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Body Position And Cornering


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We all agree that body position has an effect on cornering.

 

I am trying to figure out why.

 

Imagine the same same rider, the same lean angle, the same turn in, the same speed and the same rate of turning.

 

Why is it the rider who hangs off will carve a tighter line than the one who doesn't?

 

In watching TotW2 DVD, I can see it. But it doesn't really explain why.

 

Is it due to centripedal force?

 

 

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In short, hanging off displaces the center of mass of the system - rider and motorcycle - to the inside of the turn. In your example the lean angle of both motorcycles is the same however the angle of the plane which contains the center of mass and the tire contact patch to the vertical is greater for the rider who hangs off. This allows - requires - this rider to follow a greater curvature (smaller radius) path.

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I like to think of it this way: the rider that is hanging off can use LESS lean angle for the same turn, same speed, etc. :)

 

The reason hanging off helps is that it moves the combined center of mass of rider and bike down and to the inside.

 

When doing physics problems, it is workable (and far simpler) to calculate forces acting on a body by identifying the Center of Mass of the body, and calculating the forces as they act upon the Center of Mass, instead of trying to treat the body as an infinite number of tiny parts.

 

When you are going in a circle, inertia wants you to keep going in a straight line, instead of on a curve. Some force is required to make you turn. That force is called centripetal force, and on a bike the centripetal force is provided by the friction of the tires on the pavement. (If you were whirling a ball on a string in a circle, the tension on the STRING would provide the centripetal force, and that is one of the simplest models to picture.)

 

The centripetal force provided by the friction of the tires is a horizontal force, which acts to keep the bike on the circle. However, since the tires are on the ground, and the Center of Mass of the bike/rider is a a few feet (or so) higher and we calculate the force of inertia as it acts on the Center of Mass, the forces are not in alignment and this creates a "moment" which wants to rotate the center of mass towards the outside of the circle - making the bike want to "fall" (rotate) to the outside.

 

When a rider leans the bike into the curve, the force of gravity on the Center of Mass of the bike/rider is no longer pushing straight down to the tires, it is offset the inside, which creates a "moment" which makes the bike want to rotate inwards - to fall down to the inside of the curve.

 

At a certain lean angle the forces balance, so the bike can go around the curve without falling inwards or rotating outwards.

 

Centripetal force is calculated as: mass times velocity squared, divided by the radius of the turn (mv2/r). So the force on the tires is dependent on the weight of the bike/rider, the speed, and the radius of the turn. That doesn't change.

 

What CAN change is the location of the center of mass - if you hang off, you can do two things:

1) You move the combined Center of Mass lower, which means the "moment" that wants to rotate the bike to the outside is less (because the offset distance of the horizontal forces is less - the C.O.M. is closer to the ground)

AND

2) you move the Center of Mass to the inside, which creates a GREATER horizontal distance between C.O.M. and the point of contact of tires to ground which increases the moment (from the vertical gravity forces) that wants to rotate you to the inside.

 

So the effect would be that you either have to stand the bike up more to keep from falling inwards - OR you can go faster or tighten the turn radius, either of which increases the centripetal force and puts the forces back in balance.

 

This is a bit oversimplified (other forces are present, like wind drag, etc.) but hopefully it communicates the idea. :)

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I like to think of it this way...

 

And all this time I thought it was to look cool :D . That must be the "value-add".

 

Great answer Hotfoot!

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IMHO hanging off is over rated. I didn't say useless, just over rated. :D

 

I see lots of videos of people going around corners hanging waaay off the bike when the lean angle is barely 20-degrees and the bike will lean 45-degress without breaking a sweat. What a bother. Better to get a good grip on the tank with both knees, then you have a solid platform that allows you to relax your arms, and plenty of leverage to push and pull on the handlebars. When you hang off less, and get your eyes out from under the hand grip, you also have a better view of the road.

 

I find it easier to relax and ride when I can see where I'm going, but that's just me. I'm still riding at the limits imposed by my own personal comfort level and not at the limits of the bike and the tires. I'm also not a racer. For competitive racing, hanging off is a requirement, but only one of many.

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IMHO hanging off is over rated. I didn't say useless, just over rated. :D

 

I see lots of videos of people going around corners hanging waaay off the bike when the lean angle is barely 20-degrees and the bike will lean 45-degress without breaking a sweat. What a bother. Better to get a good grip on the tank with both knees, then you have a solid platform that allows you to relax your arms, and plenty of leverage to push and pull on the handlebars. When you hang off less, and get your eyes out from under the hand grip, you also have a better view of the road.

