How do they do that ?

eddiekay · April 20th, 2010, 06:48 AM

I saw a guy fall off his stunt bike and the bike chugged along @ like 2 mph without falling over. he chased the bike and got back on to do some more amazing stuff. I've seen this more than once...more than one bike. How do they do that?

ninja250 · April 20th, 2010, 07:12 AM

Bikes automatically stand themselves up with no rider.
It's the gyroscopic force of rotating wheels and the geometry of the frame making everything want to stay standing.
It was probably choking along in first or second no throttle. (you might notice the rpm on most street bikes is so high you can pull away in first gear using only the clutch and no throttle)

Second it stopped rolling it would have been on it's side.

CC Cowboy · April 20th, 2010, 07:33 AM

It might have something to do with the huge rear sprocket on stunt bikes. They don't stall as easy.

ninja250 · April 20th, 2010, 07:38 AM

Ah, true that too.
Big sprocket = wheelies on a dime and no stalling or easier push starting. lol

vollrathdude · April 20th, 2010, 11:23 PM

Wouldn't the big sprocket make this phenomena more weird? The fatter sprocket would lower the speed its traveling at idle rpm compared to a smaller sprocket at idle. The gyroscope effect increases with speed of rotation. I would guess its due in part to the minimal gyroscope effect at that speed, and partly due to luck that it was balanced straight up when he departed the bike.

Haider87 · April 21st, 2010, 12:18 AM

Quote:

Originally Posted by vollrathdude

Wouldn't the big sprocket make this phenomena more weird? The fatter sprocket would lower the speed its traveling at idle rpm compared to a smaller sprocket at idle. The gyroscope effect increases with speed of rotation. I would guess its due in part to the minimal gyroscope effect at that speed, and partly due to luck that it was balanced straight up when he departed the bike.

Both are plausible arguments. Big sprocket = no stall, and Big sprocket = less speed.. Only one way to tell.

I know my 250 will roll with no throttle, I just wouldn't dare pull that kind of stunt.

Tigress · April 21st, 2010, 01:08 AM

I'm not 100% sure, but I think many stunters use throttle locks as well to keep it going.

backinthesaddleagain · April 21st, 2010, 06:52 AM

Quote:

Originally Posted by Tigress

I'm not 100% sure, but I think many stunters use throttle locks as well to keep it going.

+1

Hadyn · April 21st, 2010, 07:06 AM

Caster angle.
Ever seen those two-wheeled swively skateboards? Same principle.
The larger sprocket and leftover momentum keep the bike going, the self-correcting property of the caster angle keeps the bike upright, the slight gyroscopic forces lessen the wobble of the bars.
Add those together and you've got a ghost-riding bike that you can (hopefully) catch up to before gravity does.
Posted via Mobile Device

Momaru · April 21st, 2010, 07:44 AM

The first video on the link is of a rider that seems to have scraped himself off the bike in a deep turn during a race or track day. Bike wobbles along down the track without him while he gets up, books it to the bike, catches it and resumes riding.
http://www.ninjette.org/forums/showp...8&postcount=12

Greg_E · April 21st, 2010, 07:58 AM

Throttle lock would be dangerous, but an increased idle rpm might be happening. That's one of the tricks for taking your road test is to turn up the idle so that you really don't have to use the throttle for starts and the tight patterns needed to pass.

dowmace · April 21st, 2010, 05:59 PM

Most stunters raise the idle on the bike, I know a few guys running F4I's and they all have the idle set to 4k which with a large sprocket is probably enough speed to make the bike run on it's own.

Snake · April 22nd, 2010, 06:54 AM

Don't forget the gyroscopic effect produced by the engine. Even at low speed with the bike sprocket it is probably turning at around 4K rpm.

cnichols79us · April 22nd, 2010, 09:45 AM

Quote:

Originally Posted by Momaru

The first video on the link is of a rider that seems to have scraped himself off the bike in a deep turn during a race or track day. Bike wobbles along down the track without him while he gets up, books it to the bike, catches it and resumes riding. http://www.ninjette.org/forums/showp...8&postcount=12

That was AWESOME....

LazinCajun · April 22nd, 2010, 10:49 AM

A little off topic, but wow that highside save was the craziest / luckiest thing I've ever seen on a motorcycle.

April 20th, 2010, 06:48 AM	#1
eddiekay ninjette.org certified postwhore Name: eddie Location: Lawnguylind Join Date: Nov 2009 Motorcycle(s): 300, WeeStrom Posts: A lot.	How do they do that ? I saw a guy fall off his stunt bike and the bike chugged along @ like 2 mph without falling over. he chased the bike and got back on to do some more amazing stuff. I've seen this more than once...more than one bike. How do they do that?

