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Old 04-17-2013, 08:50 AM   #1051
shaddix
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Now that makes sense. So basically I don't have enough idle speed to maintain the minimum turning radius. Therefore I dial in a constant throttle that *is* enough and slow the bike down with the rear brake to control my lean angle/turning radius.

Given that idle throttle isn't enough speed, I shouldn't need to touch the clutch at all.

That also answers my other question. The fact that speeding up allows you to turn tighter means CoG lean angle and lateral acceleration are still proportional, irrelevant of the steering angle and tire lean angle. Intuitively I was thinking I needed to go slower to turn tighter but in fact the opposite is true.
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Old 04-17-2013, 09:01 AM   #1052
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Intuitively I was thinking I needed to go slower to turn tighter but in fact the opposite is true.
I'm discovering that for myself just now, so you are way ahead of me on this stuff. But yes. Bike needs to travel fast enough to keep momentum and balance, but not too fast that the bars start to fight you and you go wide.... very fine balance. Yes, going too slow is detrimental, there needs to be some momentum behind you.
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Old 04-17-2013, 12:46 PM   #1053
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That's very interesting to recognize!

Starting from 1mph you have a turn radius determined only by steering angle alone and whatever counterweight you can manage. As you increase speed your turn radius decreases to the point where you would have to stop counterweighting since you would reach max lean angle of the bike with max steering angle.

As your speed increases further you would need to start hanging off the inside to maintain balance while still maintaining max lean angle and steering lock. I imagine this could make someone very dizzy. This also is going to be putting a huge load on the tire so you better have some sticky rubber on.

In practice this means there is a range of speeds that a bike can turn at the minimum turning radius, and that range is determined by rider body position. If you were fixed in the seat like a mannequin you would have one exact speed at which you could achieve minimum turning radius. I will probably practice doing u-turns at idle in 2nd gear today instead of trying to throttle up and play with the rear brake. The extra speed may just be enough to keep me upright and I won't need to counterweight as much. But doing it this way of course I still won't have the option of finessing on more power to pull me out of a drop and be stuck with a throttle lurch. I'll give both techniques a shot.
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Old 04-17-2013, 01:06 PM   #1054
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Originally Posted by shaddix View Post
That's very interesting to recognize!

Starting from 1mph you have a turn radius determined only by steering angle alone and whatever counterweight you can manage. As you increase speed your turn radius decreases to the point where you would have to stop counterweighting since you would reach max lean angle of the bike with max steering angle.

As your speed increases further you would need to start hanging off the inside to maintain balance while still maintaining max lean angle and steering lock. I imagine this could make someone very dizzy. This also is going to be putting a huge load on the tire so you better have some sticky rubber on.

In practice this means there is a range of speeds that a bike can turn at the minimum turning radius, and that range is determined by rider body position. If you were fixed in the seat like a mannequin you would have one exact speed at which you could achieve minimum turning radius. I will probably practice doing u-turns at idle in 2nd gear today instead of trying to throttle up and play with the rear brake. The extra speed may just be enough to keep me upright and I won't need to counterweight as much. But doing it this way of course I still won't have the option of finessing on more power to pull me out of a drop and be stuck with a throttle lurch. I'll give both techniques a shot.
very well put, exactly how I'm imagining it in my head as well. This can be observed with top riders. Depending on the speed, they lean in, neutral or counter-balancing.

I'm playing with it myself, and it seems that unless you are going really slow, on the verge of toppling over, leaning into the turn is very possible and helpful even at pretty low speeds.

Its a great feeling when you lean over the cone, and the bike turns almost around your head. Only started happening to me recently, I guess practice and faith in tire grip.
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Old 04-17-2013, 03:34 PM   #1055
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The Black Arts......
Been awhile since I practised but I find myself counter balancing, leaning out, when I'm transitioning into a slower, tighter turn with a lot of lock. I'm fairly static or leaning in on constant radius turns like GP8's. 8's through a 1 mtr gate are great for getting the feel of it, you have to get the bike from hard left to hard right in one movement.

Yup, back brake & steady throttle for speed control. I only use the clutch on the TDM when I over cook it.
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Old 04-17-2013, 05:42 PM   #1056
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I read the first few pages and the last pages of this thread and it looks like there are some active guys from Alabama....... Do you guys know anybody in Atlanta or GA that regularly get together to do this? I'd like to give it a try. Otherwise I'll ride over to Birmingham for the next event.... Maybe it's not too far away but I saw where there was an event in March so maybe I'll have to wait a while?

Shannon
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Old 04-17-2013, 06:05 PM   #1057
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wheatfly: This is their official website. I think they have a schedule of events somewhere there.

http://amgrass.com/
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Old 04-17-2013, 07:50 PM   #1058
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I read the first few pages and the last pages of this thread and it looks like there are some active guys from Alabama....... Do you guys know anybody in Atlanta or GA that regularly get together to do this? I'd like to give it a try. Otherwise I'll ride over to Birmingham for the next event.... Maybe it's not too far away but I saw where there was an event in March so maybe I'll have to wait a while?

