It's never too late to learn...

[Bumblebee]

So this is what I'm thinking. Lets take that turn and keep going. In an open parking lot we take a turn at 20mph as tight as we can with body straight up. At this point the bikes mass and you are on the very outer edge of the rotating mass. The center of rotation being the point you are circling. Now when you move your body to the inside 100+ lbs are now a few inches closer to the center. The bike can turn faster now. Not only because it can now lean more but because you have moved mass to the center of the motion. Here is the part you can't actually do. Now step off the bike and walk to the center. Now that 100+ lbs is rotating, instead of traveling around the center point. The bike in turn should rotate even faster around the center. It doesn't matter how big or far away from the center an object is to be effected by this. Our moon started off really close to the earth and the earth was spinning crazy fast. Something like a rotation every two hours or something. As the moon moved farther and farther away the spin of the earth was slowed from this same force.

There are a lot of factors that come into play with a motorcycle but this must have some effect on the turn.

The difference is in how the conditions are setup. Open or closed system. At first they appear somewhat similar however mechanically they're different.
In a closed system such as a skater pulling their arms in or the earth/moon, all the forces are internal. It's conservation of angular momentum. The skater's degrees per second rate increases. The earth rotation slows as the closed earth/moon system spreads out - then you get into the tidally locked orbital mechanics thing that keeps the same side of the moon facing the earth... Skater, earth/moon, same basic thing.
In an open system such as riding, the motorcycle is pushing against the ground to maintain the turn rate (degrees per second) or it would go in a straight line like say hitting a sheet of ice when the ground quits pushing the motorcycle to another heading. The harder the tires push against the ground away from straight ahead, the higher the turn rate will be until the outward force exceeds the coefficient of friction. At best, just having the rider on the motorcycle at all will increase the turn radius because the tires are having to shove that extra weight toward the center which keeps the circle larger due to friction limits and the further out on the circle, the lower the turn rate is.

For the motorcycle turn rate to be similar to the same mechanics as the skater or earth/moon, the rider would have to be at the center point of rotation or on the other side of the center point AND pulling on the motorcycle.

Leaning forward and in gives the best results by: 1. balancing the suspension better since the motorcycle behaves as if it's going uphill, and 2. keeping the motorcycle more vertical thus giving a better contact point for the tire against the ground for better traction which allows the turn to be tightened further.

The comparison is much like the myth of gyroscopic forces keeping a motorcycle from falling over which in that case is total bunk.

Of course all this just gets your brain involved in the process and messes up the mechanics of a turn. For those without a degree in physics all you have to remember is to sit with a good posture then lean forward and inside to increase the turn rate while at speed.


The explanation is incomplete and I'm not explaining everything too well right now since I've been up for about 27 hours straight. Bedtime eventually today...

[LOKi]

First I used this analogy to illustrate how small changes can make big differences in a rotational system. You can actually feel the difference by pulling in just a hand when your spinning.

In a closed system such as a skater pulling their arms in or the earth/moon, all the forces are internal. It's conservation of angular momentum. The skater's degrees per second rate increases. The earth rotation slows as the closed earth/moon system spreads out - then you get into the tidally locked orbital mechanics thing that keeps the same side of the moon facing the earth... Skater, earth/moon, same basic thing.

I don't see how these systems are different. A skaters arms don't want to keep going in circles, they want to go straight. That is why pulling them in accelerates the rotational speed.  Closed systems? I don't see how they are any more closed than a motorcycle in a turn.

For the motorcycle turn rate to be similar to the same mechanics as the skater or earth/moon, the rider would have to be at the center point of rotation or on the other side of the center point AND pulling on the motorcycle.

So your saying once you get to the center everything changes? Try getting on a marry-go-round. Give it a good spin and hop on. Then slowly walk to the center of the marry-go-round (if you can). Once you start to move toward the center it picks up speed. You don't have to be in the center of the system for small changes in where the mass is has large outcome on the rotational dynamics. Once mass moves toward the center of rotation dynamics change.

We are talking about centrifugal force.
Centrifugal force: An object traveling in a circle behaves as if it is experiencing an outward force. This force, known as the centrifugal force, depends on the mass of the object, the speed of rotation, and the distance from the center. The more massive the object, the greater the force; the greater the speed of the object, the greater the force; and the greater the distance from the center, the greater the force.

