1987 Grand National, stock frame and no rolled lips Please HELP

[Scarab]

I want to use a single beadlock wheel in 15inch on the rear with a 275 60 drag radial. I do not want to roll the fender lips or notch the frame. What size rim and what back space do I need to make this work? I am going to run 17x4.5 on the front. Please I have search and I don't want to make a mistake so that is why I am asking. My body is square as I have the same amount of space on both sides now with the gnx wheels.

 

[hensleyt]

I use 15X8 with a 4 in. back space .with a Cooper 275 X 60 section width of 10.7 street driven no problem lots of room. same wheel with 28/9 X15 MT Pro Bracket Radial section width 10.7 again lots of room and same size wheel, 28/9 -15 Hoosier slick was the widest 11.1 section width. It never touched the fender but ever so lightly the frame with 11 lb of air but 13 lb no rub.
The ET Street Pro at 11.4 I think would rub but the ET street R at 11.1 with a stiffer sidewall than the Hoosier slick I think would work.
I may have to go to a DOT tire and if I do ill try the ET street R but I'm liking this PRO Bracket a lot.

 

[Scarab]

so if I went with a 15x9 with 4 inch would that work with a 275/60 radial without rubbing? I want to go to beadlocks but I need to make sure I buy the correct ones.

 

[hensleyt]

all these section width numbers come from a 8 in wheel. You will need to roll the finder to run a 9 in wheel I believe.JMA
What drag radial do you wan to run?

 

[Scarab]

all these section width numbers come from a 8 in wheel. You will need to roll the finder to run a 9 in wheel I believe.JMA
What drag radial do you wan to run?

A 275/60/15

 

[Pronto]

Each car is slightly different. There are reasonably priced wheel fitment tools out there that will give you an exact fit for your car. There are plans for diy tools too.

 

[Scarab]

RIght now I have the gnx wheels on my rear with no spacers, I have the 255/60 tires and there is about 1/2 inch on both sides between frame and tire sidewall. My car sits straight. I dont know the back spacing on the gnx type wheels.

 

[1986 Buick GX1]

RIght now I have the gnx wheels on my rear with no spacers, I have the 255/60 tires and there is about 1/2 inch on both sides between frame and tire sidewall. My car sits straight. I dont know the back spacing on the gnx type wheels.

What GNX wheels do you have?
Are they the GTA mesh wheels or the GBody mesh wheels as the offset and backspacing are different.
Are they 16”x 8”?

A 275 tire is 3/4” wider than a 255, so 3/8” more on each side.
To move the tire away from the frame 3/8” you’ll need 3/8” less backspace than you have now. If you have more than 3/8” clearance to the frame don’t worry about it.
Assuming you have an 8” wide wheel now.
Going from an 8” wheel to a 9” wheel will move the tire closer to the fender given the same backspacing.
There should be an offset number stamped into the backside of the wheels you have now.

Here’s a chart that will help.

I have to draw it out so it makes sense.
This is a different setup, but a good example.

How wide are your wheels now and what’s the offset number?

 

[Scarab]

This is what they recommended.

Here is the new quote,



Front Size: 17x4.5
Options: Finish: Black, Backspace: 2.50, Bolt Pattern: 5x4.75
Finishes: Center: Black Satin (SBKS),
Price: $739.92 + $0.00 (finishes) = $739.92 (each)

Rear Size: 15x9
Options: Finish: Black, Backspace: 4.50, Bolt Pattern: 5x4.75
Finishes: Center: Black Satin (SBKS), Rim: Polished (POLO)
Price: $1186.75 + $0.00 (finishes) = $1,186.75 (each)

Total: $3,853.34 (all 4 wheels)

this is on a 275/60/15 Micky Thompson drag radial. I have the GTA dimple 2 piece welded gnx type wheels on it now with a 255/50/16 drag radial. I have about 1 inch clearance. I just want the tires to fit without me having to ship them back and forth.

 

[Eds87GN]

I have wasted a couple of hours playing with this calculator. It does have some good info. You can use some of the offset information from the nice chart posted above.

Wheel Offset Calculator

Use our wheel offset calculator to visualize the new tire position when changing wheel and tire sizes. Convert wheel offset and backspacing to calculate the correct setup for your vehicle.

tiresize.com

 

[1986 Buick GX1]

Compared to your GTA wheels. The new ones will be 1/2” in (towards the frame) and 1/2” out (towards the fender). The new tire will be on the same center line as your 255’s. As long as you have 3/8” clearance on each side of your 255’s you should be fine.
You could put a piece of 3/8” plywood against the tire, both inside and outside to be sure.

