Gymkhana

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

1. ohgoodJust givver tha berries !!!

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lots of questions...tried to answer what I understand.

what you have to remember is these two turns were easy, that next one has twice the speed to dissipate,, and the one after that is definitely going to slide the rear, and maybe the front a little. it changes from turn to turn, entry and exit, tighter or looser. I watch a very determined msf instructor makes 24' circles at 15 mph or so, hanging off, bike straight up, gaining speed now and again. very cool to see the persistence and improvements from curiosity.

IF he failed, what will happen ? a highside ?

what happens if he fails counterleaned ? a bike slide, and roll away from the back.

either way, someone will have to sweep the pavement before the next rider. I'd prefer to not get tossed myself, if I can help it.

time yourself dragging brake, tight radius, then try the boat turns. I bet 5 seconds at least difference on gp8. :)
2. bumbeenBanned

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Ok here's what I think, still not to a real computer... On vacation in Hawaii so posting from the phone.

Turning radius is determined solely by steering angle and lean angle of the bike. If you are at max steering lock and max lean angle, you will turn in a certain radius. If you are counter leaning and doing this max lean and max lock at 7mph. That means if you try it at 12mph you will not be able to counterlean because you need more weight on the inside of the bike to maintain the force from gravity to balance against inertia wanting to throw the bike out of the turn. Therefore you may sit straight in the saddle to provide enough force from gravity to counteract the increased lateral force. Given this increased speed, we have increased lateral load on the tire, making you more likely to slide out. I don't think this changes your turning radius or am I wrong? Turning radius is determined by lean angle and steering lock. A specific riding position, steering angle, and lean angle fixes your speed and turning radius. Yes?
3. MotogymkhanamanBeen here awhile

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"A specific riding position, steering angle, and lean angle fixes your speed and turning radius. Yes?"

All true, but we have to take the tyre slip angle into account. The faster we go when leaned over, the greater will be the difference in angle between the direction the tyre is pointing and the direction it is travelling.

To demonstrate zero slip angle spin a coin on its edge and as the energy decays you will see that the lean angle of the coin begins to increase and it will start to roll around its circumference. Irrespective of the lean angle the coin will not move from its starting position.

When we ride the bike we can get our wheels into a similar lean angle to our spinning coin, but due to the energy pushing us forward, instead of the wheel rolling around its circumference it has to slip along the ground instead.

The Moto Gymkhana rider takes advantage of this by minimising the slip angle through precise control of the speed.
4. HooliKenAwesome is a flavor

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The very first guy in this vid does amazing considering he is on a ZRX. NOT a light bike by any stretch to be tossing around like that.
5. ohgoodJust givver tha berries !!!

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mmm, that's math. I have no idea. we can try stuff on the bike though, its more fun anyway. :)
6. MotogymkhanamanBeen here awhile

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Tabibito-san giving his Street Triple the berries at the recent Moto Gymkhana event in Japan. Sadly he just missed winning by a fraction of a second.

Worth watching this video to see how quickly he can capsize and recover the bike.

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Been there. Left message. NO reply.
8. ohgoodJust givver tha berries !!!

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amgrass is grass roots... if you don't have interest in your area yet, guess who gets to spread the fertilizer ? ;-)

ill check in at amgrass and get the cheifs stirred up. again, its grass roots, not a box store with a payment plan, sorry :)
9. liquid_iceBeen here awhile

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I love reading this thread not only to see how gymkhana lives in other parts of the world, but also because once in a while I learn a new bit of English.

Needed Wikipedia to know what Grassroots was.
10. RedclayriderLong time gone

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Homegrown :)
11. liquid_iceBeen here awhile

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That is how they grow the roots of grass over here in Amsterdam

But now we are changing the subject

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Doing u turns. Leaning putsbthe contact patch on the side. Which puts the turning circle smaller. If u have a toy bike that the bars move or a curved side bike wheel have a play and u will notice the difference. Bikes fall over id arnt moving and leaning. So gota keep forward momentum up to fight gravity. So to keep speed down and forward momentum up rear brake is the easiest.if ur doing gymkhana and not trying to keep speed down u dont really need it. It does make you feel in control better. I dont "think" it reallyndoes but it Just feels like planting the rear wheel as a fixed pivot point.

send on a small touch screen by a guy with fat fingers
13. SckillBeen here awhile

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Hi everyone. I'm an aspiring Moto Gymkhana newbie and just finished reading through all 1000+ posts of great information on techniques and bike control on this thread. Weather is improving so I'm looking to spend more time outdoors improving skills on the bike besides just commuting.
14. liquid_iceBeen here awhile

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Compliments on reading it all, it's quite some work.

I hope the weather keeps improving and you can start practicing.

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86 pages now, a bit of knowledge on riding i recon... especially if u watched all the youtube videos
16. liquid_iceBeen here awhile

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Knowledge only gets you so far, In theory I could be quite fast

Lets not talk about in practice

But as with everything, knowledge is a nice place to begin with for whole lot of practice.
17. VulfyBeen here awhile

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I was wrong...

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18. ErikDKBeen here awhile

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Prabably 205, but:

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I just finished reading every post in this giant thread... though I didn't manage to watch EVERY youtube video. Lots of good info here, thanks to those who take the time to explain so much.
I can't wait to get started but I gotta put my bike back together first :huh I am guessing that my 1986 Honda XL250R with a broke man's super moto setup (cheap shinko street tires on 19inch-rear/21inch-front rims) should be a good bike especially since I don't mind much about laying it down.

Reading about all the different techniques and the physics of bike control is very interesting from a TRIALS riding perspective as well... Motogymkhana and trials are both VERY TECHNICAL riding sports that require huge amounts of bike control and don't require any 'high-speed-bravery' or '100ft-jump-bravery'. Don't get me wrong, there is bravery invovled with trials and motoGym but it is a different kind of bravery and the penalty/crash when you get it wrong is (usually) fairly minor when compared to other moto sports like motoGP or MotoX. Here is a sample youtube of trials riding (for those unfamiliar with this branch of dirt-biking http://www.youtube.com/watch?v=g9An21JLUNg)

I liked the questions from bumbeen, they are worth asking, and they did allow motoGman to explain some more interesting points about motoGymkhana. In that light... what about this for a faster method around the 180o cone:
pop a big endo/noseWheelie/stoppie as you approach the cone... shift hips so the back end swings around .... drop rear end so you end up facing the other direction and off you go.
You would lose a bit of time in braking but that should be made up in not having to actually do any turning. You would also need to be DAMN GOOD at stoppies but it is possible, no?
I know the first response will be for me to try it and time myself ... I will, next weekend (on my trials bike).

PS. Anybody in Victoria, B.C doing motoGymkhana already? PM me!
20. TheWall0 miles and counting

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When you try it, make sure to post a video of it here We'd love to see how it goes!

Slightly off-topic: I'd love to try my hand with a trials bike! That looks like soooo much fun!