Backspacing Question

[Marty Q]

Im getting a set of Weld Pro Stars. Im running BFG Dragradials 275/50/15 in the rear. Im thinking 15x8 rim for rear and 15x6 for front, but want to know the right backspacing for front and rear.
As of now i have the dragradials mounted on stock rims and they rub without spacers. Im hoping with these new rims to avoid using spacers with the right backspacing. Thanx.

 

[TURBOV6]

I'm not too shure on the fronts but the rears are 3.5" for the Welds too bad they don't make a 4" bs. I will assume the fronts will be the same.

 

[GNsQuick]

I am with TurboV6 3 1/2" fit fine!!!!

 

[strikeeagle]

Stock GN wheels have 4" BS, so if your tires are rubbing on the inside (you don't say) 4" BS isn't the answer - you need less...

 

[UNGN]

Originally posted by strikeeagle
Stock GN wheels have 4" BS, so if your tires are rubbing on the inside (you don't say) 4" BS isn't the answer - you need less...

Stock wheels are only 7" wide. An 8" wide wheel with 4" backspacing would fit those tires perfectly. An 8" wide wheel would move the center of the tire outward by 1/2", which should be enough to eliminate all frame rub.

 

[Marty Q]

THanx for the help, guys. Marty.

 

[billsgn]

Aluminum Drums....

My 86 GN has the aluminum brake drums. I have 255/60R15 BFG's mounted on stock GN wheels and it looks like I have an inch of clearance (on both sides) between the tire and the frame rails, but only a 1/2 an inch of clearance between the fender and tire. I plan on getting 275/60R15 DR's mounted on Pro Stars. What backspacing are guys running with aluminum brake drums?

 

[UNGN]

Re: Aluminum Drums....

Originally posted by billsgn
My 86 GN has the aluminum brake drums. I have 255/60R15 BFG's mounted on stock GN wheels and it looks like I have an inch of clearance (on both sides) between the tire and the frame rails, but only a 1/2 an inch of clearance between the fender and tire. I plan on getting 275/60R15 DR's mounted on Pro Stars. What backspacing are guys running with aluminum brake drums?

If you are using an 8" wide wheel and you DO NOT want to roll the fender lips, get 4.5" backspacing. put in longer studs and use about a 1/2" spacer. 3.5" BS will require some wheel lip mods.

 

[strikeeagle]

Maybe I'm confused. I thought backspacing was backspacing, and not offset. That is, 4" of back spacing is 4", irrespective of how wide the wheel happens to be???

 

[turboman38]

I just went thru all of this. 15X7 up front and 15X8 in the back with 3 1/2 inch backspace all the way around. I'm running BFG 275-50-15 in the back. I have a a 4 inch backspace wheel, so I had to run a 5/16 inch spacer and the aluminum drums. With a 3 1/2 inch backspace you will NOT have to roll the lips.

I have a friend who is running 275-50-15 BFG drag radials with a 3 1/2 inch backspace Weld wheel and he isn't even close to the lip.

 

[colby]

I'm running Weld Draglites 15x8's all around, rear is 3.5 b.s. ,front is 4.5 b.s., with 275x50 in back and 215x65 in front. Works great , hope this helps.

 

[UNGN]

Originally posted by strikeeagle
Maybe I'm confused. I thought backspacing was backspacing, and not offset. That is, 4" of back spacing is 4", irrespective of how wide the wheel happens to be???

The wheel lip doesn't rub, the tire sidewall rubs. Putting a 275mm wide tire on a 7" wheel causes the sidewall bulge to be greater than it would be on an 8" wheel.

If back spacing is kept at 4", an 8" wide wheel moves the centerline of the wheel (and tire) outward 1/2" vs. a 7" wheel. As the tire moves outward, the sidewall bulge on the inside is reduced (on the outside, too)

This is usually enough to eliminate all frame rubbing with a 275mm wide tire.

 

[strikeeagle]

"Putting a 275mm wide tire on a 7" wheel causes the sidewall bulge to be greater than it would be on an 8" wheel."

So you're saying the section width increases are wheel width decreases?

 

[UNGN]

Originally posted by strikeeagle
So you're saying the section width increases are wheel width decreases?

No. As wheel width decrease, the section width doesn't decrease as much as the wheel width (In fact, it decreases very little) So a 275 tire on a 7" rim "overhangs" the rim much more than it would on an 8" rim. If both wheels (7" and 8") have 4" backspacing, the greater tire overhang on the 7" rim will more likely rub the frame.