Wheel spacer max.safe thickness?

[Wes Shew <schumi@vcn.bc.ca>]

If one adds wheel spacers to increase track and fillout the wheel well,
how thick can one go without having to change to longer studs? i.e. is
there a min # of threads/length of threads the wheel nut should catch?
TIA

--
Yours in motorsport, Wesley E. Shew   [ macher ;-) ]
#99 AS 1991 PORSCHE 944 S2 cpe 3.0L(M030&LSD)Indischrot/Schwarz Kunstleder
 #53 DSP 1980 VW Scirocco Mk.I, 1.6L bal.& blueprt, Platinum Grey Metallic
  SCCA (NWR) & PCA (CWR) Vancouver, Canada  (604)737-7649 schumi@vcn.bc.ca