ZJ Wheel Question

[Mitch502]

Long time, no posts for me, but I have a question about wheels/backspacing...

1998 ZJ
Stock anniversary 5 spoke wheels
285/75/16 DuraTrac tires
Running 1.5" spacers

Currently I'm running the stock anniversary wheels, and love them. I like the look at everything, but (if my research serves me right) they are 4.5" of backspacing, and then I run 1.5" spacers. So....3" of backspacing. I feel like this is pretty close to rubbing still with my 285/75/16 tires and ~5.5" of lift.

I am convinced that my rear end (D44A) is on it's way out, as it's been "growling" at me for the last 5 years :Wow1: So, I'm planning to start a 8.8 build (just a stock 8.8 with posi, no lockers or anything that fancy). The 8.8 is something like 5/8" skinnier than the D44A, and I'm afraid I'll rub terribly.


Does anyone have any experience with this? My jeep is in my signature link.

 

[BigDaveZJ]

Factory backspacing on ZJ wheels is 5.25", so you're closer to 3.75" backspacing. I run 4" backspacing 15x8 steelies on my ZJ with 35x12.50's on 4.5" springs, HP30 front, 8.8 rear with spacers on the rear wheels. I can't remember the exact measurement of the spacers, but they're between 1-1.5". Where are you afraid of rubbing? I've had more issues rubbing the outer fenders than the inner fender walls with my setup.

 

[Mitch502]

Factory backspacing on ZJ wheels is 5.25", so you're closer to 3.75" backspacing. I run 4" backspacing 15x8 steelies on my ZJ with 35x12.50's on 4.5" springs, HP30 front, 8.8 rear with spacers on the rear wheels. I can't remember the exact measurement of the spacers, but they're between 1-1.5". Where are you afraid of rubbing? I've had more issues rubbing the outer fenders than the inner fender walls with my setup.

Right now, as it is, when I hit a decent sized bump, I rub on my pass side rear. I may need a rear track bar maybe? I am running 5.5" of lift with only a IRO drop bracket...

 

[BigDaveZJ]

Definitely get an adjustable trackbar as that seems to be your problem more than the backspacing. Also, 5.5" is a lot for short arms and puts a lot of stress on the unibody side upper control arm mounts and they will eventually begin to tear away from the unibody. If you want to stay that tall, long arms should be in your future. IRO and Clayton's are your best bets there.

 

[Mitch502]

Yea, I actually am debating between long arms or dropping down to 4.5"

I'm afraid I'll rub terribly, and not really willing to cut my fenders. What do you think my rubbing will be like at 4.5" w/ 287/75/16?

What about reinforcing the unibody on the mounts?

 

[comptiger5000]

The 8.8 is a little narrower, unless you run a c-clip eliminator setup, in which case it ends up slightly wider than the stock 44a. I'm going to agree with the track bar suggestion. If your rear axle is centered, you should have plenty of room with the 285s back there, even if they get moved in a little bit. Up front is where you usually have to push things out a lot.

If you're worried about fender rubbing and don't want to trim, you need narrower tires. 285s pretty much require trimming on the outer fenders (or very long bumpstops) on a ZJ. There just isn't that much space to move outwards. You could swap to a 255/85R16. Same diameter, but a little over an inch narrower, which will make them much easier to fit.

Factory backspacing on ZJ wheels is 5.25", so you're closer to 3.75" backspacing. I run 4" backspacing 15x8 steelies on my ZJ with 35x12.50's on 4.5" springs, HP30 front, 8.8 rear with spacers on the rear wheels. I can't remember the exact measurement of the spacers, but they're between 1-1.5". Where are you afraid of rubbing? I've had more issues rubbing the outer fenders than the inner fender walls with my setup.

Nope. Original post is correct. Stock ZJ wheels are +13mm offset (at least for the 16s), which comes to 4.5" backspacing on a 7" wide wheel.

 

[Mitch502]

I don't want to sacrifice the tires, they're pretty much new...less than 2,000 miles on brand new tires...


Sounds like I should start with a trackbar and go from there. I have found some wheels that are 4" of backspacing (steel wheels). Will 1/2" make a big enough difference to be worth getting new wheels? I' unable to find 16" rims with any less backspacing.

Thanks for all the help.

Mitch

 

[comptiger5000]

I'd get the track bar in, center up the axle and flex the Jeep a bit and see how much clearance you've got at various points in the suspension travel. Go from there when determining whether you need to change anything else.

Also, for this case, it's probably easier to look at wheels in offset, rather than backspacing (especially if you're looking at 8" wide wheels, which would fit the 285s a bit better). Backspacing is the distance from the mounting surface to the inside of the wheel, so a 7" wide wheel will sit further in on the Jeep than an 8" wheel with the same backspacing. Offset measures how far from centered the mounting surface is, so a 0 offset will sit in the same place regardless of width.

As an example, going from a 7" to 8" wheel while maintaining 3" backspacing adds 1 inch to the outside of the wheel and none to the inside, so overall, the tire moves outwards. But if we target to maintain -25mm offset (equivalent to 3" BS on a 7" wheel), going to an 8" wheel adds a 1/2" inside and a 1/2" outside, so the overall position of the tire doesn't change.

Basically, backspacing is an easy measurement to work with on something like a TJ, where you have limited inner clearance and can get as much outer clearance as you want. But on something full bodied like a ZJ, it's easier to worry about where the wheel sits overall, rather than just how far from the inner edge are you.

 

[BigDaveZJ]

You say you're rubbing the pass side rear, but where? Outside or inside?

And every ZJ I've owned has had 5.25" backspacing on the factory wheels, none of them had 4.5". Normally I'd agree on measuring from the offset like you mentioned as well, but 95% of the Jeep tech forums use backspacing so it's easier to just keep the measurements consistent.

 

[Mitch502]

I rub (if I'm not mistaken, it's been awhile since I've looked/measured...jeep has been sitting for awhile mostly) on the inside, near the spring (above the spring/on spacer/wheelwell)

Thanks for the information on offset. I knew the backspacing measurements and stuff, but never considered the width of rim vs. offset will set the wheel out more!

Thanks
Mitch

 

[comptiger5000]

You say you're rubbing the pass side rear, but where? Outside or inside?

And every ZJ I've owned has had 5.25" backspacing on the factory wheels, none of them had 4.5". Normally I'd agree on measuring from the offset like you mentioned as well, but 95% of the Jeep tech forums use backspacing so it's easier to just keep the measurements consistent.

The 15" wheels might have been different than the 16s. Both sets of 16x7 5.9 wheels I have sitting around are stamped as +13 offset, which is 4.5" BS.

 

[Mitch502]

I was thinking the anniversary wheels were 16x8?

 

[comptiger5000]

I was thinking the anniversary wheels were 16x8?

Only factory Jeep 16x8s I know of are TJ Moabs. Which wheels are the anniversary wheels?

 

[Mitch502]

The 5 spoke 5.9 wheels are anniversary wheels.

 

[comptiger5000]

Ah, yeah. The 5.9 wheels (Jeep calls them "ultrastar" wheels) are 16x7, +13mm offset.