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ok frame and suspension experts...here is a head scratcher.....

This is a discussion on ok frame and suspension experts...here is a head scratcher..... within the General forums, part of the Caferacer.net Forums category; That diagram doesn't apply here. That shows trail on a bicycle fork where the fork and neck are in the same plane and doesn't have ...

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  1. #11
    Senior Member o1marc's Avatar
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    That diagram doesn't apply here. That shows trail on a bicycle fork where the fork and neck are in the same plane and doesn't have triple tree spacing the forks out. All those angles change when you have triple trees. When moving the axle to leading or trailing both put the axle further ahead of the trees on a motorcycle than on the bicycle. Am I wrong?
    Move the center line of the neck to ground back and then make the forks straight showing the axle leading and trailing and see what you come up with.
    The diagram you show has the axle ahead of the fork center line in all 4 pics. If the axle is trailing it will be behind the center line.
    Last edited by o1marc; 01-22-2013 at 10:29 PM.
    I carry a gun because I'm too young to die, too old to take an ass whooping, and a cop is too heavy.

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  3. #12
    Senior Member Teazer's Avatar
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    That diagram is spot on. Imagine teh fork legs are like a motorcycle and you will see it doesn't change. Reduced offset => more trail. Add offset => Less trail.

    Just jack the rear end up to reduce trail and rake together. Get rake down to around 24 degrees and you probably need reduced offset to get enough trail. :-)

  4. #13
    Senior Member hillsy's Avatar
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    The fork offset on a bicycle is done by curving the fork, on a motorbike it's done by putting the stem behind the line of the forks or using a leading axle. Same outcome.

  5. #14
    Senior Member hahnda's Avatar
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    http://www.scramblercycle.com

  6. #15
    Senior Member o1marc's Avatar
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    I see where that makes sense now. I was mistaking trail for wheel base. The diagram before this reply shows that if you had a leading axle the trail in the pic would be cut in half or more and if the legs were reversed it would almost double trail. With some trees having very little offset and a leading axle fork you could conceivably have 0 trail. Would that be a bad thing?
    Last edited by o1marc; 01-23-2013 at 08:51 AM.
    I carry a gun because I'm too young to die, too old to take an ass whooping, and a cop is too heavy.

  7. #16
    Senior Member crazypj's Avatar
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    We went though this few years ago when people wanted to put modern or USD forks on 70's bikes.
    Trail increases in just about every case as the offset is less.
    Mostly it's 'A GOOD THING'
    No one complained about squirrely handling, they commented on how much more stable bike was at speed (lot of 'racing' CB350's)
    BTW, it's called trail because tyre contact patch trails the steering head line
    I dabble in rocket science, when I\'m not picking my nose
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  8. #17
    Senior Member o1marc's Avatar
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    Can someone explain to me how the rake and trail effect handling. I notice the XR750 has much less rake than my bike. I have ridden choppers with a large amount of rake and stretch and realize they completely suck for handling.
    I carry a gun because I'm too young to die, too old to take an ass whooping, and a cop is too heavy.

  9. #18
    Senior Member Geeto67's Avatar
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    ok so looking at hahnda's diagram, how does moving the axle rearward and further up (like on a leading axle fork) reduce trail?
    Frankie, the Big Kahuna: What does that mean, "we're not in?"
    Annette: Wild guess? I think it means they're not in.
    Bobby: Boy, it's quite a piece of dialogue when you intellectual masterminds get together! I should be writing this down!

    Frankie, the Big Kahuna: But what does "we" mean?
    Bobby: [impossibly sarcastic] I think it's the plural form, meaning "more than one." Would you like me to conjugate that for you, Pop? Do you know what "conjugate" means, Dad?

  10. #19
    Senior Member o1marc's Avatar
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    Quote Originally Posted by Geeto67 View Post
    ok so looking at hahnda's diagram, how does moving the axle rearward and further up (like on a leading axle fork) reduce trail?
    I f you turn the fork backwards the axle will now be behind and lower, not further up. This would widen the line between the where the neck angle hits the ground and where the center line of the axle hits the ground. It wouldn't reduce trail but lengthen it.
    I carry a gun because I'm too young to die, too old to take an ass whooping, and a cop is too heavy.

  11. #20
    Senior Member Geeto67's Avatar
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    Quote Originally Posted by o1marc View Post
    Can someone explain to me how the rake and trail effect handling. I notice the XR750 has much less rake than my bike. I have ridden choppers with a large amount of rake and stretch and realize they completely suck for handling.
    trail affects the straight line stability of the bike at the sacrifice of the wheel's ability to change direction. rake affects the wheel's ability to change direction at the sacrifice of a bike's straight line stability. The secret to good handling is finding the balance between rake and trail - which differs from bike to bike based on the chassis and suspension components. typically the more rake you have the more trail you have as well (although not always the case) so most choppers are excellent in a straight line but reluctant to change direction. Add in a skinny front tire and the fact that the longer the forks are the more weight is being distributed across them and not making it to the tire and you have an ill handling bike.

    or did you want something more sceintific?
    Frankie, the Big Kahuna: What does that mean, "we're not in?"
    Annette: Wild guess? I think it means they're not in.
    Bobby: Boy, it's quite a piece of dialogue when you intellectual masterminds get together! I should be writing this down!

    Frankie, the Big Kahuna: But what does "we" mean?
    Bobby: [impossibly sarcastic] I think it's the plural form, meaning "more than one." Would you like me to conjugate that for you, Pop? Do you know what "conjugate" means, Dad?

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