All 18" gurus chime in, please.

If you use the appropriate plus 3" tire size, like he did w/ plus 5", they should be identical. The circumfrence will be equal, and should sit in the same place. The car has no idea what is wheel and what is tire, it only sees circumfrence, width and where in the well it sits. Lowering the car will make the difference in fitment vs his car on 20"s. In theory the 4.5 is the exact same on the car w/ the same 26" +/-tall tire pkg. If you decide to do spindles (Which you didnt mention) this will make a bigger variation.
If you PM Xcessive, I bet he can give you all the info you need. His are 18",no adapters, and lowered also.
 
GregInAtl said:
If you use the appropriate plus 3" tire size, like he did w/ plus 5", they should be identical. The circumfrence will be equal, and should sit in the same place. The car has no idea what is wheel and what is tire, it only sees circumfrence, width and where in the well it sits. Lowering the car will make the difference in fitment vs his car on 20"s. In theory the 4.5 is the exact same on the car w/ the same 26" +/-tall tire pkg. If you decide to do spindles (Which you didnt mention) this will make a bigger variation.
If you PM Xcessive, I bet he can give you all the info you need. His are 18",no adapters, and lowered also.
Click to expand...

Thanks for the response, I spoke w/ good 'ol xcessiv a few times. The only thing is, he uses airbags (I think) and I won't be. I think that 275/40 18s are about 26.7" in tire height... while 275/35 18s are around 25.6". In the provided link, the guy uses cargo springs in the rear vs my 1" drop. I won't be using drop spindles up front but I will be installing SCandC's package 2 which has taller upper/lower ball joints (furthering lowering front .75" with the Eibach drop) but Mark, of SCandC, told me that an 18x8.5 would fit with that set up as he has sold many with the same combo.

Hope that info helps..
 
Oh and what do you mean "plus 3 in tire size"? Do you mean as long as the combo is the stock diameter of 26"?

Thanks again!
 
The wheels I'm looking at only offer 4.5" BS :-D. Do youthink you'd have no rubbing without the airbags?

Your car is still one of the GEMS of turbo buicks!!
 
I run 315/30R18's on a 18x10 rim with 5.5" backspace. Frame needs to be notched but I like them to tuck. Tires are WIDE!!!!!!!!!!!!! Car is lowered 1.5" in the rear.
 
Would the stance look OK with this set up:

18*8.5 4" BS
18*10 4.5" BS

I thought of 4.5" BS for the 8.5 fronts but wouldn't that make the rears look like they're protruding excessively (in comparison to the front)? I'm trying to make them look as even as possible.

They won't stick out as I have the GNx flares...

thanks in advance
 
nero said:
Oh and what do you mean "plus 3 in tire size"? Do you mean as long as the combo is the stock diameter of 26"?

Thanks again!
Click to expand...

Factory wheel is 15" plus 3" = 18" which is what you want. Plus sizing refers to wheels over OEM, and then the math of keeping the 26" +/- w/ a large wheel begins...bye bye side wall, or as I call it "slide walls".
 
GregInAtl said:
Factory wheel is 15" plus 3" = 18" which is what you want. Plus sizing refers to wheels over OEM, and then the math of keeping the 26" +/- w/ a large wheel begins...bye bye side wall, or as I call it "slide walls".
Click to expand...

I think some 3.08 cogs would help in the sidewall-less department :eek: :biggrin:
 
Bottom line is I should be ok and the "eveness" would be fine with that set up in post number 8?

:-D
 
Mine are 17x8 on the front with a 4" BS. I dont know what tire you plan on running on the front with a 8.5" wide wheel, but mind you on my car the 245/45R17 is about the max width w/o the tires kissing the inner fender lips.

The rears on my car are 18x9.5" with a 5" BS and aluminum drums with a 275/40R18 tire. In the back my tires are very close to the frame and very close to the rear quarter lips. I run about 8-10psi in the rear airbags to prevent the tires from touching the fender lips.

You need to get your car up in the air with jack stands under the rear axle and do some measuring. Each car is different, so make sure your wheels will fit! I personally think a 10" with a 4.5" BS will rub on your quarter lips in the rear, but measure it and make sure! HTH
 
fuzzy math?

8UWITH6 said:
Mine are 17x8 on the front with a 4" BS. I dont know what tire you plan on running on the front with a 8.5" wide wheel, but mind you on my car the 245/45R17 is about the max width w/o the tires kissing the inner fender lips.

