Folks,
I am about to pull the trigger on 4 Torq Thrust 18x9 wheels with the 5” backspace, I’d like to run 255/45r18 all around (27” diameter) … I have literally rear the ENTIRE 18” wheel thread, but haven’t found what I am looking for …

so, as we know we get screwed for backspacing with modern wheels, and having a later C3 (1981) we have a little extra room for a more aggressive setup.

A couple questions for the audience;

Will a 18x9 5” backspace rub the frame? I know the fender side is equivalent to the gold standard 18x8 4” backspace, so not worried there.

if I wanted to get aggressive, will a 1” spacer all around fit without poking out of the fenders?

basically the spacers would effectively 18x9 with a 4” backspacing.

another point to consider, 255/45r18 are 10” wide on a 9” wheel … 255/60r15 are 10.5” wide at the widest section (I measured on my car).

I have seen 18x10 with a 5” backspace, which on the fender side should be the same, but the pictures were not good enough to determine if they poke out at all.

I know the question, why not do without the spacers and be happy … well, I happen to think that 18x8 4” backspacing still look a little tucked in, and expect my new 18x9 5” backspace to also look a little tucked in.

sorry for the lengthy post! I’d love to see examples of more extreme 17, 18, 19, 20, or whatever wheels with aggressive backspacing. Please include width and backspacing (offset works, but a pain to calculate).

thanks!!!

 

I run 18x12 rears with 5.5 bs. No issues. Just had to relocate ebrake bracket

 

No way you fit all that under stock fenders ??? That’s basically equivalent to a 18x8 with a 1.5 backspace or 18x9 2.5 backspace …

 

Many here have fit 275 or 285 tires inside the fenders. The bigger the wheel diameter, the easier it is because of less sidewall bulge. Below are threads by Lars, and Fleming23, where they fit 305’s inside the fenders on 71’s. One of them used the Ridetech rear if I remember correctly, but their trailing arms do not offer any more clearance than stock with the parking brake bracket relocated. Five inch backspace should be fine with the relocation of the parking brake bracket. Why not run a wider tire than 255 instead of using spacers? Have a look below.

https://www.corvetteforum.com/forums...4-corners.html

https://www.corvetteforum.com/forums...ch-system.html

Bill

 

flares

 

The 18x9 will not hit the frame but the E-brake bracket must be moved as stated......
The 255 tire is too narrow on that 9" rim too......go to a 275/40/18.....
I have a 5" backspace and the wheels were tucked in a little bit too much for me so a 1/4" spacer went in......this also gave me extra clearance for the Addco rear sway bar.....

Jebby

 

thanks for the links bill!

The first link would be 18x9 4.5” backspacing equivalent… I can’t tell if skinnier 255 tires but a half inch less backspace will be an issue in the fender side …

The second link, I never seen before, Lars did a great job. Be he essentially started with the wheel in question and added 1.5” inside, his outer fender clearance looks a little tucked in still. I wonder what his figment would look like with 1” spacers …

 

Can I ask for a a side profile shot if your wheel figment? What year is your car?

Do you feel with your setup that .75 inches OUT will cause interference with your bodywork?

I liked the 255 because it’s exactly the factory diameter of 27” and I don’t need that much meat and weight for a 250hp car, haha (I am crying inside, laughing outside) …

I have done 18x9.5 with 5” backspacing with 275 tire and 18x8 with 3.5” backspacing with 245 tire in the past, and all I remember is it was perfect! Didn’t need to mess with the e brake or anything else … with respect to the past experience, I cannot recall if that setup had another half inch to come out.

 

So I did some measuring of the stock wheel with 255/60r15 tires …

backspace including tire 4.68 inches (mounting flange to innermost tire bulge)

“forwardspace” including tire 5.78 inches (backside of mounting flange to outermost tire bulge)

NOW!

if we look at a 18x9 with a 255/45r18 tire, it has a section width of 10.03”, the 18x9 wheel should be 10” wide lip to lip.

what this means is that an 18x9 wheel with 5” backspace (0 offset) and a 255 tire will have a “tire backspace” of 5.015 and a “tire forwardspace” of 5.015 … add the proposed 1” spacer and we are looking at 4.015 “tire backspace” and 6.015 “tire forwardspace” which is only .235” further out …

on paper this looks like an easy win!

if I got “crazy” and went with a 275/40r18, it’s section width is 10.93, so add .45 to each figure. So 3/4 and inch further OUT toward the fender VS stock …

 

I can tell you that on my '81 a 18x8.5 with -6 offset and 4.5" backspacing fit just fine with no mods or spacers needed so if you drop that 1/2" more width it's not a problem. I've run 235/50's, 255/45's and even 275/40's without issue.

 

Comparing to your setup, I’d be half an inch toward the fender due to a 4” backspace PLUS another half inch due to a 9” wheel … your setup is basically the same relative position to the fender as a 18x8 4” backspace.

 

Well life got in the way but I executed my plan with positive results.

so I ordered the 18x9 Torq thrust wheels in chrome but got the off the shelf 5” backspacing. I then ordered a set of .750” Motorsport wheel spacers bring the actual backspace to 4.25.

I gotta say, the fitment looks GREAT! I am thinking of swapping the rear wheels with 18x10 wheels and using the same spacers, which should take the off the shelf 5.75 backspace down to the proven 5” backspace …

ill shoot up some pictures for reference …

 

How many threads are engaging on your lug nuts? Or did you also install longer studs?

 

18 x 9 with 4.5" backspace are the same a factory tire placement. adds 1/4" more to the inner and outer edge of the tire.

but ....

I would go 18 x 9.5" with 4.75" BS and use 275 40R18 tires all around. No mods to anything including rear parking brake brackets.

 

The wheel spacers have 1/2 wheel lugs, someday when I rebuild the rear trailing arm and front hubs, I’ll upgrade the 7/16 lugs with 1/2” … thread engagement is not an issue …

 

actually you and I have the same “stance” (hate using that Honda boi term) , but I just have a little bit more room INSIDE my fender …

unfortunately I really wanted for thrust wheels. And I’ve had enough with polished (I always mess them up) soooo I went chrome torq thrust but was stuck with their non custom sizing … I really wanted 18x10 rear, but I was scared, I’ll swap them in the future and can still use the same spacers …


PS: your car looks GREAT 👍

 

My rule of thumb when it comes to a custom set of wheels,don't rely on other peoples info. I've had several sets of wheels made over the years and I've always figured out what I need to make a wheel work. I'm going to have a set of 18 rally's made for my 75 and I want to get the widest wheel/tire possible on the rear of the car. One major issue with a cast wheel is there are limited BS options. My process: I get the car up in the air,load the suspension with the stock wheel and look for the room I need.