I searched high and low. On this forum and others. I found anecdotal information for specifc wheels. I used calculators, but they just confuse me. Either I am blind or slow (likely both), but I cannot find a definitive guide to wheel fitment for our cars - without spacers.

For example, our winter wheel is 18x7.5 ET20. Is that the max ET, or will ET30 fit? If I use a calculator (like one on 1010), for 18x8, it shows a comparable ET of 26. But will 30 do? for 18x8.5 ET is 33, but will a 35 do?

Is there a rule of thumb, or a calculator, or a chart somewhere that spells things out for numbskulls like me?

Thanks.