The rears on my car are 18x9.5" with a 5" BS and aluminum drums with a 275/40R18 tire. In the back my tires are very close to the frame and very close to the rear quarter lips. I run about 8-10psi in the rear airbags to prevent the tires from touching the fender lips.

You need to get your car up in the air with jack stands under the rear axle and do some measuring. Each car is different, so make sure your wheels will fit! I personally think a 10" with a 4.5" BS will rub on your quarter lips in the rear, but measure it and make sure! HTH
Click to expand...


Thanks for the insights... here's what I'm going with, let me know ifI'm miscalculating or missing anything;

Fronts...

245/40r18 up front over some 18x8.5 with either the 4" or 4.5" BS.
The front wheels add up to being 245mm wide and 25.7" diameter. Exact same diameter and circumference as yours, so given that (and thanks for the post) I can go with the 4.5 or 4 inch BS as long as I keep it in the same 245 width, diameter and circumference you have. As another comparative, the thread I linked, the gentleman's fronts are 26.8" diameter (stock suspension).

Rears...

285/35r18 in the rear over 18x10s with 4.5" BS (same as the guy with 20s) except my tire diameter will be 25.9" (.1" lower than stock) while the guy with 20's are 26.7" diameter and 2" larger circumference than what mine will both with 4.5" BS (20x10 4.5" BS). All cars are different, but these are stock height (diameter), wider width, but I've run a 275/60r15 before with no problems and that's a 28" tire that's also 6.6" more circumference! So, I'm hoping this will workout too! I think it will and if any frame mods are needed they'll be nominal (I hope) :biggrin: :eek: :eek: ~~

What's the backspacing on a stock T wheel? That's the wheel I had on the 275s annd knowing that backspace will 1000000% let me know if I'll need frame mods or not.
 
Give props to all that are helping(helped)!

GregInAtl said:
If you use the appropriate plus 3" tire size, like he did w/ plus 5", they should be identical. The circumfrence will be equal, and should sit in the same place. The car has no idea what is wheel and what is tire, it only sees circumfrence, width and where in the well it sits.
Click to expand...

I based my calculations on this tool : Calculators and on Greg's assertion in the above quote. :) Many thanks to all who contributed in this thread for helping out before I make the purchase... I hope to have it all done before Buick day in October! :eek: :cool:
 
nero said:
What's the backspacing on a stock T wheel? That's the wheel I had on the 275s annd knowing that backspace will 1000000% let me know if I'll need frame mods or not.
Click to expand...

Found it here: Tires and Wheels in case anyone doesn't know or searches later. Stock T wheels had 3.75" BS while the GN had 4" BS both on 7" wide wheels.

Again, that makes my rears 2" smaller in diameter and about 6.6" smaller in circumference but with 10mm wider tires than the 275/60r15s... and .75" more backspace.

Thoughts?
 
Do you plan to lower the car or do any brake upgrades?? I would just think about the future a little as well if you are planning any changes. Larger disc brake mods will add around 3/8" out so keep that in mind. Also, is it necessary to have a 8.5" front rim with those tires? I dont believe it is but I could be wrong. I'm running 8" wide in the front so i can have plenty of turning radius. Good luck! Post a few pics! ------Jeremy
 
Thanks Jeremy. The fronts are going to work, Mark (genius and owner of scandc.com) said that he has many people running the set up that I'll be running; scandc package 2, 18x8.5s, 245/40, eibach lowering springs. So I'll be good up front. The rears will be stock drums for a while. When I finally get around to brakes, I'll have more coinage banked to do what's necessary w/ the frame. For now, I'm on SSBC's dual piston calipers and I'm quite happy with that setup! The Eibach springs lower the car only .8" in the rear... probably the same or higher maybe than my current soggy stockers complete with 180+K miles and 20+ years of age

:-D
 
Yeah I actually am running scandc's AFX package up front with Moog 5658 springs and C5 brakes up front. They have been waiting on Delphi to come up with the parts for 4 months now. I ordered 18x8's with a 4 3/4" offset for the fronts and bought the 245/40's for the front as well. The rears have BellTech 1.5" springs and drums on it now but I will be putting the F-Body rear discs on once the fronts are complete. I am running 18x10s with 5.5" backsapce and 315/30's for tires. I'm curious to see how it turns out! I'll keep trying to post up new info as well! ----Jeremy
 
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