Thread: Backspacing

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  1. #1 Backspacing 
    Senior Member zj-monster's Avatar
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    This little write-up for is for all the n00bies who keep wondering if 31's will fit on thier Grand. It's a question that every n00bie likes to ask. Many have no clue what backspacing is. Instead of using the trusty SEARCH feature of this and every forum out there. They ask anyway & get flammed out for it. So if you're a n00b who also wants to know, please take the time to read this Write-up & learn a little before you ask...it just might save you from drowning in those flames.



    Backspacing is the distance between the innermost edge of the wheel and the mounting surface where the wheel bolts to the axle hub. In the diagram below this is measured from A to B.


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

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

    There is also offset. Offset is the distance from the rim's mounting surface to the centerline of the rim. Positive offset means the mounting surface is moved towards the outside of the rim. Negative offset places the mounting surface closer to the axle. To figure a rims offset, meaure the rims overall width, subtract the backspace & divide by 2.


    To measure backspacing, you need to remove the wheel and lay it face down on a flat surface. You will need to 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.



    Here is a side by side comparison of the Factory rims vs Rock Crawlers. You'll also notice that there are BFG AT's tires on the Factory rims and BFG AT/KO's on the Rockies. Both are 31x10.5 & the only noticeable difference are the sidewall.


    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.


    Now keep in mind that my staight edge is a 1/2 inch think block of wood. So we want to look at the bottom of the straight edge when using the ruler...follow the red line! In the photo below you'll see that the Canyon rims have 5 inches of backspacing.


    I use the same technique to measure the Rock Crawlers and as you can see they have 4.5 inches of backspace.


    Here is a set of the ol' Saw Blades that are 15x7 & have 5 1/4 inch of backspace.



    It's simple, the lower the backspace number is, the more the wheels will stick out and clear anything they might rub on. Let me tell you about my set-up.

    I have a 2" Budget Boost on my Grand. At the time I mounted 31x10.5 BFG-AT's on my Canyons and they rubbed like hell whenever I made hardcore left & right turns. The rubbing got worse when ever I went off-roading. ( Duh!! I knew this and did it anyway.) If you're looking to go cruising around the mall then this set up will be fine. Just pray that your mallrat buddies aren't around when you turn those wheels. Shortly after, I mounted the 31's on the Rockcrawlers and with a 'lil bit of trimming to the underside of the front bumper, I never had any problems what so ever. Today I have 31x10.5 BFG MT's mounted on those Rockcrawlers and still have no problems. (Soon I'll ditch the 2" pucks for Clayton Long Arms.)

    Spacers are another item that many off-roaders use as it creates the effect of having a rim with a negative offset. They're a good item for those who want to keep the factory rims with bigger meats and they are awesome for making up the difference in axle length, such as using the Ford 8.8 axle in our Grands. Both spacers or rims with less backspace will let you run bigger meats since the mounting surface is closer to the hub (Thus the rim is pushed outside the vehicle). However, many will tell you that this also increases the stress to the wheel bearings and such.

    Just keep in mind that this is only the basics. Obviously the more meat you put on those rims the deeper the backspacing & higher the lift must be. Just use the search feature of this fourm and read about what everyone else is using, then use your own judgement.

    Be sure to check in often as I am sure this thread will continue to grow.

    Peace...
    Last edited by zj-monster; 07-15-2006 at 11:28 PM.
    Quote Originally Posted by CurtP View Post
    What a fucking concept, eh? How dare you bring logic to this thread. What are you, some kind of asshole?
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  2. #2 Re: Backspacing 
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    OverkillZJ's Avatar
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    I love it, ULTRA idiot proof pictures! Thanks for the writeup.
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  3. #3 Re: Backspacing 
    The Oil Dude MallCrawlin Vendor
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    Excellant write up.
    Your #1 Source for Amsoil Lubricants

    Lube it or Loose it!

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  4. #4 Re: Backspacing 
    Senior Member rob92xj's Avatar
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    Good write up, plain and simple.
    The Fleet:
    92 XJ 4.7L AW4 NP 242 Dana 30 with lock right 2000 XJ brakes and stub shafts, Chrysler 8.25 with 29 spline shafts and trac lock 4.56s, 35 12.5 BFG MTs on Soft 8 steelies
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  5. #5 Re: Backspacing 
    Member 2000_WJ's Avatar
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    A noobs been saved thanks
    2000 WJ

    Highschool jeeper
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  6. #6 Re: Backspacing 
    Senior Member zj-monster's Avatar
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    Sweetness.

    My task is complete now. Go forth thy n00b and spread your knowledge to those who are willing to learn.

    Last edited by zj-monster; 07-15-2006 at 11:37 PM.
    Quote Originally Posted by CurtP View Post
    What a fucking concept, eh? How dare you bring logic to this thread. What are you, some kind of asshole?
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  7. #7 Re: Backspacing 
    Member FallstonZJ88's Avatar
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    Ok Good info!!

    I just ordered some cragar soft 8's for my 96 ZJ.

    I got 15 x 8 with 4" of BS. Isnt the stock width 7"?? If so would the extra inch in width offset the loss of the inch of BS?? Just still trying to figure out if the tires are still gonna rub on the control arms...
    Mods in the sig.

    (BTW I'm away at school so next week they're getting put on, for the people that might say just go try em...)
    Now: '96 Gayest color ever 4.0L Pristine One-owner ZJ : About to get hacked up
    Sold:
    -'96 Dark Purple ZJ 4.0L : 3.5" RE lift, 32" BFG A/T KO on steelies, etc.
    -1992 Toyota Supra

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  8. #8 Re: Backspacing 
    Senior Member zj-monster's Avatar
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    My rockies are 15x8 with 4 1/2" of backspace. So your Crager 8's with 4" of BS will be fine. The extra inch in width between the factory rim and the aftermarket would have to be a factor in choosing the right backspacing.

    If you had chosen a 15x8 with the same BS at the 15x7, then the extra inch on overall width will definetly hurt you on the trail when rubbing.

    I'm still in Kenya...away from my rebuilt ZJ. I haven't wheeled since Sept of '06 so the less I wheel & work on my ZJ the less I seem to remember when it come to this stuff. If anyone else agrees or disagrees with me on this, let me know. My old fart ass is starting to forget this kinda stuff.

    Good grief I can't wait to come home.
    Quote Originally Posted by CurtP View Post
    What a fucking concept, eh? How dare you bring logic to this thread. What are you, some kind of asshole?
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  9. #9 Re: Backspacing 
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    Hi, informative post.. thanks for sharing it..
    Take advantage of latest collection of 642-427 braindumps tutorial and braindumps guide and learn how to create awesome websites. For more info, visit Columbia University, Baldwin Wallace University, Youtube and Facebook.
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