Ideal backspacing

[CJim7]

Most guys (and gals) going to a larger tire experience a wider turn radius due to the tires hitting the springs. Thus, we bring out the set screw adjustment to avoid this, which doesn't help the turn radii, but prevents the rub....or we purchase new rims with less backspacing.

My solution to this was to purchase a set of stock 15x8 steel wheels off of an early '80's AMC J-truck (J-2000). I happened across these several years ago when one of my employees was selling them. One look told me they had a crazy amount of negative backspacing (bringing the tire farther out). far more then the stock 15x8 rims used on CJ's back in the day. I jumped on them to replace the stock wheels I had, running 33's, and encountering rub.

Today I run 36's on these same rims and still do not experience spring rub due to the extra diameter.

The pics below show a typical 12.5" wide tire (which many run) on the J-truck 15x8 rims. You can see how much the tires are brought out...enough to be illegal in many states without the use of something wider then the stock flares.

On 36's:





This is on 33's (12.5's)...notice the amount of distance between the drivers side tire and the location of the front spring pack.

 

[coldair]

Thats one good looking rig you have there Jim!

 

[CJim7]

Thanks Vaughn. Built for function, I feel comfortable taking it into any offroad situation.

 

[BusaDave9]

Brock had a good post showing what the backspacing is.
Here's what he had to say:

Here ya go:

Here's the thread: http://www.jeep-cj.com/forums/f49/another-stupid-question-4459/

 

[CJim7]

Thanks for that Dave. It's hard for a lot of people to grasp negative and positive backspacing unless there is a visual.
More negative backspacing equals more distance from the WMS. It sounds backwards...and that's what makes it confusing.

 

[Posi]

Nice looking rig Jim!

What was the backspacing on the 80's FSJ rim? I thought they were the same as the 70's FSJ. 3.5-3.75" is the normal backspacing for 15" wheels. 4-4.5" for 16" wheels. Was there a chance they were aftermarket rims with 2 1/2" BS?

When you swap in the 60's chances are you'll be looking to go with positive (tire-in) backspacing even if you cut them down.

I have 2 sets of rims for my 60's with 7" and 5" positive backspacing.

 

[CJ007]

Thats one good looking rig you have there Jim!

X2!

I need to get my measurements and see where I stand as I get some rubbing on my front shocks in certain situations.

 

[Sasquach]

Jim those do not look like factory Jeep wheels to me, the triangle in a Jeep wheel is more rounded especially at the inner point. They look more like an aftermarket steel wagon wheel but hard to say from the picture.
I have been looking for the same results you have and all I can come up with is the Pro comp rock crawler with 2.5" back space and there's a non DOT stock car type wheel that is 2" backspace. I'll try and dig up some more info.

 

[Sasquach]

Pro Comp Wheels 152-5885R2-5 - Pro Comp Xtreme Rock Crawler Series 152 Black Wheels - Overview - SummitRacing.com

These are bit heavy on the bling for my CJ but maybe the bolt heads painted out would help.

 

[Sasquach]

Bart Wheels 400150813-2 - Bart Wheels Stock Car Standard Weight Black Wheels - Overview - SummitRacing.com
These may not have the correct center hole size, need to check.

U.S. Wheel 70-5855R - U.S. Wheel 70 Series White 8-Spoke Wheels - Overview - SummitRacing.com
This is the type wheel yours may be? if not a Jeep wheel.

 

[derf]

Thanks for that Dave. It's hard for a lot of people to grasp negative and positive backspacing unless there is a visual.
More negative backspacing equals more distance from the WMS. It sounds backwards...and that's what makes it confusing.

There's backspacing and then there's offset.

Backspacing is the measurement from the inside of the rim to the mounting surface of the wheel. I've never seen negative back spacing in a wheel. Except for when you try to mount a dually wheel the wrong way.

Offset is measured from the center of the tire to the mounting surface of the wheel. That's where you get the positive/negative measurement.

Typically, Americans use backspacing, especially when dealing with wheels for older vehicles.

Europeans on the other hand have used offset for their wheels for a long time. Though the trend is for some American wheels to be measured in offset now, especially when they are made for foreign brand cars.

 

[Sasquach]

There's backspacing and then there's offset.

Backspacing is the measurement from the inside of the rim to the mounting surface of the wheel. I've never seen negative back spacing in a wheel. Except for when you try to mount a dually wheel the wrong way.

Offset is measured from the center of the tire to the mounting surface of the wheel. That's where you get the positive/negative measurement.

Typically, Americans use backspacing, especially when dealing with wheels for older vehicles.

Europeans on the other hand have used offset for their wheels for a long time. Though the trend is for some American wheels to be measured in offset now, especially when they are made for foreign brand cars.

Agree, never seen negative backspace. negative offset yes.

 

[CJim7]

Nice looking rig Jim!

What was the backspacing on the 80's FSJ rim? I thought they were the same as the 70's FSJ. 3.5-3.75" is the normal backspacing for 15" wheels. 4-4.5" for 16" wheels. Was there a chance they were aftermarket rims with 2 1/2" BS?

