What is the widest rim ,I can run on the front of my 87 Grand National?

blackgn231

Money pit
I am looking at a set of riken mesh wheels for my 87GN. They are 16 x 9.5 with 4 3/4 back spacing. Just not sure this will fit the front with out hitting ? Not sure about the offset . The front rim has a 255/50/16 on it and the back has 315/40/16. Just need so help on this before ,I drive 3 hrs to go look at these rims , Any help would be great thanks.
 

fast86gn

Texas Moderator
Staff member
I've seen a 9 on the front of a G body but not a 9.5 and don't know what the backspacing was? I run 17X8's all the way around my gn with 255/50's on the back they look like they could fit the front but I have never tried it. Another 1.5 inches might be okay its just the backspacing would have to be just right for them not to rub. Tire size would make a difference as well, the rim could clear slightly but the bulge of the tire might rub. Maybe someone here has done it and will chime in?
 

1986 Buick GX1

GX1 #001 [The One and Only]
I am looking at a set of riken mesh wheels for my 87GN. They are 16 x 9.5 with 4 3/4 back spacing. Just not sure this will fit the front with out hitting ? Not sure about the offset . The front rim has a 255/50/16 on it and the back has 315/40/16. Just need so help on this before ,I drive 3 hrs to go look at these rims , Any help would be great thanks.
I have run 255/50-16’ on an 8.5 wide wheel on the front. They were corvette wheels w/ wheel adapters that equaled a 4” backspace.
The drivers side rubbed at the top inner fender over large dips with stock suspension at stock ride height.

With a 1” wider wheel and 4 3/4” backspacing the center line of the tire (tread) will move in 1/4” compared to mine.

Depending on how the body sits on the frame, you should be ok at stock height.

Assuming you have stock front suspension you may have to add steering stops as the back side of the wheel/ tire may contact the lower A-arm at full lock. Aftermarket lower A-arms have more clearance in this area.

If they rub the inner fenders or if you want to lower the car you could install some GNX fender extensions.
GNS performance use to sell them, but I think they’re discontinued.

You may be able to “massage” the top of the inner fender or you could make something similar.

A988D2EF-C74F-4B69-ACD6-329448CAC62B.jpeg


0506B8BA-3C85-49ED-AC19-93BBF2CDC4D0.jpeg


Turbo6inKY runs 18x9.5 wheels with 275/35’s front and rear, of course he’s got a whole different front suspension and “massaged” inner fenders.
 

Turbo6inKY

Short Guy
Turbo6inKY runs 18x9.5 wheels with 275/35’s front and rear, of course he’s got a whole different front suspension and “massaged” inner fenders.
9.5s can work, but you will have to make some room.

I had to make my own patch for the upper inner fender on the passenger side for the section you can see in the photo below, and the rims hit at full lock steering in each direction. I didn't have to make a patch for the driver side because my fenders are asymmetrical. I just have more room on the driver side than the passenger side. Oddness. I've had the chassis put on a rack and measured and it's not bent, and I've squared the body to the frame. The driver side wheel well just has more space on my car.

IMG_0498.JPG
 

Howling Mad

Active Member
9.5s can work, but you will have to make some room.

I had to make my own patch for the upper inner fender on the passenger side for the section you can see in the photo below, and the rims hit at full lock steering in each direction. I didn't have to make a patch for the driver side because my fenders are asymmetrical. I just have more room on the driver side than the passenger side. Oddness. I've had the chassis put on a rack and measured and it's not bent, and I've squared the body to the frame. The driver side wheel well just has more space on my car.

View attachment 349188
I was lucky and didn't have any rubbing, but none of these cars are the same lol
 

blackgn231

Money pit
Ok today ,I tried the front of the GN and the back of the rim hit my tie rod ends. and was close to the upper A arm. Looks like might have to run a spacer in the front looks like it has room for the rim to come outward just will need longer wheel studs. I found out that the rim has a 36mm offset towards the outside of the wheel which puts more inside the wheel well. will have to try using washers to get the right spacer size first.
 

