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Ok, some of these were getting me confused and thus got me thinking.

Intended questions to be answered: What is the best offset for a X rim at Y width for the front/rear for no fender rolling?

Now please don’t say Howie answered this and it’s in the FAQ because he didn’t say specifically what his 18x9 offset was. It looks like it was 48mm but I don’t know (Not flaming Howie at all, you busted your ass for us and I really appreciate it my friend)

I have seen people saying from 30s to 50s and I can’t believe we have that much play back there given our rear tires proximity to the outer fender, unless we have a butt load of inner clearance between current stock rim and strut tower.

The only way I can see this happening with a 18x9 rim in back is if it has a greater offset than stock, thus putting the majority gain of rim width (and thus tire width) inside the rear wheel well.

OK please help me to see if my math is right. Please if I have messed this up help fix me :)

Stock rims are 17x8 with +48mm offset

Given that going from and 17x8 to a 18x8 rim should have nothing to do with offset, ideal offset for a 18x8 would still be +48mm for a front rim, which Howie and many others have confirmed.

Now for the rear tire to go from 8 to 9 in width we can generally do one of three things

1. Split the 1 inch gain down the middle. We do this buy keeping offset the same at +48mm. This splits the width gain and moves the edge of the tire 0.5 inches out towards both the strut and the fender edge. I don’t think this is ideal because on my Goat I don’t think I have 0.5 inches to go out to the fender well. Under load it looks like it might possibly rub.

2. Move most of the inch gain outward towards the fender. We do this by reducing offset. If we reduce offset to +35mm we move the inside of the tire 0.0 in closer to the strut and 1.0 in closer to the fender edge. This IMHO is really far worse than #1 above as I don’t see how you won’t rub badly.

3. Move most of the inch gain inward towards the strut tower. We do this by increasing offset. If we increase offset to +61mm we move the inside of the tire 1.0 in closer to the strut tower and 0.0 in closer to the fender edge. This seems the best chance for success. But the question is, is there enough clearance between the new inside tire edge and strut?

My gut says it will be between +48 and +61mm

Now why should anyone care?

Well, since there appears to be very limited fitting information for a good 18x8 – 18x9 set up beyond our sponsors such as Howie, and places like TireRack only give us choices for the 18x8 option, we need to be sneaky :sneaky: and find our own. And given that a ton of BMW/Audi rims might fall into this category I think we might all benefit.

I for one would love to finally answer definitively the GTG Rim Size vs. Width vs. Offset chart and get it into our FAQs.

So what I am asking if we can all fill out the following info, to which I will place in a chart to help out those of us looking to get new rims and end our range of offset issues once and for all :patriot:

Front Rim Diameter –
Front Rim Width –
Offset –
Tiresize –
Rubs –
Fenders Rolled –

Rear Rim Diameter –
Rear Rim Width –
Offset –
Tiresize –
Rubs –
Fenders Rolled –

So the Stock layout (Mine in this case would be)

Front Rim Diameter – 17
Front Rim Width – 8
Offset – +48
Tiresize – 245/45/17
Tire Brand - BFG KDWS
Rubs – No
Fenders Rolled – No

Rear Rim Diameter – 17
Rear Rim Width – 8
Offset – +48
Tiresize – 245/45/17
Tire Brand - BFG KDWS
Rubs – No
Fenders Rolled – No

Thanks for all the help and thanks for having a great board to talk about our Goats on.
 

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Oh my f*ck!
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6,464 Posts
Rim Brand and Name - Pontiac Stock
Front Rim Diameter – 17
Front Rim Width – 8
Offset – +48
Tiresize – 245/45-17
Tire Brand - BF Goodrich Comp T/A KDWS
Rubs – No
Fenders Rolled – No

Rim Brand and Name - Pontiac Stock
Rear Rim Diameter – 17
Rear Rim Width – 8
Offset – +48
Tiresize – 245/45-17
Tire Brand - BF Goodrich Comp T/A KDWS
Rubs – No
Fenders Rolled – No



Here's a blank set up so that the headings stay bold when you put in the information. In this way it'll be easier to read. I also added the field for the rim manufacturer and name. Also, people should put up pictures. I put the stock configuration above so it's easy to read. I think this is a GREAT idea. Hopefully we actually learn something other than that everyone has rolled fenders :)

Rim Brand and Name -
Front Rim Diameter
Front Rim Width
Offset
Tiresize
Tire Brand -
Rubs
Fenders Rolled

