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How to measure your car for proper wheel fitment

Discussion in 'The Hokey Ass Message Board' started by wheelkid, Sep 27, 2013.

  1. RWENUTS
    Joined: Aug 9, 2011
    Posts: 136

    RWENUTS
    Member
    from Nanaimo BC

    He has a backspace of 5.75 inches. Plus 1/2 inch added to that for the tire equals 6.25 inches. His available space from the wheel mounting surface to the sheet metal is 6.5 inches. The tire would be 1/4 inch away. Not good. At least an inch on the inside would be better. You could get away with 1/4 inch on the outside if side to side body movement is controlled.
    Only way to mount a tire that adds no sidewall to the width is with a very narrow tire like a 195 or 205. You'd still be 3/4 inch from the metal. Not recommended for a narrow tire like that on an 8 inch rim. Sidewall failure in short order.
    Correct backspacing takes in to account tire cross section too!
     
  2. 46stude
    Joined: Mar 3, 2004
    Posts: 1,711

    46stude
    Member

    All fine & dandy, but answer me this:

    A person has 10-1/2" to work with. That's it, end of story. Not gonna mini-tub or radius wheelwells.

    That person is going to run a 10" wide tire on an 8" wide rim. That's it, end of story.

    Is wheelkid's procedure wrong for figuring what they'd need? Sure, 1/4" on either side is not ideal, but if a person runs that particular combo, whats your better option?
     
  3. olscrounger
    Joined: Feb 23, 2008
    Posts: 4,087

    olscrounger
    ALLIANCE MEMBER

    I buy wheels from wheel kid and his dad--they know their stuff
     
  4. AndrewnTX
    Joined: Sep 13, 2009
    Posts: 182

    AndrewnTX
    Member
    from Plano, TX

    I'm a wheel nut, for sure. It's just a lot of fun to spend the time and get it right. Stance of how the car sits, it is top priority but a key to that is wheel style, diameter, width, offset.. I mean backspacing.. a lot of work to get all the factors right and you know, when you see that just right combination, it's awesome.

    What I have done on my cars along w/ basic measurements as you guys described, is trial fit, trial fit, and trial fit. You need to have various wheels around the garage to test it out, measure and get it just right.

    The Falcon Sprint I did just that. Lots of time and work but worth it in the end.
     

    Attached Files:

  5. RWENUTS
    Joined: Aug 9, 2011
    Posts: 136

    RWENUTS
    Member
    from Nanaimo BC

    If that person runs a 10" wide tire on an 8" wide wheel with that 5.75 inch bs he deserves to cut up his tires and buy a new set that fit.
    His procedures wrong because he doesn't include the cross section and adequate tire clearance plus the correct width of the wheel.
    Allow 1" for tire clearance, 1/2 inch for cross section which leaves a 5" bs.
    On the outside allow the same 1 1/2 inches to the rim. Which leaves 2 1/2 inches fs. Total rim width 7 1/2 inches. Which equals a 6 1/2 inch wide rim.
     
  6. Why the Hell are you guys talking in mm on a traditional car site?
     
  7. RWENUTS
    Joined: Aug 9, 2011
    Posts: 136

    RWENUTS
    Member
    from Nanaimo BC

    Because like it or not most tires are measured that way!
    You got bias plys on your traditional I suppose?
     
  8. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,180

    Mr T body
    Alliance Vendor
    from SoCal

    Each build is different, but I don't necessarily want a tire centered, I want the sidewall (normally outer) to fall in a certain place. People had posted that they didn't understand why I was narrowing a rear to put the sidewall where I wanted it on my '31 build. That's the 3rd step in building (not just wheel fitment). I knew the wheel I wanted, the available width and what cross section I could tolerate. That last little step was narrowing to get it just right. If the final placement isn't that big of a concern, backspacing and cross section will get it close.
     
  9. herbet99
    Joined: Jan 16, 2009
    Posts: 194

    herbet99
    Member
    from Central NJ

  10. rfraze
    Joined: May 23, 2012
    Posts: 2,003

    rfraze
    Member

    Lots of correct posts here, but this one points out a very important fact. To get "the look" or "stance", front spacing is very important.
     
  11. J'st Wandering
    Joined: Jan 28, 2004
    Posts: 1,769

    J'st Wandering
    Member

    This is the beauty of the internet. Someone posts how to center a wheel in the opening. We get into a discussion of tire sizing, the width of the tire, metric vs. standard, and who knows what else can be added. Remember, the post was on how calculate centering a rim. :rolleyes:

    I guess the new format doesn't get rid of this crap.

    Neal
     
  12. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,180

    Mr T body
    Alliance Vendor
    from SoCal

    It is a thing of wonder. People take things in different directions according to how they interpret a post. Kinda like the first post being nothing about "centering" a wheel, just about (as the subject line states) how to measure your car for proper wheel fitment, and measuring the backspacing and offset of a wheel.
    Yes, you too are a resident of the internet......
     
