Aluminum wheels what size tires

[Victor Balonis]

Aluminum wheels what size tire  8 inch wide avanti rims 15 inch rims

[Geoff]

Here's a chart with good recommendations. Obviously some stretching can be done but literally your mileage may vary. One great example I can think of is the C4 ZR-1. That car's rear tires were (315/35-17) on an 11" wide wheel, which the chart doesn't suggest. Meanwhile the same car's fronts were (275/40-17) on a 9.5" wide wheel. The chart says that's the maximum recommended tire width for that wheel.

Here is the formula to use if you're trying to stay close to stock wheel & tire diameter for speedometer and odometer accuracy:
Cross section × profile as a percent × 2. That product / 25.4 to convert millimeters to inches. Then + the wheel diameter. So the above tire sizes would look like this:
315 × 0.35 × 2 = 220.5.
220.5 / 25.4 ≈ 8.68 inches. And then + 17 ≈ 25.68 inches. And
275 × 0.40 × 2 = 220.
220 / 25.4 ≈ 8.66 inches. And then + 17 ≈ 25.66 inches.
If you can calibrate the speedometer and odometer all of that is unnecessary.
Otherwise, it's interesting to play with cross section and/or profile changes in the digital world to discover what tire sizes your car could wear. All while heeding the above warnings from the posted picture, of course.

The 1985 Avanti you have used 205/75-15. Those are about 27.11 inches tall. Stay close to that and you'll be all set.