The Bicycle's Upright Mystery: Explained

  • Context: Undergrad 
  • Thread starter Thread starter ishansaksena
  • Start date Start date
  • Tags Tags
    Mystery
Click For Summary

Discussion Overview

The discussion centers around the mechanisms that allow a bicycle to remain upright while traveling, particularly challenging the commonly held belief that gyroscopic forces are the primary reason for this stability. Participants explore alternative explanations and the role of steering dynamics in maintaining balance.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asserts that gyroscopic forces do not explain why a bicycle stays upright, referencing research that counters this view.
  • Another participant explains that stability is achieved by steering the front wheel into the direction of lean, a mechanism common to various bicycle designs.
  • A different viewpoint suggests that some bicycles can maintain balance without relying on trail or gyroscopic effects, using alternative mass configurations to achieve similar steering responses.
  • One participant expresses confusion about the role of gyroscopic effects, clarifying that while they do not keep the bike upright, they assist in steering the wheel to correct lean.
  • Another participant emphasizes that the gyroscopic effect has not been disproven for normal bicycles, but rather that other methods can also achieve stability.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the primary mechanism for a bicycle's stability. There are competing views regarding the significance of gyroscopic forces versus steering dynamics and other design factors.

Contextual Notes

Some claims rely on specific definitions of stability and may depend on the design of the bicycle. The discussion includes references to research that may not be universally accepted or understood by all participants.

ishansaksena
Messages
5
Reaction score
0
Hi guys,

Why does a Bicycle stay upright ?
(It's not because of the gyroscopic forces applied by the wheels as shown by http://ruina.tam.cornell.edu/resear...ics/stablebicycle/StableBicyclev34Revised.pdf)

In short this bicycle has wheels of the same size rotating in the opposite direction thus countering the gyroscopic force but it still manages to stay upright.
 
Physics news on Phys.org
There is more than one way this can be accomplished, but what the methods have in common is to steer the front wheel into the direction of lean sufficiently to correct the lean and return the bicycle back to vertical orientation (although the direction of the bike will have changed).

For a normal bicycle, this is done with "trail", the point of contact with the ground is behind the point where the pivot (steering) axis of the front wheel intercepts the ground. This results an inwards steering torque due to the upwards force from the pavement being applied "behind" the extended pivot axis.

Some research type bicycles don't use any "trail", and instead use a mass mounted above and in front of the front tire, so that the center of mass is in front of the pivot axis and above the rotational axis, which again results in the front tire steering into the direction of lean, but I don't know the details involved with this type of design.
 
ishansaksena said:
I already have a similar understanding of how it turns, my question is how it tends to stay upright when it's traveling in a straight line
To stay upright it makes slight turns.

ishansaksena said:
( all the other sites say it's because of the gyroscopic effect which has now been proven wrong )
Note that the gyroscopic effect is not supposed to keep the bike itself upright. Is just steers the wheel into the direction the bike falls over, so the bike straightens up again. The trail effect does the same. This wasn't proven wrong for normal bikes. It was just shown that the same steering effect can be achieved by other means, without trail and without gyroscopic effect.

Check out this thread where Andy Ruina, one of the authors, commented himself:
https://www.physicsforums.com/showthread.php?p=3851566
 
Last edited:
Thanks, that video was really helpful.
:approve:
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 21 ·
Replies
21
Views
29K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 32 ·
2
Replies
32
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K