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  1. #1
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    Default Grasshopper front end, 0Ē trail?

    Never ran one of these before and Iím a bit confusedÖ After everything set up, I do my measurements and I come up with zero to 1/2inch trail?!?

    Itís on a rigid frame 2 inch up , 2 inch out with a 30į rake. Is it simply a matter of this frame doesnít have enough rake for this front end?

    I recall reading somewhere that sugar bear springers have a 0 inch rake which Iím not sure how that can be because itís all dependent on the rake of the frame, no?

    Iíve always strive for a 3 to 5 inch trail, Iím a little hesitant to even test ride this thing at this point. Am I overthinking this?

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  2. #2
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    Default

    The way your axle sits at close to 90 degrees from your rear rocker pivot, and the front end kinda
    'hangs' from the axle, it should be fine. The offset from the trees and the rockers account for low trail.

    from Chopper Builders Handbook:

    Springer Fork Rocker Designs

    Why Dropped Rockers Work

    Dropped rockers will give the rider the impression (perceived feel) that the bike has less trail than it actually has in reality. In addition the rider will have the impression that it takes very little movement of the forks to produce a fairly significant amount of front wheel rotation. Some people will say that riding a bike with dropped rockers is like having 'power steering' in that it takes very little effort to move the front wheel. In some cases you can steer the bike using just your finger and a few ounces of pressure on the handlebars.

    Basically what is happening with a set of dropped rockers is that you are 'tricking' the steering geometry into thinking that the bike is running a much smaller diameter front wheel that is set much further forward than the physical reality of the hardware. Of course there are several other factors involved but this is the easiest way to visualize what is happening.
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    https://chopperbuildershandbook.com/rockers.html


    springer rule of thumb
    "the 90* angle rule: this rule was set up to dictate the proper measuring and assembly of the springer rockers. First and foremost do not have any weight on the frontend. I block the front of bike frame with 2x4 and shimming stock. I set the front of the frame.75 to 1" above the final position of the weighted frame(containing motor trans and rider). For lighter riders i set closer to .75" for riders 200# or more i go a full 1". This rule dictates the position of the rear(rigid leg) rocker attachment hole. that in turn will tell you where to place your spring leg attachment hole.

    rule 1: place the blade (the long end) of a carpenter's square along the centerline of the steering axis. If not using raked trees or raked cups you can simplify this and use the centerline of the rigid leg of the springer. Align the tongue (the shorter leg) of the carpenter's square with the centerline of the axle. If using the centerline of the rigid leg, the point of the square will be where you should place your rigid leg rocker attachment hole. With this hole made you can in turn make the spring leg rocker attachment hole by setting level at horizontal zero along the centerline of the rigid leg rocker attachment hole. follow the horizontal zero forward to the intersection of the centerline of the spring leg. the point of intersection is where the spring leg rocker attachment hole should be placed. Once the frame is taken off the cribbing and the weight is applied to the frame, the rockers will preload the spring leg and naturally set the rocker attachment holes 10-20* of horizontal zero..."

    http://choppercompendium.com/ccforum...f4f7e86f6d95b8


    Go ride it, feel it, get to know how it handles.
    My Norton has a 'stock' rake aftermarket rigid frame with a +16" P&P girder, in the +10 degree rake position, and about 1" trail - it handles great, slow or fast, and handles the rough shit better than any springer I had, including a brand new +18 Jammer.

    The one issue with that style of springer, is that each spring is independent of the other, so stresses the axle, as that is the only thing working to keep it inline - a regular springer has front legs joined at the top by springer perch, and a set of springs above the spring perch. Just one more thing to watch is wheel side to side rock. Keep it all tight.

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    Freddy Hernandez Denver's Gyro:
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    Last edited by TriNortchopz; 4 Weeks Ago at 7:19 AM. Reason: 1" trail, not rake, + CC site info

  3. #3
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    Default

    You could build a 'bridge' to connect the spring rods 'front legs' to increase stability:

    Attachment 109521

    Attachment 109522

    Panhead, square tubes, shocks, builtin NY area:
    Attachment 109523

    modern interpretation of a gyro:
    Attachment 109524

  4. #4
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    Default

    "Dropped rockers will give the rider the impression (perceived feel) that the bike has less trail than it actually has in reality."

    I take issue with this statement. Dropped rockers do reduce trail. It is not "the impression" or "perceived feel," it is in REALITY a reduction of trail. Geometry and physics cannot be tricked.
    The distance from the point of intersection of the line of the steering axis and the ground plane, and the point of intersection of the vertical line from the axle and the ground plane do indeed move closer as the length of the dropped rocker increases. And of course that is the whole point of doing it.

    I personally don't care for the look, at all, but there is no argument that it works to make the bike easier to drive.

    Whether the OP will find his set-up to be driveable is a matter of experiment. A change in rocker geometry would gain trail, same way dropped rockers reduce it, if it is found to be necessary.

    Jim

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