April 20th, 2010, 07:12 AM	#2
ninja250 You are sleeping Name: Casey Location: LMFAO!!! Join Date: Nov 2009 Motorcycle(s): 2 Posts: A lot.	Bikes automatically stand themselves up with no rider. It's the gyroscopic force of rotating wheels and the geometry of the frame making everything want to stay standing. It was probably choking along in first or second no throttle. (you might notice the rpm on most street bikes is so high you can pull away in first gear using only the clutch and no throttle) Second it stopped rolling it would have been on it's side. __________________________________________________ <Yeah, it's a 250. LMFAO! Weaksauce

April 20th, 2010, 07:33 AM	#3
CC Cowboy ninjette.org certified postwhore Name: Whodat Location: Ware Is.,MA Join Date: Jan 2009 Motorcycle(s): I pass the wind! Posts: A lot. MOTM - Mar '13, Jun '14	It might have something to do with the huge rear sprocket on stunt bikes. They don't stall as easy. __________________________________________________ If everything seems under control; you're just not going fast enough!

April 20th, 2010, 07:38 AM	#4
ninja250 You are sleeping Name: Casey Location: LMFAO!!! Join Date: Nov 2009 Motorcycle(s): 2 Posts: A lot.	Ah, true that too. Big sprocket = wheelies on a dime and no stalling or easier push starting. lol __________________________________________________ <Yeah, it's a 250. LMFAO! Weaksauce

April 21st, 2010, 01:08 AM	#7
Tigress Musical Genius Name: Belinda Location: O'Fallon, MO Join Date: Aug 2009 Motorcycle(s): 09 Ninja 250R Blue AKA "The Kid" 08 Vulcan 900 Classic Blue(for now) AKA "Honey" Posts: 146	I'm not 100% sure, but I think many stunters use throttle locks as well to keep it going. __________________________________________________ ti·gress n. 1. A female tiger. 2. A woman regarded as daring or fierce.

April 20th, 2010, 11:23 PM	#5
vollrathdude ninjette.org member Name: jordan Location: edmonton, alberta, canada eh Join Date: Jul 2009 Motorcycle(s): '09 250r se Posts: 30	Wouldn't the big sprocket make this phenomena more weird? The fatter sprocket would lower the speed its traveling at idle rpm compared to a smaller sprocket at idle. The gyroscope effect increases with speed of rotation. I would guess its due in part to the minimal gyroscope effect at that speed, and partly due to luck that it was balanced straight up when he departed the bike.

April 21st, 2010, 07:06 AM	#9
Hadyn ninjette.org member Name: Andrew Location: Fairfax, VA Join Date: Apr 2009 Motorcycle(s): '06 Yellow 250r Posts: 211	Caster angle. Ever seen those two-wheeled swively skateboards? Same principle. The larger sprocket and leftover momentum keep the bike going, the self-correcting property of the caster angle keeps the bike upright, the slight gyroscopic forces lessen the wobble of the bars. Add those together and you've got a ghost-riding bike that you can (hopefully) catch up to before gravity does. Posted via Mobile Device

April 21st, 2010, 07:44 AM	#10
Momaru ninjette.org certified postwhore Name: Paul Location: Roanoke, VA Join Date: Jun 2009 Motorcycle(s): 2008 Candy Plasma Blue 250R Posts: A lot.	The first video on the link is of a rider that seems to have scraped himself off the bike in a deep turn during a race or track day. Bike wobbles along down the track without him while he gets up, books it to the bike, catches it and resumes riding. http://www.ninjette.org/forums/showp...8&postcount=12 __________________________________________________ Proud member of the Blue Army

April 21st, 2010, 07:58 AM	#11
Greg_E ninjette.org sage Name: Greg Location: central new york Join Date: Aug 2009 Motorcycle(s): 90 Suzuki gsx600f Katana, 03 Buell XB9R Posts: 868	Throttle lock would be dangerous, but an increased idle rpm might be happening. That's one of the tricks for taking your road test is to turn up the idle so that you really don't have to use the throttle for starts and the tight patterns needed to pass.

April 21st, 2010, 05:59 PM	#12
dowmace ninjette.org member Name: Jonathan Location: Sapulpa, OK Join Date: Mar 2010 Motorcycle(s): 2006 Ninja 250 Posts: 65	Most stunters raise the idle on the bike, I know a few guys running F4I's and they all have the idle set to 4k which with a large sprocket is probably enough speed to make the bike run on it's own. __________________________________________________ I just wanna ride........

April 22nd, 2010, 06:54 AM	#13
Snake ninjette.org certified postwhore Name: Rick Location: Alexandria, Louisiana Join Date: Jan 2009 Motorcycle(s): 05 Blue Ninja 250 Posts: Too much. MOTY - 2017, MOTM - Jan '19, Oct '16, May '14	Don't forget the gyroscopic effect produced by the engine. Even at low speed with the bike sprocket it is probably turning at around 4K rpm.

April 22nd, 2010, 10:49 AM	#15
LazinCajun ninjette.org guru Name: Anon Location: Atlanta, GA Join Date: Aug 2009 Motorcycle(s): 2008 Ninja 250 (Blue!) Posts: 488	A little off topic, but wow that highside save was the craziest / luckiest thing I've ever seen on a motorcycle.