Hanging off on cruisers and "non" sport bikes?

[Clint]

Like everything, it's a compromise. As someone mentioned earlier, suspension components work best near vertical. You don't really increase grip by laying the bike over more, it's just that you need more grip the further over you are, so tire makers try to accommodate that.

I just spent an hour absorbing ASP.NET jargon, so forgive me if that didn't make sense. I'm a bit fried after a long day.

[leonidas]

Originally Posted by leonidas

ummmmmm....
Ok. I'm turning pure spectator from here on in this thread.

Well, I gave it a shot, but can't stop asking myself this:
James R davis says, (quote)
"You are absolutely correct in your analysis. The forces on the tire are the same at any given speed and curve radius."

I wonder how this can be.
At rest on object pulls +1 G,
but there are vehicles that exceed +1 latteral G.
Doesn't this mean that the faster you travel thru the curve
the higher g you pull, putting increasingly greater forces on the tire?

[Clint]

I think you're taking it out of context. He probably meant that shifting weight side-to-side doesn't change the tires' side load if the other factors are constant, like what Rick and I discussed earlier. Changing the effective lean angle doesn't change the side loads.

[Thundurburd]

James Davis is responding to the first post in the thread where the poster is asking about whether hanging off gives better traction. The poster contends that it does not and states that "for a given radius turn at a given speed," in other words a specific turn radius and speed:

1. The lateral force is the same.
2. The vertical force is the same.
3. The effective lean angle is the same. (regardless of what you do with your body)
4. The forces on the tire are applied along the effective lean angle (from the center of gravity to the contact patch)

James agrees with all four points and goes on to say traction does not change at all if you hang off. He also says the contact patch is marginally smaller but I think this depends on the profile of the tire. Some tires actually have a larger contact area by design, which might have been mentioned in a previous post.

Let's go over these point by point.

1. The lateral force on the bike is caused by a centrifugal force which is dependent on the radius of the curve and the velocity. There's no mention of the lean angle or hanging off.

2. The vertical force is dependent on the mass of the bike and gravity, neither of which change by hanging off.

3. The effective lean angle is the same regardless of what you do with your body. For a specific radius and speed the is only ONE lean angle. It is determined by the gravity force pulling down and the centrifugal force pushing out, there can only be one answer. The lean angle is measured from the contact point to the combined cg and while the relative position of the rider and bike can be changed, the location of the combined cg doesn't change.

4. The resultant force on the tire is the vector addition (there's some trigonometry involved) of the the lateral force (traction) and gravity. For example a 500# bike leaned at 45 degrees will have a horizontal lateral force equal to the gravity force of 500#. The resultant force in the plane of the bike frame (this is the vector stuff) is 707#.

I hope this helps.

[leonidas]

Originally Posted by Thundurburd

The resultant force in the plane of the bike frame (this is the vector stuff) is 707#.

I hope this helps.

Well, I was with you...right up 'til the 707#.
I'll work on it.
Thanks for the info.

[Clint]

Great summary! I think I remember .707 being a sine/cosine/tangent thing, but it's been a while.

[Rickster]

No fair guys, this is suppose to be an English speaking forum.

[Clint]

Oh, it is.

[tricker]

Mike, you're using that book you sent me as a reference aren't you? Read it and was interesting but i think a little over my simple thought process.

[Thundurburd]

Originally Posted by tricker

Mike, you're using that book you sent me as a reference aren't you? Read it and was interesting but i think a little over my simple thought process.

No, in that book I just look at the pictures.

[Davecm203]

Originally Posted by Thundurburd

3. The effective lean angle is the same regardless of what you do with your body. For a specific radius and speed the is only ONE lean angle. It is determined by the gravity force pulling down and the centrifugal force pushing out, there can only be one answer. The lean angle is measured from the contact point to the combined cg and while the relative position of the rider and bike can be changed, the location of the combined cg doesn't change.

So,...you are saying that it is pointless to lean off? I rarely lean off on the street and can ride faster than a lot of my friends who insist on it when it is not needed. But, in corners that I will touch a foot peg not leaning off, I will not while leaning of yet carring the same or slightly more speed. And why do the racers do it when you have more control over the bike when you are higher up on it? I am not a physics major, but, it is my undersanding that it keeps the bike more upright.

[Davecm203]

http://www.edutopia.org/motorcycle-physics
Speed 101: Motorcycle Racing as Real-World Physics Lab
Isaac Newton hops aboard a two-wheeled teaching tool.
by Owen Edwards
Print Forward Share Comments(9) Comment RSS
A grand prix racing motorcycle is many things: most impressively, a marvel of engineering that costs hundreds of thousands of dollars to develop and build, and one of the fastest machines on wheels, capable of speeds in excess of 210 miles per hour and able to retain a grip on the road at lean angles of 60 degrees or more.

But looked at scientifically, a racing bike is nothing less than a kinetic demonstration of the laws of physics. Freddie Spencer, a legendary grand prix champion of the eighties and now "dean" of Freddie Spencer's High Performance Riding School in Las Vegas, puts it this way: "Motorcycle racing is a real-world physics lab where the penalty for wrong answers is a lot more dramatic than a bad grade."

1. Gravity:The rider shifts weight into the turn to help the motorcycle change direction and lower its center of gravity.

