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The 245-40-18 will be a little rubbery in turns on a narrow 8 inch. That's the absolute minimum wheel width they suggest for that tire. A 9.5" wide wheel, at their maximum wheel width, really sharpens the steering response in turns a lot. On a skinny wheel, the rubber tire tread/sidewall/wheel square goes parallelogram in a turn, and the tread moves that extra 1.5" to the left, but the wheel does not. That goes away when you put the widest possible wheel on the tire. And you can feel the 1.5" of slop disappear from the steering wheel. In back to back testing the results are quite dramatic. I'll bet you could run 9.5s in the front, with the same 245-40s, and the sidewall would get no closer to the frame than it does now. And it would have better steering wheel response.
That's how I got 10.5" & 11.5" wide rims on my 70 Z28 in Pro-Solo and kept them inside the stock fenders, 35 years ago. And got 1.27 Gs out of it. The exact backspacing escapes me now, but it was around 5.75".
Last edited by leigh1322; Apr 28, 2020 at 11:32 AM.
Can you tell me about that roll bar? Any interference? How hard to install?
TIA!
Paul
Sure can Paul. After stripping everything out from behind the seats, I took it to a professional, he custom bent chrome moly tubing, TIG welded it [boy does he know how to weld], cut holes through the body and welded it to the frame. It's a four point roll bar made to SCCA specs. After coming home I spent more hours than I can count polishing the darn thing, reglassed the holes around the tubing replaced carpet and reassembled compartments. He didn't follow my drawings exactly and changed the rear leg. His design is stronger but the compartment doors don't open all the way. The battery cover needs removal to change battery. That is the only interference issue there is, top goes up and down no problem. There is no paint on it, every other year or so I take some 600 grit emery to it. T
Sure can Paul. After stripping everything out from behind the seats, I took it to a professional, he custom bent chrome moly tubing, TIG welded it [boy does he know how to weld], cut holes through the body and welded it to the frame. It's a four point roll bar made to SCCA specs. After coming home I spent more hours than I can count polishing the darn thing, reglassed the holes around the tubing replaced carpet and reassembled compartments. He didn't follow my drawings exactly and changed the rear leg. His design is stronger but the compartment doors don't open all the way. The battery cover needs removal to change battery. That is the only interference issue there is, top goes up and down no problem. There is no paint on it, every other year or so I take some 600 grit emery to it. T
Front: 18x8 4.5" backspace wheels with 245/45x18 tires
Back: 18x9.5 with 5.25" backspace with 275/40x18 tires
(It sits a little lower in the front now that I have tubular A-arms)
Last edited by scottjamison; Apr 29, 2020 at 05:15 PM.
Guys running 9" wide wheels in the front, what is your backspace, and are you having any clearance issues? Gotta order my wheels and I'm trying to decide if I want to go 18x8 or 18x9 for the front. Rear will be 18x10 with a 5.5 backspace and 285/40 tire.
Guys running 9" wide wheels in the front, what is your backspace, and are you having any clearance issues? Gotta order my wheels and I'm trying to decide if I want to go 18x8 or 18x9 for the front. Rear will be 18x10 with a 5.5 backspace and 285/40 tire.
I'm running 18x10 up front with 5.5 BS. 285/35r18. I'm pretty low at 26.5 inch to fender lip. If I jack the car up and let the wheels drop, the tire will catch the rear of the fender lip as it approaches full lock. No issues on the street though. I would think that a 9 inch wide with 5 inch BS would be a very easy fit
I'm running 18x10 up front with 5.5 BS. 285/35r18. I'm pretty low at 26.5 inch to fender lip. If I jack the car up and let the wheels drop, the tire will catch the rear of the fender lip as it approaches full lock. No issues on the street though. I would think that a 9 inch wide with 5 inch BS would be a very easy fit
Hmmm so you guys have me thinking.
I think I'm playing with these two setup options now...
Option #1
Front: 18x9 with a 5" backspace and 255/45 (27" tall, 10" wide, 4.5" side wall)
Rear: 18x10 with a 5.5" backspace and 285/40 (27" tall, 11.2" wide, 4.5" side wall)
Option #2
Front: 18x8 with a 4" backspace and 245/40 (26.7" tall, 9.6" wide, 4.3" side wall)
Rear: 18x10 with a 5.5" backspace and 275/40 (26.7" tall, 10.8" wide, 4.3" side wall)
Thoughts? God I hate picking wheels. Big cost without seeing them in person, and once you commit, that's that....
