Wheel/Tire help

OllieDemon45 · Apr 27, 2023

VNTW51577658865 Torq Thrust II 17x7 & 18x8 5x4.5 Package
I want to put new wheels and tires on my 71 Demon, it now has front disc brakes with bbp and i am going to replace the old axles with bbp and drum setup 8.75 rear end.
My question is.. What backspacing and wheel offset do i need.
I've been reading and looking at everyones rides here on the forum and really like the looks of the Torque Thrust 2's. I'm thinking 17" front and 18" rear.
I have a link to what i have picked out for reference. Just not sure on backspacing and offset. Tire size is still up in the air also.

Thouhgts?

RustyRatRod · Apr 27, 2023

That's really something best to be measured by YOU. Each one of these cars is a little different due to manufacturing tolerances and "I don't give a crap where this spot weld is" attitude by factory workers. So while we may be able to give you a general idea, if you're going to get close to the limits of what these cars can handle as for size, it's best to measure. I would measure anyway.

Syleng1 · Apr 27, 2023

Agree with RRR and please use the search engine feature as this has been covered many many times before. Good luck.

Robert Dart · Apr 27, 2023

@72bluNblu has a wealth of info on this subject. You could also search his posts.

MRGTX · May 4, 2023

I agree with the comments about each car being a little bit different but this really only matters when you are absolutely maximizing tire width/diameter. There are guidelines that are helpful.

One such guideline would be to err on the higher number offset (wheels tucked under) side since a spacer can help get your wheel in the right spot. Too low of an offset (wheels sticking out), you're out of luck.

In any case, carefully measuring what you have and how much clearance you have left to work...and going from there, with will be your best bet.

More very general guidelines: If you are looking at 8" wide wheels, 0 offset (4.5" backspace) wheels usually work well on the rear axle and something at 25mm-35mm (5"-5.7"...can someone check that math?) will be a good starting place for the front. Note that this won't work with 15" wheels since the wheel will contact the upper control arm. Most 17" wheels won't have this problem...as far as I've ever heard anyway.
IIRC, the 17x8 Torque Thrusts are available with a 5.25" backspace.

Since you're looking at 17" wheels, I am guessing you are also thinking about modern tires. The selection is better than what exists for 15s but not much. I would strongly recommend tire shopping first to make sure you can find what you need in one tire model. There are some top tier performance tires available at this size but few of them will give you the diameter you likely would want in the rear. I would say that 26" would be the shortest OD tire you would probably want...so something like a 275/40/17 is going to be ~25.7" OD (a little too short) but nothing exists in a 275/45/17...and almost nothing exists in a 275/50/17 (which are ~28" tall which might be too much anyway)...

...the point is that if performance is your goal and you like turning and braking too (not just drag), you pretty much have to look at 18s.

The last thing to keep in mind when picking a wheel is the hub diameter. IIRC, 73mm is required to fit on the front. Some folks have machined out hub clearance with good luck but it's extra expense and hassle.

OllieDemon45 · May 4, 2023

MRGTX said:
I agree with the comments about each car being a little bit different but this really only matters when you are absolutely maximizing tire width/diameter. There are guidelines that are helpful.

One such guideline would be to err on the higher number offset (wheels tucked under) side since a spacer can help get your wheel in the right spot. Too low of an offset (wheels sticking out), you're out of luck.

In any case, carefully measuring what you have and how much clearance you have left to work...and going from there, with will be your best bet.

More very general guidelines: If you are looking at 8" wide wheels, 0 offset (4.5" backspace) wheels usually work well on the rear axle and something at 25mm-35mm (5"-5.7"...can someone check that math?) will be a good starting place for the front. Note that this won't work with 15" wheels since the wheel will contact the upper control arm. Most 17" wheels won't have this problem...as far as I've ever heard anyway.
IIRC, the 17x8 Torque Thrusts are available with a 5.25" backspace.

Since you're looking at 17" wheels, I am guessing you are also thinking about modern tires. The selection is better than what exists for 15s but not much. I would strongly recommend tire shopping first to make sure you can find what you need in one tire model. There are some top tier performance tires available at this size but few of them will give you the diameter you likely would want in the rear. I would say that 26" would be the shortest OD tire you would probably want...so something like a 275/40/17 is going to be ~25.7" OD (a little too short) but nothing exists in a 275/45/17...and almost nothing exists in a 275/50/17 (which are ~28" tall which might be too much anyway)...

...the point is that if performance is your goal and you like turning and braking too (not just drag), you pretty much have to look at 18s.

The last thing to keep in mind when picking a wheel is the hub diameter. IIRC, 73mm is required to fit on the front. Some folks have machined out hub clearance with good luck but it's extra expense and hassle.

Thank you for the reply, lots of great info.

OllieDemon45 · May 22, 2023

Ok so measured the rear to figure out backspacing. Looks like I have 6” from the inner fender to the outside lip of the hub.
I have 5 1/4” from the lip of the hub to the inner lip of the rear fender.
My 14” Rallye wheel has 3” of backspacing and 2 1/2” front spacing.
Do these numbers seem correct?
Still debating on 17” or 18” wheels.
I want a tire that fills the wheel well but won’t have clearance issues.
Also, will the sway bar in the front play any issues?
I’m not sure how to measure the front for fitment.