 

I find it easier to relax and ride when I can see where I'm going, but that's just me. I'm still riding at the limits imposed by my own personal comfort level and not at the limits of the bike and the tires. I'm also not a racer. For competitive racing, hanging off is a requirement, but only one of many.

 

It suddenly gets a lot more important when you run out of lean angle! If you are at MAX lean, starting to drag parts, but you want to go around the corner faster, you either have to MOVE that Center of Mass, or REDUCE the mass! Hanging off is cheaper than carbon fiber parts and quicker than Weight Watchers... :)

 

As far as hanging off when riding at a relaxed pace or when not leaned over much... well, you have to start somewhere and it's a lot easier to practice and find a comfy position and build strength at a moderate pace and shallow lean angle - it's pretty tough to all of a sudden dramatically change your position when you decide to pick up the pace, too many things to worry about all at once.

 

Also, to warregl's point.... it looks cool. B)

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IMHO hanging off is over rated. I didn't say useless, just over rated. :D

 

 

I think a LOT of things seem overrated until you need them. Like race tires, for example. It seems crazy to spend 3x the price on fancy race tires... until you start overriding the grip on a street tire. Or telemetry, that seems like a massive waste of money... until you are trying to get an extra 0.2 seconds off your lap time and really need some data to figure out where to get it.

 

Most riders find, as they progress, they hit limits, and when you hit a limit something has to change. When I first started riding, quick turn didn't make much sense to me - until I increased my entry speeds, then I NEEDED that technique. I didn't get the importance of pivot steering until one day I realized that if I went any faster through a certain corner I wouldn't be able to get the bike turned. Suddenly the technique became relevant, for me. On the other hand, the "relax" drill was something I needed RIGHT AWAY, and it made a massive difference for me on my very first school day.

 

I notice, at schools, rider learn various techniques and apply them, but inevitably at least one of the tecnhiques makes a sudden HUGE difference in their riding - because THAT is the one that breaks through their particular barrier at that moment. And they pick up the pace, and then they hit a new barrier. And it requires a different solution.

 

The feeling of breaking through those barriers is incomparable and that is one of the main things that kept me coming back to the school, over and over - it's very hard to do on your own and very easy at the school.

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IMHO hanging off is over rated. I didn't say useless, just over rated. :D

 

I see lots of videos of people going around corners hanging waaay off the bike when the lean angle is barely 20-degrees and the bike will lean 45-degress without breaking a sweat.

 

Those are the same people not wanting to have chicken strips in their tires smile.gif

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Centripetal force is calculated as: mass times velocity squared, divided by the radius of the turn (mv2/r). So the force on the tires is dependent on the weight of the bike/rider, the speed, and the radius of the turn. That doesn't change.

:)

 

That makes the leaning angle not directly proportional with the speed of the bike.

That means that between 20 and 30 degrees accommodates a wider range of speeds than between 30 and 40 degrees.

 

 

At 45 degrees, the horizontal force pushing the tires is equal to the combined weight of bike and rider.

 

If not acceleration is happening, around 40% of that force tries to skid the front tire and 60% the rear tire.

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IMHO hanging off is over rated. I didn't say useless, just over rated. :D

 

 

I think a LOT of things seem overrated until you need them. Like race tires, for example. It seems crazy to spend 3x the price on fancy race tires... until you start overriding the grip on a street tire. Or telemetry, that seems like a massive waste of money... until you are trying to get an extra 0.2 seconds off your lap time and really need some data to figure out where to get it.

 

Most riders find, as they progress, they hit limits, and when you hit a limit something has to change. When I first started riding, quick turn didn't make much sense to me - until I increased my entry speeds, then I NEEDED that technique. I didn't get the importance of pivot steering until one day I realized that if I went any faster through a certain corner I wouldn't be able to get the bike turned. Suddenly the technique became relevant, for me. On the other hand, the "relax" drill was something I needed RIGHT AWAY, and it made a massive difference for me on my very first school day.

 

I notice, at schools, rider learn various techniques and apply them, but inevitably at least one of the tecnhiques makes a sudden HUGE difference in their riding - because THAT is the one that breaks through their particular barrier at that moment. And they pick up the pace, and then they hit a new barrier. And it requires a different solution.

