[tminer]

Yea, Pontiac sent me the same info ... Howie has posted the wheel details for quite some time. That is why I did not repost it.

Yea, I'd seen his post but there was no reference to the source. There have been many different posts on various boards and several wheel dealers have the pattern listed but all seemed to split about 50/50 between the two patterns. Kind of hard to know whom to trust.

Tom

 

[GTOJer]

I saw this on another site:

The kind people at Pontiac asked that I post the following info to me on the GTO's wheels.

The GTO hub has a 5x120.00mm bolt circle diameter.
The offset is 48 mm for both 17-inch and 18-inch wheels.
The GTO wheels have 8.0 inch wide rims.

Are we sure about the 48mm offset? That is only 1.89" if my math is not failing me. It sure looks like more than that.

 

[tminer]

That is the centerline offset, but the two "halves" will be twice that different in size. It works out to about 6" backspacing. There isn't a direct correlation because of the way the two specs are measured (0 offset on an 8" wheel isn't 4" backspacing).

HTH,
Tom

 

[Howie]

Yea, I'd seen his post but there was no reference to the source. There have been many different posts on various boards and several wheel dealers have the pattern listed but all seemed to split about 50/50 between the two patterns. Kind of hard to know whom to trust.

Tom

We actually did wheel & tire test fitting. Beside if you takes off any wheel from your GTO and look on the inside it'll give you the factory wheel specs.

17x8 with 48mm backspacing

Arrowhead Performance has the correct wheel specs to fit a 9" wide wheel on the back and use a 275 series tire. Up front you are limited to a 8" wide wheel and a 245 series tire.

Feel free to contact me for more info.

 

[cjlannoy]

I thought this might be interesting because I know at least I thought that back spacing and offset were the same thing, (turns out I was wrong) see below:

Q: What is wheel backspace?
A: Backspace is the distance from the back edge of the rim to the mounting surface on the hub.


Q: What is wheel offset?
A: Offset is the distance from the wheel centerline to the mounting surface. Positive offset is when the mounting surface is outside the centerline. Negative offset is when the mounting surface is inside the centerline.

 

[tminer]

Yep, and what makes 0 offset not equal to 4" backspace on an 8" wheel is that the center line and mounting surface (same for 0 offset) are 4" from the inside of the back lip but backspace is measured from the outside of the rear lip.

Backspace is width/2 in mm (in x 25.4) + offset + 6 and then divide by 25.4 to get inches.

Offset is backspace - 1/4" - width/2 and then multiply by 25.4 to get mm.

Our 8" wheels with 48mm offset should be 6 & 1/8" backspace.

The 6mm and 1/4" represent the lip width and are just typical values.

HTH,
Tom

Edited 6 & 1/4 to 6 & 1/8. Calc'd 6.125, and blew the conversion.

 

[tdimasi]

There has been much discussion about whether a 5 x 4.75" pattern/wheel will interchange with the GTO's 5 x 120mm specs. For what it's worth, American Racing (www.americanracing.com) just updated their website with 2004 GTO Applications. Only 2 or 3 wheels, but all are listed as 5 x 4.75."

 

[tdimasi]

Received a call from a trusted friend in the aftermarket wheel business. Word from American Racing and Weld is that they won't be tooling up for GTO wheels. 18K units per year doesn't translate into enough sales to make production worthwhile.

Still can't figure out why ARE lists a few wheels (4.75") on their web-site. This recent addition conflicts with quite a bit of other info. Specifically, liability issues associated with using 4.75" wheels on 120mm hubs.

 

[nikivee]

Another tire and wheel company has fitted wheels and tires and claims that the bolt pattern is 5x4.75 standard GM pattern. Geez more confusion.

 

[nikivee]

I'm going to do my own testing this weekend. I have some 17" Boyd wheels from a Camaro. I will test fit those and post back here.

 

[Guest]

The answer is 5-120.65 or 5-4.75. Tested by me, verified by my technical department.

You will find people that say it doesnt matter either way. 5-120 and 5-120.65 but it CAN make a difference. Maybe 1-10,000. Maybe more. Either way...do you want to be that one person that has a wheel come off of the car at highway speeds when you and your family are driving???

Do it right the 1st time.

 

[cjlannoy]

Actually I contacted Jim Hopson at Pontiac and he got me the info that says the wheels are 5x120 and 48 mm offset 18x8" wheels. Whether they can or should be interchanged I have no idea. I currently have Motegi Kruz wheels on my car and they are 5x120. See link.
http://www.ls1gto.com/forums/showthread.php?t=1674

 

[yourguyry]

hey, i want to use 18x9 rear, and 18x8 front. what are the exact sizes i should use.. tire, backspacing? Howie i would like to know what you think since i know you have done much work on rims and sizing for the GTO. Thanx

 

[Howie]

hey, i want to use 18x9 rear, and 18x8 front. what are the exact sizes i should use.. tire, backspacing? Howie i would like to know what you think since i know you have done much work on rims and sizing for the GTO. Thanx

Shoot me a PM or email. I've got what you want and have a current group purcahse going for 18" Intro wheels. Thanks!

 

[Homebound GTO]

Howie,
Not to change the subject, but we ordered a set of ROH rims from you on February 10th. Please let us know when they are ready to be shipped.

 

[Howie]

Howie,
Not to change the subject, but we ordered a set of ROH rims from you on February 10th. Please let us know when they are ready to be shipped.

I'll check on it in tomorrow. Normal build time for the Stradas is 6 weeks.

 

[Homebound GTO]

Hi Howie,
Thanks for checking on our rims tomorrow, however, they are Modena's.

 

[Guest]

I was able to quadruple check and it seems as if the 1st measurement was wrong and the GTO is indeed a 5-120.

Grrrr!

 

[kenchen]

Both front and rear spacing are measured from the outside lip of the wheel and combined is one inch wider than the tire mounting surface width. So - an 8" wide wheel with 0 offset would have both a front and rear spacing of 4.5".

The spacing on the stock wheel with +48mm offset is front 2.61" and rear 6.39" for a total of 9 inches. To get this, ADD 48mm (1.89") to the center of the wheel (4.5) to get 6.39" rear spacing. To find the front spacing, simply SUBTRACT 1.89" from 4.5" to get 2.61". Another way, if you have the rear spacing, subtract that spacing (6.39") from the overall width of the wheel (9") to get 2.61" All very simple, right?

Yep, and what makes 0 offset not equal to 4" backspace on an 8" wheel is that the center line and mounting surface (same for 0 offset) are 4" from the inside of the back lip but backspace is measured from the outside of the rear lip.

Backspace is width/2 in mm (in x 25.4) + offset + 6 and then divide by 25.4 to get inches.

Offset is backspace - 1/4" - width/2 and then multiply by 25.4 to get mm.

Our 8" wheels with 48mm offset should be 6 & 1/8" backspace.

The 6mm and 1/4" represent the lip width and are just typical values.

HTH,
Tom

Edited 6 & 1/4 to 6 & 1/8. Calc'd 6.125, and blew the conversion.

 

[jasonblair]

Nothing like a response 18 months after the last post!