Ok...here we go....
When a wheel is installed on a vehicle, the backspacing is the distance between the innermost edge of the wheel and the mounting surface where the wheel bolts to the axle hub. To measure backspacing, you need to remove the wheel and lay it face down on a flat surface. Place a straightedge across the inside edge of the wheel. Then use a ruler to measure the distance from the straightedge down to the wheel mounting surface.

1. Hub
2. Brake Rotor
3. Brake Caliper
4. Axle
5. Stud

A. Inside rim lip (inside edge) :greet:
B. Dished center (wheel mounting surface) :greet:
C. Inside valley edge
D. Center weld point
E. Outside valley edge
F. Outside rim lip
G. Inside diameter 12.125"
H. Outside diameter 14.5"
I. Center of axle to outside edge of caliper
X. Back bell depth 4" (measure from A to B) :greet:
Z. Front bell depth 1.5"

 

don't forget offset..

 

Ah yes...offset...good call...I owe a six-pack on that one :lol:

Offset is the distance from the rim's mounting surface to the centerline. Positive offset means the mounting surface is moved towards the outside (away from the center of the car) of the rim. Negative offset is the opposite.

So, here is little bit about my 98 ZJ. It has a 2" BB from http://www.kevinsoffroad.com and Rancho 5000 shocks & Stabilizer from http://www.samsoffroad.com with Energy Suspension polyurethane bushings in a few places.

My ZJ came with the 15x7 Aluminum Alloy Rims.

These are my rims. I know that some of you might call these the canyon rims. However when I got my jeep, the paperwork did not say that I had the canyon rims. It said I had aluminum alloy rims.

So with that said lets see what the backspacing is on these suckers...

 

So as we learned earlier we need a straight edge and a means of measuring...easy.

As you can see I found a piece of wood I had lying around & a ruler I borrowed from my son (I traded my PS2 for this??). BTW...if you ever wondered, now would be a great time to measure your manhood...

I just recently bought a set of Rock Crawler Series 51 15x8 rims with 4 1/2 inch of backspacing from http://www.4wheelparts.com/4wp/products/productLine.asp?cat=WHE&prodline=534&catName=WHEELS&man=TECH

Here is a side by side comparison of the Factory rims vs. the Rock Crawlers. You'll also notice that I am using BFG AT 31X10.5 tires on the Factory rims and BFG AT/KO 31x10.5 on the Rockies. The only noticeable difference are the sidewall. That's it!

 

As you see, I have the tires mounted on all of the rims. This will not cause any problems for my straight edge because I managed to cut it perfectly from rim lip to rim lip. However...this is best measured with the tires unmounted. :bang:

Now we throw in the ruler...(I hope I can trade back my PS2 )
Now keep in mind that we want to look at the bottom of the straight edge...follow the red line!

So as you see...my canyon look-a-likes have 5 inches of backspace & with 31x10.5 tires on...no wonder they rub everytime I make a sharp turn.

 

Alright...here are the 15x8 Rock Crawlers...ah... :drool:...apple pie...mmmm

So...now we use the same technique to measure these suckers...

and as you can see I have about 4.5 inches of backspace on these.

 

I can tell ya that with the 15x8 Rockies with 4.5" backspacing & 31" tires that I have no rubbing at all. :thumbsup:

Here is a pic of my jeep with the factory 15x7 rims with 31x10.5 BFG AT's

This is the rear driver side with the Rock Crawler 15x8 with 31.10.5 BFG AT's. (oh...btw...i got rear ended by honda civic)

This is the passenger side.

Here are some pics of the rear wheels mounted & Kevin's Roof Rack :veryhot:

This is my jeep when I had the 2"BB & 31x10.5 BFG put on

Well now...I hope that I made this subject much clearer for anyone who wanted more help on this. I am not new to forums and therefor I encourage anyone who needs help to use the search function of the forums to find what they need. Nothing sucks worse than having to repeat the same to someone who is just plain lazy to look it up in the search. I am not an expert in tires & rims, I know what I know thru trial & error.

I would also like to give a mad shout out to SWAMPY who has inspired me to tear into my ZJ almost every week...YOU FU ING RULE DUDE!!!

Next I will do the backspacing on a Buddy's 95 ZJ Factory rims...STAY TUNED!!!

 

Nice...

I'm happy that I could help clear this subject up!

I'll be adding more rims with photos to this thread soon. I just hope people find this thread 1st before posting questions about backspacing. As you can see this subject isn't hard at all.

I am very happy with the Rock Crawlers and just so everyone knows, my jeep gets a lot of offroad time. So dont let the shiny red & white parts fool ya

If anyone else wants to add their rims on here please include photos of your work. Maybe a set of actual 15x8" Canyons or perhapse a set of 16x7" factory rims.

Always remember...

 

Alright...time to bring this thread back from the dead! :dark:

As promissed...I'm gonna show you the back spacing on my buddy's factory 15x7, 5 star alloys on his 96 ZJ. Let me tell ya, if you thought that my 15x7 factory alloys rubbed bad with 31x10's & 5" backspacing (which they did!) wait till you see the backspacing on my buddy's rims.

Yea...I see more of these rims on ZJ's than the Canyon look-a-likes

Take a close look and you'll see that these rims have almost 5.25 inches of backspace!

Keep in mind that my buddy does not have a lift or oversized tires on his ZJ. However, assuming that his 96 ZJ and my 98 ZJ aren't that much different, I can only imagine how much rubbing he would have with 31's on a lift under 3 inches.

Stay tuned kiddies, more to follow!! :monkey:

 

excellent tutorial.
been wanting to post up here for a while though.... when i measured my '95 factory "5 stars", i got the same B.S. as a set of "canyons" i bought from a buddies 98 grand... 5 inches.
also, the author makes his new 4.5" BS rims out to be night and day better. pretty minimal change imo.
if all you need to do is keep your 31s off your lower CA's, you can just add a shim or two under the steering stops located on the D-30 knuckles.

 

Green,

You are correct sir! But now you have effectivly changed your turn radius, pretty minimal change yes but change none the less. Lets not forget to mention that tire size will play a huge role into the back space issue in relation to scrub. I run 32" x 11.5 tires on a set of stock 5 stars (5.9 wheels). I've had to use 1.5" spacers and I can still scrub the LCA's and brake line bracket.

 

minimal change is right. i had my stops spaced out like .25" on one side, which is quite a lot cuz if you go too far you could easily bend the damn thing over upon full lock.
Anyways, i wheeled with many grands through very tight stuff like that, never noticed any decrease in turning radius on mine vs. theirs. The steering is pretty bound up and inaccurate at full lock anyway.
I ran 31x11.5 LTBs on stock rims like that , no spacers, fit great.

Glad to see this outa the "hardcore" section. should be stickied here if anything.