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Help Needed: 450gp/Supersingle setup

Discussion in 'Tech' started by 90kacoupe, Nov 9, 2022.

  1. 90kacoupe

    90kacoupe Novice seeking Help

    Hello fellow racers, I'm building a 2 stroke super single out of a 2009 Husky wr250. I've hit a point in the build where I'm worried about my geometry. My rough initial calculations were not accurate. I'm using a gsxr600 front end, similar to what Geoff at GPtech was doing with his 450gp bikes.

    Right now I'm sitting at 19.5 degrees of rake (calculated 78mm of trail). and 10 degree of swingarm angle. I believe Geoff's bikes were running pretty flat swingarms but I'm not sure how flat they were, or how steep his front ends were.

    It seems GPTech is no longer around, but does anybody have experience with his setup? He was obviously finding a compromise with geometry that was working well.
     
  2. grasshopper

    grasshopper Well-Known Member

  3. Kurlon

    Kurlon Well-Known Member

    When I talked to him while exploring this idea myself, his advice was:

    "The geometry “is wrong”, definitely unconventional, but it works. Many different reasons really. The suspension doesn’t move much because the weight is so low with the engine where it is, the linkage on dirt bikes can go negative anyway, the wheelbase is long, stiff sidewall tires work better, etc, etc.

    Start with the front end you want to use. Then adjust the bike on the bench to the least amount of swingarm angle you think you can get away with, and shorten/revalve/spring the shock to your choice. Likely lighten the springs in front end too."
     
  4. 90kacoupe

    90kacoupe Novice seeking Help

    That is what I'm thinking. I was trying to keep my swingarm angle at 10degree but it seems like I'm going to end up around 5 degree to get the front end close.
     
  5. drewnabobber

    drewnabobber Well-Known Member

    I ran a 450GP for a few seasons. GSXR forks with ohlins extenders and I did use 28mm offset triples to get a little more rake and trail (these are the same mods that lots of people did to the same year GSXRs). Basically you set the front up the way you want (I pretty much copied 250GP numbers) and then the back ends up where it is. I think it is around 4-6 degree swingarm angle. Between a relatively stiff spring, weight distribution, the long wheelbase and the fact that you are ~60 HP or less there isn't that much weight transfer. I never felt the bike wanted to run wide, it handled really well and felt very balanced on corner entry and exit.

    Still miss riding the bike. Don't miss kicking it in leathers.
     
    90kacoupe likes this.
  6. 90kacoupe

    90kacoupe Novice seeking Help

    Thank you for some real world insight. This makes me feel a little less crazy for trying to project. Your numbers sound very similar to where I am. I'm hoping to make some good progress this month.
     

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