This is the force that prevents a motorcycle from falling over when your leaned into a turn. It's the force that makes a skaters hands feel like they are fly out. Or make it hard to walk to the center of a marry-go-round. If it's moving in a circle these forces are at work and ANY movement to the inside of the rotation of mass will have an impact on that motion.

This is just making it more complicated than it has to be. What I was trying to get at is you don't have to move a great deal or a lot of mass to make an big impact on the dynamics of rotating bodies.

[talespin]

Sir Jackie Stewart, three-time Formula 1 champion, said "Go slow to drive fast." That slowness is where the smoothness comes from.

I've been working a bit with CB's "kiss the mirror" trick. It's almost scary how much quicker the bike turns when I do that.

[Option13]

Bumblebee is right.


Loki, what you're forgetting is the scale of your analogy. An ice skater pulling her arms and legs in is moving a much greater portion of her mass (legs compared to whole body) closer over a much larger portion of the initial radius (going from, say, 2 meters to one meter. Halving the radius, not to mention that the axis the skater is rotating on is within her own body)

Compare that to a bike. What's a radius of a turn you might take on a bike - 40 meters? And you're moving a portion of your body over half a meter, compared to the 450 pound weight of your bike. The difference between these two is so great that the effect you're speaking of is virtually nil.

[LOKi]

Compare that to a bike. What's a radius of a turn you might take on a bike - 40 meters? And you're moving a portion of your body over half a meter, compared to the 450 pound weight of your bike. The difference between these two is so great that the effect you're speaking of is virtually nil.

So if you had a 40m merry-go-round and put a 450lb weight on the outside then moving towards the center won't make any difference? Because it certainly would.

Sorry I'm just having a hard time throwing Newtons laws out the window because we are talking about a bike. It works on the moon/earth relationship it works on the star system to galaxy relationship it works on small scale too. Electrons and around the atom core. But for some reason bikes are excluded from this and fallow different rules? If you lean 10% of the total mass in 2.5 feet then you have changed the rotational mass and it will effect the bike.

The end result it the bike does not need to lean as much and you get more contact patch. The underlining cause is physics.

Come on you physics people. Back me up here.

My analogy is not invalid.

[LOKi]

Plug it in and see for yourself.

Fc = mv2/r

where
Fc = centrifugal force
m = mass
v = speed
r = radius

[Option13]

Correct me if I'm wrong, but I think Bumblebee is a physics major.


I'm not throwing anything out the door, you're just attributing most of the effect of of lean angle to the wrong rules.

[Poligrafovich]

Neglecting front/rear weight transfer, for a given radius and angular velocity, the center of mass of the rider+bike has a fixed relationship with the tire contact point. The inward lean, in terms of the angle between vertical and the line between contact point and COM, must exactly match the centripetal force associated with the turn or the bike falls in or out.

Leaning or hanging inward indeed moves the rider's COM inward, but the overall bike+rider COM must stay the same or the system is no longer balanced and they fall inward. Any inward transfer of the rider's COM must be balanced by an outward adjustment of the bike's.

This means two things: One, there is zero net change in centripetal force. Two, the bike itself negotiates the turn more nearly upright.

[Option13]

Poligrafovic, that's a different (IMO, better) way of wording what I said on the first page.

An explanation of leaning off the bike/kissing the mirrors, in layman's terms:

When you take a turn, you have to lean the bike over to the inside in order to keep the bike balanced in the turn and prevent the bike from flipping over to the outside. We all know this, correct? The center of gravity is now closer towards the inside of the turn compared to the contact patch, and the bike is balanced. The force of gravity pulling the bike down is equal to the centripetal force.

When you lean to the inside, whether you're simply kissing the mirrors, or moving your entire body over, you're moving the center of gravity towards the inside of the curve without moving the bike. As a result, the bike itself doesn't have to lean as far over to be balanced going through the turn, because you are leaning in it's place. This will let you, at a given lean angle, go faster through a turn, or lean the bike less while going the same speed.

The inverse also true at speed - lean to the outside and you will have to lean the bike farther to the inside to compensate. At a given lean angle through the same turn you will be slower, and at a given speed the bike will be leaning over farther (have less clearance).




The height of the center of gravity vs. lean angle is more complicated to explain, but what you need to know is - keep your weight forward, low, and inside.

[Bumblebee]

If you lean 10% of the total mass in 2.5 feet then you have changed the rotational mass and it will effect the bike.

