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Geometry Alignment for Porsche 911 964 Carrera 2

Jcx

Well-known member
Joined
15 Aug 2013
Messages
3,876
Folks,

The title is SEO'd for easy finding in the future as many searches on t'interweb found little.

It's a year since I last had my geo done and all was not quite right. At very low speeds when entering quite tight but smooth bends - like a roundabout - the back end would be slow to turn, sometimes dragging/hopping a bit. In addition the car felt a bit too safe, too steady, too heavy.

So I set about some research. I wanted to make the rear chase the front round bends and I wanted the front to be a lot more reactive, more pointy, lighter. Of course I didn't want to lose high speed stability but I know there is a trade-off.

There is lots on the web that explain camber, castor, toe (in and out), thrust, etc. But only really in engineering terms and not in my hunting did I find anything that prescribed a solution for my needs. So I decided to figure out my own edits. Crazy? Maybe...

My previous settings (per wheel) were:
FRONT: Toe-in +12'. Camber-50'. Castor=4degs.(Max achievable)
REAR: Toe-in +15'. Camber-1deg50'.

To make the front more pointy we cut the toe-in by 33%. This aids turn in and makes the front react faster. To keep the rear stable we kept the Toe the same. To 'lighten' the car we reduced camber front and rear but maintained an offset, albeit a smaller offset front to back to stop the rear exiting the bend before the front.

My new settings (per wheel) are:
FRONT: Toe-in +8'. Camber-25'. Castor=4degs.(Max achievable)
REAR: Toe-in +15'. Camber-1deg.

The car now feels more like Mohammed Ali than Joe Bugner. It's up on its toes at any speed which makes for much more pointy driving. It's a lot more fun in the twistes and its way more fluid. It is a little bit less stable at higher speeds but that's no worry as my fun driving is not had at jail-bird speeds on public roads. The trade off is well worth it.

I should also say I have H&R springs with Bilstein B6/HD shocks set just above RS height.

Last thought, man these things are so subtle when being setup. The slightest edit to one setting changes everything on the ramp. Takes a lot of patience. The guys prob spent 3 hours on it with me 'helping'.
 
Top post Joe, very informative :thumb:
There are many ways to skin a cat as they say, but I like the idea of a 'Realistic' every man set-up that won't alarm anyone, but encourage spirited driving.

When my wheels are finished I shall be going whole hog and getting everything set up on The Baron from corner weights to caster as it feels like your bull riding at times. Although to be fare the chap in the Cayman must have thought i'd got rocket boosters attached when I bested him a couple of weeks ago :oops:

Now give us some tyre pressure settings to go with the above............
 
Chief said:
Top post Joe, very informative :thumb:
There are many ways to skin a cat as they say, but I like the idea of a 'Realistic' every man set-up that won't alarm anyone, but encourage spirited driving.

When my wheels are finished I shall be going whole hog and getting everything set up on The Baron from corner weights to caster as it feels like your bull riding at times. Although to be fare the chap in the Cayman must have thought i'd got rocket boosters attached when I bested him a couple of weeks ago :oops:

Now give us some tyre pressure settings to go with the above............

Naughty boy Chief! Do you try to tickle snakes too?!! Oh go on then... Tyre pressures... 36PSI all round on 17" rims.
 
What a great debate that was last year eh Joe! A couple of points that maybe of interest....small point but you have + not - toe. Now the suspension has been on some time you may like to measure the ride heights again. Briefly I had some inner front tyre wear so had my settings rechecked. Everything fine apart from tyre pressure 3-5psi down due to a dodgy gauge and what was a ride height of RS+5mm had settled at RS+0. This was with 1/4 of a tank.

Problems soon became clear when we simulated a full tank plus luggage. The ride height dropped a further 12mm but more important was the change in toe. What began as +5' was now -10' which together with together slightly low pressure had been the cause of the tyre wear on my long Euro trip. Lesson learnt, be careful on full loads and especially when at low ride heights.
 
Good info big Joe but a bit too technical for me :oops:

But Kwik Fit can normally do these jobs in 20 mins with a full tyre inspection :thumb:
 
ras62 said:
What a great debate that was last year eh Joe! A couple of points that maybe of interest....small point but you have + not - toe. Now the suspension has been on some time you may like to measure the ride heights again. Briefly I had some inner front tyre wear so had my settings rechecked. Everything fine apart from tyre pressure 3-5psi down due to a dodgy gauge and what was a ride height of RS+5mm had settled at RS+0. This was with 1/4 of a tank.

Problems soon became clear when we simulated a full tank plus luggage. The ride height dropped a further 12mm but more important was the change in toe. What began as +5' was now -10' which together with together slightly low pressure had been the cause of the tyre wear on my long Euro trip. Lesson learnt, be careful on full loads and especially when at low ride heights.

Happy days Rob :)

Regarding the Toe, yes, i always think of Toe-in being negative from the straight ahead hence why i wrote it as -8' but you are right that if qualified as Toe-in it is a positive measurement +8'. I will update my original post for clarity.

My ride height looks to the eye about the same as it was. I didn't measure it accurately but the fingers in the gap method have it about the same as it ever was. Not scientific i know :) I stuck a full tank of fuel in before the setup.

I was looking for something close to 0' toe-in which is why we went with +8' as we know it will change under loads (braking, people and luggage on board etc.) and we didn't want it to toe-out.
 
Zingari said:
Good info big Joe but a bit too technical for me :oops:

But Kwik Fit can normally do these jobs in 20 mins with a full tyre inspection :thumb:

LOL
 
Zingari said:
Good info big Joe but a bit too technical for me :oops:

But Kwik Fit can normally do these jobs in 20 mins with a full tyre inspection :thumb:

Hopefully this is said in jest right?
 
the add did not fool you then rob you cant get better than a kwik fit fitter i use them all the time :?:
 
ray stobbs said:
the add did not fool you then rob you cant get better than a kwik fit fitter i use them all the time :?:

Molegrips in hand...what could possibly go wrong eh Ray! :eek:
 
ras62 said:
What a great debate that was last year eh Joe! A couple of points that maybe of interest....small point but you have + not - toe. Now the suspension has been on some time you may like to measure the ride heights again. Briefly I had some inner front tyre wear so had my settings rechecked. Everything fine apart from tyre pressure 3-5psi down due to a dodgy gauge and what was a ride height of RS+5mm had settled at RS+0. This was with 1/4 of a tank.

Problems soon became clear when we simulated a full tank plus luggage. The ride height dropped a further 12mm but more important was the change in toe. What began as +5' was now -10' which together with together slightly low pressure had been the cause of the tyre wear on my long Euro trip. Lesson learnt, be careful on full loads and especially when at low ride heights.

What is your suspension Ras as a soft suspension would in theory accentuate the numbers so trying to figure out if these are firm numbers or soft numbers?
 
My car has KW V1 and H&R roll bars. Front wishbones are poly bushed. The figures change not because of soft or hard suspension but because at or below RS ride height the hub connections to the various components don't function correctly resulting in toe issues and bump steer.
 
Yes. You sound surprised. A full tank and luggage will weigh about 80kg. Try sitting a 14 stone guy on the front bumper and see what happens to the ride height.
I raised the car 6mm so I largely overcome the problem. I rarely run with full tanks and luggage but if I do then I need to take care. I also add a few psi to the front tyre pressures.
 

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