17-18" wheels on 89?

[Lincv8]

Anybody put 17-18" wheels on an 89 and was able to get proper back spacing to keep wheel and tire inside body line so no rubbing or bottoming out and hitting fender?

 

Which wheel manufacturer?

[Geoff]

I do not have direct experience here although you could buy this,
https://www.speedwaymotors.com/Wheel-Fitment-Tool-for-Tire-Fit-Testing-Size-Measuring-Mockup,485869.html
and try to find points of interference.

Alternatively, finding your current wheels' width, backspace, & offset could go a long way to discovering how you might manipulate the existing space with new wheels.

Not very many in the Avanti community deviate too far from stock diameter wheels. One Avanti owner in the AOAI Facebook group has his 1984 with the following setup:
225/45-17 on 17 x 7 wheels and 4" of backspacing front
245/45-18 on 18 x 8 wheels and 4.5" of backspacing rear
Avanti through 1985 were on a different frame than Avanti 1987 and after. I don't know if or how that may play into the problem.

I'm about to try to shove 17x11 wheels under all 4 corners of my Avanti later this year, although I have to lean heavily on my planned body, frame, and suspension customization to make that work.