car changes the `bump steer` tendencies of the car ie: the exagerated arc the steering arm ends scribe as the wheel moves up and down.

This is because the horizontal line the steering rack is positioned to is now lower relative to the hub where the steering arm is joined so I suggest the arm is now set longer to compensate and will be noticeable on 'lift off' of the suspension (forceing toe in) (forcing toe out on compression)

Therefore its vital that the rebound damping is set properly as the correct setting when braking into corners is important and can unsettle the turn in. I`ve not noticed it on mine (KWV3) so consider the settings have dialed some of it out but it will have changed nonetheless from manufacturers settings so suggest its in there somewhere.