Wheel alignment set up

[Kiko]

Does anyone has the OEM set up for the 996 turbo?

The highly prestiged British company called JZ Machtech gave me their fast road wheel set up with OEM front arms, which is good for both road and track reducing the understeer dramatically and giving some stability on high speed track turns but the problem is we use mm not inches over here in Portugal can anyone help with the toe figures putting them in mm?

Front axle:

Camber 1º40' (maximum allowed by OEM arms)

toe 12'' (total)

Rear axle:

Camber 1º30'

Toe 28'' (total)

Regards

Francisco

[Loren]

It depends on the suspension. Stock US, stock RoW, X73?

[ar38070]

12" is 12 minutes of degree

12/60=0.2 degrees

tangent of 0.2 degrees x 317.5 mm tire radius = 1.1mm

28" = 2.6mm

[Kiko]

Loren,

Stock RoW please, just for comparison...

ar38070,

Thank you, over here people use distance not angles on those Hunters laser machines.

Regards

Francisco

Edited August 12, 2005 by Kiko

[Loren]

Stock RoW

Front

Toe: - 1° 50' ± 30'

Camber: - 30' ± 15'

Rear

Toe: + 10' ± 5'

Camber: -1° 25' ± 15'

[Kiko]

Wait a minute... if my calculations are correct if 12´' is 1,1mm then 1º50 is around 8,25mm total toe!!! Something is not right here...

Apart from this I understand what JZ changed:

Decrease front toe - increases turning in response and decreases understeer

Increase Front camber - to decrease understeer (very effective)

Increase rear toe - this usually plants the rear and decreases throttle oversteer... (probably not so keen on this one...)

[Loren]

Toe is measured as Toe difference angle at 20° lock.

Toe unpressed (total) would be + 5' ± 5'

[ar38070]

Loren gave you the "Toe Difference angle) not the "Toe unpressed".

The Toe unpressed is +5'+_5'

Also I believe the Porsche numbers are per wheel toe, not total toe (sum of both sides).

[Kiko]

So, JZ guys by suggesting 12'' are actually keeping the OEM factory number on the front and increasing the toe (the double) on rear... am I correct?

[ar38070]

Toe can be be either toe in (negative numbers) or toe out (positive numbers). The Porsche spec is for slight toe out. Toe out, generally speaking, makes the car less stable in a straight line. Toe out in the front helps to turn the car. Toe in in the front helps the car track in a straight line. Toe in in the rear helps the car stay in a straight line under acceleration. Excessive toe (in or out) increases tire wear as in general the car spends most of its time going in a straight line.

Your alignment will be a compromise balancing tire wear versus performance.

[Kiko]

Toe can be be either toe in (negative numbers) or toe out (positive numbers). The Porsche spec is for slight toe out. Toe out, generally speaking, makes the car less stable in a straight line. Toe out in the front helps to turn the car. Toe in in the front helps the car track in a straight line. Toe in in the rear helps the car stay in a straight line under acceleration. Excessive toe (in or out) increases tire wear as in general the car spends most of its time going in a straight line.

Your alignment will be a compromise balancing tire wear versus performance.

Its the other way round though... Toe in is positive numbers and toe out is for positive numbers.

I finally set the car up!

After long hours of reseach I ended up with the following set up (very close to GT2 apart from front toe):

Rear GT2 anti-sway bar set at hole #2 (being 1 the softest and 4 the stiffest)

Front Axle:

Toe 3' on each (6' total)

camber -1º05'

Rear Axle

Toe 10' (RoW OEM)

Camber -1º25' (RoW OEM)

Impressions:

On the track where all cars understeer severely, this one when tested both by me and by a Professional International Racing driver the car showed very mild understeer (near apex) with good turn in (from beginning of the turn up until apex) and slight overtsteer when provoqued (from the apex to end of turn)but overall a very "safe" car to drive even with PSM off...

On the road and using 34psi front and 39 in the rear the car's steering felt slightly darty (loose) at highway speeds (very, very slightly) kind of when you run with empty tank vs full tank and this was due to less toe in which increases turn in sharpness but has the side effect. The car now on the road (this is very important since you spend 99% of the time on the road) feels neutral with slight power oversteering. The only thing that still bothers me is the tire pressure as I was used to increase tire pressures (BMW's) and in this car I had to lower them and quite a long way (from 44 to 39 in the rear), I wonder why is this and if tire wear increases noticeably...

[ar38070]

Its the other way round though... Toe in is positive numbers and toe out is for positive numbers.

On the road and using 34psi front and 39 in the rear the car's steering felt slightly darty (loose) at highway speeds (very, very slightly) kind of when you run with empty tank vs full tank and this was due to less toe in which increases turn in sharpness but has the side effect. The car now on the road (this is very important since you spend 99% of the time on the road) feels neutral with slight power oversteering. The only thing that still bothers me is the tire pressure as I was used to increase tire pressures (BMW's) and in this car I had to lower them and quite a long way (from 44 to 39 in the rear), I wonder why is this and if tire wear increases noticeably...

You are right the Porsche spec is for slight toe in not out. I do not know if it is me or Porsche but + to me would mean out not in.

I think that the high spec rear pressure is to promote understeer i.e. for safety. I too run less in the rear and more in the front than spec.