I have read just about every thread that i could find on this site and think i have found the wheel tire size that will be ideal for my resto-mod. That being said I would like to double check with everyone here before I spend 4k on something that will not work. I have a 1972 Buick GS Stage 1 hardtop. I have bought a fender lip roller to roll the fender lip and create a little more room. I have 4-wheel disk breaks, and Baer technical support told me that their kit does not change the backspace at all. I currently am running stock suspension with plans of converting to coil-over in the future, with the exception of a 1 3/4" front swaybar and a 1" rear swaybar. The wheel tire combination that I am looking into is: Rear Wheel: 18x10" rims with 5 5/8" backspace Tire: 305/40R18 Nitto NT 555R II extreme Front Wheel: 18x8" rims with 4 3/4" backspace Tire: 245/45/R18 Nitto NT 555R II extreme I do know that the front tire is ~1" shorter in overall diameter than the rear. I more or less want to verify that these will fit. Also, if anyone is currently running this combination please post some picture. Also, Does anyone know a website that makes custom aftermarket rims with custom backspacing? Cheapest I have been able to find are $700 a rim from wheelpros.com One more thing, I also have 5 15" stock ralley wheels for sale they are in pretty nice condition with minor imperfections asking $100 per wheel plus shipping. If anyone is interested I can send pictures. Thank you for any help you can provide. -Christopher
Running a 10" wide rim is right at the limit for the stock wheel well. That back spacing is correct and gives you the best chance of fitting without modification. The only problem you might have is some side to side variation, having more room on one side then the other, pretty common on our cars. Being you are willing to roll the fender lip, I'd say you should be fine, but no one can guarantee anything. The correct back spacing for an 8" wide wheel is 4 1/2". You say your wheels are 4 3/4" so the wheel clearance at the inside of the tire is 1/4" less. You should be OK with a 245 section width tire I would think, but I'd feel better about 4 1/2" back spacing. Phil Sedlon is running P325/60R-15 tires on a 10" wide rim with 5 5/8" B.S. The rim height does not change back spacing requirements. There is more info in this thread including pictures on page 2. http://www.v8buick.com/showthread.php?15046-My-new-new-15x10-s-are-here!!!
So thoughts on 255/40/18 on the front on 18x8 with 4.5" backspacing and stock suspension? Will they fit or rub? Also, how about a 295/35/18 rear on a 18x9 with 5.5" backspace to give a smidge more room at the outside lip? I run 245/60/15 front and 295/50/15 rear now. More worried about the fronts than then rears.
Right now, you run a P245/60R-15 on the front. You want to run a P255/40R-18. The 255 tire is 10mm wider. That is less than 1/2". Do you have 1/4" on either side of the 245 tire you are running now? Yes? Than why are you worried?:grin: I'd be worried more about the rear.
I had to go with 245/45/18 in the front. Without a wheel well molding the 255/45 may have worked but with it was just too tight with it. The 245/45 is still tight but no issues. The back could have used way more tire but I am happy with the 285/40/18. 295/30 would be fine but I did not want that small side profile. My old setup with 15's. I gained a little ground clearance with the 18's so my headers are thankful. LOL
You should be fine on the rear. I run a 325 tire on the back, so yours being 20mm narrower will give you the clearance you need.....most likely without having to roll the fender lip. I can't speak for the front. Good luck.
