993 Wheel off sets / Spacer Calc ??

[sandd_nz]

Hi,

My local Porsche guys, tell me that there is a formulae for calculating the required spacer sizes based on the offset of
the wheels etc.. ( they did not give me the formulae... )

Apparently, there is a number on the back of the wheels (
genuine ) ET xxx... which is used a part of the calc..

Currently my Car 944S2 has 15mm spacers on the back and to get the 993 wheels on but need to get the geniune Porsche spacers for local vechile compliance reasons... The porsche ones
are alot winder hence I want to check...

Any one done this before... or got the formula... Last time I did
this it was trial and error... but the part I need has to come from
Germany and costs $$$$$$ and 3 weeks to arrive, so need to get it right..

Thanks in advance..

Simon