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Discussion Starter · #1 ·
The time for new tires is here, probably overdue. I have been back and forth in my mind, probably longer than one man should, about what direction to go. I like the stock 18s a lot. I have had them on my 2004 since 2005 when I bought them through Arrowhead Performance. Yeah, I was one of the lucky ones that actually got their shit in that group buy. I am still rocking the 2005 era BFG KDWs on them. No dry rotting or other signs of age, but definitely not considered road worthy by today's standards.

I have followed the threads about people widening the rear 18s to put a respectable 275 or 285 size tire on them. I also have taken a liking to the VMR wheels. Today I just scored a pair of stock 18s for cheap on eBay. I'll have them in a week. I can send those off to get widened and I can keep the stock look.

I have been trying to understand the offset and backspacing math and the effect widening the wheels has on offset. I am leaning on 1.5" widening to accommodate a 275/35 Michelin tire. I have read where 1" of widening will suffice a 275 wide tire. Regardless of how much you widen to the inside, you need to figure on your offset increasing from the stock 48mm to 12.7 more positive for each inch you go. Is that correct? If so, then a 15 to 19mm adapter will be needed to achieve a 48-52mm offset with a 18x19.5 widened stock wheel. Right or wrong?

Having searched extensively, it seems like 50-54mm of offset is the sweet spot for an 18x9.5 wheel. To you guys that have been there and done it, what sayeth you? I'm OK with spending the money to make the stockers work.
 

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Wol Gemut
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one, I agree with your assessment, the stock 18 is an absolutely phenomenal looking wheel. two, math is also correct, you add width/2 to the offset +48 for your new offset, so for 1.5", adding about 19mm. And also, yes, +50 to +54 is ideal rear offset. I like +50 but CCW had it at +54 and they surely knew what they were doing. And also yes, although 275 is ideally spec'd for a 9.5" wheel, it is well within specs and reason to put a 275 on a 9" and then only require a small spacer of approx 7mm..
 

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Discussion Starter · #4 ·
one, I agree with your assessment, the stock 18 is an absolutely phenomenal looking wheel. two, math is also correct, you add width/2 to the offset +48 for your new offset, so for 1.5", adding about 19mm. And also, yes, +50 to +54 is ideal rear offset. I like +50 but CCW had it at +54 and they surely knew what they were doing. And also yes, although 275 is ideally spec'd for a 9.5" wheel, it is well within specs and reason to put a 275 on a 9" and then only require a small spacer of approx 7mm..
If you were in my shoes wanting to do what I was plotting, what would you do? To provide more insight, a Pedders xA coil over kit and brembo brakes are going on in a couple of weeks. I was planning to leave the ride height at close to max height for the time being, in order to accommodate wider tires. I would prefer not to roll or cut the fenders.

I have plenty of time to work on this, so nothing has to happen right away. Now if I see a killer sale on tires soon, I may have to act and buy them. 245/40s up front and 275/35s out back. I don't think 285s out back is worth the added possible trouble, but correct me on that if need be.
 

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Wol Gemut
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In my view you are on the right track with 275s. I do run 285s but they measure from absolute end to end (inner well to fender) and definitely require a +50(what I wish I had) or +51(what i have) offset, there is really no good reason to do that. I would do 275s on 9" and use the 7mm spacer to get it right at around +54. The +50 even on 275s might require rolling fenders and maybe that is why CCW chose +54 with 275s, it might be the perfect spot that requires no fender rolling but is still off the well. I believe you could even lower it if you want. alternatively 9.5" with a 13 or 14mm spacer would be good, just not sure if a spacer that size is an issue or not. I am guessing you have already done your research on Brembos fitment with the stock 18s, I am not acquainted with their fitment. so that is what i would do and what I will do if i can one day get a second GTO. that or run stock 18s as is.
 

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Discussion Starter · #6 ·
I appreciate the info. To elaborate on the Brembos, the stock 18s will fit them with no modifications required. You will have to watch the balancing weights on the inboard side of the wheel for contact with the caliper, but aside from that, there are no issues with the 18s. The guy that designed the brackets that sell on Bohnmancustoms.com did a great job on them.

My wheels should be arriving by next Wednesday. As long as they are good, this project will be a go. I am going to keep searching and figure out what to do from there. I am good with using a thicker adapter instead of a thicker spacer to make this work.
 

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Wol Gemut
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I appreciate the info. To elaborate on the Brembos, the stock 18s will fit them with no modifications required. You will have to watch the balancing weights on the inboard side of the wheel for contact with the caliper, but aside from that, there are no issues with the 18s. The guy that designed the brackets that sell on Bohnmancustoms.com did a great job on them.

My wheels should be arriving by next Wednesday. As long as they are good, this project will be a go. I am going to keep searching and figure out what to do from there. I am good with using a thicker adapter instead of a thicker spacer to make this work.
if thicker adaptor is a nonissue, I would definitely make them 9.5". that would be perfect for 275s.
 

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Discussion Starter · #9 ·
if thicker adaptor is a nonissue, I would definitely make them 9.5". that would be perfect for 275s.
I was just reading a thread from 2006... the guy did 1.5" with a 275 tire... put a 19mm adapter on and the clearances sucked, took it off and put the wheel on without it and it was much better, but not perfect. Looks like he went with a 1/4 hub centric spacer and longer studs to achieve what he wanted, and rolled his fenders. I guess I am gonna have to just do this and play around with it to figure out exactly what I need. I have two 3mm spacers and can go buy some more just to play around with. I'm leaning on 9.5 with a 275, possible future growth in mind...
 

