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    Measuring rear wheel offsets

    Whenever you do a wheel conversion on your motorcycle there are three things to be mindful of when considering alignments:

    1.) Centering the rear wheel in the frame
    2.) Aligning the rear wheel with the front wheel
    3.) Chain Alignment

    As a general rule you proceed in the order mentioned. This thread is about step #1

    1.) Get the rear wheel centered in the frame
    for a GS this is simple;the GS swing arms are centered in the frame so center the wheel in the swing arm; the distance between the inside of the swing arm fork to a reference point on the wheel (like the lip of the wheel) should be the same on both sides. Another simple way is to put a straight edge across the tire and measure the distance to the inside of the swing arm. To do this measurement make sure that the rear axle is parallel with the swing arm bolt (measure distance between the ends of the bolts and make sure they are the same on both sides; the swing arm markings could be used as well).

    So how is it best to make these measurements? I finally realized that an alignment very similar to the string method should also work on the wheel alignment as well. It is simple and unambiguous.

    There are so many variables and people seldom have the exact same configuration that it is best to recommend doing a final check of measurements regardless of how you do the spacers.

    You need to put a straight edge against each side of a bare wheel and project the wheel edges forward to the wing arm bolt. In order to measure the wheel to frame alignment you also need to clamp a reference to the swing arm bolt location also. Here is a simplified diagram with some pictures to follow.






    Measuring offset between the wheel and the inside of the fork





    Measuring offset between the wheel and the frame



    You could probably also use a string method to project the sides of the rim forward, but the same measurements would apply. Use the rear wheel alignment marks to make sure the wheel is true in the swing arm. This should be of sufficient accuracy to ensure that the spacers are sized correctly and that the wheel is properly centered in the frame.

    A couple of points to make:

    A. ) The wheel should always be centered into the frame (as a guide use a tolerance of +/- 4mm max )

    B.) The wheel should be offset in the forks by a measured offset of the swingarm forks.

    C.)Use the above measurements to check your wheel spacer selections. Continue on with the Wheel and chain alignments after you are done.





    Further references here:

    http://www.thegsresources.com/_forum/showthread.php?t=147705


    I'm an engineer learning how to do this in the backyard. I have had extensive discussions with Katman as well. For further reference Tone is an expert at chassis modifications and has done this professionally. Here is a link to Tone's alignment overview.

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    Last edited by posplayr; 07-27-2012, 03:05 PM.

    #2
    Subscribed
    1983 GS 1100E w/ 1230 kit, .340 lift Web Cams, Ape heavy duty valve springs, 83 1100 head with 1.5mm oversized SS intake valves, 1150 crank, Vance and Hines 1150 SuperHub, Star Racing high volume oil pump gears, 36mm carebs Dynojet stage 3 jet kit, Posplayr's SSPB, Progressive rear shocks and fork springs, Dyna 2000, Dynatek green coils and Vance & Hines 4-1 exhaust.
    1985 GS1150ES stock with 85 Red E bodywork.

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      #3
      I like the tutorial
      You are right, it's easy to get lost and it's not obvious to start from a solid reference point.
      There is one further point maybe worth mentionning which is the fact that the wheel must be secured tightly in the fork before measuring.
      Most times the fork is slightly pinched when the wheel spindle is tightened.
      It's not garanteed that the pinch will be symetrical....
      sigpicJohn Kat
      My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
      GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

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        #4
        Here is an example of using Powerpoint to layout the spacer/spacing/offsets. You dont have to use ACAD, Powerpoint allows you to dimension spacers and even measure by scaling an object to the distance you want to measure.




        Here is an original Powerpoint file for when I did my Bandit Swingarm conversion.



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          #5
          Originally posted by John Kat View Post
          I like the tutorial
          You are right, it's easy to get lost and it's not obvious to start from a solid reference point.
          There is one further point maybe worth mentionning which is the fact that the wheel must be secured tightly in the fork before measuring.
          Most times the fork is slightly pinched when the wheel spindle is tightened.
          It's not garanteed that the pinch will be symetrical....
          Probably no need to have more than about 1mm slack between the stack and the forks or frame.

          With a little persuasion zero slack can work by spacing the forks a little.

          Yes the forks should be tightened so that the wheel doesn't more around on you while doing the measurements. And if it is not obvious by now there is some trial an error until you figure out the right combination for the wheel spacing and chain alighnment.

          Comment


            #6
            Great post posplayr, thanks for your efforts. This is a particularly timely given that I am embarking on this process. I have purchased the bushes from katman (centered swingarm), and he has advised a .650 sprocket side spacer (from the GS) using the bandit wheel and GS hub. I haven't got around to measuring yet, but it appears that this would leave me with 5-6mm gap between the arm and the brake hanger. I will measure up, but would appear that the .780 spacer would be closer to being correct.

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