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Help USD ZXR forks on a CBR RR

Discussion in 'Honda 250cc In-line 4's' started by Tim_, Oct 22, 2014.

  1. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    Ok so I'm planning on doing a front end conversion on my CBR RR and I plan to use ZXR250 upside down forks... the big issue i can see is fork leg length... the ZXR forks are a lot longer so i will need to have the forks sticking through the top of the triple clamps... any heard of any issues with doing this? i do plan on getting a adjustable rear shock in the future. thoughts?
     
  2. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    hey Tim, I would have a chat with @simidau , I have heard quite a few racers have doen the conversion, he may have some insights as to ride height
     
  3. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    cheers mate..
     
  4. simidau

    simidau Well-Known Member

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    The ZXR forks are upside down - and will require you use a ZXR triple tree, wheel, brakes etc.
    It's possible the only thing you need to take care of is the steering head bearings that fit the ZXR tree and CBR bearing recesses.
    The biggest possible problem is the height of the ZXR tree, it would need to be very close to the height of the CBR tree for the bearings to bit on the tree and match the recesses.

    Cheers
    Simon
     
  5. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    I have an entire front end from a build i was working on but hit more problems then the bike was worth.. only thing i will need to do is swap the rubber over and paint the rim... Just measured the distance between the top and bottom clamp and both the honda and kwaka have 200mm between the top and bottom
     
  6. Th3_Huntsman

    Th3_Huntsman Senior Member Premium Member Contributing Member

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    Just get your pimp lean on haha,
     
  7. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    pimp lean and front end jacked up...lol 2 inches is a lot of lift in the front end... hahahahaha
     
  8. Th3_Huntsman

    Th3_Huntsman Senior Member Premium Member Contributing Member

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    It'll look old school great for Harry's diner bike night haha,also are you measuring fork length with full weight on it? Or after taking apart??
     
  9. Th3_Huntsman

    Th3_Huntsman Senior Member Premium Member Contributing Member

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    It'll look old school great for Harry's diner bike night haha,also are you measuring fork length with full weight on it? Or after taking apart??
     
  10. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    thats measuring @kiffsta forks and mine while there were on side stands side by side..

    you can see the height difference clearly between the two
     
  11. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    chopper style.. @Tim_ Time to grow a moe with handlebars :thumb_ups:
     
  12. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    bahahaha... open face helmet with finger less gloves and vest?...
     
  13. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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    Motorcycle rake, trail and offset explained

    Often mentioned in the main stats when looking at a new motorbike, but what do motorcycle rake and trail actually mean and why would you need to know this? Firstly, these terms refer to steering geometry and so rake, trail and offset effect handling and are directly linked to each other, altering one will effect the other. So if you want to alter the handling, cornering ability or straight line stability, rake, trail and offset are some of the first things that you should look at.
    Motorcycle rake
    Rake can be described as an angle at which the headstock of the motorcycle is inclined when compared against a vertical line drawn perpendicular to the ground. The rake angle effects steering ability, the smaller the rake angle then the easier the bike is to corner but will be less stable in a straight line.
    Motorcycle trail
    The distance on the ground between a straight line drawn through the center of the front wheel spindle and a line drawn through the center of the headstock axis. The greater the trail distance, then the greated the straight line stability but the harder it is to make the bike corner.
    Motorcycle offset
    The distance between a line drawn through the centre of the steering stem/ headstock axis and the centre line of the front fork tubes. Typically the offset inversely affects trail, if offset increases then the trail will decrease.
    The diagram below illustrates each of the measurements and how they are calculated:
    [​IMG]
    The relationship between rake, trail and offset
    • If you increase the rake, the trail increases
    • If you increase the trail, the rake increases
    • If you increase the offset for both yokes then the trail decreases
    • If you increase the offset for only the top yoke/ triple tree then the trail will increase
    • If you increase the offset for the bottom yoke/ triple tree independantly then the trail will decrease
    How to alter a motorcycles rake, trail or offset
    So why would you want to alter these values? Well if you plan to cruise mainly straight roads then you don’t want your arms getting tired by constantly correcting and holding the bike in a straight line, so you would want to increase the trail and decrease the rake. Which is why the American choppers have such long front forks to give great straight line stability. If you wanted handling around corners you would do the opposite to allow you to throw the bike around the corners and of course there is a fine balance to get the best of both. Also such inventions like steering dampers allow you to have a very low rake but keep the bike stable by stiffening the steering movement which you can buy as an after market part. So, love the look of the bike and the performance of the engine but hate the handling? Alter these values.
    You don’t need to be a mechanic or an expert to be able to alter the steering geometry and it can be done in a variety of very easy ways, just remember that you’re the one who has to ride it, so you take your life in your own hands. So for instance with my Yamaha XS750 the front forks were originally quite long, which is pretty useless for a cafe racer, so new shorter forks were put in to lower the rake and to improve the handling around corners.
    Motorbike rake and trail are also not only affected by the frame construction but by a myriad of other factors (which you can alter) such as:
    • Rear suspension – lowering it will increase rake and trail
    • Front forks – shorter forks will decrease rake and trail, also you can alter their position in the yokes to help shorten their distance
    • Aftermarket yokes/ triple trees – alter the offset to then alter the trail without affecting rake
    • Wheel diameter – smaller front wheel will decrease rake and trail, smaller rear wheel will increase rake and trail
    • Tyre thickness – same as the wheel diameter
    More importantly when riding the bike, braking and suspension travel will also dynamically alter the rake and trail, for instance, as you brake hard on the front, suspension will compress under dive thus decreasing trail and rake potentially inducing wobble in the bike. Bare that in mind if you make any alterations as you could end up with negative figures under extreme braking conditions. Additionally heavy luggage or pillion on the rear may also effect your rake and trail measurements slightly – which is why you should always alter your rear suspension preload.
    Also remember that while any alterations may seem small and un-noticeable at slow speed at higher speeds their effect will be magnified, such as reduced straight line stability!
     
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  14. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    Amazing read mate.. thankyou..
     
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  15. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    Whilst I was disassembling the ZXRs today i noticed something... the ignition lock on the ZXR is longer the the ignition lock on the CBR.. which means the ignition lock is mounted a lot lower on the ZXR so i would either need to disassemble the locks and rebuild one so i could bolt it to the ZXR triple clamp...
     
  16. aky141

    aky141 Well-Known Member

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    Dude, Nsr250 forks!!
     
  17. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    NSR forks are hard to come by. and already had the zxr forks here plus only took 2 spacers and it fit perfectly... rides frikkin awesome now.. apart from blowing the forkseal..lol
     
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  18. PeterUK

    PeterUK Member

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    Hi Guys i did fit zxr400 forks on my mc19 and all i did was swap the stems over they press out. The ignition lock just bolted straight in.

    just for reference in case anyone else was looking to do the same
     
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  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Don't mean to rain on your parade Mr Grey but . . . .

    "If you increase the trail, the rake increases"
    FALSE
    The values for these two both change as the suspension moves but rake is independent of trail.

    " . . . so you would want to increase the trail and decrease the rake. Which is why the American choppers have such long front forks to give great straight line stability. If you wanted handling around corners you would do the opposite to allow you to throw the bike around the corners and of course there is a fine balance to get the best of both. "
    FALSE
    You would increase both the trail and the rake and vice versa for the sports bike.

    Tony Foale has written some of the best available material on this subject and well worth a read.
    cheers
     
  20. Tim_

    Tim_ resident nutcase Premium Member Dirty Wheel Club Contributing Member

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    I am sure I did a Build thread on this? any way we can merge the threads?
     

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