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Old 12-27-2004, 04:10 PM   #1
sportbike_pilot
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Default Re: So how do you actually turn a motorcycle?

The only problem is that Keith Code, at least as quoted here, is not exactly correct about this.



In order to steer a bike it must lean. The countersteer is merely the most efficient way to initiate lean.



The sequence of events works something like this for most bikes:



- Countersteer rake and trail combine to steer the bike out from underneath its center of mass (gyroscopic effect has litte to do with this phase)



- As the bike leans a gravitational torque causes the "roll motion" of the bike to accelerate since the bike has a pretty large moment of inertia about it's roll axis the change in angular momentum causes the front wheel to precess in the direction of the intended turn



- this precession causes the front wheel to swing back in the direction of the intented turn and stops the roll of the bike towards the ground.



- the turn is executed.



There are numerous factors that muddy up this general scenario but that's the gist of it. I would note that there is a fair amount of argument even among physicists about the finer points of this, but not about the basics.



Even Tony Foale agrees that this is basically correct which is why I imagine that his seminars recently with Keith must have been interesting.



-sbp
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Old 12-27-2004, 04:43 PM   #2
naco_traficante
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Default Re: So how do you actually turn a motorcycle?

In my world (which usually bears no resemblance to the real world) I think of turning as intentionally making the bike fall over.

Countersteering is what makes the bike fall in the correct direction. However, my bike fell over so well a few months ago that I am currently bike-less, so what do I know.

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Old 12-27-2004, 05:12 PM   #3
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Default Re: So how do you actually turn a motorcycle?

Great comments (those that I understood). As with most debates, I suspect the reality about steering is somewhere in between two opposing viewpoints. Those who focus solely on countersteering avoid the benefits of "hanging off" relative to lowered center of gravity, reduced lean angle, steering the rear wheel, etc. Those who swear by body position seem to discount the fact that their movement is allowing for better (quicker, lighter, more controlled, whatever) countersteering. So if countersteering is all about the efficiency of turning / leaning a bike, it seems that body position is about efficiently managing the inputs and outputs of that process. Doing one without the other is incomplete.
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Old 12-27-2004, 05:17 PM   #4
Vlad
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Default Re: So how do you actually turn a motorcycle?

sbp:



I looked at your explanation, and it works for me. I think that the confusion exists because Code is trying to prove that "body english," aka the rider's leaning, isn't what turns the bike. It's countersteering (as in your explanation) that does the trick. We, as riders, lean with the bike. I'm one of the strange people in the world who has practiced swerving, and I don't lean to start anything, I just keep up with the bike. Once in the corner, then your CG can affect the bike's lean angle, but changing direction is dependant on countersteering.



Just my two Euros.



FC
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Old 12-27-2004, 06:42 PM   #5
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Default Re: So how do you actually turn a motorcycle?

Well, I can steer my motorcycle and my bicycle without my hands on the bars. However this is only possible because the forks arent welded solid.

It happens because I use body language to initiate movement of the headstock, and normal motorcycle physics takes over from there. It's not that hard, but I wouldnt want to try tight corners.

It's not as accurate and reliable as turning the bars, obviously, but on one outback stretch of road, I once did 40km without touching the bars - gentle curves and all.

I do get that Code's point is to illustrate to riders how important countersteering is, and how that knowledge can make them faster, safer riders.
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Old 12-27-2004, 06:47 PM   #6
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Default Re: So how do you actually turn a motorcycle?

Turn... schmurn. I wanna know why KPile's 205 MPH thread got pulled. We had a real flamefest in the making there!
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Old 12-27-2004, 07:23 PM   #7
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Default Whazzup?

Yeah, whazzup wit-at!



I put up a lame post, 'cause I came in second, but I was figuring on a blood bath, later...with K-speare doing his, "Once more into the breach," (of reality) routine.
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Old 12-27-2004, 07:24 PM   #8
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Default Re: So how do you actually turn a motorcycle?

I think that our board may have been compromised this evening. Haven't heard back from Sean yet but we may have a real haymaker in the offing. Hope I am wrong tho.



How are things down in yer neck of the wood? Not much snow up here except up high. You?
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Old 12-27-2004, 07:57 PM   #9
jungkvist
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Default I Ain't Never Rode A Black-Board!

Anything over parking lot speed, I counter steer.



Going into a right-handerÂ…I push my right knee against the tankÂ…I lever the right-side of my butt off the seatÂ…I push the right grip forwardÂ…The bike leansÂ…I hang-off, with the inside of my left knee hooked on the left side of the seatÂ…The bike does everything else.



Counter-Steering initiates the turn; all other actions are for keeping the most tread on the road, and my hard-parts unblemished. Leaning, I figure, is the natural result of the physical laws of motion and inertia (which I donÂ’t much care thinking aboutÂ…while dragging my A$$Â…probably faster that I shouldÂ…around a curve).



Hey, I like physics as much as the next guy, but I ainÂ’t never rode a black-boardÂ….works for me!

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Old 12-27-2004, 08:26 PM   #10
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Default Re: So how do you actually turn a motorcycle?

I'm sure that I'm not the only one to note that counter-steering begins at a threshold speed. Before that threshold the Bike steers intuitively (turn right to go right).



Vector analysis shows that the lean angle will increase with an increase in velocity in a constant radius turn to balance the increased centrifugal force the centripetal force must increase equally. These forces must be in equalibrium for both the tire acting through it's contact patch to maintain the intended track and the bike/rider combo to prevent highside/lowside. When you consider that the actual (acting) center of gravity may pass to a point outside of the contact patch, (along the center of the tire) through air to reach the surface amoung many other variables throughout a Motorcycles chassis it is not surprising that Physicists and other smart people find that there is still plenty of "Art" to the science of handling. IMHO



On the banks of Daytona the bikes can approach 90 degrees of bank relative to the earth and the "g-force" can daze a rider with their helmet slamming off the tank with increased force when hitting bumps.



Little wonder that the Fastest guys I've known when I've asked for "Secrets of Speed" have concured "If you want to go fast work on being smooth, speed will come."



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