Backspacing Options for the Wheels

[RCman]

Okay so I know this has been hashed a bunch of times and for that I apologize but I can't find a clear answer. I have read through the Tire Combos thread but that just seems to make it even worse. 

At the moment the front end is all apart and I'm going to be installing Dr. Diff's 13" Cobra PBR setup. My understanding is that this increases the track width by about 3/16" on a side. When I spoke to Cass on the phone during ordering he recommended at least 5" of backspacing. I'm looking at the Torque Thrust II VN215 wheels. So my options for a 17x8" wheel are either Backspacing of 4.810" (+8mm offset) or 5.480" (+25mm offset). When I talked with Cass about it he told me to go with the 5.480" backspacing for the 8" wide wheel. Looking at a Nitto 555 G2 245/45/r17. Car should end up being a little lower than stock but not drastically dropped.

I do have an older 15" Jeep wheel that I used for fitment and that works with the stock disc brakes (won't fit over the new stuff). Here's where the confusion is started when I tossed that on the side with the stock setup. That wheel is a 15x7" with 5.25" backspacing. When on it contacts the tierod and when drooped it just kisses the upper ball joint. Now the upper balljoint issue will probably be solved with the 17" diameter but I'm not sure the tierod will. Given the wider track and the new wheel dimensions (5.480"-0.1875" = 5.2925" backspacing effectively when comparing to the old stock disc setup) I should be closer to the tierod and thus probably hitting it. I could use a thin ~1/4" spacer maybe to avoid contact or would I be better off with the 4.810" wheel? Seems like I may have fender and brace issues then. I don't have rolled fenders and the car is painted so that isn't an option.

For the rear I should be pretty good, I think. I've got a '68 B-body D60 and Cass's 1.5" offset kit. If I am measuring correct with a 10" wide wheel, 285 series tire, and 5.740" backspacing I should have about 1/2" clearance to the leaf spring and about 5/8" or so to the fender. Is that enough? I'm used to trucks/Jeeps with miles of clearance compared to that. Probably about 27.1" tall so I should be okay with the height..

Thanks for the help everyone!

[WildJones]

Stock tie red or aftermarket with bump steer spacers (like Hotchkis)?  Are you set on 17" wheels? An 18" would clear the tie rod and allow for a wider wheel. Food for thought.

[72bluNblu]

So, I run 17x9" wheels with 5" of backspacing (0 offset) and 275/40/17's all the way around on my Challenger. Front suspension uses the later 11.75" rotors, but stock FMJ spindles. In the rear I have a 68-70 B body 8 3/4 and 1" offset springs courtesy of a Dr. Diff kit.

In the front, you want to be pretty close to 0 offset to fit the widest tire. With the 13" rotor kit that will end up at about +5mm. A 17" wheel will not clear the outer tie rods if there's too much backspace, an 18" wheel fits over the top regardless. That's not as big of an issue on an E-body because you run out of tire-to-frame clearance at full lock at about the same time the rim to tie rod interference issue comes up. If you're planning on running a 17x8 and a 245/45/17 I would run the 17x8 with a +8 offset (4.81" backspace). That rim will sit a little closer to the suspension/frame than it does to the fender, but you'll have more clearance than I do which means plenty. The 17x8 with 5.48" of backspace and a 245/45/17 will have almost a 1/4" less clearance than I have on my set up, which means the tires will hit the frame at full lock AND the rim will probably hit the tie rod. On a 17" rim the maximum backspace you can run is about 5.25", that's about where the rim to tie rod clearance becomes an issue. That 5.29" backspace number you'd get would probably mean you'd need a spacer, I have a little less than a 1/4" clearance to the outer tie rod with my set up. And since you have plenty of room to deal with there's no reason to set the rims up that tight on the inside.

In the rear with the 17x9's and 0 offset the wheels are almost perfectly centered in the wheel wells. If you're looking for a 10" rim I would say 5.5" to 5.75" should be right on to center the rim and run the widest tire possible. A 27" tall tire shouldn't be an issue unless your car sits really low in the back.

[RCman]

Stock tie red or aftermarket with bump steer spacers (like Hotchkis)?  Are you set on 17" wheels? An 18" would clear the tie rod and allow for a wider wheel. Food for thought.