1986 Buick GX1

GX1 #001 [The One and Only]
Ok today ,I tried the front of the GN and the back of the rim hit my tie rod ends. and was close to the upper A arm. Looks like might have to run a spacer in the front looks like it has room for the rim to come outward just will need longer wheel studs. I found out that the rim has a 36mm offset towards the outside of the wheel which puts more inside the wheel well. will have to try using washers to get the right spacer size first.
According to the charts a 9.5” wide wheel with a +36 offset has a backspacing of 6.63”.
That’s a lot more than the advertised 4.75” backspacing.
Can you confirm the 6.63” (6 5/8”) backspacing?
You may need to use a 1.5”- 1.63” wheel adapter that bolts to the hub, then the wheel bolts to it.

E042CF74-EAB1-41DE-BB3E-1925562C8ACD.jpeg
 

blackgn231

Money pit
I might be wrong looked at a chart on the internet that said if the rim is 9.5x 3.75 it will have a offset of 38 so it might be 3.75 and not 4.75 back spacing .
 

1986 Buick GX1

GX1 #001 [The One and Only]
I might be wrong looked at a chart on the internet that said if the rim is 9.5x 3.75 it will have a offset of 38 so it might be 3.75 and not 4.75 back spacing .
Can you measure the wheel to see what the backspacing is?
When you said “I found out that the rim has a 36mm offset towards the outside of the wheel which puts more inside the wheel well” made me think it was +36 when maybe it’s really -36.

Measuring the backspacing would help put my mind at ease.
 

Turbo6inKY

Short Guy
According to the charts a 9.5” wide wheel with a +36 offset has a backspacing of 6.63”.
That’s a lot more than the advertised 4.75” backspacing.
Can you confirm the 6.63” (6 5/8”) backspacing?
You may need to use a 1.5”- 1.63” wheel adapter that bolts to the hub, then the wheel bolts to it.

View attachment 349311
Never use those adapters on a car that's actually driven. They will break. Seen it multiple times, and it's terrifying when your front wheel suddenly comes off.

My fronts have a backspace of 6.75", and it's about 1" too much. I'm running 1/2" spacers to make it work, but I really need new wheels with the right offset.

The reason? When I bought the wheels, I was running an old Wilwood 2508 front kit which widened the track at the hub. My current brake kit puts the hub face back to a stock width, so now my wheels have the wrong offset.

The thing to do is go to a wheel manufacturer web site and download the measurement form. They all have one. Measure your car and fill it out, then email them the sheet. They'll respond with exactly the dimensions you can fit on your car.
 

1986 Buick GX1

GX1 #001 [The One and Only]
Never use those adapters on a car that's actually driven. They will break. Seen it multiple times, and it's terrifying when your front wheel suddenly comes off.

My fronts have a backspace of 6.75", and it's about 1" too much. I'm running 1/2" spacers to make it work, but I really need new wheels with the right offset.

The reason? When I bought the wheels, I was running an old Wilwood 2508 front kit which widened the track at the hub. My current brake kit puts the hub face back to a stock width, so now my wheels have the wrong offset.

The thing to do is go to a wheel manufacturer web site and download the measurement form. They all have one. Measure your car and fill it out, then email them the sheet. They'll respond with exactly the dimensions you can fit on your car.
I used billet adaptors from Vette Brakes and Products (now out of business) for about 3 years without any troubles before getting correct wheels, but you’re right, long wheel studs and spacers would be a safer way to go.
 

NY Twin Turbo

All the good stuff.....Times 2.
I'm thinking out loud here. Help me out.

If you use the same backspacing as the factory rim, and the overall diameter of the rim and tire combined is the same as factory, then it shouldn't matter how much wider you go towards the outside of the wheel well as long as maintain the factory backspace and total diameter. No?

I know if the wheel sticks out too much it will end up looking like Joe Dirt's ride :eek: . But It would seem like almost 2 inches can be gained this way before the wheel, when positioned strait ahead, is flush with the wheel well trim molding. No?
 

blackgn231

Money pit
Can you measure the wheel to see what the backspacing is?
When you said “I found out that the rim has a 36mm offset towards the outside of the wheel which puts more inside the wheel well” made me think it was +36 when maybe it’s really -36.

Measuring the backspacing would help put my mind at ease.
 

blackgn231

Money pit
You right it’s a 6 something I might not be able to use these wheels. Would take a 1 adapter to make it work and that’s a maybe .
 
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