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    1. #1
      Join Date
      Jan 2008
      Location
      Elk Grove, CA
      Posts
      213

      What Back Space?

      Ok, I have a question that I’ve been meaning to ask. I have a 69 Camaro with a 10 bolt rear end which measures 60” width. I also have a 12 bolt rear end out of an earlier Nova that measures 57.57 width that I was planning on using. My question is: what back space would be appropriate for the widest wheel for the rear?



    2. #2
      Join Date
      Aug 2004
      Location
      Pittsboro, NC
      Posts
      194
      Decide on what size tire you want to run, buy the tires and mock them with rear diff in car. Measure with a tool like wheelrite, etc. This is the only proper way to get exact fit as all these cars can be off 1/4 to 1/2" which can make the difference between clearing and rubbing.

    3. #3
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      Stock Camaro would be 9.5” with a 5.5” backspacing.

      Subtract the width of the new rear end from the original. Divide the difference by 2. Subtract that number from the 5.5” backspacing.

      60-57.75=2.25
      2.25/2=1.125
      5.5-1.125=4.375 backspacing

      Don’t forget to adjust for any offset introduced by non stock brakes.

      If you want to give yourself a little wiggle room add .25” to the backspacing so you can adjust with a small spacer.

      Don
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    4. #4
      Join Date
      Nov 2008
      Location
      Lawrenceburg, TN
      Posts
      4,083
      Country Flag: United States
      Quote Originally Posted by dhutton View Post
      Stock Camaro would be 9.5” with a 5.5” backspacing.

      Subtract the width of the new rear end from the original. Divide the difference by 2. Subtract that number from the 5.5” backspacing.

      60-57.75=2.25
      2.25/2=1.125
      5.5-1.125=4.375 backspacing

      Don’t forget to adjust for any offset introduced by non stock brakes.

      If you want to give yourself a little wiggle room add .25” to the backspacing so you can adjust with a small spacer.

      Don
      ^^^^ yep

    5. #5
      Join Date
      Jan 2008
      Location
      Elk Grove, CA
      Posts
      213
      Quote Originally Posted by dhutton View Post
      Stock Camaro would be 9.5” with a 5.5” backspacing.

      Subtract the width of the new rear end from the original. Divide the difference by 2. Subtract that number from the 5.5” backspacing.

      60-57.75=2.25
      2.25/2=1.125
      5.5-1.125=4.375 backspacing

      Don’t forget to adjust for any offset introduced by non stock brakes.

      If you want to give yourself a little wiggle room add .25” to the backspacing so you can adjust with a small spacer.

      Don
      I agree, that is great information! Thank you

    6. #6
      Join Date
      Jan 2008
      Location
      Elk Grove, CA
      Posts
      213
      I think they would have to be special ordered, most wheels are either 4” or 4.5” backspace

    7. #7
      Join Date
      Oct 2011
      Posts
      696
      Try searching for a euro bolt pattern like 5x120. That’s same as 5x4.5” bolt pattern. Much more options out there. You can use an offset calculator to see what the conversion is from mm to inches. For example if you plug in 12” width rim and want to have 5.5” offset that equals 25mm on the calculator. Plenty of 5x120 wheels that are 12” wide with 25mm offset.

      https://tiresize.com/wheel-offset-calculator/

    8. #8
      Join Date
      Oct 2004
      Posts
      2,544
      Country Flag: United States
      Quote Originally Posted by joeko23 View Post
      Try searching for a euro bolt pattern like 5x120. That’s same as 5x4.5” bolt pattern.
      You meant 4.75" bolt spacing, not 4.5" which is the Camaro pattern.
      Red Forman: "The Mustang's front end is problematic; get yourself a Firebird."

    9. #9
      Join Date
      Oct 2011
      Posts
      696
      Quote Originally Posted by 68Formula View Post
      You meant 4.75" bolt spacing, not 4.5" which is the Camaro pattern.
      Yup! Sorry

    10. #10
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      Quote Originally Posted by elwaupo View Post
      I think they would have to be special ordered, most wheels are either 4” or 4.5” backspace
      Go with 4.5” backspacing and add a small 1/8” or so spacer if needed.