 

[Chuck Leeper]

. I just want the tires to fit without me having to ship them back and forth.

You can just about forget that idea.
ONCE you have a special built, U own it.

 

[PSID6]

I want to use a single beadlock wheel in 15inch on the rear with a 275 60 drag radial. I do not want to roll the fender lips or notch the frame. What size rim and what back space do I need to make this work? I am going to run 17x4.5 on the front. Please I have search and I don't want to make a mistake so that is why I am asking. My body is square as I have the same amount of space on both sides now with the gnx wheels.

I have a 15x10 rear with 4 in BS w/255:60 15 MT Drag radial with 1 1/2” drop springs with unrolled fenders it does rub if i have anyone in the back seat but a 15x9 might cure the problem

 

[1986 Buick GX1]

This is what they recommended.

Here is the new quote,



Front Size: 17x4.5
Options: Finish: Black, Backspace: 2.50, Bolt Pattern: 5x4.75
Finishes: Center: Black Satin (SBKS),
Price: $739.92 + $0.00 (finishes) = $739.92 (each)

Rear Size: 15x9
Options: Finish: Black, Backspace: 4.50, Bolt Pattern: 5x4.75
Finishes: Center: Black Satin (SBKS), Rim: Polished (POLO)
Price: $1186.75 + $0.00 (finishes) = $1,186.75 (each)

Total: $3,853.34 (all 4 wheels)

this is on a 275/60/15 Micky Thompson drag radial. I have the GTA dimple 2 piece welded gnx type wheels on it now with a 255/50/16 drag radial. I have about 1 inch clearance. I just want the tires to fit without me having to ship them back and forth.

The 15x 9 4.5” backspace wheels would be the same as hensleyt’s setup (same tire and wheel centerline), just with a wider wheel.
It would correlate with your GTA wheels as well (same centerline), it would be 3/8” wider towards the frame and 3/8” towards the fender lip as well.

 

[Scarab]

I have a 15x8 wheel on the car now with a 4.75 backspacing and I have ½ inch clearance between tire and frame now.

My tire has a section with of 10.4 for my 255/50/16

The new tire has a with of 11.1 for a 275/60/15



We are going from a 15x8 with a 4.75 backspace to a wheel to a 15x9 with a 4.50 backspace.



Can you figure out what the clearance will be? I have racked my brain and I am burnt out.



Please help me out so I can stop over thinking this. I just can figure out what clearance I will have

 

[SCOOBY DOO]

Okay, so I ran the Billet Specialty with the 275/60/15 DR and 28 inch drag slick with both having the same section width and 15x8 with a 4.5 BS with the aluminum drum which is a tad thicker than the stock cast iron...and I required a 7/32 shim to get it off the frame. Lips were not rolled on my car. I'm gonna say you're gonna need a shim to get it off the frame...especially if you're using the cast iron drums.

 

[SCOOBY DOO]

Just to prove what I stated above, here's a launch pic with the 28 inch slick on the Billet Specialties.

 

[SCOOBY DOO]

If you already purchased the rims...then do what I did. Bolt 'em on and see if they fit. If it's on the frame rail then you'll have to play with spacers like I did. I'm fairly certain I had read Grumpy ran the same tire/BS with a shim, so I knew they'd fit.

 

[Chuck Leeper]

Sounds like si

I have a 15x8 wheel on the car now with a 4.75 backspacing and I have ½ inch clearance between tire and frame now.

My tire has a section with of 10.4 for my 255/50/16

The new tire has a with of 11.1 for a 275/60/15



We are going from a 15x8 with a 4.75 backspace to a wheel to a 15x9 with a 4.50 backspace.



Can you figure out what the clearance will be? I have racked my brain and I am burnt out.



Please help me out so I can stop over thinking this. I just can figure out what clearance I will have

I have a 15x8 wheel on the car now with a 4.75 backspacing and I have ½ inch clearance between tire and frame now.

My tire has a section with of 10.4 for my 255/50/16

The new tire has a with of 11.1 for a 275/60/15



We are going from a 15x8 with a 4.75 backspace to a wheel to a 15x9 with a 4.50 backspace.



Can you figure out what the clearance will be? I have racked my brain and I am burnt out.



Please help me out so I can stop over thinking this. I just can figure out what clearance I will have

 

[SCOOBY DOO]

MT's site say 11.1 for section width...and in brackets it says 8. You're running a 9 inch...which I would think would increase your section width...which means you'll be closer to the frame and wheel lips.

ET Street® S/S

ET Street® S/S

www.mickeythompsontires.com