The end result it the bike does not need to lean as much and you get more contact patch.

Newton is doing ok with this. The problem is that there is no actual rotational mass involved. The turn is being imparted on the motorcycle by brute force. Degrees per second heading change is completely dependent on the ground and not in a closed system. If it were a closed system (orbital mechanics type thing) it would be an extreme out of balance condition in which the planet would not be held in a circular orbit at all and would go careening off in a straight line. This is more of a roulette wheel without a counterbalance than a bucket on a rope where the system is mechanically rotating around a center of mass point.

Actually what is happening is the combined rider/motorcycle vertical CG line is still vertical with the net force vector shoving down and out and aligns with the tire contact point. The motorcycle is physically standing slightly upright thus the better contact patch. The rider is countering the motorcycle's individual outward force by individually leaning inward. IOW, in relation to the downward force vector imparted by the turn, instantly remove the rider and the motorcycle flops over outside, or instantly remove the motorcycle and the rider flops over toward the inside.

Now sit the rider completely upright and not leaning sideways. For every motorcycle roll angle there is an equivalent rider off the seat motorcycle roll angle that is slightly less that will give the same degrees per second heading change. IOW at each angle, either way that it is done, you can obtain the same turn radius and the same degrees per second turn rate. The limiting factor is when operating near the coefficient of friction limit of rubber on concrete. Eventually the tire will slide. By having the rider off the side, the motorcycle has a little extra reserve traction left before it slides than if the rider were sitting upright. THAT is where the maximum turn rate will increase rather than low siding into the hay bails. I don't know the real world numbers because I'm not going to crunch numbers but it's probably somewhere in the 2-5 degree range of extra traction by being off the seat.

My analogy is not invalid.

You are not entirely wrong, you're just kinda pushing on a rope a bit though.

Look at the component vectors involved. Earth gravity down is very significant. Outward force pushing at 90 degrees to gravity to go sliding off outward in a straight line is the remaining force vector. Draw a box and the resulting hypotenuse of those two force vectors is the resultant lean angle to balance gravity and outward force. It's g forces just like in an airplane. 45deg=1.4g 60deg=2.0g

Now your concept almost works to some extent however you're overlooking one teeny little detail:
All base references below are to the motorcycle's vertical line regardless of lean angle in relation to the earth. Consider where the motorcycle+rider vertical CG is located. Sitting upright, thus as high as the rider can raise the riders individual CG, the combined rider/motorcycle CG is now at a base reference point. Leaning off the seat, means the rider lowers his butt slightly which lowers the riders CG toward the motorcycle's CG which means the combined CG point is now lower. Also leaning forward lowers the rider's CG further since the riders CG is now closer to the motorcycle's CG. That lowers the combined CG even further. Take those two combined CG reference points and lean the motorcycle over to the resulting turn roll angles and plot them on a component vector drawing. If you do that you will see that it's almost at the same point on the drawing..if not slightly outward (downward also), not inward, as your initial lean concept implies. It's the horizontal (outward) vector that's important here since gravity is a constant and the tire starts sliding once it breaks free due to excess outward vector forces.

Right basic concept. Wrong formulas to get the correct answer.

Come on you physics people. Back me up here.

You see, that's the problem. I can't. Granted that it's been a few centuries however I come from a physics/mathematics background at university. Oopsie.

[Burgi]

On a much simpler note...
I got a reminder today that the paint they use to mark lines on roads is hella slippery when wet or new. It seems while I was out of town the city decided to repaint STOP on all corners in my area where there is a stop sign.
I came through a turn (no stop my direction) and caught one of these. Drifting on a bike isn't my thing. 

[cmyers]

I came through a turn (no stop my direction) and caught one of these. Drifting on a bike isn't my thing. 

My front slid out on a paint strip recently as well, just enough to check the pucker factor.

It is just a reminder that streets are never predictable.

[gammer]

All I know is if our wives/partners knew we were talking about this stuff on an internet forum, they'd pretty much pee themselves laughing. 

Please do continue...its all good stuff 

[NHPep]

This means two things: One, there is zero net change in centripetal force. Two, the bike itself negotiates the turn more nearly upright.

The BB/Loki discussion is beyond me, but I did understand the above to be true.

[coffee_brake]

I quit reading any post over a sentence long, a page ago.

Ya'll done lost me. I know what ya'll know I know...not much else.

[gammer]

The way I see it: you get what you get...and thats what you get.