anesthes

iTrader: (12)

Looking at ordering some "star" style drag wheels for my '88 Formula. Running a 4th gen LT1 rear end.

I found an old post from @Orr89RocZ that said a 5.5" backspace should work on a 15x8. Planning on running a 255/60/15 tire in the back and a 215/65/15 in the front on a 15x7 with 4" backspace.

Just wanted to check if the consensus is that the 5.5" backspace does work with the LT1 rear end and doesn't stick out.

I believed the 245mm 16x8 4th gen wheels I'm currently running are 6" backspace.

-- Joe

Orr89RocZ

iTrader: (20)

I think that should still be good. 7.25 worked for 10” wheel. 2” narrower leaving the lip where it was, puts you near that 5.5

anesthes

iTrader: (12)

I'm struggling with the math on this.

The 4th gen rear is 2" wider on each side.
I measured a 16x8 4th gen wheel and it's 6.25" bs.
Supposedly 16x8 rear gta wheels have a 5"" bs.

​​​​​​So if I ran a 15x8 wheel with a 5.5" bs wouldn't it stick out 3/4"?

I also find it interesting that the 4th gen diff is 2" wider on each side but the wheels have only 1.25" more back space.

-- Joe

Roorancher

This may help.....

http://www.tacreationsusa.com/firebird_wheels.htm

anesthes

iTrader: (12)

I was actually looking at that earlier. What's odd is the measurements they list don't seem to jive with what I measured earlier.

The other thing I was thinking about, if I run a 7" with 4" bs in the front and 8" with 5.5 in the rear, I'll actually end up with more wheel lip in the front like a GTA or formula rim, which I always thought looked dumb.

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anesthes

iTrader: (12)

Here is a third gen 15x7 with a 235mm tire I had in the shop. I measured the BS and came up with 4.0" exactly. With the 4th gen rear this sticks out about 3/4" past the fender lip at the sidewall bulge.




So it sounds like the 5.5" BS wheel on a 15x8 would actually place the wheel 1/2" more inside the wheel well, but if I want to run a 255mm tire I'm not sure if that changes things. I'd think the bulge would be in the same spot, but the tread would be 10mm more on each side.

Then there is the next question of, is a 27" tire too much for a 3.42 gear. In 1:1 gear at 6,000 RPM that would put me at 140mph, and it's unlikely that the car will trap anywhere near that. I'm guessing closer to 128-130mph.

So then, the question is, if we're swapping the rear end eventually to maybe a 3.73 or 3.70, do we go with thirdgen width, and if so would the 5.5's tuck too much.

The last remaining issue is the fact that the front wheels will simply have more lip reveal. Ideally, a 15x8 5.5 on the rear and a 15x6 3.5 on the front would probably look best. Unfortunately, it appears only weld offers a 15x6 front.

-- Joe

anesthes

iTrader: (12)

So doing some reading, it appears PBR/LT1 brakes have clearance issues with most non factory 15" rims. I've heard the draglites and other weld wheels do not fit and hit the caliper or parking brake assembly.

For illustration, this is how close it is to a factory 15" wheel:




Any of you guys running the Vision 521 or summit / jegs 521 prostar knockoffs with PBR/LT1 brakes ?

-- Joe