Effect Of Hanging Off

[littlefield]

This is getting off topic for the turning radius thread so I'll start a new one. Following is a simple equation to estimate the effect on the lean angle of hanging off the motorcycle.

 

This was derived using the bike in a straight up and down positon. In other words, the angle from which the center of gravity (cg) deviates is between a line from the center of the contact patch with the bike upright up through the bikes cg and another line from the center of the contact patch through the bike + rider cg. This wouldn't be totally correct when the contact patch moves to the edge of the tire but the idea is the same.

 

DR = distance the cg of the rider is moved off the centerline of the bike

HR = height of the rider cg above the pavement

HB = height of the bike cg above the pavement

WB = weight of the bike

WR = weight of the rider

 

The angle the bike + rider cg deviates as described above = arctan (DR/(HR + (HB*WB/WR))

 

This is how much more the bike would be upright as a result of hanging off. Intuitively it makes sense. Angle increase with DR and decreases with HR and HB.

 

So for a 400 lb bike, 175 lb rider, HB = 20 inches, HR = 40 inches, DR = 6 inches the angle is 4 degrees.

[racer]

I'll have to devote more time to work it through, but, it sounds good to me.

 

Not to be a piddly pedant, but... would it be better to label rider and bike mass rather than weight?

[littlefield]

It would indeed.

[tweek]

OMG - I started a monster.

 

from experiments in the labratory I can tell you that the impact of hanging it out is huge. The whole hook turn thing has a dramatic effect on the bike. It was fun to enter turns with my shoulders and head 'high' and then as I passed the apex to drop them down low. the change in my line was dramatic.

 

Have fun modeling this.

 

BTW - Lean Angle != turn radious

[racer]

OMG - I started a monster.

But a fun monster to be sure!

 

 

from experiments in the labratory I can tell you that the impact of hanging it out is huge. The whole hook turn thing has a dramatic effect on the bike. It was fun to enter turns with my shoulders and head 'high' and then as I passed the apex to drop them down low. the change in my line was dramatic.

You mean you keep your head and shoulders higher to quicken your turn-in (hook) while establishing lean angle... then lower them to reduce the lean angle (maintaining radius) enabling more throttle application? Is this a technique taught by the coaches/classroom?

 

 

Have fun modeling this.

We will, we will!

 

BTW - Lean Angle != turn radious

...for a given velocity.

[Leftlaner]

Well I'm no scientist, and I'm not very gifted when it comes to algebra og physics, but my "common sense" tells me that:

 

- The more the CG of the bike+rider is biased inwards, the less lean angle for a given speed (no surprises there, I know..)

- The higher the CG of the biker+rider, the less lean angle for a given speed

 

or in the reversed sense:

- At a given lean angle, you can carry higher speed the more the CG of the bike+rider is biased inwards

- At a given lean angle, you can carry higher speed by placing the CG of the bike+rider higher up

 

 

So why is everyone tucking behind their windscreen, getting the combined CG as low as possible? Well, first and most foremost because a lower CG gives greater stability and makes the bike less "oversensitive" to handlebar inputs. Secondly because tucking in reduces wind drag. Thirdly because it helps keeping those elbows loose (thus minimizing unwanted handlebar input). Finally and most importantly, because it looks better..

 

That's my theory anyway.. I might be awfully wrong though, as a lot of the physics seem "backwards" and counter-intuative when it comes to bike handling (i.e. the rear end will tend to RISE as you get on the throttle, the bike will turn left when you turn the handlebar right, the front end will grip better if you load the rear more etc etc)

[Leftlaner]

 

 

I believe the last two pictures strengthen my theory. BUT this only shows how the LEAN ANGLE is affected by the riders "height" so to speak. It does not tell wether this has an impact on the turn RADIUS (or how we can use this to adjust our line).. And remember, LEAN ANGLE != RADIUS..! So there is no direct correlation between the two.

 

Tweek said: "It was fun to enter turns with my shoulders and head 'high' and then as I passed the apex to drop them down low. the change in my line was dramatic."

