Help with rims / offset on 69 firebird
 

I want to put these rims on my 69 firebird but cant seem to figure out what offset I need. https://www.weldwheels.com/weld-stre...heels/s77.html

Any help? Is it possible to do staggered rims? If I have space to go a little bigger and wider I would like to.

Current sizes on my car - rear is 10.8" and 18X10.5 front is 8.1" and 17X7

Is the car lowered or at stock height? A stock height vehicle can hold a larger wheel as the tire will not run into the fender or 1/4 panel wheel lips. It may rub on the top of the tire over bumps, but general not contact with the tire sidewall. If the car is lowered, you need the wheel to fit inside the wheel house and at that point, getting the offset right is critical.

if you currently have an 18x10.5 on the car that fits properly, take the wheel off and look at the inside spokes. There will typically be something that shows the offset. It'll be labeled something like "ET7." ET means Einpresstiefe which translates from Italian to "insertion depth." This measurement is in millimeters. Then choose the same offset where possible. If you can't get it exactly, you can use this tool to see what the change is going to do. https://www.wheel-size.com/calc/

A "typical" wheel size for a factory frame 1969 firebird, without mini-tubs in the rear would be a an 8' wide wheel in the front with around a +7 offset and a 9.5" wheel in the back with again somewhere around a +7 offset. Having drums first discs, how thick the rear disc hat is and the axle flange offset will make a difference in the rear. I believe that most BOP axles for a 69 firebird will have a 2.75" axle flange offset.

245 section width front and 275 section width rear is the common tire width when looking at 17" or larger wheels. An 8" or 8.5" wide wheel in the front with a +5 to +7 offset and a 245/45/17 or 245/40/18 tire will just touch the inside frame at full lock. You won't hear it and it won't damage the tire, it will typically be just enough to scuff the paint off the frame where it contacts.

Nominally the rear wheel well on the 69 from the inboard wall to the outboard lip is 12". This is typically enough to fit a 10" wide wheel which will typically measure 11" when looking at the outside edge to outside edge of the wheel rims. This gives you half an inch of clearance on each side, if you nail the offset correctly. A 285 section width tire will mount successfully here and you should expect minor rubbing when entering or exiting driveways, or undulations in parking lots, but not while actively driving the car.

You've got to measure front and back however when going this wide with a lowered car. You have to nail the offsets otherwise you get into rubbing issues that become annoying and dangerous.

If the car isn't currently lowered but you intend to lower it at all, do that first before you purchase wheels. Don't guess and don't take the word of the internet (including this post) as gospel that a certain offset will fit your car. There's too many variables that can change.

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