More thoughts on GTA rim spacing

G

GNVAIR

Member
Joined
May 24, 2001
I was sitting down the other day thinking about how I can space the rear wheels out on my GN. According to some info I found, the GNX's had 8 inch wide rear rims with approx 3.5 inches of back spacing. I know my slicks are mounted on 15x8.5" rims with 3.5" of back spacing. These fit fine and look great.
From my measurements I found that in order for the GTA rims to approximate the same positioning in relation to the wheel lip, I would need a 7/8" wheel spacer with the "front" offsets which are approx 4 3/8" back spacing. Problem is no one makes a suitable bolt on spacer in less than 1" thickness.
What I am thinking is using 2 rear offsets which measure out at approx 4.9" back spacing with a 1.5" spacer (1.4" would be ideal)
which is readily available. What do you guys think?
 
Really, I'm not a big fan of spacers. Also, in Pa. I understand the max legal spacer is 1/2". Have you tried Classic Wheel(in Ca. I think) and see if they can get/make you what you're looking for.
 
You don't have to use spacers, but you can use billet adapters to do it "right"
There are a couple places that selll them. On the pricey side but they are nice pieces. I had them on my 91 Z28 in order to use C-5 wheels.
Do a search for Andris Skulte. He runs a business that can get these in many sizes for you.
 
Another source for billet, bolt-on spacers is http://www.vettebrakes.com . I used these on my '68 Firebird to bolt on 1993 T/A wheels. Never a lick of trouble out of them but they are quite spendy.

About the idea of using rear offset GTAs: While that may serve to put the wheel in a different orientation, the rear-wheels just don't look as nice because they dont have much "dish" to them. Just my opinion, but to me, I'd rather have the fronts mounted slightly inboard than look at the funky appearance of the GTA rears.

BTW, I have four front GTAs on my GN with X-flares. I used 7/32" spacers in the rear to push those wheels out a bit. To me, it looks OK. And this is coming from someone who had to look at three, genuine GNXs everyday at work when I was at Hypertech. :p
 
So gregg, is what your saying is that you left the fronts alone (at 0 offset) and you put spacers of 7/32 on the back? Do you have any pictures of what your car looks like with the X flares and this spacing? Thanks
 
The dish is barely noticeable unless you have the 2 different rims side by side. Heck, GM did it with the GTA's that way. But I digress, the thing I disliked about the stock GN wheels was the fact they sat so far into the wheel wells. It just doesnt like look right. It makes the car look narrower. I have seen a few GNX's and they look wide......not just because of the flares, but because the wheels sit out.
 
Originally posted by GNX548
So gregg, is what your saying is that you left the fronts alone (at 0 offset) and you put spacers of 7/32 on the back?
Click to expand...
Yes. Got the spacers from Summit racing.
Do you have any pictures of what your car looks like with the X flares and this spacing? Thanks
Click to expand...
There's a few shots on my GN Web page.
 
Another cool benefit with the billet wheel spacers is you could widen T-type wheels on the back side to 8 or 8.5" and no one would know.
 
>>According to some info I found, the GNX's had 8 inch wide rear rims with approx 3.5 inches of back spacing. I know my slicks are mounted on 15x8.5" rims with 3.5" of back spacing. <<


I think this info is incorrect. I am pretty sure that GNX's came with just over 5" of BS on a 8" wheel. They are listed as having 23MM of positive offset which comes out to just over 5" of BS if I am doing the math right.


Sully
 
The "rear" offset GTA rims are 4.9" back spacing and will definitely foul the frame rails on the rear bolted on as is. The GNX's used the same axle housing as the standard GN/Turbo T. I think you are fudging on your math. There is no way a GNX had over 5" back spacing unless GM used some large wheel spacers.....which they didnt.
UNGN posted measurements he had in this thread http://www.turbobuick.com/forums/showthread.php?s=&threadid=34275&highlight=GNX+wheels
The rear rims on a GNX are darn close to 3.5" back spacing.
Maybe UNGN can step in on this one?
 