Rim Brand and Name -
Rear Rim Diameter
Rear Rim Width
Offset
Tiresize
Tire Brand -
Rubs
Fenders Rolled
 

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Ok i want to put 19X10-11 on the back and 19X9 in the front, what off set do i need and im assuming i will need to roll the fenders... Does anyone know any brands that make the rims im seeking? I have a Black on Yellow 04 GTO BTW
 

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Ok i want to put 19X10-11 on the back and 19X9 in the front, what off set do i need and im assuming i will need to roll the fenders... Does anyone know any brands that make the rims im seeking? I have a Black on Yellow 04 GTO BTW
Going to have to go with a custom setup most likely. 19x11 will not fit with rolled fenders only. 19x9 in front will be a tighter fit as well.

Most people run 19x8.5 front and 19x9.5 rear with wheels bought off the shelf.

Ideal offset for the rear is 54-56mm.
 

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2morow I should be receiving 17-8 fronts and 18-9 rears oz racing ultraleggaras both with 40mm offsets. 245-45-17 bfg kdw2 and 295-35-18 bfg drag radial 2. Im pedders 20 mm lowered and I am planning on rolling the quarters!!! I just hope that's enough, I'm alittle worried
 

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2morow I should be receiving 17-8 fronts and 18-9 rears oz racing ultraleggaras both with 40mm offsets. 245-45-17 bfg kdw2 and 295-35-18 bfg drag radial 2. Im pedders 20 mm lowered and I am planning on rolling the quarters!!! I just hope that's enough, I'm alittle worried
That probably won't work man. Cannot roll where the bumper meets the fender.
 

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Owns a slow GTO
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An 18x9" rear wheel with a 40mm offset will stick out 1mm more than my 18x9.5" rear wheels with a 47mm offset. I have my rear quarter panel lips rolled quite heavily, and my suspension is slammed quite low with the Pedders Xa's. My driver-side rear 275/35/18 Dunlop Star Spec will rub if I have a passenger in the rear driver-side seat when I go over large bumps, mainly because I need to raise the ride height a tiny bit on that side. Star Specs run wide as well.

What I am trying to say is that you will most likely have a lot of difficulty fitting a 295 width tire in back, especially with a lowered suspension. I also question why you are putting a 295 on a 9" wide wheel. A 295 is more suited for a 10-11" wheel. The sidewall will probably bulge out a decent amount. There are very few GTO's out there able to fit 295's without a perfect offset 10" wheel, cut fender lips, and a perfectly centered rear cradle. Most people running 295's or wider also have a mini-tub kit as well. The widest tire most can safely run without significant modification is a 285.
 

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DUH!!! My bad. They're 275-35-18 bfg drags. Don't know why I said 295!?!? So u guys think I'll be alright with rolling or should I just order bags 2morow?
 

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They really are 40mm offset 18x9. I was really looking forward to 2morow but now I'm kinda worried.
 

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Holdiac Performance
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ballpark calculation

With the old tires and wheels mounted place some thin cardstock type paper flat against the sidewall and measure the gap between the paper and the lip. Since it's lowered you will need to measure from both the narrower tread section as well as the wider sidewall section. Rolling the fenders will add another .25" clearance at best.

Determine how much clearance the new setup requires. Go to tirerack.com or the tire mfg's websites and look up both tread and cross section widths of the new tires vs what's on it now. Take half the difference and add 8mm since the stock wheels offset is 48mm.

After you roll the fenders and mount the new rears get 2 large friends to sit in the trunk to determine if you need spring spacer pads.
 

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Growing up is an option
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20mm drop all around, full poly bushes

Fronts
Rim Brand and Name - Pontiac Stock
Front Rim Diameter – 17
Front Rim Width – 8
Offset – +48
Tiresize – 245/45-17
Tire Brand - Firestone Firehawk Wide Ovals
Rubs – No with -1º camber
Fenders Rolled – No

Rears
Rim Brand and Name - Pontiac Stock
Rear Rim Diameter – 17
Rear Rim Width – 9" (Weldcraft)
Offset – +60.5 (My effective offset is like +55.5 due to 5mm spacers)
Tiresize – 285/40-17
Tire Brand - Firestone Firehawk Wide Ovals
Rubs – Absolutely none with -1.4º camber
Fenders Rolled – Mildly


Just to clarify when a wheel is widened the outside stays in the original position and half of the increased width is added to the offset (i.e. 1" widening increases the offset by 1/2", roughly 12.5mm). Altho the wheel goes in towards the center of the car 1" offset is calculated by measuring from the center of the wheel to the inside face of the wheel. When you make a wheel 1" wider you are moving the center of the wheel over half of that and thus increasing the offset 1/2" (12.5mm).
 

