33x12.50 OWNERS: OPTIMUM BACKSPACING

[DOGMAN]

I would appreciate those of you who run 33x12.50's to give me your opinion of what backspacing on an 8" wheel you think works and looks best.

I have a 91 4dr with 5.5" Superlift and will be installing 33x12.50's soon. The stock backspacing is 4.5" on the 7" wheel.

I'm trying to take all angles into consideration: appearance (do the wheels stick out too far; not enough), contact with the swaybar at full turn, wheel bearing and ball joint life, turning radius, and fender contact.

The range I've seen people run is from 3.25" to 4.5", with most between 3.5" and 4.0". Will the 3.25" stick out too far, or will it work and look fine? Does the 4.0" give you enough clearance? Is 3.5" to 3.75" the optimum? I'm really looking for your experienced based opinions.

Thanks for your help. It will make my decision much easier.

DOGMAN

 

[tiessen]

I was running 8" wheels with a positive offset of .25" ie: 4.25" of backspacing. My 33x12.5's did not rub on the sway-bar but did still rub on my Superrunner radius arms. Also, they were getting pretty close to the back edge of the fender when I turned hard in compression. You are damn if you do and damned if you don't I say. I am now running 33x10.5's on the street and may buy some Swampers or Mudders for fun later, but I'll mount them on stock rims and live with rub on the radius arms. Better than doing inadvertant bodywork on my fenders.

Cheers

Dale

 

[RangerX]

DOGMAN,
When going to a larger tire, you want to move the tire out somewhat to avoid rubbing things on the inside. The question is how much? I ran 33X12.5 on stock rims(15X7-4.5"bs) for several years before switching to 15X8 with 4" bs, and recently to 15X8.5 with 3.75" bs and 37X12.5 tires. I have the Rancho radius arms, which are straight, so I had/have some rubbing with all tire/rim combos, stock rims and 33"s being the worst. I think that 3.75" bs should work fine for you with 33"s, and IMHO any less (3.5 and down) is asking for problems with bearings, tire scrub, etc.

 

[DOGMAN]

Thanks for your help guys. The problem I run into is that I see a style of wheel I like, only to see that it has too much or too little backspacing.

RangerX,

What brand of 37" tire? Do you do any fender trimming? I'd like to see it.

DOGMAN

 

[RangerX]

DOGMAN,
Ask about custom backspacing if the rim you like has a less desirable offset. I bought Rock Crawler rims from 4WPW, and they do any offset free, you just have to wait several weeks.
I have two sets of tires/rims. Offroad, its 33" BFG MT's. Onroad, its 37" Denman Coyotes, actually 315/85R15. I had to trim 2" off the back of the front fender openings. It's a 93 Ranger, which I think has slightly larger fender openings than Explorers.

 

[DOGMAN]

An observation -- My stock 7" wheel has 4.5" backspacing, which means a positive offset of 1.0" (the center of the wheel is 1.0" inside the mounting surface). An Eagle 589 15x8 wheel has a 3.25" backspace, which translates to a negative offset of 0.75" (the center of the wheel is 0.75" outside the mounting surface).

It makes sense to me that the greater the offset is, the more pressure is put on the wheel bearings and ball joints, which makes them wear faster. How much faster, I'm not sure. Does anyone have any data on this?

The question I would like answered is: Does the direction of offset make any difference on the load transferred to the wheel bearings and ball joints? In the example above, the stock wheel's center sits 1.0" INSIDE of the mounting surface, and the 589's center sits 0.75" OUTSIDE. I know that the 589 is an inch wider than the stock wheel, and it will hold a wider tire, which influences wear and tear, but, if all things were equal, both wheels of the same width, but one has say a 1.0" positive offset and the other one has a 1.0" negative offset, is one worse than the other, or are they the same?

If anyone has this knowledge, I'd really appreciate it if they shared it with me. I'm very curious.

Thanks.

DOGMAN

 

[ExplorGM]

Has anyone with a 95-97 gone to 33x12.5 (or larger) tires? If so, what wheels, tires, backspacing and or offset are you using? Any rubbing?
Thanks,
Rick

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Rick
95 Explorer Sport Expedition
Dead Link Removed