I should also note, option 2 has better tire options for the rear (275 vs 285). Surprisingly 285/40 18 has limited options. Might be worth option 2 just for that reason. I'd only lose .4" of width....and actually, I run a 275/60 15 right now, so I'm not losing width, I'm just not gaining the .4" by going to a 285. I'm not sure how I feel about going narrower in the front though. I currently have a 255/60 16 up front, so I'd be losing .4" width going to a 245. Probably negligible when it comes to handling though right?
Last edited by 80vette21; May 1, 2020 at 05:57 PM.
Guys running 9" wide wheels in the front, what is your backspace, and are you having any clearance issues? Gotta order my wheels and I'm trying to decide if I want to go 18x8 or 18x9 for the front. Rear will be 18x10 with a 5.5 backspace and 285/40 tire.
On the 69 the front back spacing is 4.5 inches with 18x9s. Same on the 6t8. Don't 80 vettes have more of a flared fender than the 6t8 &9s? The 18x10 inch wheels that are on the 69 on the rear have a 5.0 B/S and they DON'T stick out. Stock wheels come at 15x8 with a 4" B/S or 8" divided by 2 equals 4". It is a nice balance when the backspace is the half of the width of the wheel. After the expense of a new set of wheels why would you want to make the wheel track narrower? T
On the 69 the front back spacing is 4.5 inches with 18x9s. Same on the 6t8. Don't 80 vettes have more of a flared fender than the 6t8 &9s? The 18x10 inch wheels that are on the 69 on the rear have a 5.0 B/S and they DON'T stick out. Stock wheels come at 15x8 with a 4" B/S or 8" divided by 2 equals 4". It is a nice balance when the backspace is the half of the width of the wheel. After the expense of a new set of wheels why would you want to make the wheel track narrower? T
That was what I was thinking, the 80-82s have more flare with the bumper change they got in the front, but most of the fitment info in this and other threads is more about pre-80 C3s.
I agree I don't want to go narrower than the 255 I already have. I think the 255/45 and 285/40 will be best, luckily one of my top 2 tire choices is available in the 285....just sucks that size is so limited with options.
I think I'm playing with these two setup options now...
Option #1
Front: 18x9 with a 5" backspace and 255/45 (27" tall, 10" wide, 4.5" side wall)
Rear: 18x10 with a 5.5" backspace and 285/40 (27" tall, 11.2" wide, 4.5" side wall)
Option #2
Front: 18x8 with a 4" backspace and 245/40 (26.7" tall, 9.6" wide, 4.3" side wall)
Rear: 18x10 with a 5.5" backspace and 275/40 (26.7" tall, 10.8" wide, 4.3" side wall)
Thoughts? God I hate picking wheels. Big cost without seeing them in person, and once you commit, that's that....
I should also note, option 2 has better tire options for the rear (275 vs 285). Surprisingly 285/40 18 has limited options. Might be worth option 2 just for that reason. I'd only lose .4" of width....and actually, I run a 275/60 15 right now, so I'm not losing width, I'm just not gaining the .4" by going to a 285. I'm not sure how I feel about going narrower in the front though. I currently have a 255/60 16 up front, so I'd be losing .4" width going to a 245. Probably negligible when it comes to handling though right?
Hey 80Vette21, sorry I haven't seen these posts sooner.
As a fellow 80 owner, I can offer you some insight. My car has offset trailing arms, and VBP rear monoleaf and VBP front monoleaf and upper/lower control arms, but I think I can still help you out some.
I am running 18 x 9.5, 5.1 BS front and rear with 285/35R18 tires all 4 corners. I am still running the stock sway bar out back, and that is the limiting factor. As others have said, if you relocate the parking brake cable on the stock arms, with an 18" wheel, the offset t/a's really don't buy you anything. If you want to keep the rear sway bar, I don't think you can fit 5.5" backspace. You could probably get to a 5.25", but any more than that will hit the sway bar. That being said, you can order the 5.5" BS, and if you find it hits, you can always run a small slip on spacer to get the clearance you need. Much easier to space a wheel out than tuck it in further. Up front, on the 80, I have found there is more room than out back. I am running a .25" spacer (making them effectively 4.85" BS) up front to bring the wheel out a little further to fill up the fender a bit better, but there is a ton of room up there on these cars. I don't think having the VBP arms will make a difference as to wheel fitment, but I could be wrong. I cannot speak to the steering stops as mine are not original, but for 95% of driving you'd be fine for sure.