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Wol Gemut
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With 275s on a +40 offset wheel, tire will be past fender lip.
 

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Owns a slow GTO
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^^^^ I disagree slightly. A 275/35/18 on an 18x9 with a 40mm offset will only stick out 1mm more than my 275/35/18's that I have on an 18x9.5" with a 47mm offset. The width of the wheel also factors into offset - an 18x8" wheel with a 40mm offset will obviously sit much differently than an 18x9" wheel with a 40mm offset.

If your quarter panel lips are cut/rolled/grinded/whatever, and you have the rear cradle aligned, depending on the brand of 275, they might fit ok even with the drop springs.

Here is a great way to visualize wheel offsets:

http://1010tires.com/WheelOffsetCalculator.asp

And here, you can see my 275/35/18 Star Specs actually tucking in somewhat into the rolled quarter panels, and Star Specs are known to run wide.



Edit: I also run a lot of negative camber on my car, so that helps with clearance as well but will also wear the inner edges of the tires more quickly. Either way, it's going to be close as to whether they will fit without rubbing. Good luck and let us know how it works out.
 

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Growing up is an option
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^^^^ I disagree slightly. A 275/35/18 on an 18x9 with a 40mm offset will only stick out 1mm more than my 275/35/18's that I have on an 18x9.5" with a 47mm offset. The width of the wheel also factors into offset - an 18x8" wheel with a 40mm offset will obviously sit much differently than an 18x9" wheel with a 40mm offset.

If your quarter panel lips are cut/rolled/grinded/whatever, and you have the rear cradle aligned, depending on the brand of 275, they might fit ok even with the drop springs.

Here is a great way to visualize wheel offsets:

http://1010tires.com/WheelOffsetCalculator.asp

And here, you can see my 275/35/18 Star Specs actually tucking in somewhat in the rear, and Star Specs are known to run wide.
He may still have a problem. The fender lips for sure are going to have to come off or be rolled flat. Your wider wheel pulls the side bulge in more. Also wheels that seem to fit going down the road can still rub under hard cornering due to suspension flex and tire roll.
 

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950 psi
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The wheel itself will stick out 21mm or about 7/8" more than stock. The tire is just over 1" wider than stock. If you split the difference on the tire width to about 1/2" on each side, you can figure your newly procured tire/wheel combo will stick out just under 1.5" more than stock. I can't see this working lowered.
 

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950 psi
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correction! I was not considering jacking the camber out of spec to tilt the tire in
 

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Thanks guys. I'll let u guys know 2morow night how it works out. Either way I'll get them to fit. Gonna order the pedders rear camber bushings 2morow a.m. anyway. Either way im gonna make it work cause my 18x8 with 235-40's are a frigin joke!!! Psu goat were you at ECS a month or so ago? I think I recognize ur car cause I was checking out ur maverick man stuff.........I likey!!!!
 

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Owns a slow GTO
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He may still have a problem. The fender lips for sure are going to have to come off or be rolled flat. Your wider wheel pulls the side bulge in more. Also wheels that seem to fit going down the road can still rub under hard cornering due to suspension flex and tire roll.
Very true, tire bulge could be an issue for him.

Thanks guys. I'll let u guys know 2morow night how it works out. Either way I'll get them to fit. Gonna order the pedders rear camber bushings 2morow a.m. anyway. Either way im gonna make it work cause my 18x8 with 235-40's are a frigin joke!!! Psu goat were you at ECS a month or so ago? I think I recognize ur car cause I was checking out ur maverick man stuff.........I likey!!!!
Sorry, my car has never been at ECS. I must have a doppleganger. lol.
 

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right foot maniac
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shave 3mm off of the rears,that'll help you out some
 

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Rim Brand and Name - BBS Challenge
Front Rim Diameter – 19"
Front Rim Width – 8.5"
Offset – 35
Tiresize – 245/35/19
Tire Brand - Continental CS3
Rubs – no
Fenders Rolled – yes

Rim Brand and Name - BBS Challenge
Rear Rim Diameter – 19"
Rear Rim Width – 9.5"
Offset – originally 40, then machined to 43
Tiresize – 275/30/19
Tire Brand - Continental CS3
Rubs – no
Fenders Rolled – yes
 
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