2. Kinetic Energy:At speed on a straightaway, a motorcycle’s energy is directed forward.
3. First Law of Motion:Newton stated that a body in motion persists in a straight line unless compelled to change.
4. Thermodynamics:Slowing the motorcycle from high speed for tight turns causes heat buildup in its brakes and can diminish effectiveness.
5. Centrifugal Force:In fast turns, lean angle and forward motion counteract the powerful pull toward the outer edge of the track.
6. Friction:A special compound in these rounded tires allows traction on asphalt even at lean angles of 60 degrees and more.

Credit: Fiat Yamaha Team


According to Charles Falco, the University of Arizona's chair of condensed-matter physics and co-curator of the Guggenheim Museum's The Art of the Motorcycle exhibition, the initial physics lesson to be learned watching a racing bike hurtle into a tight turn is Newton's first law of motion: "Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it," explains Falco. To a rider, this means that the faster a motorcycle is going, the less it wants to turn.

Converting a bike's kinetic energy from straight ahead to turning requires a negotiation with physics in a couple of ways. First, a rider pushes the handlebars slightly away from the direction of the turn. Because the wheels act as gyroscopes, this countersteering leans the bike in the opposite direction (into the turn), which puts the tires at an angle, narrowing what engineers call the contact patch and making the bike easier to turn.

At the same time, the rider moves off the bike in the direction of the turn. The lean angle of the motorcycle shifts the center of gravity to the side, causing the bike to turn, while the weight redistribution lets the machine stay slightly more upright. At the point of maximum lean required to get through a turn at the highest possible speed, centrifugal force wants to pull the bike machine off the track, and the rider uses traction, gravity, and momentum to stay in the game.
To explain why the machine moves at all, Falco invokes Newton's second law of motion: A force applied to an object will cause it to accelerate. "This will happen until the rider runs out of track, or other forces become nonnegligible, such as wind resistance," says Falco.

On some tracks, grand prix motorcycles approaching tight turns must slow from more than 200 mph to around 40 mph. Friction on the brakes (primarily the front brakes) makes this possible. "All that excess energy has to be dissipated by the brakes in the form of heat," Falco says, thus bringing up the law of conservation of matter and energy. Some of this heat is transferred to the hydraulic-brake fluid, which can cause brakes to lose stopping power, with potentially disastrous consequences. Engineers use space age ceramic materials to avoid this problem, and riders become skilled at getting on and off the brakes quickly.

Successful race riding is a lot like paying taxes: You want to push the rules as far as you can without breaking them. There is a very fine line between optimum cornering and crashing, where outward, downward, and forward forces balance precisely. But rules are rules. "Speaking on behalf of physicists everywhere," Falco declares, "nothing that ever happens on a motorcycle breaks the laws of physics. In fact, motorcycles are excellent examples of just how well physics works."

[Clint]

Originally Posted by Davecm203

So,...you are saying that it is pointless to lean off? I rarely lean off on the street and can ride faster than a lot of my friends who insist on it when it is not needed. But, in corners that I will touch a foot peg not leaning off, I will not while leaning of yet carring the same or slightly more speed. And why do the racers do it when you have more control over the bike when you are higher up on it? I am not a physics major, but, it is my undersanding that it keeps the bike more upright.

I think you're misunderstanding what's meant by "effective lean angle", which is defined by the location of the center of mass, as opposed to the bike's lean angle.

[Thundurburd]

Originally Posted by Davecm203

So,...you are saying that it is pointless to lean off? I rarely lean off on the street and can ride faster than a lot of my friends who insist on it when it is not needed. But, in corners that I will touch a foot peg not leaning off, I will not while leaning of yet carring the same or slightly more speed. And why do the racers do it when you have more control over the bike when you are higher up on it? I am not a physics major, but, it is my understanding that it keeps the bike more upright.

The effective lean angle which is to the combined cg of both rider and bike doesn't change when you lean off, but you can change the relative position of each. If you lean into a turn for example the bike will lean out (straighten up) which is exactly what you do when you drag a peg and want to lift it up slightly. Moving around on a bike is only an adjustment of internal masses and forces of the bike and rider system and won't change the effective lean angle of the combined cg. For that you need and external force such as what results from steering.

One of the main benefits of hanging off like racers is that the suspension works better when the bike is more upright. One of the things the suspension does for us is to keep the tires in contact with the road, and it does that better when it's vertical. At least from what I've read, I don't ride like that.

[tricker]

i just prefer to ride like a bat out of hell and hope for the best!



ok maybe not... but it sounded good?

[Thundurburd]

Originally Posted by tricker

i just prefer to ride like a bat out of hell and hope for the best!

This year I'm going to keep the rubber parts on the bottom!

[Davecm203]

Originally Posted by Clint

I think you're misunderstanding what's meant by "effective lean angle", which is defined by the location of the center of mass, as opposed to the bike's lean angle.

I thought I was misunderstanding him. I understand better now. I am easily confused.

[Wuby The Wabbit]

I used to stay inline with my handel bars on my KZ but when I got my sv i noticed I was leaning more with my shoulders and shifting my wait a bit more to the inside of the turn. I can actually take turns faster and at a greater attack angle(entrance angle) and less of an exit angle. I.E. hittin the apex. Also, I can carry more speed and use it more fluently.

[NCxM50]

So, do you guys all ride with calculators and protractors taped to your handlebars?

[Wuby The Wabbit]

haha no i can just notice things lol i dont stop and measure the angle at which i enter the turn this isnt the movie click i cant stop real time haha