One thing I did, was I ordered 2 wheels at a time, and tried them front and rear before I ordered the second set. Mostly that was because I ordered the Weld RTS-77 and they are EXPENSIVE. But it was helpful to confirm fitment without the massive outlay of cash.
I've attached some pictures to try to show the fitment of the wheels in the wheelwell, as well as the clearance under the car to the rear swaybar and spring/shock. Hopefully this is helpful. Let me know if you have any questions or want to see any other pictures of clearance, etc.
Hey 80Vette21, sorry I haven't seen these posts sooner.
As a fellow 80 owner, I can offer you some insight. My car has offset trailing arms, and VBP rear monoleaf and VBP front monoleaf and upper/lower control arms, but I think I can still help you out some.
I am running 18 x 9.5, 5.1 BS front and rear with 285/35R18 tires all 4 corners. I am still running the stock sway bar out back, and that is the limiting factor. As others have said, if you relocate the parking brake cable on the stock arms, with an 18" wheel, the offset t/a's really don't buy you anything. If you want to keep the rear sway bar, I don't think you can fit 5.5" backspace. You could probably get to a 5.25", but any more than that will hit the sway bar. That being said, you can order the 5.5" BS, and if you find it hits, you can always run a small slip on spacer to get the clearance you need. Much easier to space a wheel out than tuck it in further. Up front, on the 80, I have found there is more room than out back. I am running a .25" spacer (making them effectively 4.85" BS) up front to bring the wheel out a little further to fill up the fender a bit better, but there is a ton of room up there on these cars. I don't think having the VBP arms will make a difference as to wheel fitment, but I could be wrong. I cannot speak to the steering stops as mine are not original, but for 95% of driving you'd be fine for sure.
One thing I did, was I ordered 2 wheels at a time, and tried them front and rear before I ordered the second set. Mostly that was because I ordered the Weld RTS-77 and they are EXPENSIVE. But it was helpful to confirm fitment without the massive outlay of cash.
I've attached some pictures to try to show the fitment of the wheels in the wheelwell, as well as the clearance under the car to the rear swaybar and spring/shock. Hopefully this is helpful. Let me know if you have any questions or want to see any other pictures of clearance, etc.
No problem, I came across the pictures of your car from earlier in this thread, the Welds look great on your car. Thanks for the extra info, its a huge help, its nice having some input from an 80-82 car versus the earlier C3s.
My car also has VBP offset trailing arms and monospring, and then up front Vansteel tubular A arms and coilovers. I'm not necessarily set on the 5.5" backspace in the rear, that just seems to be what most guys say works with 10", and it would put it at a 0 offset. I would actually prefer a slightly negative offset if possible, just not sure if it's doable with a 10" wide wheel without poking out of the fender.
I have no rear sway bar, so that won't be an issue. I don't hate the idea of just going with 9.5" on all 4 corners, then I could actually rotate my tires haha. I'd like a little more sidewall and overall diameter, so my plan was 285/40. How do you like the 285's on the 9.5" rim? I know supposedly the max tire width for a 9.5" wheel is 275, but I mean right now I'm running a 275 tire on an 8" wheel that's supposed to have a max of 245 so.... lol
How close are you to the front fender lip with the 4.85" backspace using the spacer? Wondering if I'd be better going with an 18x9.5 with a 4.75" backspace or 5" backspace. If I could get away with the 5" without using a spacer I could do that up front and then 5" in the back instead of 5.5" and have all 4 wheels the same. I do agree though, having too much backspace is easier to fix than not enough, but I'd like to avoid spacers if possible. Looking at your picture, it's hard to tell but looks like you have a little more room to the fender lip front and rear.
You've got me thinking about the Welds again, theyre just so damn expensive and I'm not sure how I'd like the S76 on my car. I wish I could see it in person first
Last edited by 80vette21; May 7, 2020 at 01:46 PM.
Yes I do. The rear suspension in brand new and not set up. When ball parked the rear camber the wheels fit. I did have to go to a narrow swaybar but the spring does clear.
