custom wheel fitment

[Boeing737D]

Hello, guys.

I am new here and soon to be a new owner of 91' GL.
So what I need help with is what is the max diameter of the wheel, width, and the best offset for this car?

im doing neck breaking researching and has been for the last 7 days. I wanted to make sure its correct so i dont have to spend so much time on returning or losing money.

[theastronaut]

Here is the wheel and tire fitment guide. 13x6 with 165/65-13 tires is the best all around option for tire availability, improved handling, and ride quality. The biggest I'd personally go is 14" with 165/55-14 tires, the sidewall is getting pretty short at that point and ride quality goes downhill but is still decent. I've had 15x6" in the past and they're too heavy with too short of a sidewall, wheel/tire weight really kills off acceleration and mpg. Wider than 165 will hydroplane easier since these cars are very light weight.

You can go up to 7" wide wheels but you need small diameter Advanced Coilovers, -3.5* camber, rolled/pulled fenders, tires no wider than 165, and the offset has to be pretty much exactly +20mm. Any lower and they will poke and rub/cut the tires on the fenders, any higher and they won't clear the coilovers.

https://fordfestiva.com/forums/forum/customized-modifications/custom-suspension-brakes-wheels/1248976-festiva-wheel-and-tire-fitment-guide