When you swap in the 60's chances are you'll be looking to go with positive (tire-in) backspacing even if you cut them down.

I have 2 sets of rims for my 60's with 7" and 5" positive backspacing.

I will have to measure again...but I think they are 2½"
Yep, I will be looking for more backspacing when I do the axle swap for that very reason. Im going full width, but I still want to fit between trees I plan on 17's with 43" SX stickies.

Jim those do not look like factory Jeep wheels to me, the triangle in a Jeep wheel is more rounded especially at the inner point. They look more like an aftermarket steel wagon wheel but hard to say from the picture.
I have been looking for the same results you have and all I can come up with is the Pro comp rock crawler with 2.5" back space and there's a non DOT stock car type wheel that is 2" backspace. I'll try and dig up some more info.

Good eye! the picture that shows the rim holes is actually the closest spare rim I could find and I searched high and low for a match...The other 4 are more rounded

There's backspacing and then there's offset.

Backspacing is the measurement from the inside of the rim to the mounting surface of the wheel. I've never seen negative back spacing in a wheel. Except for when you try to mount a dually wheel the wrong way.

Offset is measured from the center of the tire to the mounting surface of the wheel. That's where you get the positive/negative measurement.

Typically, Americans use backspacing, especially when dealing with wheels for older vehicles.

Europeans on the other hand have used offset for their wheels for a long time. Though the trend is for some American wheels to be measured in offset now, especially when they are made for foreign brand cars.

Correct! And maybe Im old (or maybe it was a Montana thing lol)....but back in the day when I was in the market for wheels, that's how they were being measured and advertised....measured from the wms to the inner rim edge.. more negative backspacing brought the tire in, reducing wheelbase...positive backspacing was bringing the tire outward. so 2" negative backspacing is farther from the axle then 4" negative backspacing.
...Daves illustration shows what Im talking about....WMS to rim.
Tomato tumaughto? perhaps

 

[Sasquach]

So you have WT axles yes? Was not aware that WT would have the rub issue?
Anyway I have been thinking along the lines of a wheel with less back space for my NT axles than my stock CJ 3.75" BS wheels to gain a bit of stability along with providing better turn radius.
Hate to give up my "old school" NT look though.

 

[CJim7]

So you have WT axles yes? Was not aware that WT would have the rub issue?
Anyway I have been thinking along the lines of a wheel with less back space for my NT axles than my stock CJ 3.75" BS wheels to gain a bit of stability along with providing better turn radius.
Hate to give up my "old school" NT look though.

Yep, WT axles. When i first started running the 33's on my stock wheels, I encountered a slight bit of rubbing at full turn. Turning out the steering stops solve it, but when I ran across these other wheels I jumped at the chance to regain the lost radius.
Maybe my stops were turned in more then normal to begin with...but knowing there was more turning capability it was disheartening to have to limit it.

 

[derf]

Correct! And maybe Im old (or maybe it was a Montana thing lol)....but back in the day when I was in the market for wheels, that's how they were being measured and advertised....measured from the wms to the inner rim edge.. more negative backspacing brought the tire in, reducing wheelbase...positive backspacing was bringing the tire outward. so 2" negative backspacing is farther from the axle then 4" negative backspacing.
...Daves illustration shows what Im talking about....WMS to rim.
Tomato tumaughto? perhaps

You're thinking of offset when you're talking about negative vs positive.

Take, for example, an 8" wide wheel.

If you have 0" backspacing, the WMS of the rim is exactly even with the inner edge of the wheel. On the other hand, the offset for that wheel will be -4" because it's 4" to the inside from the center of the wheel.

An 8" wide wheel with 2.5" backspacing will have the WMS 2.5" from the inner edge of the wheel. Measured in offset, this will be -1.5".

If you had an 8" wide wheel with 4" backspacing, you'd have 0 offset because you're in the center of the wheel.

The same 8" wide wheel with a 6" backspacing will have a +2" offset. Now that you're pushing the WMS to the outside of the wheel, you're in the positive offset category.

If you went crazy with the backspacing, you could have an 8" wheel with a -1" backspacing. That would be a -5" offset.

Make sense?

 

[Sasquach]

 

[CJim7]

As the image shows, offset is simply the center of the wheel to the wms. Backspacing is clearly shown as the wms to the wheel edge.

 

[BusaDave9]

If you have 0" backspacing, the WMS of the rim is exactly even with the inner edge of the wheel. On the other hand, the offset for that wheel will be -4" because it's 4" to the inside from the center of the wheel.
Make sense?

As the image shows, offset is simply the center of the wheel to the wms. Backspacing is clearly shown as the wms to the wheel edge.

Sounds like you guys are in agreement and just don't know it.

 

[CJim7]

Sounds like you guys are in agreement and just don't know it.

Lol...I think so
Anyway, the point of my thread was to offer a good alternative wheel to run to avoid tire rub on the springs.