 

From the sound of it, lowering the CG will somehow improve the Apex-to-exit part of the corner. So how can we improve this part of the corner, what do we want more of (or less of)..?

Will the lowered CG create a second "hook" in the line, which might come in handy at double apex turns or DR turns etc? My guess is as good as yours..!

[racer]

The last two photos are somewhat inconsistent. The c/g in the left photo is in line with the centerline of the bike. The c/g in the last photo is offset from the centerline of the bike.

 

Where did these pictures and captions come from?

[littlefield]

Just goes to show you can't believe everything you read even it's got a nice picture. Lowering the center of gravity increases the required lean angle? Not true. It's not nice to fool with Mother Nature.

[racer]

In any case, we need to be careful about how we define "higher" and "lower" wrt c/g.

 

If the c/g is higher or lower in line with the centerline of the bike, it makes no difference to lean angle at a given speed per se. However, moving the upper body off the bike (inward, long and low) moves the c/g significantly forward as well as inward putting weight on the front which is what is going on with the "hook turn", I believe.

[2bigalow]

Lowering your upper body down and to the inside shortens the bike's wheel base. Thus, a tighter line.

[racer]

Lowering your upper body down and to the inside shortens the bike's wheel base...

 

...because the fork is shortened due to weight on the front end created by the c/g moving forward via the upper body moving off the bike.

[2bigalow]

Yup!

[racer]

PS - You so totally just gave away the answer to the other thread ...

[racer]

Well I'm no scientist, and I'm not very gifted when it comes to algebra og physics, but my "common sense" tells me that:

 

- The more the CG of the bike+rider is biased inwards, the less lean angle for a given speed (no surprises there, I know..)

- The higher the CG of the biker+rider, the less lean angle for a given speed *

 

 

or in the reversed sense:

- At a given lean angle, you can carry higher speed the more the CG of the bike+rider is biased inwards

- At a given lean angle, you can carry higher speed by placing the CG of the bike+rider higher up *

 

 

So why is everyone tucking behind their windscreen, getting the combined CG as low as possible? Well, first and most foremost because a lower CG gives greater stability and makes the bike less "oversensitive" to handlebar inputs. Secondly because tucking in reduces wind drag. Thirdly because it helps keeping those elbows loose (thus minimizing unwanted handlebar input). Finally and most importantly, because it looks better..

 

That's my theory anyway.. I might be awfully wrong though, as a lot of the physics seem "backwards" and counter-intuative when it comes to bike handling (i.e. the rear end will tend to RISE as you get on the throttle, the bike will turn left when you turn the handlebar right, the front end will grip better if you load the rear more etc etc)

 

You are correct that lowering the center of gravity stabilizes the bike due to creating an effectively shorter lever for unbalanced (or unbalancing) force inputs of gravity and lateral G-force, ie. bumps (or handlebars) to act on. Everyone knows a longer lever will do more work, ie. a long wrench makes it easier to loosen a stuck bolt.

 

 

And, I think being higher up at the turn point makes it easier to flick quick. The longer lever makes the bike more "unstable", hence, it "unbalances" easier/faster, ie. with less force.

 

Tweek said: "It was fun to enter turns with my shoulders and head 'high' and then as I passed the apex to drop them down low. the change in my line was dramatic."

After getting leaned in, I imagine dropping the head and shoulders not only stabilizes the bike, but, more importantly, allows the bike to carry less lean angle or lift up, increasing traction and allowing more throttle to begin the exit. I'm not sure if that is what Tweek is talking about, but, it sounds good to me.

 

 

* That said... the height of the CG wrt to (inline with) the centerline (C/L) of the bike+rider (ie. length of lever) has no effect on the (balanced) lean angle for a given speed and radius. At a stable lean angle, gravity (down force) and lateral G (cornering/sideways) force are balanced wrt to the lever (or moment arm) of the bike+rider. By definition, the lean angle where the bike balances in a turn is the angle where the forces of gravity and lateral G are balanced. If the cornering force is low, the bike needs to be more vertical to balance, if the cornering force is high, the bike needs to lean more to balance. But, long or short, the bike (lever) will balance at the same lean angle between the same forces.

