Gymkhana

Discussion in 'The Perfect Line and Other Riding Myths' started by Vulfy, May 6, 2012.

  1. Vulfy

    Vulfy Been here awhile

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    575
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    Great job today guys, great session, great fun.
    For those of you who are not on Facebook and want your timed laps video, PM me here and I'll send you a Dropbox link.
  2. Vulfy

    Vulfy Been here awhile

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  3. lulo

    lulo Cochino Aventurero

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    Thank you for putting this toguether, can't wait for next time :clap
  4. Vulfy

    Vulfy Been here awhile

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    You are welcome, got your message, upping your videos to dropbox.
    Meanwhile here is the obligatory silly video of today's session :D


    <iframe width="560" height="315" src="//www.youtube.com/embed/TYv_YDWPiCY?rel=0" frameborder="0" allowfullscreen></iframe>
  5. Rango

    Rango Phaneropter

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    :jack
    Cool editing. Nice work.
    Looks like a success session too, well done.
  6. Vulfy

    Vulfy Been here awhile

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    I've had a few people asking where I'm getting the cones for our courses.
    Bellow is the link to e-bay seller who has them in different colors. You specify which color you want at the checkout with a "note to seller". They also do 25/25 split of two colors if you want.

    Please note, that I'm not affiliated with the seller, and I'm just sharing where I get my cones.

    Also note, that these cones are not the official cones that are used in Japanese, UK and Alabama events. However they are proven to be excellent cones for our NYC purposes by being cheap, portable in large quantities, durable (been run over multiple times without cracking), and wind proof, so that they don't fly off or move with gusts of wind.

    http://www.ebay.com/itm/350598833414?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
  7. Rango

    Rango Phaneropter

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    :clap
    Thanks. Great find.

    Cheap as chips too :1drink
  8. Vulfy

    Vulfy Been here awhile

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    Just a quick update on the front brakes of SV650. Changed out brake fluid, that didn't do anything. Travel was still excessive and with hard braking was pinching my fingers on the throttle.

    Dug into the interwebs and found out that its a pretty common occurrence on the bikes, and not only on SV650.

    Seems the cause of that is either a bad seal inside master cylinder, or in my case just a grimy piston that is sticking in the caliper.

    Removed front calipers from the forks and squeezed brake lever to see what was going on. One piston in each caliper was sticking and not moving out fully.

    Drained the system, removed pistons, cleaned everything out, lubed pistons and seals with brake grease, refilled and re-bled the system.

    Now front brake is nice and firm, and engages at proper distance from the handle bar.
  9. Vulfy

    Vulfy Been here awhile

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    :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0! :y0!

    Session this Saturday 07.13.
    8am - 1pm

    PM me if you plan on going, and I will send you the location and details.
    Alternatively, if you are on Facebook, join our group that has schedule and all the details.


    https://www.facebook.com/groups/motogymkhananyc/
  10. Vulfy

    Vulfy Been here awhile

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    07.10 Trykhana GP practice.

    34 seconds and less = Gymkhana God
    35 seconds = Master
    36-37 = Good
    38-39 = Young Grasshopper
    40-44 = You can do better
    45-54 = Need more practice
    55 and up Enjoying the cruise :wink:

    <iframe width="560" height="315" src="//www.youtube.com/embed/lN3SGi8YD_c?rel=0" frameborder="0" allowfullscreen></iframe>
  11. Vulfy

    Vulfy Been here awhile

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    This is incredibly fast!

    <iframe width="560" height="315" src="//www.youtube.com/embed/G0MTjh-gPF8?list=PL7bwKoVPEQxUHik7TUEMngp1x83S6QYkx" frameborder="0" allowfullscreen></iframe>
  12. Harvey Krumpet

    Harvey Krumpet Long timer

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    That is off the scale.

    Notice the size of the rear sprocket on the green bike?

    And the hip flexibility of the blue rider....
  13. ohgood

    ohgood Just givver tha berries !!!

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    I missed the dimensions and pattern for the trykhana (or is it gp trykhana ?) you posted a video of.

    looks like no " 8 " is involved, but a left right left for each corner ? is there a gate ?
  14. Vulfy

    Vulfy Been here awhile

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    ohgood: here is the diagram for Trykhana with all the dimensions. It is a sort of a figure 8.

    http://caramel.xsrv.jp/hgc/trycahna.html

    Harvey: yeah I wonder if there is some sort of formula or calculation to figure out the rear sprocket size.
  15. RichBeBe

    RichBeBe All Hail Seitan!!!

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    The top guys likely carry an assortment and look to max revs in first gear on fastest part of course. If I come Saturday I want to try a smaller front sprocket, I run larger than stock for sustained high speed, but will go down one smaller than stock to play.
  16. Vulfy

    Vulfy Been here awhile

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    You think its matched to the max revs at the fastest stretches?

    I always assumed it was for the hardest torque to accelerate as much as possible out of the corners. I've seen some of the guys do a wheelie out of a corner.

    Wouldn't larger rear sprocket drop your RPMs?

    I'm still very hazy on the whole concept of how sprocket size affects top speed, torque and acceleration.
  17. Sckill

    Sckill Been here awhile

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    Using a smaller front sprocket or larger rear sprocket results in 3 things:

    1. Higher engine RPM needed to maintain a given rear wheel speed
    2. Higher torque / acceleration
    3. Lower top speed

    It all comes down to the ratio of the front to rear sprockets.
  18. Harvey Krumpet

    Harvey Krumpet Long timer

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    Some bikes have quite a big gap between 1st and 2nd, I should imagine for gymkhana this could be irksome, over revving in 1st or under revving after the up shift. Lowering the gearing would give more flexibility in 2nd & fewer gear changes.
    I've geared down pretty much every bike I've owned. For some reason the open road speed limit does not match the engines happy place. On the TDM with standard gearing 100kmh in top was about 3700 rpm, just under that happy place & lacking responsiveness when i opened the throttle. One tooth less on the front & it sits at 4000rpm but has significantly more torque available when i roll on or for hills & strong head winds. Makes the bike nicer (& lazier) to ride.
  19. lnewqban

    lnewqban Ninjetter

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    Imagine that your transmission has only one gear combination with which you have to live.

    Sprockets are nothing but levers.

    That lever attached to the output shaft (front sprocket) can do with the twisting force coming from that shaft (output torque) only what levers do: to apply a tangential force at its free end (tension on the chain), more if the lever is short (few teeth), less if the lever is long (more teeth). For the same reason, that chain will move slower in the first case and faster in the second case. As transmitted power = force x speed, it remains the same for either case.

    The lever attached to the rear wheel (rear sprocket) can do with the tangential force at its free end (tension on the chain) only what levers do: to apply a twisting force to that rear tire (wheel torque), which becomes a rearward pushing force at the contact patch. That force will be less if the lever is short (few teeth) and more if the lever is long (more teeth). For the same reason, the bike will move faster in the first case and slower in the second case. As transmitted power = force x speed, it remains the same for either case.

    For brilliant acceleration, you want big force at that contact patch (a = F / m).
    That twisting force coming from the transmission shaft (output torque) reaches its peak value only for the range of rpms' at which the manufacturer of the bike claims that maximum torque is achieved by the engine.

    The right combination of sprockets should put your engine in that sweet spot for the power demanding part of the particular Gymkhana exercise.

    :1drink
  20. Mazaev

    Mazaev Been here awhile

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    The rotten apple.
    Finally made it out today. Tons of fun, and surprised how exhausting it gets. Boots all scuffed from scraping (and kicking cones) :lol3.

    Some pics:

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