Stock tie-rod setup.
I'd like to stick to 17s because truthfully I like the 15s better but I can't run them with big brakes. Trying not to have the wheels 'pop' out at you when you look at the car.

So, I run 17x9" wheels with 5" of backspacing (0 offset) and 275/40/17's all the way around on my Challenger. Front suspension uses the later 11.75" rotors, but stock FMJ spindles. In the rear I have a 68-70 B body 8 3/4 and 1" offset springs courtesy of a Dr. Diff kit.

In the front, you want to be pretty close to 0 offset to fit the widest tire. With the 13" rotor kit that will end up at about +5mm. A 17" wheel will not clear the outer tie rods if there's too much backspace, an 18" wheel fits over the top regardless. That's not as big of an issue on an E-body because you run out of tire-to-frame clearance at full lock at about the same time the rim to tie rod interference issue comes up. If you're planning on running a 17x8 and a 245/45/17 I would run the 17x8 with a +8 offset (4.81" backspace). That rim will sit a little closer to the suspension/frame than it does to the fender, but you'll have more clearance than I do which means plenty. The 17x8 with 5.48" of backspace and a 245/45/17 will have almost a 1/4" less clearance than I have on my set up, which means the tires will hit the frame at full lock AND the rim will probably hit the tie rod. On a 17" rim the maximum backspace you can run is about 5.25", that's about where the rim to tie rod clearance becomes an issue. That 5.29" backspace number you'd get would probably mean you'd need a spacer, I have a little less than a 1/4" clearance to the outer tie rod with my set up. And since you have plenty of room to deal with there's no reason to set the rims up that tight on the inside.

In the rear with the 17x9's and 0 offset the wheels are almost perfectly centered in the wheel wells. If you're looking for a 10" rim I would say 5.5" to 5.75" should be right on to center the rim and run the widest tire possible. A 27" tall tire shouldn't be an issue unless your car sits really low in the back.

Thanks for the huge wealth of information! 
Okay, so I'll go with the 4.81" backspaced wheel. This also sorta goes with the tread I was seeing with backspacing when I took notes from the picture thread (it just goes against what Cass told me).
You're thinking I won't have fender clearance issues? Some of the guys from the other thread mentioned having to roll the lip and I'd rather not have to get into that and/or repaint.

Sounds like I've got the rear figured out and you confirmed it. Thank you.

[YellowThumper]

To throw another in the mix.
I made custom widened Rallye's that are 8-1/2" wide with a back space of 4-3/4. Run 275-60-15s. No issue at all at the fender. Also clears the factory stock location springs by about 1/2 inch.

[72bluNblu]

Thanks for the huge wealth of information! 
Okay, so I'll go with the 4.81" backspaced wheel. This also sorta goes with the tread I was seeing with backspacing when I took notes from the picture thread (it just goes against what Cass told me).
You're thinking I won't have fender clearance issues? Some of the guys from the other thread mentioned having to roll the lip and I'd rather not have to get into that and/or repaint.

Sounds like I've got the rear figured out and you confirmed it. Thank you.

No, the 17x8 with 4.81" of backspace and 245/45/17's should have plenty of room to the fender. Even with the extra +5mm from the 13" brakes you should have almost a full 3/4" more room to the fender than I do with my 275's, and an extra 1/2" to the suspension. Ie, plenty of room    . I did have to remove my fender braces that go to the backside of the wheel opening on both sides to clear my 275's, but my car also sits pretty low and the wide 275's definitely played into that as well. The driver's side fender on my car still didn't need any fender lip rolling though, and the passenger side only needed a little. But like I said that's with 275's and the ride height lowered 2"+ from stock, and you should have almost an extra 3/4" to the fender compared to mine. You could totally run 255/45/17's up front with your wheel combo and STILL have plenty of room.

As for the brakes, they're awesome. I run the 13" cobra style package from Cass on my Duster. A big improvement even over the later 11.75" mopar rotors.
Here's a shot of my Challenger, showing off it's 17x9's and 275/40/17's. Notice the ride height is pretty darn low.


And the 13" rotors on my "Duster".

[RCman]

Great. Glad I checked and posted up before ordering!

I appreciate the help!