# 18x9 275/35r18 Offset?



## QuikslvrGoat (Apr 3, 2010)

I'm going to be buying wheels for my 05 GTO in the next couple of days and after searching through a couple pages of threads i haven't found an answer as to what is the best offset to get on an 18x9 rear wheel. I want to run a 275/35r18 tire most likely the Nitto NT05, and read it can be done without rolling the fenders but haven't found a clear answer on what offset to use. the front wheels will be stock offset 18x 8's so I'm not worried about that but i would like to stick that extra inch of rubber in the rear without bending the panels.


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## Discount Tire (May 9, 2008)

QuikslvrGoat said:


> I'm going to be buying wheels for my 05 GTO in the next couple of days and after searching through a couple pages of threads i haven't found an answer as to what is the best offset to get on an 18x9 rear wheel. I want to run a 275/35r18 tire most likely the Nitto NT05, and read it can be done without rolling the fenders but haven't found a clear answer on what offset to use. the front wheels will be stock offset 18x 8's so I'm not worried about that but i would like to stick that extra inch of rubber in the rear without bending the panels.



My guide recommends running a 55-65mm offset but this is not easy to find. Most aftermarket wheels in 18x9 for your vehicle will come in 40 -45mm offset. Wheels in this range will require fender modifications. 

Let us know if we can help you more. Welcome to the forum! :cheers


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## danfigg (Sep 27, 2009)

*re wheel back space*

This also confuses me but I dont think 55-65 inches of back space is enough. The two important measurements are hub mounting surface and inner quarter. The GTO axle width puts the hub mounting surface just inside of the outer edge of the rear quarter which requires almost 7 inches of backspace. DONT forget about OFFSET. The mounting surface for our rim is forward of the centerline of the rim which is know as positive offset like a front wheel drive car. If this measurment is not correct then the edge of the rim will be either inside of the outer quarter or past the quarter and that is why some people get rubbing when the car squats down. Backspace is the measurement from the mounting surface to the back side of the rim and what ever is the closest thing the inner sidewall of the tire can rub against. As mentioned above if the measurement is incorrect you could have a tire that rubs the inner quarter or stick out past the outer quarter and the tire will rub. I think with the stock 17 rim and tire there is something like 2 inches of inner quarter clearance. SO if they make a rim 17 X 9 with a little more positive offset it will bring the outer edge of the rim inside the outer edge of the quarter and bring the inner edge of the rim closer the the inner quarter and everything should tuck in nicely. Unless of course everything is said is wrong but I think im on the right track willy: please correct me if that is the case.---------Danfigg


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## svede1212 (Nov 1, 2005)

This is getting way too confusing. It *IS* about offset. Offset defines where the mounting surface is compared to the midway point of the wheel. As the width of the wheel widens the distance from the center of the width of the wheel to the mounting surface (offset) needs to get larger too. An inch wider wheel (25.4mm) needs an offset increase of about 12.5mm (half of the total increase) to even the additional width to the inside and outside. A stock wheel has an offset of 48mm, a 9" rim should have about 60mm (not inches) of offset. Period. If it does it MAY fit. The factor not considered is that no two of these cars are exactly the same so if someone says "Mine fits" it doesn't always mean that it will fit on yours. Go out and measure from the outside of the tire to the fender lip on each side. You'll probably find that the 2 sides are different. The amount the rear cradle is off centered varies. It may require a mild fender roll/grinding or a BFH to the inner fender to gain a little more room but if you can find one with ~60mm you should be good to go without jacking your car up in the air like a 4x4.


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## 740tank (Mar 23, 2009)

im getting some rims in hopefully tue. they are 9in. in the rear I got them at coast 2 coast customs tell them Jeremy Little sent you and talk to Danny


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## GM4life (Mar 18, 2007)

https://www.rsracing.com/tech-wheel.html


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## svede1212 (Nov 1, 2005)

740tank said:


> im getting some rims in hopefully tue. they are 9in. in the rear I got them at coast 2 coast customs tell them Jeremy Little sent you and talk to Danny


I'd be curious to see that you get as almost every wider wheel I've seen doesn't have enough offset and either needs the lip rolled/ground or the car jacked up (with wide tires). Try to find out what offset you have


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## MorpheusRS (Mar 5, 2009)

i am running 60 offset with 7mm spacers with absolutely no issues and no fender rolling/rubbing.. 9.5" rim with 275/35/18 general exclaim uhp's. (had no issues with stock suspension, and no issues with pedders drag springs.


