Hanging off the seat- revisited - Sportbike Forum: Sportbike Motorcycle Forums
 
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post #1 of 10 (permalink) Old 06-18-2001, 06:25 PM Thread Starter
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Question Hanging off the seat- revisited

Before we had our server melt-down, there was a pretty interesting thread going on about wether or not hanging off the seat does anything for you. The concencus was that it does, but there were a number of reasons submitted as to why.

I suggested the following: By hanging off the seat to one side you shift the center of gravity to the inside of the turn, thereby extending the moment arm [defined as the product of a physical quantity (your center of gravity) and its perpendicular distance from an axis (the contact patch of the tire)] into the direction of turn, putting greater force on the contact patch, creating greater traction, allowing you to corner faster.

Does anyone know if this is correct? This kind of shit keeps me up at night .

Don't try to keep up with my life, you'll only get hurt.

-Mike
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post #2 of 10 (permalink) Old 06-19-2001, 06:02 AM
 
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by physics

Maybe it is so you will be more likely to low-side instead of high-side if you lose it because you are lowering the weight that is pushing out on the tires?
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post #3 of 10 (permalink) Old 06-19-2001, 07:26 AM
 
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Basically it shifts the center of gravity of the bike/rider combination. This change in CG means that the bike will be able to go through the turn with less lean angle for any given speed. Less lean = more rubber on the track = good.
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post #4 of 10 (permalink) Old 06-19-2001, 10:56 AM
 
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Never thought I would say this sentence, but "Lucifer has it right." By getting off your seat, you move the center of gravity low enough, without having to lean the bike as far. Try it for yourself. Oh, and if you've never ridden a dirtbike before, this may really screw with your head.

Find yourself a nice broad sweeping corner, that you can take at a comfortably slow speed, but still be fairly leaned (those looped entrance ramps to the freeway work well). Halfway through the corner start sliding off the seat, but maintain your turning radius. You'll notice that you naturally reduce your countersteer, and the bike stands up a little bit to balance you hanging off the side. Or do the opposite, come into the turn leaned, and slide back onto the seat. You'll notice that you have to feed in countersteer to maintain your radius. (For those of you who bodysteer, and haven't figured out countersteering yet, don't try this. We don't want to have to scrape you up.)

In the end, this keeps the bike more upright, and keeps more rubber on the road, also the force Normal to the contact patch is kept closer to perpendicular to the road. All of which means more traction.

Also, it makes it easier to slide your knee, which looks really cool.
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post #5 of 10 (permalink) Old 06-19-2001, 11:01 AM
 
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Re: Hanging off the seat- revisited

Quote:
Originally posted by Stake
I suggested the following: By hanging off the seat to one side you shift the center of gravity to the inside of the turn, thereby extending the moment arm [defined as the product of a physical quantity (your center of gravity) and its perpendicular distance from an axis (the contact patch of the tire)] into the direction of turn, putting greater force on the contact patch, creating greater traction, allowing you to corner faster.

Does anyone know if this is correct? This kind of shit keeps me up at night .
One thing I forgot to mention, a bike turns by shifting the center of gravity. For a given turning rate (same radius, same speed) you have to put the center of gravity in the same place everytime. If you move the center of gravity any farther then that, either by sliding off the seat, or leaning farther (both motions have the same net result) You either turn faster, or go down.

I'm hoping for turn faster........
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post #6 of 10 (permalink) Old 06-19-2001, 11:15 AM
 
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Cool

Hang off... go fast.
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post #7 of 10 (permalink) Old 06-19-2001, 11:48 AM
 
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Thanks Stake for bringing my thread back. Here is the article by Keith Code again. It was the last thing I posted on this topic before...

Go to: http://www.tiltedhorizon.com . Click "Tech Tips" at the bottom. "The Bad Side - Lefts or Rights?" at the top.
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post #8 of 10 (permalink) Old 06-19-2001, 01:19 PM
 
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Turning

Well, everyone is right. Can you believe it. If one were to explain it using engineering principals, there are several things happening.

1st - Lowering the center of gravity for the rider/bike combo is always good. It decreases the lever arm or "moment" along the vertical axis, allowing the bike to turn easier.

2nd - When you hang off, you are not lowering the center of gravity very much. You are mostly increasing the lever arm perpendicular to the wheel's axis (left or right). By doing this the bike will try to turn to the side the center of gravity has moved to.

3rd - To demonstrate the above principal try this. Take both hands off at 50 to 75 mph and as the bike is slowing down, try to put your body weight first on one footpeg then the other. You will notice the bike starting to turn with no handlebar input. The action will be fairly small, because the lever arm perpendicular to the longitudinal (front to rear), ie. the footpegs are very close to centerline. This means that while countersteering works, it is not the only actions on the bike.

4th - The last benefit of hanging off is for the same turn, if two riders were taking the same turn (one hanging off, one not), the rider hanging off will have his bike more upright. This means a larger contact patch which is always better.
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post #9 of 10 (permalink) Old 06-20-2001, 12:41 AM
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"Ditto", and...the suspension works better with the bike more vertical. The force is not as directly downward causing it to come closer to bottoming out on rougher corners. That can translate into a softer suspension/shock setting as well which will be more forgiving on washboard corners or corners with bumps. The only thing I say is I see people trying to hang off at speeds that don't really require it and they still haven't put enough effort into gauging corner speed or some other more elementary cornering techniques. Happy motoring!

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post #10 of 10 (permalink) Old 06-20-2001, 02:16 AM
 
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All of the above it true, as well as one last thing. While leaning off maintains the bike upright providing for a larger contact patch, we then push it farther down achieving a full lean (as far as the bike will go) while having the most amount of weight counteracting the force of inertia, thus allowing us to corner faster that we could have maintaining our ass where the manufacturer intended.
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