Originally posted by V6 Beast
>>According to some info I found, the GNX's had 8 inch wide rear rims with approx 3.5 inches of back spacing. I know my slicks are mounted on 15x8.5" rims with 3.5" of back spacing. <<


I think this info is incorrect. I am pretty sure that GNX's came with just over 5" of BS on a 8" wheel. They are listed as having 23MM of positive offset which comes out to just over 5" of BS if I am doing the math right.


Sully
Click to expand...

The article on GNT-type.org is incorrect on how "positive" and "negative" offsets are meaasured. It's just that simple.
 
Here is some good info on GNX wheels:

BuickGNX.com

Note that the factory back wheels are marked -23, implying they had -23mm of offset.
 
Well if what you say is true... then the book that comes with each GNX would have to be wrong. Cause I re-checked and it clearly states 23 MM positive offset...


So then I called my dad and had him go out and measure his rims(#258) from the outside edge (on front side) to outside edge of the center part of the rim and it came out to be 4.5" if we assume that the center section is about 1" thick (he did it to the spokes not the lugnut area so it would have to include about the widest part of the center piece) then the backspacing would indeed be about 3.5" or ~ 23 MM neg. offset.
so I guess the book really is wrong.

From this we would have to infer that the rims that came on the GNX were NOT rims that were built for a 87 TA in black( they had 4.75" BS front and 5.25" rear) but a unique run of rims with a different backspacing than everything else.

Sorry my 1st post was inaccurate as it was based on info from the books that came with the GNX's.

Sully
 
There is no way you would fit anything with more than 4.5" back spacing on the rear of a Regal without a wider rear and/or wheel spacers. I really dont think GM did either of the above. That was why I said they cant be 5" as you first posted. I dont think you could even get a rim with 5" back spacing on to the car as the rim would most likely bottom on the frame rail before you got the lugs through.
 
Just to clarify... not saying my math is wrong... 23MM positive offset would be ~ 5.5" BS on a 8" Rim. It is the book that came with the car that is wrong. It lists it as postive when it is really negative.

Sully
 
Ok, sounds like you guys have this one down packed, I have a set GTA rims from classic with 0 offset. What do you recommend for my spacing to look as close to a GNX as possible?? Front and Rear. Thanks
 
I just received a set of the Classic zero offset rims and understand your problem with using these on the rear. The inside clearance between the tire and frame is not enough for a car that has been lowered, and/or will see high side G loads (as in fast road racing or autocross).

The following are three solutions I have looked at:

(1) Use hub centered spacers, in my case I am looking for negative offset of 10 to 12mm. You are correct in that adaptors are limited to a minimum thickness of @ 1.00" because of the thickness required for countersunk bolts.

Note: hub centered spacers have a tapper to seat in counter sunk portion of wheel backside. I am making my own because have not found anyone to make them.

(2) Have new outer rim and bead installed to increase rear wheel width by 3/4 inch which would keep BS same but would offset center of tire and wheel to a negative 10mm offset. This would stiffen the sidewall of the 255 x 50 x 16 tires.

Note: A change from 8 inch to 8.75 inch wide rim using same tire would reduce oversteer (power induced).

(3) Have center cut out and installed on new shell with width and offset desired (most expensive).

As you can tell, I am trying my own hub centered spacers before I spend the money on modifying the rims.

Regarding these rims being used on your B-Spindle front setup:

If my information is correct the B-spindle increases the front center to center spacing of the tires by about 1-inch. Can you confirm if this information is correct.

If this is correct then the use of the zero offset rims in conjunction with the B-spindles will push the outer edge of the tire out to a point that is the same as a wheel (on stock spindle) with a negative offset of 12mm which is close to the GNX front wheel offset.

On another subject:

How did your test go when you ran your car without the rear swaybar??

Deep Enough

Donald McMullin
 
Taste test.

OK folks, you be the judge.

Here is a photo of my GN in comparison to GNX #276.

I have 245/50 front tires and 255/50 rear tires just like a gennie X. As stated before, I used 7/32" spacers to push the rears out a tad. In building my car I certainly wasn't looking to fool anyone. I'm just paying tribute to the meanest Buick built. :cool:

To me, the four, front GTA rims do a good job. :)

What do you think?
 
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