 

The feeling of breaking through those barriers is incomparable and that is one of the main things that kept me coming back to the school, over and over - it's very hard to do on your own and very easy at the school.

 

Very, VERY well said! B)

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I'm with Crash on this. Hailwood won races despite never hanging off. Doohan used to drop his bum yet his head was close to the outside handlebar - without scientific evidence I'd say he was pretty balanced, ie he could just as well have sat in a neutral position. And he won a title or 5, didn't he? Then you have Elias that hangs so low on the bike that the effect probably isn't more than a tall person sitting errect in the seat without hanging off at all.

 

My guess is that throwing the body around have a greater effect than the actual "passive" position when hanging off. It can help change direction more rapidly. And you can push the bike up while still hanging off, countering forces and hence be able to get on the throttle a litle earlier out of bends. I'm pretty convinced that hanging off in itself also improve cornering speed enough that it's worth while for a racer trying to win.

 

Out on public roads, however, my personal opinion is that hanging off is not ideal. It also allow you something in reserve as you can throw your body down to the side if you unexpectedly need to tighten your line. Also leaning in will, like Crash said, limit your vision ahead around blind corners.

 

I do not expect many to agree with this, and that's fine. I'll just continue to fool myself and enjoy my existense in my bubble :D

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Out on public roads, however, my personal opinion is that hanging off is not ideal. It also allow you something in reserve as you can throw your body down to the side if you unexpectedly need to tighten your line. Also leaning in will, like Crash said, limit your vision ahead around blind corners.

 

I do not expect many to agree with this, and that's fine. I'll just continue to fool myself and enjoy my existense in my bubble :D

 

Ah - good point. I didn't mean to imply that hanging off is ALWAYS necessary. It's just a solution to the specific problem of running out of lean angle. If you aren't in a situation where you are running out of lean angle, or just generally need or want to use less lean, it may not be useful. I agree that hanging off while riding in the street can be a waste of energy and could compromise your vision. I don't ever hang off while riding on the street, because I don't go fast enough to need to, nor do I hang off during slow sighting laps, where I need to sit up and look around.

 

I just don't agree with the statement that it is "overrated", because it solves a very significant problem!

 

Crash - your description of people hanging WAAAY off when the bike is barely leaned over made me grin, and made me think of the people that put giant lift kits and huge wheels on their truck but then never take it off city streets. A bit of overkill, perhaps... :)

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As far as hanging off when riding at a relaxed pace or when not leaned over much... well, you have to start somewhere and it's a lot easier to practice and find a comfy position and build strength at a moderate pace and shallow lean angle - it's pretty tough to all of a sudden dramatically change your position when you decide to pick up the pace, too many things to worry about all at once.

 

Also, to warregl's point.... it looks cool. B)

 

 

Crash - your description of people hanging WAAAY off when the bike is barely leaned over made me grin, and made me think of the people that put giant lift kits and huge wheels on their truck but then never take it off city streets. A bit of overkill, perhaps... :)

 

Of course. Some people hang off uselessly or because they see someone do it without knowing why it is done. They do it to look cool. Just like some trucks have big tires and wheels and the truck is running a skyjacker. And it does look cool. :)

 

As for my original question, thanks for the answer.

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I'd say public roads are no place for FULL FLEDGE hangoffs ... USUALLY.

 

but in emergencies ,one cheek/Full fledge is ok if it saves your bacon.

 

 

 

In respond to body position, IMHO i usually concentrate on the upper body

 

 

eg, amount of front/back , which part of the tank should I rest on on different gradient slopes/ hi/lo speed turns etc

 

eg amount of left/right , and head positioning too.

 

also how fast you do it , its like quick flicking only with your body and then the bike, kinda like the visual 2 step system.

 

its sampling too, once you hit the sweet spot, you can go at least 5% faster without upsetting the bike or scaring yourself .

 

 

 

 

 

 

 

 

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My guess is that throwing the body around have a greater effect than the actual "passive" position when hanging off. It can help change direction more rapidly. And you can push the bike up while still hanging off, countering forces and hence be able to get on the throttle a litle earlier out of bends. I'm pretty convinced that hanging off in itself also improve cornering speed enough that it's worth while for a racer trying to win.

