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WEEEEEEE
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Discussion Starter #1 (Edited)
I have Pedders Xtreme coilovers/springs and have rolled the fenders.
My current rear tire is a 255/45/18 on an OEM 18X8 rim.

I'm looking to put on a 275/35/18 on an 18X9 rim.
The way the car sits now I have what appears to be a ton of room between the tire and suspension. Measured it and got about 1 1/2" (38mm).
On the outside, I have just over 1/2" (12.7mm) from the tire to the rolled fender.

Am I correct that I would need to buy a rim with a 55mm offset to keep the tire well clear of the suspension and fenders?
 

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Don't just look for suspension clearance, but also the inner fender well. I believe that is what rubs first. I would think you will be safe with a 275 with the stock offset since you rolled the fenders. Might have to bang a place or two on the inner fender wells.
 

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the 1010tire calculator is the one I've always used. Looks right.
Take a ruler with the stock wheel mounted and measure the difference. As maradamx3 said, in your case the inside is what you need to pay attention to.

Compared to your 9" wheel with 55mm offset, my 9.5" wheels with 45mm offset have 4mm more inner clearance and extend 16mm more (.63"). I have my fender lips cut to clear the tires with as much positive camber i can get out of eccentric control arm bushings. While close on the inside IIRC you should be okay. Verify with measurements before dropping the car off the jack.
 

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TACHNUP
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The rear tire will rub the plastic shields and inner wall of the fender well before it contacts any suspension bits.
 

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WEEEEEEE
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Discussion Starter #7
I think I found the rims I want. The company has blanks, meaning they can set the hub bore and offset to whatever I want.
The fronts will be 18x8.5 and the rears will be 18x9.5.
My fenders are rolled and I have Pedders coil overs to make adjustments.

Four questions for you guys:

1. GTO hub bore is 69.5 correct?
2. For offset, what do I need in the front (will +48 still work)?
3. For the rear (+55)?
4. Front tire size?

Rear tire size I am thinking 275/38/18

Thanks!

*They couldn't tell me anything about the GTO in the advertisement picture so I have no idea what they were running to get them to fit.
 

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I think I found the rims I want. The company has blanks, meaning they can set the hub bore and offset to whatever I want.
The fronts will be 18x8.5 and the rears will be 18x9.5.
My fenders are rolled and I have Pedders coil overs to make adjustments.

Four questions for you guys:

1. GTO hub bore is 69.5 correct?
2. For offset, what do I need in the front (will +48 still work)?
3. For the rear (+55)?
4. Front tire size?

Rear tire size I am thinking 275/38/18

Thanks!

*They couldn't tell me anything about the GTO in the advertisement picture so I have no idea what they were running to get them to fit.
Those are one piece cast wheels so there will be limitations to what they can machine to.

1. Their wheels most likely have a bigger bore than the car has, so you will likely need hubrings down to the 69.5, just like I’m running.

2. I am pretty sure the 48 front will rub the strut, especially depending upon the tire size. My 45 offset is just clearing. Thought I would have to run a small 3mm spacer but I cleared.

3. If your fenders are rolled you should be good with the same 45 offset I am running, assuming how much they are rolled and of course your suspension. 50 would be safer but I would be willing to bet they can’t machine it that high.

4. A 245 width would be the safest. A 245/40-18 would be a matching front to your 275/35-18 rear. Those would also be stock diameter so your speedo should not be effected.


Edit: if you like the height of your 255/45-18 on the rear now, the 275/40-18 that I am running is basically the same height.
 

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WEEEEEEE
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Discussion Starter #9
Awesome. Thanks for the input.
Based on what I've been able to research I'm going to call them and see if they can do this:
Front. 18x8.5 +45 245/40/18
Rear. 18x9.5 +45 minimum up to +50 depending on what they can do. 275/35/18
 

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Awesome. Thanks for the input.
Based on what I've been able to research I'm going to call them and see if they can do this:
Front. 18x8.5 +45 245/40/18
Rear. 18x9.5 +45 minimum up to +50 depending on what they can do. 275/35/18
If you see my last thread on the wheels i just put on, it will give you and idea of what you will need. I have
18x8 40mm offset 245/40/18
18x9 45mm offset 275/35/18

It clears everything and doesnt rub the inner fender on the front. The rear i rolled just a little for insurance.
 

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WEEEEEEE
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Discussion Starter #12 (Edited)
I pulled the trigger. I hope I don't have too many fitment issues.

Front: 18x8.5 +40 245/40/18 Michelin Pilot Sport 4S
Rear: 18x9.5 +45 275/35/18 Michelin Pilot Sport 4S

I won't have them for a couple of weeks but I'll post pics and any issues then.
 

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I run the same width and offset wheels only with 19's but the OA diameter is the same.
The fronts will be close to the fender lips depending on camber but they do clear.
I did cut the rear fenders to about the same size as yours are rolled.
 

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The fronts will come close to the lip. Overall, you should be able to make that setup work.
 

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Pontiac Fanboy
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Those are some really rolled rear fenders. I'd be surprised if they rubbed.
 

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WEEEEEEE
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Discussion Starter #17 (Edited)
New question. If I wanted to replace my REAR wheel studs before I mount he new rims/tires, what is the correct part number for OEM length, ARP studs?

This is what I am finding:
ARP-100-7708
Wheel Stud Style: Press-in
Wheel Stud Thread Size:12mm x 1.50 RH
Underhead Length (in):2.500 in. (I thought this was quite a bit longer than OEM studs)
Knurl Diameter (in.):0.509 in.
Knurl Length (in):0.315 in
 

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TACHNUP
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New question. If I wanted to replace my REAR wheel studs before I mount he new rims/tires, what is the correct part number for OEM length, ARP studs?

This is what I am finding:
ARP-100-7708
Use those studs and cut off the excess length if you're using closed lugnuts.
 
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