Backspacing question.

[71LS5Formula]

Hey all. I have a question. I am looking at rims. Year One with 17x9's are set with a 5'' backspacing. It was either car craft or hot rod that said I can put 17x9.5's on the car with a 6 inch backspacing. My question is if I split that number to 5.5'' backspacing I should still be good.

Car is a 71 Firebird Formula. Global West Suspension all the way around. Thanks for yalls time.


Ben

[71LS5Formula]

Bueller? Bueller?

[Schwartz Performance]

How will you split the difference to 5.5" if the YearOne wheels are 5"?

[Canon_Mutant]

Unfortunately, this also depends on what tires you will be using? On my G-body 442, with a factory 15x7" SSIII with a 4" BS on, I have 1.7" from the rear lip to the frame. So, my 18x9.5s I am ordering with only a 5.25" BS which combined with 275/40s sets the wheel/tire exactly in the center of my fender well. I am going 17x8 up front with a 4.5" BS to set those wheels exactly in the center of the front wells with 245/45s on them. This is all without any spacers which I won't run.

Always better to put a stock wheel on knowing its BS and do some number scratching. That said, a 6" BS would not even go on my 442 and 5.5" BS would put the tire right on the frame.

Obviously, if you are lucky to find someone on here with a 71" Formula . . . they may have the calculations already done.

[71LS5Formula]

How will you split the difference to 5.5" if the YearOne wheels are 5"?

Hot Rod mag or car craft says 17x9.5s with a 6 inch backspacing fits.

Canon. I can't put the stock wheels on the car. Brakes are too big. I'm gonna run 275 40 17's. Yea. There's not too many of us formula guys. Everyone wants a T/A.

[Buryingthesun]

One way to figure out if they fit is to use a tape measure, Obviously its easy to just ask questions and hope someone knows. . . But the better solution is to just do the work yourself and learn.

[Schwartz Performance]

Ok so what are your wheel plans? 9.5 or 9?
It sounded like you were looking at getting YearOne wheels but they aren't available in 5.5" BS.

Too much BS and you'll rub the inside. To little BS and you'll rub the outside. A 9.5" with 1/2" less BS than you referenced will be .
1/2" closer to rubbing the fender.

I know this doesn't exactly answer your fitment question but just trying to understand what you're trying to achieve.

[71LS5Formula]

With a 17x9 rim I would need a 5 inch bs. 17x9.5s a 6 inch bs. I found a deal on 17x9.5s with a 5.5 bs which split the difference between the two. I would measure with a used tire, but 275 40 17's are not to be found here in Montana.

[PRRC]

If a 6 inch BS fits with out issue then a 5.5 on a 9.5 wont work. If your clearances are tight with a 9.5 a 1/2 is a lot to move in either direction.

[71LS5Formula]

If a 6 inch BS fits with out issue then a 5.5 on a 9.5 wont work. If your clearances are tight with a 9.5 a 1/2 is a lot to move in either direction.

17x9 with a 5 inch also fits.

[akio]

9" rim with 5" backspacing has 5" "frontspacing" = 0 offset
9.5" rim with 6" BS has 4.5" FS = +.75 offset
9.5" rim with 5.5" BS has 5" FS = +.25 offset

So, if the first rim doesn't hit, then the third one shouldn't hit either, but this is dependent on sidewall bulge.

Found a clearance comparison calculator online. I ran a quick simulation of your situation, but it could use better data points if you have them. Also, they calculate backspacing wrong, just add 1/2" to whatever they report.