  13. RWENUTS
    Joined: Aug 9, 2011
    Posts: 136

    RWENUTS
    Member
    from Nanaimo BC

    Information!
    Correct information is never crap!
    And we never dabbled in the way the measurements where made. The plum bob is square with the world so the outer measurement of 4" is likely correct.
    The inside measurement could be skewed if the hub surface isn't also square with the world. THe vehicle needs to be level and the centre line from the axle to the floor equal and the hub surface square with the world to be accurate.
    And what about the inside measurement from the hub to the spring pack. Could be less.
    I'd betcha it's less than the 6.5" to the sheet metal.
    But that's a subject for another day!
     
  14. rfraze
    Joined: May 23, 2012
    Posts: 2,003

    rfraze
    Member

    I read it to say "How to measure your car for proper wheel fitment". Wheelkid got us off to a GOOD start, but I don't think he was planning to run any wheels without tires, and I am pretty sure he was trying to instruct the wheel and tire should, at least, roll. Do it right, is all anyone is saying.
    If the O/T subject of how to turn on a light was posted, wouldn't someone have to mention checking for an operating bulb?
    What do you say, Wheelkid?
     
  15. blowby
    Joined: Dec 27, 2012
    Posts: 7,272

    blowby
    Member
    from Nicasio Ca

    If the vehicle is not level the plum bob won't be accurate either... :)
     
  16. Personally, I accept this method for positioning the wheel itself. I then factor in the tire to the equation and adjust wheel size accordingly. I believe that Wheelkids example which left 3/4" then needs to be followed up with something like, "add section width of tire to wheel size and check for clearance. Reduce wheel or tire size accordingly".
    Whatever you end up with, the wheel itself will be in the right place, which I believe was the original intent.



    Posted using the Full Custom H.A.M.B. App!
     
  17. wheelkid
    Joined: May 25, 2006
    Posts: 1,204

    wheelkid
    Alliance Vendor
    from Fresno, CA

    I should have just used a 15x7 for the example. It would have been simpler. Some people seem to be missing the point. This centers the wheel in the available space.
     
  18. wheelkid
    Joined: May 25, 2006
    Posts: 1,204

    wheelkid
    Alliance Vendor
    from Fresno, CA

    If you're ok with the wheel sticking outside the fender, this would be fine. Most people don't like that. A 4.5" backspacing will also have a frontspacing of 4.5" and we only have 4" of space.
     
  19. rfraze
    Joined: May 23, 2012
    Posts: 2,003

    rfraze
    Member

    Wheelkid, As original poster, what is your description of proper wheel fitment?
     
  20. pitman
    Joined: May 14, 2006
    Posts: 5,030

    pitman

    Thanks for the equation, most handy to locate the rim offset.
     
  21. Weasel
    Joined: Dec 30, 2007
    Posts: 6,694

    Weasel
    Member

    I don't have a dog in this fight but I do have years of fighting wheel and tire fitment problems. I will throw into the mix two things I do not see mentioned yet. The first is taking into consideration how wider wheels and especially deep dish wheels are going to load up your wheel bearings and cause excessive and premature wear. The other is that certain brands of rear axles have a significant amount of end play - they move from side to side. One glaring example of this and a rear end that I avoid like the plague for this very reason is the Chrysler 8-3/4". Having spent a small fortune on having some custom Chrysler wires built and then adding some expensive whitewalls, after a very short time the tire sidewalls had rubbed through to the canvas even though I had allowed enough clearance to get my fingers between the tire and the wheel well. The rear end moved so much, even mounted on the factory original parallel leaf springs, that it rubbed the tire against the inner wheel well when any lateral forces came in to play. So this whole tire measurement game is not that easy if you intend hogging out the entire available space. But them again I am not sure how traditional that is anyway....
     
  22. wheelkid
    Joined: May 25, 2006
    Posts: 1,204

    wheelkid
    Alliance Vendor
    from Fresno, CA

    An even amount of clearance on both sides.
     
  23. rfraze
    Joined: May 23, 2012
    Posts: 2,003

    rfraze
    Member

    Got it Wheelkid. Thanks. What would proper wheel fitment be on a fenderless car?

    Pitman, Offset is one more step in the math that is so often avoided.

    Weasel, 8 3/4 rear ends have an internal adjuster on the axle which sounds like was loose or the bearings were moving on the axles.
     
  24. 2dr_sedan
    Joined: Mar 25, 2005
    Posts: 265

    2dr_sedan
    Member

    I've found this thread to be quite informative. Thanks to the contributors. :)
     
  25. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,648

    mgtstumpy
    Member

    This cheap and easy home made tool bolts on face of drum with lug nuts and is adjustable for either side of wheel. Turn it around to identify where clearance issues may arise.
     

    Attached Files:

  26. Luther Grimace
    Joined: Jul 6, 2011
    Posts: 28

    Luther Grimace
    Member

    That is a great idea for a fitment tool. Much cheaper than the other option I have seen.
     

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