15 x 8 Rally Wheel back spacing

[djmachinist]

does anyone know what the back spacing is on these wheels?

Thanks,
Dale

[gots2fish]

I'd say "4 inches".

[djmachinist]

Originally Posted by gots2fish

I'd say "4 inches".

That sounds about right! I'm having a tough time finding custom wheels in 8 and 10 inch widths with a 4 inch back spacing on a 15 inch dia. rim. Every thing I look at is less than 4 inches or way over 4 inches. I am really frustrated. It does'nt seem to be a problem in 5 lug wheels but is a problem with 6 lug wheels. What gives?

Dale

[michael bustamante]

I found out 6 lug wheels have a deeper dish than the 5 lugs. I was hoping to fing 5 lug rallys that had the same backspacing as 6 lugs but no go

[lolife99]

15x8 (5-lug) has 4" BS.
15x8 (6-lug) has 3-5/8" BS.

[djmachinist]

Originally Posted by lolife99

15x8 (5-lug) has 4" BS.
15x8 (6-lug) has 3-5/8" BS.

Keith,

Thanks for the info. So, the 15 x 8 6 lug is 3.625 back spacing. I wonder why the 6 lug is different from the 5 lug? That may explain why I cannot find a 6 lug wheel with a 4" back spacing.

I think I read your name helping Nate work on his truck. Good Job!!!

Dale

1969 GMC Fleet SWB

[lolife99]

Just curious why you are stuck on 4" backspace.
What are your plans?
Lowering?
Air ride?

Alot of your suspension details will determine the wheels you can fit under the fenders.
And the width of the rim will determine the needed backspacing.

Alot of people say that Coys wheels or Torque Thrust II wheels are "played out".
I hate that term.
The real item that is "played out" is wheels with the wrong backspacing.

The trucks already have a wider track width up front from the factory. Just look at your truck from the front or the back, you can see it.
Now add disc brakes and the front gets wider than the drum brake set-up.
Then lower it and it gets a little wider, due to the lower a-arm being more flat or horizontal.

Meanwhile the rearend stays the same. The 67-70 truck have a narrower (.750" per side) than the 71-72 rearend. This make the front seem worse!

So,... my real question is,... what width/diameter wheels to do you plan on running?
A 4" BS on a 7" wide rim up front will work up front,... but will a 4" BS on a 10" wide rim work?

[djmachinist]

Originally Posted by lolife99

Just curious why you are stuck on 4" backspace.
What are your plans?
Lowering?
Air ride?

Alot of your suspension details will determine the wheels you can fit under the fenders.
And the width of the rim will determine the needed backspacing.

Alot of people say that Coys wheels or Torque Thrust II wheels are "played out".
I hate that term.
The real item that is "played out" is wheels with the wrong backspacing.

The trucks already have a wider track width up front from the factory. Just look at your truck from the front or the back, you can see it.
Now add disc brakes and the front gets wider than the drum brake set-up.
Then lower it and it gets a little wider, due to the lower a-arm being more flat or horizontal.

Meanwhile the rearend stays the same. The 67-70 truck have a narrower (.750" per side) than the 71-72 rearend. This make the front seem worse!

So,... my real question is,... what width/diameter wheels to do you plan on running?
A 4" BS on a 7" wide rim up front will work up front,... but will a 4" BS on a 10" wide rim work?

Keith,

I'm not stuck on 4" back spacing. I was going by the 15 x 8 6 lug rally wheels I have on the truck now. I was told they had a 4" back spacing, hence the desire for 4" back spacing. I plan on putting outlaw II's, 10"x 15" on th rear and 8" x 15" on the front. BF Goodrich Radial TA's, P275x60 R15 Rear and P255x60 R15 in the Front. Looks like I had the backspacing wrong so the back spacing of the the outlaw II's appear to be ok at 3.75".

If you are interested in my build Plans, Please look a few threads down, I posted my build plans earlier today. See thread titled "1969 GMC Build"

I would appreciate your input.

Thanks,
Dale

[lolife99]

Like Nate's (72BlckButy) build,... project Blank Slate,...
Nate soon found out that an 8" wide rim up front wouldn't work, or look right with the BS that the stock 6-lug ralleys had. So he got a set of super rare 6-lug ralleys that were only 7" wide. (And the 7" wide rims do have 4" BS)

Still the front track width is wider up front even thought he has a narrower rim up front.

Your 10's in the back will help make things look in porportion with your 8's up front.
You may need to do your suspension work first, then buy wheels.

[djmachinist]

Originally Posted by lolife99

Like Nate's (72BlckButy) build,... project Blank Slate,...
Nate soon found out that an 8" wide rim up front wouldn't work, or look right with the BS that the stock 6-lug ralleys had. So he got a set of super rare 6-lug ralleys that were only 7" wide. (And the 7" wide rims do have 4" BS)

Still the front track width is wider up front even thought he has a narrower rim up front.

Your 10's in the back will help make things look in porportion with your 8's up front.
You may need to do your suspension work first, then buy wheels.

Good idea, I will wait until I get the suspension and disc brake conversion done, then look at wheels.

Dale

[philB]

want to install rally wheels on my '69 c10 short bed 2 w/d drum breaks, vendor with the aftermarket rallys said that need a -25 and not offered, am I looking at this wrong or what do I need to look for to get a set of 15" 6 lug X 7 and 8" rims.

[lolife99]

Originally Posted by philB

want to install rally wheels on my '69 c10 short bed 2 w/d drum breaks, vendor with the aftermarket rallys said that need a -25 and not offered, am I looking at this wrong or what do I need to look for to get a set of 15" 6 lug X 7 and 8" rims.

You need a -25mm offset on what width wheel?
Wheel width and offset are directly related.
This is a good chart to look at.

[philB]

thanks for info, and other info as well, now to find some place to get what is correct.