Backspacing Question

[JeepCJ5]

So - the PO had 35x12.50R15's installed on my CJ. They look great, and the ride is nice. It has a 4.5" Rubicon Express lift kit.

They are almost new, and I planned on just sticking with them until: I was crawling around underneath and noticed some writing on the inside of the wheels. It says Max tire diameter - 31" !!! Why 4WheelParts would install 35's on these wheels, I have no idea.

For my tastes, I would much prefer to run 33x10.5R15's on the jeep. I think they would look nicer and I am not a fan of the look of 12.5's until you hit the 37" diameter tires.

As far as I know, my axles are stock - I haven't cracked the dif yet to check the gearing. The PO also had to put on pretty darn thick spacers to fit these tires. I would like to ditch these.

My question - what backspacing do you guys recommend? Am I correct in assuming that a centered backspace is the best solution? I plan to put the 33x10.5's on 15x8" rims.

Thanks for any advice!

 

[Lumpy Grits]

Who made the rims? I have never seen such markings.
Use the same back spacing you have now. What is the width of your rims?
LG

 

[Torxhead]

I am thinking those 35s might be on a 7" rim.

 

[JeepCJ5]

This is the wheel:
http://www.ultrawheel.com/wheel/124/175-rogue/

It says it has a -44mm backspacing. I guess that is about 1.75"? That seems shallow - I guess that is why the spacers were needed. I haven't measured the spacer, but I would guess it is 1.25", so that combines for around 3" of backspacing. I suppose if I go with 3 or 4" backspacing with a skinnier tire, I should be good.

 

[Lumpy Grits]

What really scares me about those wheels, is where they were made(China).
If you have to run spacers(I hate those, BTW), then yes, get to new wheels.
Would like to know the rim's width.

FWIW: My ALCOA alum wheels run about 3 3/8" backspacing to the edge of the rim's 'lip'.

LG

 

[JeepCJ5]

I want to run 33's, so I plan to ditch the wheels (and spacers unless necessary). I'll double check the width when I get home. I was sure they were 15x10's.

On my old TJ, I once ordered 33x10.5's on 15x8 rims. When I picked them up from the shipper, they had somehow put 33x15.5's on a 15x8 rim! They looked like moon tires!

 

[Lumpy Grits]

I have run 33" BFG/AT's on 15x8 ALCOA rims for many years. Never been an issue and the 8" width somewhat protects the tire's sidewalls in rocks.
LG

 

[JeepCJ5]

I've been looking at these M/T's:

Mickey Thompson - Classic Baja Lock, 15x8 with 5 on 5.5 Bolt Pattern - Matte Black (1958402) | 4WheelParts.com Classic Baja Lock

Can't tell where they are made. Apparently some are made by Alcoa, but some are Chinese.

 

[Lumpy Grits]

3.6" backspacing might be a bit much with your narrow track axles.
Good outfit to deal with.
Wheels for 1981 Jeep CJ5/CJ7
LG

 

[JeepCJ5]

Yes, I was looking at that site also. They list offset instead of backspacing. I didn't understand the difference between offset and backspacing, but I think I've got it now.

On a 15x8 rim an offset of zero means a backspacing of 4" right?

If the offset is -25.4mm, then that is the equivalent of a 3" back space right?

 

[HackFabrication]

33x10.50-15 Tires on 8" wide rims with 3.5-3.75 inches of back spacing would be my recommend if you want 33's that aren't too wide.

Spacers are sketchy, depending on the materials used in their manufacture. The benefit to spacers, is getting the wider tire further away from the springs at full lock (or changing wheel bolt pattern). Big problem when running wider tires on a narrow track CJ is that they will contact the springs at full lock.

FWIW, I'm running a 2.5" lift, 32x11.50-15 TSL/SX tires on 8" wide Eagle Alloys:



I needed to adjust the 'stops' to keep the tires from contacting the springs and the sway bar.

 

[Lumpy Grits]

Hack-I had to do the same on my '85 and I have wide track.
JeepCJ5-I believe you are correct on the backspacing deal. Will never
understand the 'logic' of using metric here.

LG

 

[JeepCJ5]

Thanks Hack, that helps a lot!

 

[tarry99]

Yes, I was looking at that site also. They list offset instead of backspacing. I didn't understand the difference between offset and backspacing, but I think I've got it now.

On a 15x8 rim an offset of zero means a backspacing of 4" right?

If the offset is -25.4mm, then that is the equivalent of a 3" back space right?

Backspace and offset are totally different terms , all wheels are not created equal in the sense of backspace or offset..........Most wheels are sold to fit a particular OEM specification that has to do with how the engineers of a particular car or truck set up there steering geometry.......and brake package.

In either case the offset used is engineered and matched to other measured components within the system that make up terms like Scrub radius and steering axis inclination..........add a different offset wheel to your Jeep and it screws up all of the above like: adding additional leverage & strain to your steering components , adding additional force to turn , wearing out parts sooner and also adding additional wear to your tires.........

Do yourself a favor and Google up wheel offset and run through all the terms until you understand how important they are to be closely followed and then apply the best wheel to your application.

I just had Walker Evans build me 5 custom 17 x 8.5 beadlocks for my latest project that has 1-1/2 ton components mated to a Ford 9" center section.........matching up the intended OEM Geometry out at the spindles was obviously very important to make this handle more like a car than a tractor.

 

[HackFabrication]

Big problem when running wider tires on a narrow track CJ is that they will contact the springs at full lock.

I should have also added larger diameter tires to the above ^^^

IMHO, I'm not a huge fan of lifts over 2-3" on a CJ5 . Narrow track, short wheelbase, high center of gravity. Makes for a 'twitchy' vehicle if the suspension, wheels/tires, and the steering aren't set up properly. Think mini-van pulling out in front of you and having to make an evasive maneuver at speed. Then there's the problems with matching axle ratios to wheels/tires/Transmission /etc, and the brakes needed to stop larger wheels/tires. Stock CJ brakes (disk/drum) should have little if any problems with 33" (I know guys who have 35's and no problems), as long as they are in perfect condition.

Common internet lore: Good stock CJ springs will allow you to run 31" tires with minimal issues.

I could actually stuff a set of 34x9.50-15 TSL tires under my CJ5 with the 2.5" lift. They would be fine around town and Limited off-road (very mild trails). In fact, I'm looking for a taller tire to run exclusively 'on the street', as I'm geared with 4.56's. But I haven't found a 34-35" all terrain radial tire, in a 15" rim size I like, that is less than 12.5" wide.

 

[JeepCJ5]

Thanks for the comments guys. I probably wouldn't have gone with the 4.5" lift if I bought a stock vehicle, but that's what I have. As I mentioned, I am happy with the driving characteristics so far, but I haven't had a minivan pull out in front of me yet!

 

[Peanut Butter]

I've been looking at these M/T's:

Mickey Thompson - Classic Baja Lock, 15x8 with 5 on 5.5 Bolt Pattern - Matte Black (1958402) | 4WheelParts.com Classic Baja Lock

Can't tell where they are made. Apparently some are made by Alcoa, but some are Chinese.

I use to have a Cherokee that I ran as an Emergency vehicle in Colorado. I did a 3 inch lift on it. I used Pro Comp Rock Crawler wheels 15x8 and MT Baja Claws (radial) 31x10.5x15. They took me everywhere I wanted to go in all kinds of weather. We lived at 7000 ft. I ran 90+ mph with no problems. They wore well and never failed me. Cost was good too. Just food for thought. Good luck with your choice, it's gotta be better then what you have.