Center-of-Gravity

[charismaticmegafauna]

There's recently been a few comments about center of gravity -- what's that all about? From what one reads here it would seem 'the lower the better' -- is that true? Suzuki once added weight to the bottom of their AMA Superbikes (maybe? an idea for a farkle?). Funny thing -- the popular magazines don't show where it is on their road test spec. pages.

Similarly, seat height is often purported to be better low -- yet, there's been some discussion of distance to the pegs. Maybe the same holds true for (low) center-of-gravity -- it ain't necessarily true.....? :dribble: :blink: :huh:

 

[odot]

I was riding home from work last week, traveling through one of the canyon roads that connect my home and work. I had just gotten back to work the previous week from a five month disability leave for neck & back problems. Getting back to work and picking up where I left off was important to me. Riding my FJR after the five month time was good. I didn't feel that I was "rusty" from the lack of riding. I was wrong.
The canyon roads are often filled with many challenges. The sharp curves, gravel on the road, drivers that are filled with road rage, etc. Normally I ride through being "hyper alert", seeking out danger and avoiding it. On this day I noticed the road had the usual gravel obsticals on the roadway. I make a point of avoiding as much as I could. The curve ahead, I spot gravel and set my line around the outside. What I didn't realize is that I must have been traveling faster than I should. My turn was fairly tight but not scrapping the pegs. I broke one of the commandments of riding... my focus shifted to where I was headed - Off the road. In a brief moment I realized that I was going off the road. The decreasing radius turn, gravel, and my "rusty" riding skills led me to a place I have never been. Sliding off the roadway I hit several trees. I don't remeber being able to see much but I do recall hearing the sound of my FJR being torn apart. Very quickly it was over. I lay prone beside a pine tree. opening my eyes I could see branches filled with pine cones. My body hurt all over. My left leg and arm were in pain. I could barely move, so I lay there hoping someone would come to my aid. Time passed and eventually a motorist drove by and yelled that his cell phone didn't work in the canyon but he would get help. As I lay there I couldn't imagine what I just did. I felt like such an idiot. How the hell could I have done that? My FJR! I know it was damaged, but no idea of the extent. I hear vehicals approaching. Forest service personel, they tell me not to move. Lots of questions: Do you know where you are? Can you move your toes? Did you lose conscieneness? The CHP arrive. More questions... Have you been drinking? How fast were you going? I told the CHP officer that I wasn't drunk, just stupid. Over the next several hours, from the ambulance ride to ER, CT scans, xrays, etc. As I lay on the gurnny I see my son come into view. He holds my hand and asks if I'm ok. I'm lucky, I'm alive and know that things could have turned out much worse. The doctor finally comes back and informs me that nothing is broken. I have contusions (bruises) in many areas, but NOTHING BROKEN. I tell the doctor that since nothing is broken, I'll be dancing out of here! Over the next several hours I push myself to get off the bed so I can see how my leg feels. It was difficult to stand but I did. I think the doctors eyes were going to explode out of his head when he walked by seeing me standing up. After convincing the doctor that I was Ok, he discharged me and my wife drove me home.

The next day, while the pain was bad. All I was thinking about was my FJR... how is she? My wife drove me to the tow yard so that I could get my MC and get it into the repair shop. The owner of the tow asks me if I was the rider. He looked a bit shocked... and said to me "God loves you very much". I ask to see my bike and he points to where it is resting. I approach... the windscreen is gone, the mirrors are missing, the sides are scrapped to hell, the front end is smashed in, forks bent, front wheel forced back into the radiator, tweaked. I feel sick looking at it. My wife tells me I'm lucky. I tell her I know.

The FJR hit the trees and threw me over. A few bruises, that are healing... a FJR that could be repaired for $7000. I'm lucky to be alive. So what next? I don't think I will get the FJR fixed. I'm not sure what to do with the bike now. My wife thinks I should get a new red FJR. She says "it's only money". I guess she's right, it's only money and I'm pretty damn lucky. Would God still love me if I got the red one?

K9

Great Story. My wife would shoot me first (to prove that motorcycles seriously injure), then NEVER let me ride again!