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## 6QTS11OZ (Mar 27, 2005)

MorpheusRS said:


> i am running 60 offset with 7mm spacers with absolutely no issues and no fender rolling/rubbing.. 9.5" rim with 275/35/18 general exclaim uhp's. (had no issues with stock suspension, and no issues with pedders drag springs.


That puts you at 53mm for a 9.5" wheel which is perfect. I've been telling folks that for a 9.5" wheel an offset between 52mm and 56mm will more than likely prevent you from having to do too much modifying if any at all depending on the section width of the tire you choose. When I mount my '93 Vette wheels (9.5" wide) with a 56mm on my goat the driver side tire barely rubs the inside of the wheel well with 275/40/17 MT E/T Streets drag radials. I never noticed it rubbing until I remove the wheels so I'm assuming it rubbed under hard launches and not normal driving. I think a 54mm offset will be the best, if you can find it, no matter if you run a 275/30, 275/35 or 275/40 tire regardless of the make of the tire.


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## Bluestreak018 (Jul 24, 2009)

Im kind of in a similar situation. Im looking at a set of tsw's that are 18X9 in the back with a 35mm off set and some nitto nt05's that are 265/35...im not quite sure if they will work either.The tempting issue im having is the guy will give them to me for $500...dont mean to snake your thread but seeming I have a similar question i thought i may ask for some advice.


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## 6QTS11OZ (Mar 27, 2005)

Bluestreak018 said:


> Im kind of in a similar situation. Im looking at a set of tsw's that are 18X9 in the back with a 35mm off set and some nitto nt05's that are 265/35...im not quite sure if they will work either.The tempting issue im having is the guy will give them to me for $500...dont mean to snake your thread but seeming I have a similar question i thought i may ask for some advice.


You need to get a set with a 45mm offset or you will have to shave the crap out of your fender.


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## svede1212 (Nov 1, 2005)

6QTS11OZ said:


> You need to get a set with a 45mm offset or you will have to shave the crap out of your fender.


yup, tho 45mm would be iffy and take a lot of grinding/rolling. 55mm would be much better


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## 6QTS11OZ (Mar 27, 2005)

svede1212 said:


> yup, tho 45mm would be iffy and take a lot of grinding/rolling. 55mm would be much better


True that. A 55mm would certainly be the way to go. Sadly though the TSW's biggest offset is 45mm. I have 9.5" TSW Thruxtons and I took them to a wheel shop and had them shave another 3mm (that was the safest amount they could remove) off the hub surface. I had already trimmed the fenders down to about a 1/4" before that and know with 275/30/19 BFG KDW2s, I have absolutely no rubbing. I wish they would have came in a 55mm so I didn't have to cut on the fender at all.


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## danfigg (Sep 27, 2009)

*re*

Just for FYI when if you shave the hub mounting surface on the rim you are changing the backspace aswell and if you shave to much, the tire may rub on the inner quarter of what ever is closest to the inside of the tire. As a rule of thumb when changing rims from 17 to 18 inch just go by the original size of the 17 inch rim and tire and calculate the height and width of a simular size 18 inch rim and tire. I have a 77 chevy Monza (Vega cousin) that originally had 13 inch tires and rims on it and know I have 16 inch GTA trans am wheels on it. I had the biggest 13 inch tire which were like a 195 60 13 and compared it to a 15 inch tire 195 60 15 and saw they were simular in height until I was able to match up a front and rear combo. Then next thing you know Im running 245 50 16 on it using the 89 GTA Trans am rims (using spacers of course) but the point is to measure every thing first getting the rim and tire as close to the inner quarter with out rubbing. Then figure out the outer quarter lip measurement. If the rim sticks out slightly then the rear will need some lift. If the rim tucks in then your good to go. Some people like the lowered look for handling and other are looking towards the Drag race aspect so we have to different reasons for wanting bigger tires and rims figure out what your purpose is. I like drag racing so I am using a set of 95 S-10 blazer rims with a 26X8 inch slick. Dont know the offset but its is positive offset im guessing at least 50mm and the back space is 6 3/4s inches. That is this year project and if I have rubbing on the outer lip of the quarter I have a set of X3 BMW springs to lift the back, again for DRAG RACE PURPOSES. Springs are easy to change.-----Danfigg


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