Backspacing on an 18" wheel?

[charlief1]

Well I've gotten a set of 18's for the car so the plans have changed again to some degree. Did a lot of searching on backspacing and never really got a good answer for the use of these wheels. The front tires and rims measure 9.75" wide and measuring from the inside, the backspacing with tire mounted is 5.625" on a 245/40/18. The backs are 11.5" wide mounted with a 6.5" backspacing with tire mounted and a 285/35/18 on them. Since my car has already been converted to LS1 rear discs and will have the Blazer knuckles and brakes on the front I'm thinking a spacer will be needed. On the back I was thinking a .75" thick one and maybe a .5" on the front. I'm not a big fan of spacers myself but if they're installed properly and not the cheap cast ones they're ok in most cases.

I'm also considering doing a slight notch on the rear and maybe mini tubs to help with clearance on the backs. Still need a little rust repair on the fender wells so this would solve some of the issues that still need to be worked out. Has anyone put a set of 18" rims with these kinds of measurements on their can and how did it work out?

 

[nonosv6]

I think the fronts will definitely need at least a .75 spacer but with a frame notch the backs should fit good. You'll probaly have to trim or roll the quarter lip but you might get away with not having to.
Right now I have 18x10 with a 5" backspace in the rear of my car with a notched frame. Not as deep into the frame as you can go with it but I have at least 2" or more from the tire to the rail. I'm running a 305/40-18 right now which is about 28" tall 12.2" wide. Actually planning on some wider wheels next year and was going to go with 9-9.5 up front and 11.5 in the rear with a similar backspace. Fronts I'm still not sure on back spacing as of yet.


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[nonosv6]

Oh couple more thoughts. The ls1 brakes in the rear push the wheel out alil more than the drums do. And I'm not sure if the blazer stuff will or not in the front. I just changed over from the ls1 brakes up front to blazer spindles with c6 brakes with hopes that it will bring the wheel back in alil and for the bigger brakes obviously. When I ordered my wheels I forgot to take into account that the wheel would sit slightly further out and at the height I'm at it rubbed the upper inside of the fender well. Sorry if I'm all over the place here. I am going the bite the bullet and buy a Percy's wheel fitment tool to make sure all will clear before I order my next set of wheels though. Lol.


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[charlief1]

The nice thing is the rears are out about .2" further because of the disc brake conversion so that helps some. With a .75" spacer on the back that would give me almost 1" so I'd be a 5.55" rather than the 6.5" I'm at now and a 1" spacer would knock it down to 5.3". The biggest question is the fronts and how much I need to space them out.

 

[phil_jordan]

Hey Charlie, I'm in the same predicament as you, except my rims aren't nearly as wide as yours, as they are 8.5" all around. Good luck!

 

[charlief1]

I'm actually thinking about using an A body rear I've got laying around which will move the backspacing needed further out. I'll have to change the LCA mount on the axle to a G body style but it would make things a little easier in the end.

 

[Hot Air]

Charlie,
Check with Scot W. He has CCW 18" wheels.
Conrad

 

[dsapper]

I think they will fit depending on how low your going and tire choice. I have the 4.75" BS on a 10" wide 18" wheel and there is tons of room. Almost 2" room before it would touch the frame and with the rear fenders rolled almost an inch clearance. Because of the setup with the brakes you may have to play with spacers but I'd bet money they would fit without notching the frame.

I put a 295 up there on a wheel jig and it would work, no frame notch. Considering buying new hoops to make it happen.

For the front I put my 10" wheel up there with 4.75 and guessed I'd have to go closer to 5.75 to make it work since it stuck out a hair, you might get lucky there

 

[charlief1]

Thanks Dave, you may have helped more than you know.

 

[dsapper]

One more thing. When I put the 10" wheel on the front it hit the swaybar, I'm looking into the ridetech muscle bar. Seems that it will have room with that or something similar.

 

[charlief1]

If you've read my build thread it's not a conventional build like yours isn't Dave. I may end up having to use a front bar that's a little different but until I get it all together I won't k=now for sure.

 

[dsapper]

I saw it awhile ago, I think the last time I saw it you still had it off the frame. Do you have the link, I searched but couldn't find it.

Hind sight being 20/20 I wish I would have gone a bigger wheel/tire combo from the beginning. I had read to many threads stating nothing bigger could fit, frame notches were needed etc etc. Now that the car is assembled (it was off the frame, I couldn't measure it when I ordered the wheels) and I've actually measured... I would love to go with 295's on all 4 corners. I probably will once I need a new set of tires.

 

[charlief1]

Here you go Dave. Some of the frame mods aren't shown so they don't get copied but if you are interested I can show you in a pm. The frame mods are towards the end so you might look about 1/2-3/4 through.
http://www.turbobuick.com/forums/threads/finally-got-some-time.322115/

 

[MikeS]

I know this is a long shot on such an old thread, but did anyone get 10" wide wheels on the front or something in the area of 285 front and 295-305 wide rears? Have pics? Backspacing/spacers, etc...? I'm looking at xxr521 wheels with GNX flares for the GNX look, but slightly more muscular. I'd like the tires to be almost even with the fender flares, if possible. Like this picture:

 

[robert duncan]

Well, if you want fat tires, or as much as you can fit in your wheel well, if you go bigger than 4.75 backspace, you're going to have to use a spacer to avoid tire/frame contact. These are 305 30 20s and because these 10" rims have a 5" backspace, I had to use a .4" spacer.


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[1986 Buick GX1]

I know this is a long shot on such an old thread, but did anyone get 10" wide wheels on the front or something in the area of 285 front and 295-305 wide rears? Have pics? Backspacing/spacers, etc...? I'm looking at xxr521 wheels with GNX flares for the GNX look, but slightly more muscular. I'd like the tires to be almost even with the fender flares, if possible. Like this picture:

If you want the wheels flush with the flares you’ll have to cut the fenders out like the GNX and trim the flairs.
The aftermarket flares are just for looks and don’t provide additional space for the tire.

Here’s how the GNX fenders were cut. You may have to go more extreme if you want to lower your car.

Your setup will be different than most so you’ll have to make the fender mods and do some measuring.

I am doing the same with no flares. 285/35-18’s on 10” wheels front, 295/35-18’s on 10.5” wheels rear.

 

[grass doctor]

love to see posts from" the great one "Charlief1

 

[MikeS]

Thanks, that's a big help.