Cyclaholic

OK, my spelling and grammar aren't the best, in fact they're pretty bad, granted. English isn't my first language, by the way, so that may just have something to do with it.

Do you have a reply to the actual topic at hand?... you know, the one about the physics of cornering on a bike? I presented you with a reasonably detailed description of how I understand it to work, can you do something similar with your 'gyroscopic motion' theory?

City_Smasher

The topic of this thread isn't about the physics of cornering on a bike. If you want to discuss cornering on a bike, start a new thread.
But first you might want to practice typing 'as', a couple of hundred times so you know how to spell it.

Original Post:

Cyclaholic

The reason you can't balance a stationary bicycle is because it is a statically and dynamically unstable system, the reason you can balance a bicycle in motion is because you can alter the relative positions of the tire contact points with the road and the center of gravity so as to dynamically balance the forces of gravity and inertia, just like in my diagram except that the centripetal force is much smaller in magnitude and alternates in direction.

Now, do you have anything to prove that the PHYSICS rather than the spelling or grammar in my explanation is flawed?

frankenmike 

Cyclaholic, your explanation reads like my physics textbook, so I doubt anybody who tries to find flaws with it will have much success. That being said, even though gyro forces really don't do much for stability most of the time, on high speed descents (40+ mph) I can feel a stabilizing force which I believe to be gyroscopic in nature- like the bike stays up without any balancing necessary on my part. City smasher, even just on the face of it, physics aside, It's usually (always) futile to dispute the likes of Jobst and Sheldon.

City_Smasher

Well for starters, centripetal force only comes into the equation if you're planning to ride your bike in a small circle really, really fast.

Cyclaholic

<shakes head>

oh well, I tried.

City_Smasher

Cyclaholic after attempting to post an emote.

No centripetal forces involved in that! Centripetal Force: The external force required to make a body follow a curved path

This supports what I said in an earlier post. I rest my case, Cyclaholic!

Cyclaholic

In my world that's quite a compliment so thank you.

You know, having hit some scary speeds on the bike I can totally understand someone feeling like that is the case... and I definitely wasn't thinking about physics at speed, except for the physical consequences of an unscheduled dismount

Ultimately it really doesn't matter because an understanding of the underlying physics has absolutely no bearing on someone's ability to ride a bike. However, if someone wants to understand what's going on in terms of the physics of a bicycle (the whole point of this thread) then that paper that CB HI linked to is a good starting point. Here it is again...

https://socrates.berkeley.edu/~fajans...eerBikeAJP.PDF

...here's a little something to ponder: a bike underway is always turning, either one way or the other, it's never truly going straight but the minute correcting turns average out into a straight line in the direction you're going. That's the nature of a dynamically unstable system.

graywolf

If a rocket had gyroscopes big enough to do that it would never get off the ground. They use small gyroscopes to control servos that move the rocket engines enought ot control direction. The gyros only dectect change of direction, in other words they act as an autopilot.

In fact be glad that the gyroscopic force involved on a bicycle wheel is small, because if it was large you would not be able to control the bicycle.

Bicycles are dynamically stable, a criterian bicycle slightly so, a roadster very much so, but they are statically unstable. Which is why it is so hard to balance a unmoving bicycle, you have to do all the work with body movement; and so easy to balance a moving one, you only have to correct for perturbations. In fact if you had a perfectly smooth level road with no wind your bicycle would follow a straight line without a rider until it slowed down to the point where it would fall over.

deraltekluge

I've seen videos of that from a motorcycle race...rider fell off, cycle kept going a looooooooong way before it crashed.

deraltekluge

A gyroscope doesn't maintain its orientation without help. If a force acts on a gyroscope in such a way as to change the orientation of its axis, the gyroscope moves (or tries to move) in a direction 90° to its axis and to that force...think of a spinning top wobbling. In a gryostabilized system, sensors detect that and their signals are used as controls to whatever steering mechanism is involved, to correct for the original perturbing force. A very small gyroscope can stabilize a very large vehicle...

Pocko

Equilibrium...

https://www.youtube.com/watch?v=1hokS...next=1&index=4




.

tatfiend 

As I believe I mentioned earlier in this thread "Bicycling Science" third edition by David Gordon Wilson is an excellent reference for many questions on cycle physics and technical information. It is published by MIT press and is available on Amazon for a reasonable price, under $20.

If you want to experiment try a bike with locked steering and see how unrideable it is. Back in the days of friction steering dampers on motorcycles I tried riding with it overtightened and it made the bike very difficult to control. The minute steering corrections done automatically to control machine balance could not be done readily with the tightened down steering damper. The whole bike felt out of control, not a safe feeling.

This was true even at speeds well above normal bicycle speeds and with wheels and tires much more massive than on any bicycle. These should have provided much more gyroscopic force if such force actually aids stability, which according to the above mentioned book it does not.

Tried on both a 1967 Triumph and a 1972 BMW so engine layout and orientation did not change the result of the overtightened friction steering damper.