This is a technique question and thought some of you trail riders might understand how this works and know the answer. If you stand on the pegs while riding, therefore transferring 'all' of your weight to low on the bike on the pegs (as opposed to the weight of your butt on the seat), does that lower the center of gravity and make the bike more maneuverable . . or does the center of gravity actually rise because the mass of your body is higher and the bike becomes in essence more top heavy? All opinions will be appreciated!
It's physics, and (at least in our universe) not subject to opinion. The center of gravity (or mass) gets lowered because your mass is attached to the bike's mass at a lower point. Simple.
Center of gravity for the system is higher but the bike is more maneuverable since you are separated from the bike allowing two masses to move independently.
D'oh! Indy's right. I just did a bunch of Googling, and the center of gravity does, in fact, rise when you stand up. But, as he says, you increase your ability to balance anyway because your mass is much more adjustable when standing. So... um... never mind.
It relieves the bike's suspension from having a giant mas just sitting on top of it. Your legs are acting in series with the suspension taking some of the load off of it. Same reason you put your weight on the pegs at a race track.
Also the body is amazing, it will naturally compensate for movement of the bike and your now using your whole body weight to move the bike.
Summary: CoG rises when you stand up. Despite this, controllability improves because you are more easily able to move (higher) CoG on the bike.
The effective COG is lower as your weight becomes suspended weight which is being carried at the pegs. Seated the weight is in effect fixed weight.
No. If this were true a two-tonne truck would handle like an F1 car, since its weight is carried at the axles.
How do you control the bike if you are separated from it? I will assume your hands and feet are still connected though. For low speed..trail riding and trials it is better to stand as the higher weight [COG] has a much greater effect on the control of the bike. For high speed [road racing] you need to lower the COG..as in hanging off and dragging a knee. Now on to countersteering and the correct oil to use
If more maneuverability is what you want, standing on the pegs is best. However, the reason is not the new height of the combined (bike+rider) center of mass. Standing on the pegs doesn't do much for the vertical location of the CG of the bike+rider system, especially for light riders and heavy bikes. In order to understand the physics behind the more dramatic and dynamic changes that happen when we stand on the footpegs, one needs to understand the concept of "moment of inertia". "In classic mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a property of a distribution of mass in space that measures its resistance to rotational acceleration about an axis...........and is the rotational analogue to mass. Mass moments of inertia have units of dimension mass × length. The moment of the inertia force on a particle around an axis multiplies the mass of the particle by the square of its distance to the axis, and forms a parameter called the moment of inertia. The moments of inertia of individual particles sum to define the moment of inertia of a body rotating about an axis." http://en.wikipedia.org/wiki/Moment_of_inertia http://en.wikipedia.org/wiki/List_of_moments_of_inertia The concept of moment of inertia sounds difficult, but it is not so much. The bike+rider system always rotates around the combined or system's CG, either during hard braking-acceleration or during quick flicking. Sitting on the bike, our body has a somehow rigid connection with the bike and; hence, there is one moment of inertia, which has a high value (the system has more inertia to be rotated). Standing on the pegs, our body has a flexible connection with the bike (via our arms, elbows, shoulders, legs, knees and hips); hence, there are two masses connected by a flexible link. That flexibility reduces the total moment of inertia because the smaller mass of the bike can rotate around its CG with certain margin of freedom respect to the mass of the rider. Note that the value of the moment of inertia depends on the value of the mass, but also depends on the square of the distance that separates the CG and the pivot around which it rotates. Standing on the pegs drastically reduces the moment of inertia or rotational inertia to flicking the bike or to perform a wheelie.
Inewqban hit it right. Same idea if you take a rod of say wood and cut it in to several different lengths. Say one about a foot long and the other about as long as a boom handle. Now try to balance each up right by placing one end on your open palm and only by moving that hand around. It will be much easier with the longer broomstick length as it has more of it's weight spread over a longer distance. You can even pick a smaller diameter rod so they weight the same and you will find it still is easier to balance the longer length. Another concept to check out is "Dynamic Stability", which is why even a very slow motion forward is easier to balance than remaining still. Counter intuitive to have motion increase stability but there you go.
You can more easily move ya junk around while standing. Your connection points to the bike are spread wider and you can use your weight and respond more rapidly. Or we can overthink it. Turning moments, angular momentum, sums of different systems.....good god people....it's about balance and freedom of movement to achieve same.
Stand up, lean somewhat forward, eyes high---- You will never see any of Jim Hydes instructors settin on their ass when off road. You can get all techie and propose all sorts of laws of nature if you so desire, but get off your ass stand up and ride the mofo!!!
Yup, when you stand (versus sit) your CoM (Center of Mass) increases by about a foot, and the overall CoM of the system (you + bike) increases by about 6" (bike is 500# you are 200# so you have to do the physics) which isn't that much. But what you gain is that maneuverability. With the weight on the pegs, lateral (side-to-side) shifts are easier because of the CoM height increase, as are the forward-back shifts of weight to weigh the shocks or rear tire. If your butt is on the seat, you're have to overcome the friction force to slide forward, back and sideways, therefore taking more energy. So when you raise up, you gain greater control over your bike (for better or worse).
Effective center of mass. Seated, the weight is carried on the seat. Standing, the weight is carried on the pegs and is in effect, suspended weight. Standing on the pegs has 3 values, increased sight distance, less work load on the suspension, and the bike is not working against the mass of the rider. All of this is natuarlly assuming the bike is in motion and the rider isn't riding in a rigid, frozen position. To the OP, when the going gets rough, get up on the pegs, your body starts working with the suspension, not against it. Ride relaxed and confident, dont strangle the grips, and enjoy the ride. PS, keep you eyes up, don't look directcly in front of you, unless of course you are choosing a landing spot
