Full Lean To Full Lean

You're not entirely wrong but you're talking about about a different situation. Entering a turn like that is a more gradual affair; the bike doesn't need to be thrown from one side to the other.

I'll try a different tact to get you to see what I'm talking about: In a fast transition, the bike may rotate 90 degrees or more in less than a second. If the rider is at the long-travel end of that rotation, he would experience a very strong centrifugal acceleration trying to separate him from the bike. However, we don't feel that. Why?

 

Actually it is entirely possible to flip yourself right off the bike by transitioning to fast.

A motorcycle operates the same manner weather it one left turn or a series of turns, the principals remain the same, there is no invisible force acting thru the riders head to control the direction of travel.

I understand how it seems that everything rotates off your head when riding, it's where your eyes are and your equilibriem(sp?), It is where you find your balance.

 

And that will even be more the case the higher your bike is... (another drawback)

 

when you guys talk about measuring rear ride height, you mention "eye to eye".. what is eye to eye? the upper and lower mount bolts?

 

Yes, although you might want to verify terms with the person giving you measurements (ie if they mean center of bolt hole to center of bolt hole, outside edge of bolt to outside edge of bolt etc).

 

I have never seen nor heard of that happening (that didn't involve inducing traction loss of some sort).

Let's try something else: Instead of me trying to teach you what I understand about the physics, you teach me what you understand about the physics. How exactly does a motorcycle initiate a quick turn-in, and how does a high center of gravity aid that (both from straight up-and-down and transitioning from side to side)?

I'll be pretty surprised if your view both makes more sense to me and proves mine wrong, but I will listen/read with an open mind.

 

The higher the bike, the further the CG is from the front wheel's contact patch. This increases the leverage and makes it easier for the available tyre forces to pitch the bike down.

Adjusting the handle bars out (further from the CG), makes it easier for the rider to manhandle the bike.

 

I thought I had already explained my understanding of how a bike turns.

Here's a pretty good basic explination of PART of the Physics involved.

http://www.howeverythingworks.org/page1.php?QNum=1502

Basically a Low CG provides for a very stable bike, when a turn is initiated with a low CG it is easier for the wheels to find there center back under it. The wheels want to rotate around there axles when turning(if the tire is not in contact with the ground or loses sufficient traction they do turn around the axle centerline) so the farther Below the axle centerline the more stable the bike and conversly the farther ABOVE the axle centerline the more unstable. It is easier for the weight to get ahead of the wheels and initiate the turn AND stay farther above the axle ceterline so the wheels have more leverage to pick it back up.

 

i disagree. going back to the old balancing act with an axe, broom or baseball bat placed on your hand, which way is easier to maintain balance...with the weight high or low? how far does your hand have to travel to catch up with the balance point when the weight is low? what?!? you couldn't keep up and dropped it? thought so.

years ago, a bonneville guy built this really fast two-wheeled sled. he did everything right, so he thought. he had the weight low and everything but, the thing was unstable, nearly unridable and that was just in a straight line! he couldn't get up to speed without dangerous handling issues. while talking to one of the "vets" out there, the vet said "you made a mistake putting all the weight down low. put some weight up top". so he did and guess what? the bike handled.

btw, i read your link. the guy's observations are incomplete. before the bike leans in the direction he wants it to, the front wheel WILL counter-steer before floppin' over into the turn direction. he missed that PART.

as a side, i suspect this moment when the steering assembly changes its pointed direction to be responsible for the low sides not induced by poor brake management or suspension. it occurs right when you've reached the desired lean angle induced by counter-steering. the steering flops into the turn and viola', you just asked the tire to take on another chore during that transition...it gives up traction as the contact patch twists on the pavement. you can witness it yourself when you push the front end into a slide cuz that's the moment you'll be able to induce that slide.

 

Do you drop the stick and weight because you can't keep up or because you constantly over correct?

I agree that link did not include everything that happens but its a fairly good explination of the basics.

Iwould say the bonneville deal was another issue that was complicated by the low cg, too far below the axle centerline could make it difficult to control though.