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I have two GTOs. My 06 Torrid red I had polished my factory 18s and then had the rears widened 1 inch back in December 2008. Started off with 275s. To run 275 35 18s the 235 40 18s looks better up front because of sidewall height. I switched over to 285s and ran a small spacer then went with 245 40 18s up front. Really liked that setup. Then I tried to run the rears without a spacer and had no issues. Might just be the Michelins tires I was running. Actually the 285s fit better on the widen 9 inch than the 245s on the factory 18s with less bulge. Been running that set up for many years with even tire wear.
 

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Discussion Starter · #12 ·
I have two GTOs. My 06 Torrid red I had polished my factory 18s and then had the rears widened 1 inch back in December 2008. Started off with 275s. To run 275 35 18s the 235 40 18s looks better up front because of sidewall height. I switched over to 285s and ran a small spacer then went with 245 40 18s up front. Really liked that setup. Then I tried to run the rears without a spacer and had no issues. Might just be the Michelins tires I was running. Actually the 285s fit better on the widen 9 inch than the 245s on the factory 18s with less bulge. Been running that set up for many years with even tire wear.
I read many of your posts about it when I was searching but none of your pics are visible anymore.

So you still recommend 1" over 1.5" with a 275 or 285 wide tire? Do you have any current pics of your car? I am in the middle of a Pedders xA coilover and Brembo install, so my spare 18s i just bought are sitting in the garage on hold.
 

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I would probably start off with the tires you prefer. Some have a thicker sidewall for rim protection. You will have to go with a hub centric spacer if you go 1.5" wider and maybe with 1" can make it close. I like hub centric spacers because you can put the wheel exactly where you want it in the wheel well. My Barbados with C6 19x10s before mini tub and widened I was running 295s lowered in stock wheel well with hub centric spacers. I think I have tried so many different spacers and tire sizes over the years. But I like widen 1" and the 285 35 18 rears and 245 40 18s front the best and can do it without hub centric spacers. The 285s look great and same height as the 245s means no issues with the ABS having different size tire heights. The 275s sidewall height is more like the factory 235s and look like a smaller tire on the rear.
 

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Discussion Starter · #14 ·
I've been looking at tires just to see what is out there but I keep going back to the Michelin Pilot Sport 4S. Mileage and wear are not a concern because it isn't daily driven, but according to the 4S reviews, in a nutshell, it does everything very well, dry traction being its best attribute.

I've been set on 275/35 out back and 245/40 up front but I am open to a 285. I was trying to avoid fender modifications. I don't mind slight inner well work, but if that can be avoided, so be it. I did install ARP wheel studs with the Brembo upgrade so I have no issue running a spacer or adapter. I have been leaning with a hub and wheel centric spacer since the ARP studs out back are pretty long and can handle a spacer. My plan was to send the wheels off and get them widened, then blasted and powder coated or painted, then get the tires, then get a bunch of washers and put the wheels on and figure out what size spacer will be best.

So in a nutshell, minimal if any, mods to fenders, good tire on a widened stock wheel, ARP studs installed, will use a spacer if needed. With the Pedders coilovers, I wasn't planning on lowering it much if at all. Making the tires work is the priority.

I like the stance of your car. I would probably have it a tad higher, but that is me. The tires look like they fit well.
 

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They do fit well. You will have to roll or cut a tad off the fender lip with 285s. 275s will bolt right up without any modifications.
 
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Discussion Starter · #16 ·
I shipped my wheels off on Thursday. I decided to go 1.5" wider. With the ARP studs on the car, a hub and wheel centric spacer will be fine. If I have to roll the fender lips some, so be it. Still researching tires but it will be 245/40 up front and 285/35 out back.

This is gonna take a while because the lead time at Weldcraft was 3-4 weeks and then the wheels need to be blasted, curb rash fixed and then powder coated. I will just update this thread as progress happens.
 

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I shipped my wheels off on Thursday. I decided to go 1.5" wider. With the ARP studs on the car, a hub and wheel centric spacer will be fine. If I have to roll the fender lips some, so be it. Still researching tires but it will be 245/40 up front and 285/35 out back.

This is gonna take a while because the lead time at Weldcraft was 3-4 weeks and then the wheels need to be blasted, curb rash fixed and then powder coated. I will just update this thread as progress happens.
real interested in how this setup turns out. After you get it all worked out minding posting exactly what parts you used and if you had to roll fenders, etc. and feedback? I’m leaning toward this setup myself.
And of course pics of these bad boys installed. (y)
 

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Discussion Starter · #18 ·
real interested in how this setup turns out. After you get it all worked out minding posting exactly what parts you used and if you had to roll fenders, etc. and feedback? I’m leaning toward this setup myself.
And of course pics of these bad boys installed. (y)
Will do. Right now, I have ARP wheel studs on the rear, part number 100-7708. I am going to order Motorsport Tech spacers once I know exactly how thick I need them. I will take plenty of pics and provide the details, but like I said, it is gonna take some time.
 
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