Oh, center of gravity?....that what we're yappin bout? I just felt a nice release of joy by repeating what someone else said and adding nothing to it. :blink:

 

[temp357]

In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the system's mass behaves as if it was concentrated. The center of mass is a function only of the positions and masses of the particles that comprise the system. In the case of a rigid body, the position of its center of mass is fixed in relation to the object (but not necessarily in contact with it). In the case of a loose distribution of masses in free space, such as shot from a shotgun, the position of the center of mass is a point in space among them that may not correspond to the position of any individual mass. In the context of an entirely uniform gravitational field, the center of mass is often called the center of gravity — the point where gravity can be said to act.

 

[2WheelTiger]

To put it simply:

The center of gravity is the point at which you could suspend the bike and it would be balanced in all directions.

 

[okmac]

In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the system's mass behaves as if it was concentrated. The center of mass is a function only of the positions and masses of the particles that comprise the system. In the case of a rigid body, the position of its center of mass is fixed in relation to the object (but not necessarily in contact with it). In the case of a loose distribution of masses in free space, such as shot from a shotgun, the position of the center of mass is a point in space among them that may not correspond to the position of any individual mass. In the context of an entirely uniform gravitational field, the center of mass is often called the center of gravity — the point where gravity can be said to act.

WHAT ?

 

[Bustanut joker]

WHAT ?

[SIZE=36pt]What?[/SIZE]

Zat better Mac?

 

[Rickster]

Clicky

 

[wfooshee]

See, I don't think he was looking for a definition of center of gravity, I think he was looking for a discussion of: is lower better, is there an ideal, yada yada yada. And maybe asking if anybody actually knew where it is on the bike?

 

[2WheelTiger]

That argument has been going on since the beginning of time. I'm not gonna restart it here, except to say that motorcycles handle more quickly when the mass is concentrated as closely as possible to the CG.

The rest of the argument all has to do with the motorcycle's purpose and use.

 

[v65]

See, I don't think he was looking for a definition of center of gravity, I think he was looking for a discussion of: is lower better, is there an ideal, yada yada yada. And maybe asking if anybody actually knew where it is on the bike?

Dan Gurney has some thoughts on the subject. :blink:

 

[radman]

Betcha didn't know that one of the key advantages to having a dry sump oil system in a race car is it's very shallow pan-allowing the engine to sit as low in the chassis as possible, lowering-yup-it's center of gravity. Anything to reduce it's roll momentum, lower it's CG improves handling, notice when adding wedge to a car, the weight is hung as low as possible, same reason. In a bike, it reduces the "top heavy" feel, and allows quicker transitions when turning. Mass in motion tends to remain in motion until some force counteracts it, this applies when a bike is leaned over to initiate the turn. Chassis dynamics, car or bike or Reno Air Racer, are FASCINATING!

 

[Scab]

You should teach classes, Rad.

 

[odot]

That was either an impersonation of spock or karl sagan.

 

[dhalen32]

I think that nowadays the engineers are actually trying to place the motorcycle's center of mass/gravity at the bike's center of rotation rather than as low as possible. When you hear the Honda, Buell, Yamaha, etc Marketing people talk about mass centralization that is what they are talking about. This reduces inertia and allows the bike to roll or turn more quickly. This why sometimes you read about a manufacturer actually raising a heavy component like an engine or transmission in the chassis or frame of the bike.

Dave

 

[2WheelTiger]

The only thing I'd add to clarify your statement is that moving the center of gravity will move the center of rotation.

We're gonna confuse those folks who believe that a motorcycle's center of rotation is at the contact patch........

(.....and off we go! ......)

 

[RonBB]

If you drop your bike a low cg is a good thing when you pick it up.

 

[Shane]

You should teach classes, Rad.

You might be interested to note that in fact, Radman does teach classes, but a few experienced words of caution...

1. Arrive naked, or wearing latex only. :dribble:

2. No spoken words are allowed inside the classroom (garage).

3. The teacher is always correct. :angry2:

4. Thank you sir, may I have another? :blink:

5. TV show, So You Think You Can Dance? is required learning, with pop demonstration quizzes weekly. :clapping:

6. All tuition fees are 100% directed to the PISSONIT -- Preservation International Society of Spotted Owls Now In sTomachs.

We tease Rad a lot here in MN, but it's what he loves, and we're lucky to have him as a resource.

Shane

(the classes are real)

 

[Scab]

You should teach classes, Rad.

You might be interested to note that in fact, Radman does teach classes, but a few experienced words of caution...

1. Arrive naked, or wearing latex only. :dribble:

Hell, I'm good to go then. Latex is all I wear anyway.

 

[odot]

..................is that assless latex?