      Don
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    11. #11
      Join Date
      Aug 2007
      Location
      Normal, IL
      Posts
      234
      Since nobody else mentioned it, if you're planning on putting disc brakes you need to factor in rotor thickness and wheel spoke to caliper clearance.

    12. #12
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      Quote Originally Posted by badbu68 View Post
      Since nobody else mentioned it, if you're planning on putting disc brakes you need to factor in rotor thickness and wheel spoke to caliper clearance.
      Post #3:

      Don’t forget to adjust for any offset introduced by non stock brakes.

      Don
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    13. #13
      Join Date
      Oct 2015
      Posts
      362
      Country Flag: United States
      4.75" is 120.65mm so while 120mm may bolt on it is definitely not ideal. Chances are it will vibrate.
      My half a$$ed build thread.https://www.pro-touring.com/threads/...elle-6-0-4L60E

      Tighten it till it strips & back it off a quarter turn.

    14. #14
      Join Date
      Aug 2005
      Location
      Hamilton, NJ
      Posts
      4,291
      Country Flag: United States
      +1 they are not the same
      Quote Originally Posted by Alwhite00 View Post
      4.75" is 120.65mm so while 120mm may bolt on it is definitely not ideal. Chances are it will vibrate.
      Scott from NJ.

      Vent Windows Forever! ...

      Feather-light suspension, Konis just couldn't hold
      I'm so glad I took a look inside your showroom doors

    15. #15
      Join Date
      Oct 2004
      Posts
      2,544
      Country Flag: United States
      Quote Originally Posted by Alwhite00 View Post
      4.75" is 120.65mm so while 120mm may bolt on it is definitely not ideal. Chances are it will vibrate.
      To add, it creates a lot of stress on the studs which could result in failure.

      OP,

      The wheels would need to fit hub centric to the car they are going, and then PCD variation bolts (aka wobble nuts) could be used to properly mate the lugs to the wheels. Here's a good explanation: https://www.team-bhp.com/forum/tyre-...s-reality.html

      I'm sure there are people that have gotten away with bolting them straight on (after all, there is some tolerance variation to everything), but that doesn't make it a good idea.
      Red Forman: "The Mustang's front end is problematic; get yourself a Firebird."

    16. #16
      Join Date
      Oct 2011
      Posts
      696
      Check out this thread. I personally put 5x120 on my Camaro. The wheels I purchased come setup for conical lug nuts. I also bought a hubcentric adapter and everything bolts up and is free of vibrations. People have done this and are currently doing it. Maybe I’m just making myself feel better about the situation. Time will tell.

      https://www.thirdgen.org/forums/whee...-vs-5x120.html

    17. #17
      Join Date
      Aug 2005
      Location
      Hamilton, NJ
      Posts
      4,291
      Country Flag: United States
      A while back one of the engineers from AME put up some diagrams showing the stress on studs for both proper 120.65 fitment and 120. The 120s had so much more stress on the studs. Iirc his comments were along the lines of lots of folks do it, but I wouldn't. I decided he's smarter than I am, I'll listen to him. To each their own. I like headrests, 3 points, US made suspension parts and no one in the back seat with rollbars too lol.
      Scott from NJ.

      Vent Windows Forever! ...

      Feather-light suspension, Konis just couldn't hold
      I'm so glad I took a look inside your showroom doors

    18. #18
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      I remember that thread with the FEA analysis. The trouble was that he did not post a scale with his simulation results which made it pretty much impossible to draw any real conclusions from. He subsequently deleted it.

      Don
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    19. #19
      Join Date
      Jan 2008
      Location
      Elk Grove, CA
      Posts
      213
      �� That’s a lot of information

      - - - Updated - - -

      Quote Originally Posted by dhutton View Post
      Go with 4.5” backspacing and add a small 1/8” or so spacer if needed.

      Don
      Thats looking like the best bet, keep it simple

    20. #20
      Join Date
      Jan 2008
      Location
      Elk Grove, CA
      Posts
      213
      Quote Originally Posted by dhutton View Post
      Post #3:

      Don’t forget to adjust for any offset introduced by non stock brakes.

      Don
      I’m running the stock disc brakes at least for now. Hopefully that won’t be a problem.

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