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we are now dealing with center of mass, which is different than CoG . Dusty
As usual Dusty is pretty much spot on. Honda figured it out in the '80s. You can do the vectors if you wish but..I prefer bikes with lower center of gravity. They feel like fun. A modern trials bike would be too far for a street bike but I liked the horizontal singles I've ridden.
Picture a lollipop. One standing with the pop on top, the other with the pop on bottom.Which would tip over easier?
Phil Irving wrote a book, Motorcycle Engineering . It's my go to book for questions like these for it covers this as well as other good stuff. When I go out to the shop tomorrow I'll look at it. See if you can find a copy, it'll make you the smartest guy in the room.
Hugo, you seem to like mind stretches, concept manipulation - have you read "The Upper Half of the Motorcycle, on the unity of rider & machine", by Bernt Spiegel. Recommended. I think you'd like it. For example - part 1 is entitled "It's a miracle that motorcycling works at all".
Hmmm...Just a couple of quick ones Dusty.A bike does not “know” it is leaned over in a balanced turn because the sum of forces are zero, other than the centripetal force accelerating it towards the centre of the circle..andWhy is the centre of mass different than the centre of gravity, when the sum of gravitational vectors acts through the centre of mass ?
When considering this concept, the rider and machine are a single mass with only one centre of gravity (mass).
You're doin' my head in cobber. One needs a few beers before contemplating this type of esoterica. Mass carried high, i.e further away from the pivot will have greater inertia at speed (in relation to the arc of leaning motion, not the bike's linear motion). Therefore, the whole mass becomes less 'chuckable' or 'flickable'. Greater countersteering effort is required to counter not just the gyroscopic effect of wheels in rotation, but the 'arc of inertia' (my own ridiculously pompous name for it) of mass. Once flicked or chucked over, the gyro effect counterbalances the combined mass through the bikes 'linear' cornering arc unless further attitude changes (lean angles) are called for, such as straightening up again. Think of it as an arc of a pendulum. The further away the mass is placed from the pendulum, the greater the 'strain' on the pivot for a given velocity of motion..... I think! Bugger me, I'm not so sure at all anymore....Sideways mobile masses have a greater effect the further they are from the pivot point. Which is why leaning my own corpulent, portly arse to the inside of a bend off the bike's seat makes a substantial difference to lean angles: not the prettiest sight, but extremely useful in the wet.
The one with the pop on top is inherently more statically unstable, but can be stabilised more readily by moving the point of support back under the mass when displaced from vertical than the upside down one.Put the one in the picture on your hand and balance it by moving your palm, you’ll have some success.Now try moving the pop halfway down the stick, you’ll have less success maintaining dynamic stability.When a point of support is moved under a mass to maintain balance, we rely on inertia to hold the c of m still, in a spatial sense as that point of support is re positioned.
Which would cause more reaction, an input on the "pop on top" or the other one?Hugo asked---how a bike will change angle of lean quickly due to the “low centre of gravity”.
I’m a big supporter of blind loyalty Aaron, but I was addressing the voracity of the statement that a bike is more “flickable” due to it’s “lower centre of gravity”.If I wanted muddy waters, I’d go for a dip in the Mississippi, or put on a CD of an old blues man..Just a bit of focus on what I was asking about and a response based on physics, not “how you feel”, or what you (or I), “prefer..”
As I see it, when you introduce an input from the ‘bars, the wheels are displaced laterally and the centre of mass initially tries to remain in the same plane of motion, centred somewhere around your nether region.
We must remember that when viewed from the front, a bike does not have the rider move about above the wheels to initiate a lean, the wheels move about below the rider.
I already am, I’m the only guy in the room..
Math is hard! Did you make it around that last corner without falling over? Its all good then!
So in the real world, I’m suggesting that a given bike would be more “flickable” with a bag of cement strapped to the tank than without....!Different thing in the static state at the lights though..the bike with the added upper weight would be more flickable in that that it would be easier to start the lean with the added weight that high. but once the lean is started the inertia of the extra weight would make it harder to stop that motion. it would tend to keep going over until another force stopped it.relates to polar moment of inertia on a race car in which one attempts to keep the weight between the wheelbase. weight at the extreme ends makes the vehicle easier to rotate around the central axis (hanging the tail out) but harder to stop that rotation. think corvairs and porsches
the bike with the added upper weight would be more flickable in that that it would be easier to start the lean with the added weight that high. but once the lean is started the inertia of the extra weight would make it harder to stop that motion. it would tend to keep going over until another force stopped it.
There's a big difference between top-heavy and flickable. My VX800 felt topheavy -- it wanted to fall into slow turns -- but wasn't flickable. Thanks to a long wheelbase and I suppose relaxed head angle it felt stable in a straight line and in high-speed turns.[/quot]my point exactly