[Leftlaner]

The last two photos are somewhat inconsistent. The c/g in the left photo is in line with the centerline of the bike. The c/g in the last photo is offset from the centerline of the bike.

 

Where did these pictures and captions come from?

 

I got them from here: http://www.southbayriders.com/forums/showthread.php?t=33243

 

As you can see from this forum post, they are referring to a magazine (don't know which one though)..

 

Anyway, if CSS and Keith say that this stuff is BS, then I will promptly disregard it..

[Leftlaner]

And, I think being higher up at the turn point makes it easier to flick quick. The longer lever makes the bike more "unstable", hence, it "unbalances" easier/faster, ie. with less force.

 

This makes sense.

 

After getting leaned in, I imagine dropping the head and shoulders ... allows the bike to carry less lean angle or lift up, increasing traction and allowing more throttle to begin the exit.

 

How do you explain the physics behind this??

 

Doesn't this contradict what you're saying here?

 

The height of the CG wrt to (inline with) the centerline (C/L) of the bike+rider (ie. length of lever) has no effect on the (balanced) lean angle for a given speed and radius.

[racer]

After getting leaned in, I imagine dropping the head and shoulders ... allows the bike to carry less lean angle or lift up, increasing traction and allowing more throttle to begin the exit.

 

How do you explain the physics behind this??

 

http://forums.superbikeschool.com/index.ph...post&p=5193

 

 

Doesn't this contradict what you're saying here?

 

The height of the CG wrt to (inline with) the centerline (C/L) of the bike+rider (ie. length of lever) has no effect on the (balanced) lean angle for a given speed and radius.

 

This is what I was talking about... needing to be careful how one defines higher and lower wrt CoG (or anything) on a bike in a corner.

 

Let me try again...

 

I imagine that dropping the head and shoulders wrt gravity and 'up' and 'down' as the rest of the world sees it regardless and irrespective of the C/L or lean angle of the bike ... etc.

 

I sometimes assume that certain things are obvious from context. Sorry for the ambiguity.

 

Generally speaking, I assume the larger operational frame of reference, ie. if I don't specifiy higher on the bike, I am not using the bike as a frame of reference. So, if I use "up" or "down" when speaking about a bike in a corner, I am refering to the rest of the world, not the bike.

 

racer

[Leftlaner]

This is what I was talking about... needing to be careful how one defines higher and lower wrt CoG (or anything) on a bike in a corner.

 

Let me try again...

 

I imagine that dropping the head and shoulders wrt gravity and 'up' and 'down' as the rest of the world sees it regardless and irrespective of the C/L or lean angle of the bike ... etc.

 

I sometimes assume that certain things are obvious from context. Sorry for the ambiguity.

 

Generally speaking, I assume the larger operational frame of reference, ie. if I don't specifiy higher on the bike, I am not using the bike as a frame of reference. So, if I use "up" or "down" when speaking about a bike in a corner, I am refering to the rest of the world, not the bike.

 

racer

 

OK, so in a more practical sense, what you're saying is that tucking in vs. keeping shoulders high will only affect lean angle as long as the rider is hanging off..?

[racer]

OK, so in a more practical sense, what you're saying is that tucking in vs. keeping shoulders high will only affect lean angle as long as the rider is hanging off..?

 

Yes. Sort of.

 

The best time to hang-off is before beginning to brake for a corner. So, in that circumstance, I don't know that it is really accurate to characterize "tucking in" as the opposite of "keeping shoulders high". While the bike is straight up and down, hanging off with upper body off to the side, but, the head and shoulders above some arbitrary level that might best be defined by your own ability or range of being able to move up and down while hung off. 2bigalow (or tweek) could probably offer a better, or more precise, description.

 

So, as I understand what tweek is alluding to (albeit somewhat imprecisely), shoulders "high" and "low" refer to body position while already hung off.