Can any adverse effects be expected running 8J's with stock offset in the front of a 1990 C4 with 205x55x16 tires. I know 8J's are stock in the rear with 6J's for the fronts. Would the wheel be too wide for the tire, or would a different width tire be needed? Any other problems ?

 

Since 8" is beyond the spec range for almost all 205/55x16 tires. I would say the it is not a good idea.

You do, in general, want to use a rim at the wide end of spec. which is 7-7.5" for a 205/55

 

Exactly. I'd look for a 7-inch width wheel...keep an eye out, however, for wear on the A/C line running along (I believe the drivers' side) wheel arch. A wider wheel may rub there. (the 15-inch fuchs on our 86 Carrera did this, so we put 16-inch 6 and 7's with 205 and 225's respectively)