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Thread: Tech Tech Tech, or...So you want to build a trike?

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    Default Tech Tech Tech, or...So you want to build a trike?

    So here we go.
    In cooperation with Stinger (and any other tech head that wishes to contribute) the beginning of a place to put tech info.

    As this is in the VW thread it will have a heavy VW tilt to it. But many aspects of of building is universal.

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    Geometry.....

    Whether you put a kit on a wing or hand build a big ole v8 you must have certain things right.

    Rake and trail.

    Just like a motocycle but in trike form typically a lot less trail.

    Rake....not no big deal. Make it what you want it to look like. You may effect turning radius but drivability will be ok.

    Trail....the big deal. No matter what rake angle you choose the trail must be right. Typically around 2 inches or even less.

    8152290896_75e1300982_o_zps7iq9xgov.jpg

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    Tech link.

    The chopper builders handbook.
    Same rules and theory as a bike, but possibly less trail used.

    http://www.chopperhandbook.com/rake.htm

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    Alert...Alert...Alert

    If you are looking at a used custom build
    CHECK THE TRAIL
    lots of home builders dont do the math, just want it to look cool with the front all angled out there.
    It is a very rare thing for a front end off a bike that has been welded on with increased rake to have correct trail.
    Luckily too much trail is not deadly. Makes for hard steering and head shake on decelerating.

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    subscribed

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    I bet our friend Zook can tell us a first hand story about trail. I think he has a kitted bike.
    Wings and glides are factory made with lots of trail. Their intended purpose is highway cruising with high speed stability, slow steering, no twitchyness at all.
    So those bikes have around 4 inches of trail.
    You can buy the trike kitted bike and the "ez steer kit" is an option (and an expensive one).
    Lots of folks skip the option.
    Guess what....too much trail for a trike.
    Heavy gorilla arm steering and decell head shake.
    So what then? Ez steer kit.
    What it is is carefully designed raked trees.
    Reduces trail to around one inch.
    Instant "power steering" feel and no decell head shake.
    So when you buy a kit or a kitted bike go ahead and get the ez steer kit (or whatever the vender calls it today). The venders like to hide the theory from you (change in trail).
    So there......you can hop over the the wing section and learn about the same design concerns as we have with our custom builds. Geometry is geometry. Watch your numbers.

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    Great info snu, I've been dealing with trail for a couple months now, reading and expirementing with different rockers. Also at the same time trying to get the "flop" out. I have an old rusty DNA springer 10" over at 53 degree rake. Trail is at 9" at this time and It acually drives ok. I never really cared for the cheap dna anyway so yesterday I finally bit the bullet and sent deposit for a Sugar Bear springer. I told him what I had been dealing with and of course he said no problem, he could make my troubles go away,lol. Very cool fellow btw. Looks like they'll be 26-30" over with the #4 rockers. Expensive and 3-4 month wait but excided as hell. We'll be talking again in a few days so i'll be sure to mention it's a trike so thanks for that info.

    choptrk

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    Well that is a killer way to fix it!!

    Be sure to give sugar bear absolutely correct numbers. All his math will be based of what you tell him. His drop pivot rockers are ZERO trail.
    And they work.

    Styles of front ends is probably the next discussion.

    On the lucky side for us is that the rear engined vw trike is so light weight in the front. It does not take gorilla arms to steer big trail. Backing up is a pain and some low speed decell shake.

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    So a recap.

    Now we know that there is no "ideal" rake.
    Differences in rake will give a bike different characteristics.
    Take a crotch rocket..... very steep forks, not much rake and also not much trail. Very very quick handling, twitchy, the sports car of the bike world. Exciting to drive and you have to pay attention and drive it all the time.
    Then the long front chopper. Assuming it is built correct, not too heavy on the bars, slower to change direction, takes more input to make a change, lazy, forgiving, does not take constant attention to keep it in a straight line.
    In general all the same traits when applied to a trike. Except a trike will not forgive large trail like a bike that leans.

    Ok so now you have read the tech link and have a grasp on the general theory.
    Put the rake on it however you like or want.
    I dont like long rake and the long front ends that go with them. My personal choice based on how I want mine to perform. I am more of a middle of the road, I want the looks of rake but I want to keep it bit more quick handling but not a crotch rocket personal choice, make your personal choice based on what matters to you.
    Then.....
    Make the trail fit.
    You have the angle you just have chosen.
    As the diagram above shows, get the relationship of the neck angle to the front axle.
    Now you know where the front axle must be.
    Next is picking a front end that fits those dimensions.

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    Tech link.

    http://www.chopperhandbook.com/forks.htm

    Different styles of front ends. This wite up is more to do with rocker or pivot style lever front ends. The basics of with apply to springer, shockers, leading links, drop pivots and such.

    Mine on my trike is a drop pivot linked shocker.

    http://www.chopperhandbook.com/rockers.htm

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