Wheel Size and Backspacing Help... And disc brake help...

Spartan · Jan 18, 2017

Hey guys,

I need some help getting sizing sorted out for my 68 Roadrunner build.

I have the Hotchkis TVS suspension system and QA1 shocks ordered and being shipped.

Car is currently away to the bodyshop for fresh paint and I work away in remote locations so there is a good chance I won't see it till spring.

I plan on ordering disc brakes for all the way around. I looked at the Wilwood options and then decided I might try to save a bit of cost in this area and get the MRM 12" Big brake kit from Pirate Jack's. My concern with this is, when I was researching it mentions that the Pirate Jack brakes move the front wheels out 1/4" on each side. Possibly the rear as well, not sure? Does the Wilwood kit also move the wheels out?

I want to order rims and tires so they are in by spring but this will have an effect on sizing and backspacing I assume.

I am hoping to run a staggered 18x10 and 19x12 or a 19x10 front and 20x12 rear wheel setup on the car. I am just unsure as to whether or not this setup will fit without rubbing issues? The Hotchkis kit already lowers the car down from stock height so that also probably needs to be taken into consideration. My main concern is the front and the offset required for the rear, if need be I am willing to mini-tub the rear to make it work.

Thanks in advance for any assistance you guys can provide, Vendors are also welcome to chime in.

1967coronet440 · Jan 18, 2017

Ugh I'm not looking forward to going through this with my 67, but I have to address it soon so I'll be watching this thread.

747mopar · Jan 18, 2017

Based on my 69 Charger I'd say you might wanna start planning on mini tubbing it. I'm running 10" wide 19"s in the rear with 285's with no issues. I'm confident 295's will fit but recently stuck a friend's 305's in there just to see..... zero room. The 305's measured 12", to look right you'll want the tire slightly wider than the rim and also keep in mind that rim width is measured at the bead not outside to outside (my 10"s measure 11" outside to outside). If you want a 12" tire I'd go with a 10" rim and 305's. On my car I'm running a 5" backspace, going mini tub with 12's you'll likely want 4.5".

Tempest 455 · Jan 19, 2017

Yes when I installed the Wilwoods, it moves them out. You have to account for the thickness of the "hat" in relation to the axle flange. It's actually the difference between the drum and hat.

Yatzee · Jan 19, 2017

Spartan said:
Hey guys,

I need some help getting sizing sorted out for my 68 Roadrunner build.

I have the Hotchkis TVS suspension system and QA1 shocks ordered and being shipped.

Car is currently away to the bodyshop for fresh paint and I work away in remote locations so there is a good chance I won't see it till spring.

I plan on ordering disc brakes for all the way around. I looked at the Wilwood options and then decided I might try to save a bit of cost in this area and get the MRM 12" Big brake kit from Pirate Jack's. My concern with this is, when I was researching it mentions that the Pirate Jack brakes move the front wheels out 1/4" on each side. Possibly the rear as well, not sure? Does the Wilwood kit also move the wheels out?

I want to order rims and tires so they are in by spring but this will have an effect on sizing and backspacing I assume.

I am hoping to run a staggered 18x10 and 19x12 or a 19x10 front and 20x12 rear wheel setup on the car. I am just unsure as to whether or not this setup will fit without rubbing issues? The Hotchkis kit already lowers the car down from stock height so that also probably needs to be taken into consideration. My main concern is the front and the offset required for the rear, if need be I am willing to mini-tub the rear to make it work.

Thanks in advance for any assistance you guys can provide, Vendors are also welcome to chime in.

View attachment 388931 View attachment 388932

I would never order wheels in advance until I can actually visualize the fit on the car and space available inside the wheel housings. There seems to be an issue where people purchase the wrong size front rims/tires only to find they scrub on the sub fram or worse the fender edges. Wait until the car comes back and using plumb lines dropped to the garage floor plot (with chalk) the inner most position of the leaf springs, the depth you want of the tire from the fender lip and the actual front working surface of the rear drum or rotor surface that the rim will touch. You'll have three chaulk marks on the floor that will indicate the limitations of your tie position. Do the same for the fronts but don't let the suspension droop ( support under the A-arms ). Knowing the diameter of the intended front tires, and back-set as well as tire and rim width, you can mock up a make shift gauge using stiff wire or a thin strip of metal that will run across the front working surface of the drum/disk, the same lenght as the tire diameter and bent back on the ends to represent the depth of shoulder of the intended tire. Swing your steering to it's extremes, left and right and confirm clearance. Barring this exact confirmation method, take your best guess using the existing rims and tires and hope for the best when the new ones arrive. As unfortunate
as it may seem, the people who process your orders really have no idea if the product shipped will actually fit your application, they rely on the information you give them.

Yatzee · Jan 19, 2017

Yatzee said:
I would never order wheels in advance until I can actually visualize the fit on the car and space available inside the wheel housings. There seems to be an issue where people purchase the wrong size front rims/tires only to find they scrub on the sub frame or worse the fender edges. Wait until the car comes back and using plumb lines dropped to the garage floor, plot (with chalk) the inner most position of the leaf springs, the depth you want of the tire from the fender lip and the actual front working surface of the rear drum or rotor surface that the rim will touch. You'll have three chalk marks on the floor that will indicate the limitations of your tire position. Do the same for the fronts but don't let the suspension droop ( support under the A-arms ). Knowing the diameter of the intended front tires, and back-set as well as tire and rim width, you can mock up a make shift gauge using stiff wire or a thin strip of metal that will run across the front working surface of the drum/disk, the same length as the tire diameter and bent back on the ends to represent the depth of shoulder of the intended tire. Swing your steering to it's extremes, left and right and confirm clearance. Barring this exact confirmation method, take your best guess using the existing rims and tires and hope for the best when the new ones arrive. As unfortunate as it may seem, the people who process your orders really have no idea if the product shipped will actually fit your application, they rely on the information you give them.

747mopar · Jan 19, 2017

I made a jig just for determining rim and tire size but they can be bought from places like Summit. It's an easy way to duplicate different combos and can be rotated just like a wheel.

Superb Bee · Jan 19, 2017

one of the best tools I ever bought, I never figured i was use it as much as I do..

The best way to use this is to, pick a wheel and tire you want, your starting point, then dial the gauge in and bend your wire to the tires profile. Now fit that and see where you are, if you can go larger and want to go to the next size tire and see if that first rim choice will work, if you have to adjust the backspace make sure a the wheel exists...
A lot of times we come up with wheel sizes that no one makes, so the best way to do it is pick your wheel, record the available backspacing, and test it over and over, and dont forget about your suspension, lol..

I put the car on the lift and then drop it on a stiff leg to simulate ride height, you can do your suspension travel math from there... Its really handy when making custom mini tubs and fitting shortened axles that were not made for said vehicle.. I really like this silly looking plastic tool..

Spartan · Jan 19, 2017

Thanks guys, appreciated. I will order the tool and hopefully get a chance to get over to do some measurements within the next month as, depending on what wheel I go with, there seems to be a decent wait time between ordering most of when they are shipped.

I am looking at some of the prowheels.net wheels at the moment, hoping to trim some spending a bit and these are still expensive enough but should be able to get all for for around 3200 or so instead of $4000 plus.

Wheel Size and Backspacing Help... And disc brake help...

Spartan

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1967coronet440

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747mopar

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Tempest 455

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Yatzee

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Yatzee

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747mopar

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Superb Bee

Well-Known Member

Spartan

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