Geometry setup

[checkers]

I recently had my OPC check and adjust
the chassis geometry on my 991T
The report sheet showed all green after
adjustment with the exception of the OSF castor angle. I queried this and the technician said castor was not adjustable but the setting was within factory tolerances.
I still don’t understand why if the castor
angle flagged a yellow it is acceptable.

 

[ralphmusic]

Castor angle is affected by changes to camber and toe and on stock suspension tends to be a result, rather than being set.

I would possibly be concerned with a significant difference between left and right castor angle. My ‘settings‘ were sufficently different after my alignment was changed by a local firm and the car was very floaty at the front at over 125mph on track. I had it checked and corrected by my regular guru and all was well again.

 

[checkers]

Thanks for the explanation . My results
were LF 8.07 and RF 7.46 which based
on your advice would seem OK.

 

[Lancerlot]

Caster angle affects the steering - more caster = more self centring. You can read about this in the 991 forum Tricks and Tips (members only) section here https://www.porscheclubgb.com/forum/tm.aspx?m=989365#989365

If caster is unequal it may be due to a worn top mount, ball joint, stabiliser mounts or slight chassis misalignment. It's a delicate setting and consequently production tolerances are allowed - small discrepancies will not significantly alter vehicle performance.
Regards,

Clive