 

Ahhh... is this the elusive 'body steering' technique I sometimes hear about? wink.giftongue.gif

 

Remember that when you 'push the bike up' when you're coming out of the corner it's all to do with your steering inputs at the handlebars. Just as you countersteer to turn the bike into a turn, you countersteer to 'stand up' the bike coming out of a turn. Nothing at all to do with where your bodyweight is. But having the correct body position will make those steering inputs alot easier. The most efficient steering inputs will be in a horizontal plane of motion (hanging off and getting your body low, pushing on the 'bars towards the front of the bike), rather that sitting upright and putting your efforts into downwards pushing motion.

 

Do you think it's true to say that hanging off reduces the 'actual' lean angle? Think of two riders, going through a turn with the bike at the same lean angle. But one rider is hanging off with their body low over the tank - the other is sitting upright and in-line with the bike. Are they really both using the same amount of lean angle? Since the actual lean angle must be measured from the center of mass to the center of the tyre contact patch...?

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At 45 degrees, the horizontal force pushing the tires is equal to the combined weight of bike and rider.

Not true I'm afraid. The amount of centripetal (cornering) force produced, as Hotfoot says, depends on the amount of weight and how far inwards (horizontally) it is of the contact patch. This varies with lean angle of course, and a tall bike will thus produce more of it than a short one at the same lean angle.

 

My guess is that throwing the body around have a greater effect than the actual "passive" position when hanging off.

More weight on the inside of the bike means more cornering (centripetal) force. You can see it at a standstill, if you sit on one side, the bike will fall that way. More fall = more cornering.

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At 45 degrees, the horizontal force pushing the tires is equal to the combined weight of bike and rider.

Not true I'm afraid. The amount of centripetal (cornering) force produced, as Hotfoot says, depends on the amount of weight and how far inwards (horizontally) it is of the contact patch. This varies with lean angle of course, and a tall bike will thus produce more of it than a short one at the same lean angle.

I beg to differ. 45 degrees is exactly the point where sine(x) = cosine(x), so the vertical and horizontal forces are equal.

All this, assuming you are riding in a perfect circle at a constant, etc. But it should be close enough in reality.

 

I have happily forgotten all the university 1st year mechanics so I will let it rest here, should you still disagree.

 

Kai

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At 45 degrees, the horizontal force pushing the tires is equal to the combined weight of bike and rider.

Not true I'm afraid. The amount of centripetal (cornering) force produced, as Hotfoot says, depends on the amount of weight and how far inwards (horizontally) it is of the contact patch. This varies with lean angle of course, and a tall bike will thus produce more of it than a short one at the same lean angle.

 

If you watch the attached diagram with your head tilted to the right, you will see a bike rolling on one side of the tires, over an inclined road, and carrying a weight somehow higher than its natural weight (bike+rider).

The leaned bike is balanced because all the forces go to ground through the tires, just like when it is traveling in a straight up position.

 

When properly leaned in a turn, a motorcycle is as stable as when perfectly straight.

The reason being that the weight of the bike plus the forces generated by the circular movement don't point vertically down but towards an angle between vertical and horizontal.

 

Hence; the height at which the CG is located has no influence on the total (bike+rider) lean angle.

post-23333-0-73751500-1331744446_thumb.jpg

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I'm with Crash on this. Hailwood won races despite never hanging off. Doohan used to drop his bum yet his head was close to the outside handlebar - without scientific evidence I'd say he was pretty balanced, ie he could just as well have sat in a neutral position. And he won a title or 5, didn't he? Then you have Elias that hangs so low on the bike that the effect probably isn't more than a tall person sitting errect in the seat without hanging off at all.

 

 

These riders you're mentioning were using the accepted body position at the time. They would be taught differently if they rode today, or they wouldn't win. And Elias IS the perfect example for this. He can't keep heat in the tires of the GP bikes because of this poor body position, so he's no longer in that class. This is where Hailwood and Doohan would be, had they used the same body position of their time.

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Hailwood did a comeback at an advanced age after 8(?) years off bikes, with a little beer gut, and still smoked the competition in several races in 1978/79 when hanging off had become the norm. He was never convinced hanging off was required to win races. But I guess riding positions have contined to evolve since then as well, so it may not be entirely relevant compared to current times.

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At 45 degrees, the horizontal force pushing the tires is equal to the combined weight of bike and rider.

Not true I'm afraid. The amount of centripetal (cornering) force produced, as Hotfoot says, depends on the amount of weight and how far inwards (horizontally) it is of the contact patch. This varies with lean angle of course, and a tall bike will thus produce more of it than a short one at the same lean angle.