 

Back to the broom. When you balance left & right on your hand, where does it pivot? Not around the palm of the hand...

A tyre profile will do abosultely nothing on the roll axis of the bike. It will affect many things but won't do a thing to the instantaneous roll axis position.

A lower cg isn't necessarily the best way to go on a bike. A team once tried putting the fuel tank under the engine. It mades things worse because it move that weight further away from the CG then if it was on top. It increased the inertia of the bike.

Two things about fuel: it's heavy and the weight varies as the race goes on. Things like that need to be concentrated as close as possible to the CG.

 

i think it shows that a bike with precise steering(beyond human precision cuz i don't think that's the kinda thing you'll be able to practice too many times) can be a bike with a low center of mass but it'd need a computer to maintain flight control, there'd be no way of catching it if it were heading over the edge otherwise. conversely, a bike with higher CM will be more easily controlled providing the rider does their part...if you can definitively make that connection between bikes and broomsticks.

 

Yeah, the stick pivots in your hand. If it didn't you would not have to balance it. The cg at the end of the stick remains fairly still because you are balancing it by keeping the pivot point located underneath it to support it. When you initiate a turn on a bike you Knock it off balance then chase the cg with steering angle to keep from falling. It pivots from the contact patch of the tire or a instant center very close to it as it leans over then to finish the turn drives the wheels back under itself.

 

We may be saying the same things but using a different route or words. We agree that while the hand moves left and right, the cg is still (except for a up-down component because of the broom angle). So the broom rotates primarily around its CG as you balance it.

 

.02 perspective...
no doubt that the weight of motorcycles is concentrated higher vs lower relative to the machine as a whole. the question seems to be whether you take that weight incrementally higher or lower than what the engineers deemed to be appropriate for the application. as RM somewhat stated, "higher is better, to a point". we're taking the original application, street oriented sportbike, and tuning it for race applications. there has to be some inertia in the moment lever to dampen the twitchiness of going high, that's why there's a limit to "how high". too low and the added weight in the lever makes for a slug(too stable) in the handling department...it won't react quick enough to your inputs and you'll be forced to overpush it to control it. essentially, unridable for racing.

on the other hand, twitchiness in a street application would be a bad thing for the average rider. joe can't handle twitchiness cuz it shakes his confidence. he wants a more stable slug cuz he ain't got the mad skilz. the stability he desires is engineered into the product while said slug would be a bad thing for a racer.

 

Right but when you stop balancing it what happens? When a bike is going straight down the road it is balanced, when we turn it we knock it off balance.

 

the arc it cuts across the pavement maintains its balance. same as if you lean the stick and accelerate with your hand to keep it in a balanced state. after all, a turn is just lateral accelleration.

 

Exactly

When we lean the stick how much movement of the hand does it take to initiate the fall compared to how much the weight moves till you catch it?

We are almost thinking a like.

 

I agree with this statement.

But from earlier...

Actually, the only thing the contact patch provides is a pressure point where the reaction forces are loaded. I'd hate to bring back the threadmill (w/o the airplane) analogy but it could be interesting. If I wanted to tilt the bike to initiate a right turn, I'd have to countersteer left, the front tyre would make a side movement to left, tilting the bike on the right pivoting on its CG axis (the top of the windshield would pivot right) then I would steer right to catch the fall of the bike.

Actually, of the three options, the 5# weight at a foot above your hand is the easiest to balance because of the inertia of the weight gives the system and the leverage your foot long stick provides. This is also the logic behind making the bike higher to make it easier to turn.

 

puttin' it that way, you gotta look at steering input. that's the analogy to hand movement. a little input, a little turn...big input, big turn. it's easier to get the top-heavy stick to turn than it is the bottom-heavy stick, tho'. when it comes to bringin' that stick back upright, you'll be chasin' the bottom-heavy stick all day. with the top-heavy stick, one quick flick and it's up.

are we arguing the same point? i thought you were part of the lower CM camp?