Square fin LH sticks out more than RH?

[luhbo]

I don't pretend to understand this one at all. Perhaps bikers that are perfectly centred veer left in the Northern Hemisphere and right in the Southern?

 

This has something, indeed. To stay inside this picture: a perfectly centered bike then would behave as if running on the aequator line. It would never know whether to pull to the right or to the left.

 

It's simply the fact that a bike needs some forces applied to the front wheel to stabilize it. If the masses are hanging on the right side for instance, the bicycle reacts with a tendency to the left until a new equilibrium is reached. This is what lets you go straight. The alternative would be riding in drunken style

 

Hubert

[Guest Nogbad]

Nope, still can't see it.

 

Out of centre masses would tend to make the bike handle asymmetrically, dropping into a right hander more quickly than a left. Hardly desirable.

 

Also, you would end up leaning the bike slightly to the opposite side, whereupon the C of G would again be in the middle of the track.

 

If you don't believe me, hang a bag of shopping off one handlebar or fill one pannier with bricks and get someone to film you riding along.

 

Finally, have a look at a light racing pushbike. Insignificant off centre mass if any, and you dont see the man in the blue jersey wobbling about like he consumed one stein too many.

[pete roper]

Nope, still can't see it.

 

 

Me neither . What makes a bike stay upright is the gyroscopic effect of the wheels. What makes it go straight is the steering geometry, the machine's rake and trail.

 

Sorry, I don't buy it, and certainly my earlier Tontis are all, (Within the bounds of construction tollerances.) *symetrical* in that the crank centreline is directly under the centreline of the frame spine. Also there would be no need for the crank to be off centre anyway. If your theory holds true there are heaps of other asymetric bits to keep things sweet, in the gearbox, the driveshaft, UJ et al.

 

Pete

[Paul Minnaert]

the 5 speed spines have the engine off center. This was corrected when the 6 speed gearbox was used. As far as I have measured, it is 10 mm, that's how much I moved my engine back. And that fitted perfect. Howto?: http://www.fastguzzi.nl/howto/6speed.htm

[luhbo]

Me neither . What makes a bike stay upright is the gyroscopic effect of the wheels. What makes it go straight is the steering geometry, the machine's rake and trail.

 

Sorry, I don't buy it, and certainly my earlier Tontis are all, (Within the bounds of construction tollerances.) *symetrical* in that the crank centreline is directly under the centreline of the frame spine. Also there would be no need for the crank to be off centre anyway. If your theory holds true there are heaps of other asymetric bits to keep things sweet, in the gearbox, the driveshaft, UJ et al.

 

Pete

 

I never said it was important to have the crankshaft out of center. I said the bike at all, its mass distribution needs to be off-centered. If it's not the bike than the driver will sit out of the center line (verticaly).

 

There's no need for any gyroscopic effects, they hamper more than they help you. Think of those who want their wheels as light as possible, or of those who don't have any wheels at all, like inline 2-ski bobs. Such things exist and are used much to the joy of their owners. They stay upright without any gyroscopic effects (and without the feet down to the ground).

 

The miracle here is to keep the contact points (wheel/road or ski/snow) exactly below the COG. Have you ever balanced a screwdriver on the tip of your finger? That's it. BTW, its easier to balance the longer ones, beginners should try it with a broom

 

What makes it go straight is the geometry, in fact, but of course not directly. What is working are the resulting forces. An angle or a length of something per se won't hold your tyres on the street.

 

The mechanism is called "Seitenführungskraft", I'd translate it as "lateral applied forces". You need such forces by definition to keep your bike, your car, your self on track. This may sound a bit esoteric, but in winter on ice plates it's quite easy to understand what happens without them.

 

What I was mentioning in the upper posts was the influence of these lateral applied forces. They stabilise the bike, forcing it into a stable equilibrum of forces and reaction forces. Without them you could't go on a straight line, you had to wave around it, always in search of a helping counterforce to lean against.

 

Another example: has anyone ever noticed how "surprisingly" uncertain a car or bike can "feels" if it goes over ice and snow, mud or wet "Cat Heads" (that's how we call the well polished basalt pavement). That's exactly a result of the suddenly and sometimes drastically decreased "lateral applied forces", a result of the decreased friction coefficient.

 

Thanks Paul for your line about the Tontis. Those who felt the need to drive broader tires like 150 or so, they had much more than 10mm offset.

 

Hubert

[g.forrest]

you's fellows just gotta understand. torque mass has to be in line with direction of travel, ie propellant mass has to be for foward motion. not aimed at passing environment. ain't that the way all fast v twins do it.

[luhbo]

Yes, it's probably a profile thing...