RE: tires [backspacing]

From: Jason Jennings (jason@spray-tech.com)
Date: Fri Feb 05 1999 - 09:44:15 EST


thanks....Yeah, I think I am going the 15" route.... It seems I can
find a ton of tires for 15s, so.... Thanks for the help.

Jason
2/5/99 9:49 AM

        -----Original Message-----
        From: Bob Tom [SMTP:tigers@bserv.com]
        Sent: Thursday, February 04, 1999 4:45 PM
        To: dakota-truck@buffnet.net
        Subject: RE: DML: tires [backspacing]

        Jason

        I think this began with using drag radials on 15" rims.
        If so, then it makes it easier because you only have to
        consider tire clearance in the rear.

        The stock rims for the R/T are 17x9. For measuring purposes,
        a 9" rim is considered to be 10" wide. The extra inch is
        because of how rims are made ... on a rim there is
        1/2" more on the inner and outer part of the rim lip for the
        bead of the tire.

        I don't know what the backspace of your stock rim is so for
        illustration purposes let's suppose it's 4". Let's also for
        illustration purposes suppose that there is 1" between the
        bulge of your tire to the nearest part of the truck (usually
        the leaf spring).

        Stock R/T rim:
                      clearance
          leaf spring <-- 1"--> tire bulge
                                    inner rim lip outer rim lip
                                       | |
                                       | |
                                       | mounting surface |
                                       | | |
                                       | | |
                                       | | |
                                       |< 4" >|< 6" >|
                                        backspace front space

        clearance + tire bulge + backspace = x"
                                        

        15x8 rim:
                       clearance
          leaf spring <--?--> tire bulge
                                 inner rim lip outer rim lip
                                   | |
                                   | |
                                   | mounting surface |
                                   | | |
                                   | | |
                                   | | |
                                   |< 5.5" >|< 3.5">|
                                     backspace front space

        As long as clearance + tire bulge + backspace does exceed x",
        the rim and tire should be okay.

        You need to measure the distance from the bulge to the nearest
truck part,
        the bulge (use the stick across the bulge and the stick across
the rim lips),
        and the backspacing of your R/T rim.

        The R/T P255/55R17 tire has almost the same outer diameter of a
P275/60R15
        tire.

        The P275/60R15 will have a wider cross section (10.83") than on
the
        P255/55R17 (10.04"). A guess on my part is that the bulge on
the
        R/T tire is maybe .25" and the bulge on the P275/60R15 on a 8"
rim
        is about .9"

        Hope this helped.

        Bob
        Burlington, Ontario

        '97 CC Sport, 5.2L, 3.55 auto., flame red
          Gibson duals, KN drop-in
          Coloured-keyed grille guard, running boards
              and hard tonneau cover
          Deflectors, grille insert
          AR-211 15x7 rims (4.75" backspace)



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