Shannon
always ready for another... you can always start one with your buddies, just some cones and a lot.

come on over, we'll have a blast
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Old 04-18-2013, 08:23 AM   #1059
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Set up a couple cones last night for GP8.
Definitively harder than it looks.
I noticed the jerky throttle going from closed to slightly open. It made tight turns difficult. Ill try keeping a little more throttle on next time and not go completely closed.
Need to work on brake and clutch modulation. Especially the clutch as it is till pretty much on or off for me. I can engage it smoothly but dont really have the control to do a partial engagement. I know thats not the best technique for fast moto gymkhana but it is a riding technique I am weak on.

I will be working this some more. Thanks for all the tips and videos everyone.

Craig
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Old 04-18-2013, 11:10 PM   #1060
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Set up a couple cones last night for GP8.
Definitively harder than it looks.
I noticed the jerky throttle going from closed to slightly open. It made tight turns difficult. Ill try keeping a little more throttle on next time and not go completely closed.
Need to work on brake and clutch modulation. Especially the clutch as it is till pretty much on or off for me. I can engage it smoothly but dont really have the control to do a partial engagement. I know thats not the best technique for fast moto gymkhana but it is a riding technique I am weak on.

I will be working this some more. Thanks for all the tips and videos everyone.

Craig

Great to read that. "fast" gymkhana may well be a pipe dream for me but learning good bike control is not. Starting this has been a bit of a revelation for our riding ability.
Keeping the throttle open & modulating speed with your rear brake is the way to go. Yeh, sounds harsh but works a treat. Enjoy!
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Old 04-19-2013, 02:16 AM   #1061
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Hi Shaddix, welcome to the world of Moto Gymkhana!

The minimum turn radius with full lock and maximum bank angle is the source of much confusion amongst new riders. Take a look at the following video of Noboru Yoshino on the GP8 course. You will notice that although the bike is changing direction very rapidly as it rotates around the pylon it's not actually going very fast.





What riders are looking for is the exact combination of speed and bank angle that will give them the maximum direction change in degrees per second. This will vary according to the particular capabilities and constraints of the bike and rider combination.

The optimum rotation rate is about 144 degrees per second which equates to a full 360 degree rotation in about 2.5 seconds. Get a friend to time you making a 360 degree rotation and that will give you some sort of baseline to work from. Make only one change at a time such as the amount of throttle or your body position and try another roatation aginst the clock, if you are faster than your original time then that was a good change, but if you are slower you will have to try something else instead.

All improvements in Moto Gymkhana riding come from riding against the clock, so it is worth your while getting into the habit of timing everything you do.
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Old 04-19-2013, 08:41 AM   #1062
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It looks easier if you're able to accelerate out of every corner. Just drop it in and gas it out, even if you're falling to the earth you will have completed your turn before you go down and throttle will pick you back up. I'm sure it isn't that easy in practice... Supposed to be sunny this weekend and I'm going to try my hand at this gp8.
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Old 04-19-2013, 04:47 PM   #1063
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Originally Posted by shaddix View Post
It looks easier if you're able to accelerate out of every corner. Just drop it in and gas it out, even if you're falling to the earth you will have completed your turn before you go down and throttle will pick you back up. I'm sure it isn't that easy in practice... Supposed to be sunny this weekend and I'm going to try my hand at this gp8.
A constant lets low side it and recover it at the last moment.

send on a small touch screen by a guy with fat fingers
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Old 04-19-2013, 06:42 PM   #1064
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... here is an interesting theory in my head, while I'm preparing for tomorrow's session. Its a bit geeky, so if you fall asleep after first paragraph I'm not blaming you. Plus I'm not quite sure how solid my calculations are.

Motorcycle is rear-drive. Rear wheel pushes the entire motorcycle, while front does the steering, same as rear drive car.

We can not rotate motorcycle around rear wheel, if the rear wheel is stationary. Rear wheel always needs to move forward and push, in order for the front wheel to rotate around (I'm talking about riding circles).

When the motorcycle swings around the cone, the rear (powered) wheel, only moves in a short arc, while front wheel draws a much wider arc around the cone, covering a much greater distance.

So motorcycle still needs to put in that same amount of power to swing the front around, whatever distance the arch is, as it would if it was covering same distance in a straight line.

Lets assume that we have a motorcycle that is 7 foot long, from rear contact patch to front patch.

Because rear wheel still needs to move, and can not pivot just around itself, we can assume that an 7 foot long motorcycle will be drawing a circle around a cone with radius of around 9 feet. Basically the radius can not be equal or smaller than the length between contact patches. So 9 feet for a 7 foot length is just a safe assumption.

That is if we are really good, and we are managing steering, lean and power in such a way, that rear wheel moves the smallest distance around the cone, while still providing enough power to push front around.

So 9 foot radius gives us circumference of around 57 feet.

Given that a good rider can do a 360 rotation in 2.5 seconds, means that he has to cover 57 feet with his front wheel in 2.5 seconds. Converting that to miles / hour speed we get...

Around 16 miles per hour.

Thats the speed of the FRONT wheel, NOT rear. So if your speedometer sensor is mounted on front wheel, and you are doing around 15-16 miles per hour in a turn that is about 18 feet wide, you should be in the ballpark of good Gymkhana riders.

... Beuller?
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Old 04-19-2013, 07:17 PM   #1065
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... something like this?


turnSpeedTheory by rkcilf999, on Flickr
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