1970 Trans Am Wheel Selection

[jtwoods4]

Well after several weeks of wheel and brake fitment measurements I have decided that I have to move up from the Year One Rally II 17x9 to the Wheel Vintiques Rally II 18x9.5. This will allow me to use the Forged Narrow Superlite brakes from Wilwood on the front and rear of my 1970 Trans Am. They cannot be used on the 17x9 because it is actually a 15 inch inside diameter wheel. Anyway, lets not focus on that issue.

Here is where I am having trouble. The wheels come in 2 back space options 5 inch or 5 1/2 inches. How do I know what will work better for me? I am assuming the 5 1/2 bs on the rear tire will move the tire in towards the leaf spring and the 5 inch back space will move the tire out and away from the leaf spring.

How do I know what I need? The tires I will be running are

BFGoodrich Rival
245/40ZR18 front
275/35RZ18 Rear

Here are links to the 2 different backspace options
5 inch bs
https://www.yearone.com/Product/1967-81-firebird/1500-93-8923405

5 1/2 inch bs
https://www.yearone.com/Product/1967-81-firebird/1500-9389234052

[1974TA]

What are you planning to do with the 17x9 wheels?

[jtwoods4]

What are you planning to do with the 17x9 wheels?

SCCA pdx and NASA hpde road course. Autocross events.

[tonykim]

The year one 17x9 wheels are 5 in backspace so use that as a reference. If you choose the 18x9.5 with 5.5 in backspace it will pull the wheel inside 0.5" closer to your springs and the outside lip will be roughly where the year one 17x9 was. if you do 5 in backspace it will push the wheel out 0.5" closer to the fender well.

I am in the process of going from 15x8.5 wheels to 17's right now on my 78 Firebird. I ordered 17x9.5 MB racing old school wheels with 5.5" backspacing
for the rear and with my measurements they will clear everything. however, if my tire choice is above about 26.5 in tall they will hit the tail pipes.

I think either would work. one thing to check is if the wheel sits further outboard with the 5" backspace, how low are your springs and what clearance will you have between the tire and top of the wheel well arch. check the specs for the 275/35 tire and compare that to what you were running on the 17x9s. from what i am measuring the tires will be about .5 to.75 shorter on the vertical due to deflection.

Hope it helps.

[jtwoods4]

Great thank you so much looks like the 9.5 are going to work best. And thank you for pointing out the height of the tire I need to check on that.

[tonykim]

Glad I could help. After my 17x9.5s arrive i can take a few pics of the test fit so you can what the width looks like.