 

If you watch the attached diagram with your head tilted to the right, you will see a bike rolling on one side of the tires, over an inclined road, and carrying a weight somehow higher than its natural weight (bike+rider).

The leaned bike is balanced because all the forces go to ground through the tires, just like when it is traveling in a straight up position.

 

When properly leaned in a turn, a motorcycle is as stable as when perfectly straight.

The reason being that the weight of the bike plus the forces generated by the circular movement don't point vertically down but towards an angle between vertical and horizontal.

 

Hence; the height at which the CG is located has no influence on the total (bike+rider) lean angle.

 

 

The confusing/misleading part about the statement above is that we are not trying to change the COMBINED bike PLUS rider lean angle. We are just trying to change the BIKE lean angle.

 

The diagram above shows the simplified model using one combined center of gravity for both bike and rider. Hanging off changes the relative position of bike and rider to each other, which means to see the actual BIKE lean angle you have to treat the the bodies (bike and rider) separately. We all know from experience on motorycycles and bicycles that if you lean YOUR body way into the turn, you can stand the bike up more and use less lean angle, and that if you lean your body AWAY from the turn, you have to push the bike down underneath you (steeper bike lean angle) to balance. The lean angle of the COMBINATION of bike and rider does not change (for a given mass, speed and radius) but when you change the relative position of the bike and rider to each other, the RIDER can lean in more while having to lean the BIKE less.

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If you look at this video, it looks to me like the sportbike leans more than the following bike(s) despite the former hanging off and the latter appears not to. Am I just seeing things, being fooled into that because the rider hang off so far?

?
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If you look at this video, it looks to me like the sportbike leans more than the following bike(s) despite the former hanging off and the latter appears not to. Am I just seeing things, being fooled into that because the rider hang off so far?

 

?

 

 

Holy smokes, it's pretty hard to compare lean angles when one bike is in front of the camera and the others is behind - or under? - the camera!

 

But, here is something I did notice - the rider being filmed (the one in front) for the first part of the video is not hanging off effectively. He is sticking his knee way out and rotating his hips off to the inside, but if you look closely at his upper body it is crossed up - he leans back over the bike with his upper body so that his helmet is actually at or past the centerline of the bike. You can REALLY see it in the preview photo - see how the bike is leaned to the right but the rider's head is actually closer to the LEFT mirror? He is pushing the bike down underneath him, instead of leaning his upper body into the turn.

 

So although he gets PART of his body mass to the inside, a good part of it (possibly the heaviest part) is either on top of the bike or even a bit to the outside. He isn't moving the combined Center of Gravity very much, if it all, so his lean angle is probably about the same as a rider who isn't trying to hang off.

 

In contrast, the rider that is filming DOES seem to get his/her head off to the inside, and presumably the upper body with it; you can't tell much, but if you watch the position of the mirrors relative to the camera, you can kinda tell.

 

Towards the end of the video we see another rider that is sitting straight up (but does go nicely with the bike, no counterleaning). That rider doens't use a lot of lean angle, but it appears to me that it is a lighter-weight bike and he doesn't seem to be going as fast, so he wouldn't need to use as much lean angle to get around the turns.

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If you look closely, you can see the same rider hanging off - effectively or not - in front of the rider that you find not going as fast. And the bloke hanging off seems to be leaning just as much then.

 

Check out Doohan in this clip - not all that unlike the bloke in the other video, is it?

 

http://www.youtube.com/watch?v=mkiwtIzT9xs&feature=related

 

 

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The confusing/misleading part about the statement above is that we are not trying to change the COMBINED bike PLUS rider lean angle. We are just trying to change the BIKE lean angle.

 

The diagram above shows the simplified model using one combined center of gravity for both bike and rider. Hanging off changes the relative position of bike and rider to each other, which means to see the actual BIKE lean angle you have to treat the the bodies (bike and rider) separately. We all know from experience on motorycycles and bicycles that if you lean YOUR body way into the turn, you can stand the bike up more and use less lean angle, and that if you lean your body AWAY from the turn, you have to push the bike down underneath you (steeper bike lean angle) to balance. The lean angle of the COMBINATION of bike and rider does not change (for a given mass, speed and radius) but when you change the relative position of the bike and rider to each other, the RIDER can lean in more while having to lean the BIKE less.

The new diagram is exaggerated regarding angles and locations of centers of gravity, but shows the basic principle.

post-23333-0-69169900-1331924737_thumb.jpg

post-23333-0-87415100-1331924749_thumb.jpg

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