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For whatever reason, Holden didn't make the wheel wells particularly roomy. There's only so much tire that'll fit. Think of the wheel well as a room with a vaulted ceiling that peaks in the middle: It gets narrower as you go upward. When you go from a 17" wheel to an 18" wheel, therefore, you have to go to a slightly narrower tire.

I've got the 17s on my GTO, and I'm happy to have the extra 10 millimeters of tread width. Some people like the look of bigger wheels, though--even if it means a narrower tire.

Check out an article in the current edition of Car and Driver in which they test an SLP-modified GTO and Corvette. The mods added 55 horsepower to the GTO, but because SLP also switched to some snazzy-looking 18" chrome rims on Nitto tires, the car was scarcely faster than a bone-stock GTO on 17" rims.
 

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The width of the 235/40/18's is almost identical to the 245's on the 17's


Going to a 17" wheel won't mean you can stuff a bigger tire in there FYI
 

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I just put a 245/35/19 in front and a 275/30/19 in the rear. I was hoping not to roll the rear fenders, but I'm going to have to. They rub when I give it 1/2 trottle and the rear end swats. The fender roller is on order and should be here within the next couple of days!!!
 

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RedRacer said:
I just put a 245/35/19 in front and a 275/30/19 in the rear. I was hoping not to roll the rear fenders, but I'm going to have to. They rub when I give it 1/2 trottle and the rear end swats. The fender roller is on order and should be here within the next couple of days!!!
why cant a body shop roll a feaken fender. i need to roll mine because if i put adults in the back i better wacht out. how do we roll em
 

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EEZ GOAT said:
why cant a body shop roll a feaken fender. i need to roll mine because if i put adults in the back i better wacht out. how do we roll em
Some can...others won't. Here's the deal... I know that I can do it. I have confidence in myself, but I don't have the confidence in a body shop that I don't know. The price of the tool ($250) is close to the amount a body shop will charge to do the work. I can sell the tool (anyone interested???) and make back most of my money.

Here's a link to the tool that I bought... http://www.eastwoodco.com/jump.jsp?itemID=6159&itemType=PRODUCT

The link give a good picture of what needs to be done.

I only have the fender lip hitting. It is very close to the strut and wheel well, but as far as I can tell, it is only the fender lip. I guess that I'll know more once the fender lips are no longer hitting.
 

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Here's some good reading and testing of different size tires. I am running ROH Drift R 18x8 w/ a 245/40/18 tire - 49lbs and ROH Drift R 18x9 w/ a 275/35/18 tire - 51lbs :eek:

Anyhow, I've calculated that if I go with a 245x40 18" tire up front (or 245x35 19") I get the same rolling diameter as stock. But with that I would want to mate it to a wider rear for a little extra meat. In which case, a 275x35 18" (or 275x30 19") would be the closest match, roughly 0.1" shorter than the front.

The catch here is, will a 275x35 mount on an 8" wheel without problems, or will that be an issue? These wheels have a 42mm offset if I remember correctly. Will that in itself be an issue with such a wide rear tire? (with or without rolling the fender lip)

The OTHER option is to go with a 235x40 18" front (or 235x35 19") and a 265x35 18" (or 265x30 19") on the rear which should mount on an 8" wide wheel just fine. This would be a comperable rolling diameter from front to rear but slightly different than stock so the speedo might be off slightly. The drawback here is, these are both very hard to find sizes compared to 245's and 275's.

I remember seeing someone that had mounted 275's on the rear of stock 17x8 GTO wheels and had no problems to speak of, but wondered really what the drawback is going that wide on a narrower wheel and if it was a danger in any way? The simple fact is, I might have to go with the 235's and 265's like it or not, but that'd really limit tire options.

Results of yesterday's wheel & tire test fitting w/ ROH wheels:

Factory wheels & tires:
17x8 w/ 245/45/17
55lbs each (wheel & tire)
5x120mm stud pattern
48mm backspacing

17's
Front:
245/45/17 is still the best fit
255/40/17 fit but had to use a 8.5" wide wheel, the required backspacing hadthe wheels/tire sticking out too from the body line
275/40/17 didn't fit, using a 9" wide wheel, the tire was rubbibg the strut. Again using a different backspacing would have the set sticking out too far

ROH Drift R 17x8 w/ 245/45/17 - 47lbs
ROH Drift R 17x9 w/275/40/17 - 49lbs

Rear:
275/40/17 fit no problems on a 17x9" wheel
These stick out just a little more than the factory tires, but I think they still look great!

Recommendation for 17" wheels: Use your factory tires and and put them on 17x8" custom wheels or 17x8" wheel front w/ 245/45/17 tires and 17x9" wheel rear w/ 275/40/17 tires

Personally I would just reuse the factory tires and put 17x8" wheels at all four corners. This will be cheaper to do and looks good.

18's
By far the best way to go!!

Front:
18x8 w/ a 245/40/18 tire - fit is perfect
18x8.5 w/ 255/40/18 - again sticks out too far

Rear:
18x9 w/ a 275/35/18 tire - fit is perfect

Recommendation for 18" wheels: Without a doubt the best set is 18x8 up front with 245/45/18 matched with 18x9 out back w/ 275/35/18. This set looks great, fits porportionally and lets you pick up some width out back. The ride quality is also great. Or use 18x8 and 245/40/18 at all four corners.

