backspacing question

[GR8-68]

I have decided to go with the weld wheel draglites for my 68 c10 project. I want to go with the 15x12 in the rear I am lowering it 3" in front and 4" in rear can anyone tell me what backspacing I need to go with so they will fit in the wheelwells? also what spacing do I need for the front? thankyou

[GR8-68]

anyone have an idea??

[lolife99]

Well,... a 15x8 ralley has a 4" BS. So I would assume a 15x12 would require an 8" BS (to fit the same on the outside).
With that said. Here's a few other things to think about.
What rearend are you using? 67-70 style (6-lug) or 71-72 style (5-lug)that is 1.5" wider,... OR a 67-70 with conversion 5-lug axles?
Is it mini-tubbed? (Almost definitely required).

It''s actually better to use a rim that you have, (with no tire mounted on it),... and do the measuring yourself.
Just remember that a 12" rim will actually measure 13" outside to outside edge.

[lolife99]

What size wheel are you using up front?

[GR8-68]

Originally Posted by lolife99

Well,... a 15x8 ralley has a 4" BS. So I would assume a 15x12 would require an 8" BS (to fit the same on the outside).
With that said. Here's a few other things to think about.
What rearend are you using? 67-70 style (6-lug) or 71-72 style (5-lug)that is 1.5" wider,... OR a 67-70 with conversion 5-lug axles?
Is it mini-tubbed? (Almost definitely required).

It''s actually better to use a rim that you have, (with no tire mounted on it),... and do the measuring yourself.
Just remember that a 12" rim will actually measure 13" outside to outside edge.

I will be putting the 70-72 rear in it to switch to 5 lug, and yes I plan on mini tubbing it to give plenty of tire clearance. Backspacing is measured from the back of the mounting flange to the rear edge of the wheel correct?

and I will probably run 8 inch on the front thanks for the response Lolife

[lolife99]

Originally Posted by GR8-68

Backspacing is measured from the back of the mounting flange to the rear edge of the wheel correct?

Correct.

[Shane]

Originally Posted by GR8-68

I will be putting the 70-72 rear in it to switch to 5 lug ...

FWIW: a 1970 rear end is a 6 lug ... 5 lug did not start until '71

[Houston54]

You will need to measure the side to side distance from the inside of one fender well/tub to the other. Then measure the distance from the wheel mounting flange side to side on the axle you are using. Subtract the fender dimenstion from the axle dimension and divide by two. This is the space you have available to fit your rim and rubber into.

Typically tires extend past the rim about one inche and you will also want about one inche of clearance between the inside sheetmetal and the rubber.

In the case of a stepside bed the following is how it works out with a 2nd gen F body axle.

Outside bed width = 50"
Axle width flange to flange - 60"
Max side to side space = 5"
Subtract 2 inches for tire width and inside clearance

Proper backspacing is 3"

Of course we do not live in a perfect world and finding rims with the proper BS without going custom is difficult but that is while spacers are used for. Just don't go too thick on the spacers that your lug nuts do not fully thread past the head.

So to get it right for your application I would suggest getting the tape out and sizing up what you have. You should be able to work it backwards easily enough to see what size tube you will need. The 12" rims will not fit without some added clearance. Remember not to put the rubber too close to the outside sheetmetal or you could cut the sideway on turns where the suspension is in compression.

I try to maintain at least one inch of clearance on both sides of the tire. Some say that using a rear sway bar allows you to cut this down some.

[GR8-68]

Originally Posted by Shane

FWIW: a 1970 rear end is a 6 lug ... 5 lug did not start until '71

ok thanks for that info

[GR8-68]

Originally Posted by Houston54

You will need to measure the side to side distance from the inside of one fender well/tub to the other. Then measure the distance from the wheel mounting flange side to side on the axle you are using. Subtract the fender dimenstion from the axle dimension and divide by two. This is the space you have available to fit your rim and rubber into.

Typically tires extend past the rim about one inche and you will also want about one inche of clearance between the inside sheetmetal and the rubber.

In the case of a stepside bed the following is how it works out with a 2nd gen F body axle.

Outside bed width = 50"
Axle width flange to flange - 60"
Max side to side space = 5"
Subtract 2 inches for tire width and inside clearance

Proper backspacing is 3"

Of course we do not live in a perfect world and finding rims with the proper BS without going custom is difficult but that is while spacers are used for. Just don't go too thick on the spacers that your lug nuts do not fully thread past the head.

So to get it right for your application I would suggest getting the tape out and sizing up what you have. You should be able to work it backwards easily enough to see what size tube you will need. The 12" rims will not fit without some added clearance. Remember not to put the rubber too close to the outside sheetmetal or you could cut the sideway on turns where the suspension is in compression.

I try to maintain at least one inch of clearance on both sides of the tire. Some say that using a rear sway bar allows you to cut this down some.

very useful info you gave there much appreciated thanks