ROH Drift R 18x8 w/ a 245/40/18 tire - 49lbs
ROH Drift R 18x9 w/ a 275/35/18 tire - 51lbs

19's

Front
245/35/19 on a 19x8" wheel

Rear
275/30/19 on a 19x9" wheel

Recommendation for 19" wheels: GO BACK TO 18"!! While the look great on the car the ride quality is horrible. If you could care less about feeling every bump in the road and want all the look, these are for you. If you just gotta have them then use 19x8 w/ 245/35/19 front and 19x9 w/ 275/35/19 rear or the 19x9 w/ 245/35/19 all the way around.

I have some pics from the fitting I just need to get them off of my disc. I'll get some pics of my Goat with the set up I'm going with and personally recommend,
18x8 w/ 245/4018 front and 18x9 w/ 275/35/18 rear. If I'd been working at Pontiac this is what I would have sold the car with!!

By the way, anyone interested in ROH or other custom wheels contact me I now have pricing and availability info!!

18X8 on front with 245/40's 18X9 on the rear with 275/35 Michelin Pilot Sport AS's
Unfortunately Boyd put a +48 offset on the rears and they rubbed, so I rolled the fenders. Boyd was willing to make another pair but I was tired of waiting. It's been about three months already. I think a +55 would be a perfect offset for these on the rear and Boyd could definately do that.


NEW BOLT PATTERN FOR GENERAL MOTORS 5x120mm

WIDTH OFFSET WIDTH OF TIRE
7.0… +26/+65 215/225/235
7.5 +33/+61 215/225/235/245
8.0 +39/+55 225/235/245
8.5 +45/+48 235/245/255
9.0 (MAX) +48 245/255

REAR ONLY
8.0 +36/+65 245/255
8.5 +42/+65 245/255
9.0 +48/+65 255/265/275
9.5 +55/+64 265/275/285

Offsets greater than shown above will rub on rear fender lip (25mm fender lip).

Another fella posted this: "I have a set of wheels from ROH, the rears are 18x9 51mm 275/35 and front are 18x8 41mm 245/40, with Nittos, no need to roll. BFG or Dunlop you may need to roll?"



The Arrowhead Performance Yellow Jacket 2004 GTO prototype. Thos are Hurst inspired wheels. We got 18x8' rims with 245/40/18 Toyo meats in the front and 18x9' rims with 270/35/18's in the rear. The exhausts exit out each side just before the rear wheels.

Hope this helps. :D
 

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Paisan said:
Ok guys debating getting the 17s v. 18s on my new GTO. What's the deal with them? Why are the 18s only 235 v. 245 on the 17s? I'm tempted to get the 17s just cause they are wider.

-mike
Awesome post, O5GTO. Your car looks great, too.

Regarding the 235/245 thing -- the factory BFG tires have a square shoulder. If you buy a tire with a rounded shoulder, like the Falken Ziex, you can get more rubber under there. I'm running 2454018s on all four corners -- with no rubbing at all.
 

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b_a_betterperson said:
Awesome post, O5GTO. Your car looks great, too.

Regarding the 235/245 thing -- the factory BFG tires have a square shoulder. If you buy a tire with a rounded shoulder, like the Falken Ziex, you can get more rubber under there. I'm running 2454018s on all four corners -- with no rubbing at all.
do u get passengers in the back? is there any rubbing there?. put i 2 kids in the back and i could not get a finger under the rear fender lip. drove 85 miles home and did not rub but i belive if i get adults back there iam in trouble
 

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One consideration no one has mentioned

If you switch from 17s to 18s, you must get the correct size combination so that the height of the tire is the same or very close. Otherwise your speedometer, and I assume your odometer as well, will be inaccurate. The "245" is the width in mm. If you divide by 25.4 you get the width in inches. The "45" means that the height of the tire is 45% of the width of the tire. Therefore, on the stock 17s, the height of the tire is 17" (wheel) + 8.7" (two times the height of the tire (lower and upper height) = 25.7 inches.
 

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Something else to consider is that 17" chrome wheels seem (to me atleast) to look smaller on my car than 17" painted wheels with the same tires. It might just be my first impressions since switching to 17" chrome and may go away, but at the moment the 17" chomes look smaller than 17" painted wheels.
 

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Please be aware that there is currently an issue that is showing up, at least with the 17" OEM's, with strut rub on the fronts that is causing serious tire wearing issues. Some have reported finding cords showing after 10K miles. Pontiac (GM) is not acknowledging that any problem exists (surprise!). This is a serious issue. I have reported the issue to the NTSA and would encourage fellow GTO owners to do the same.
 

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I believe that with the 17" wheel with wider 245mm tires with taller sidewalls will have much more tire flex than the 18" wheel with 235mm tires with the lower profile. In hard cornering the outer wheel's tire will flex in toward the stut causing the rub. This is why 04" owners suffer this problem. My advice is to either use 18's with a lower profile, slightly narrower tires or wheel spacers.
 

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I was thinking of using 5mm wheel spacers but think it would be better to replace the existing studs with ones that were also 5mm longer so I still get all the threads needed to keep the wheels torqued right. Adding the spacer should be no different than getting aftermarket wheels with less offset to solve the strut rub issue. Has anyone tried this or know where we can get longer threaded studs?
 
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