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5.2 Gyroscopic reactions of the wheels and engine:5.2.1 Contribution:- Gyroscopic reactions play a major role in keeping a 2-Wheeler standing up and steering WITHOUT hands on the handlebar. - They also play an important role in supporting countersteering maneuvers WITH hands on the handlebar. 5.2.2 Limits:- These gyroscopic reactions do not explain that the minimum stable speed WITHOUT hands on the handlebar is close to double the speed WITH hands on the handlebar. - Also, they do not explain the major difference in steering ease and precision at all speeds, between the cases WITH and WITHOUT hands on the handlebar. 5.2.3 Better understanding of gyroscopic reactions:
- If we lean it to the left around axis (1) on the figure, it will not lean to the left. It's surprising at first sight, but the gyroscopic reactions will rather orient it towards the left around axis (2). It can even be proved mathematically. - Similarly, if it's oriented towards the left around axis (3), it will lean to the right around axis (4). Note that the wheel does not let itself turn around axes (1) and (3) without generating a strong gyroscopic counter-reaction opposing these rotations. Also note that if the wheel is turned 10 degrees around (1) or (3), it will not automatically turn 10 degrees around (2) and (4). It may turn more.
5.2.4 Effects of gyroscopic reactions on 2-Wheelers:
b) The rear wheel and the crankshaft plus flywheel of a transverse engine, will also lean around axis (5) and generate gyroscopic reactions around axis (6) of the 2-Wheeler. But the front wheel is in contact with the ground at about 1.5 meter (5 feet) forward of the rear wheel. This front wheel will thus hold the 2-Wheeler against freely turning left. However, these gyroscopic reactions can act against the front fork steering axis and around the front fork trail to help the front wheel orientation around axis (6), in order to hold the 2-Wheeler against falling. c) If the 2-Wheeler leans, the centrifugal forces must be strong enough to bring it back to the vertical. The front wheel must thus turn fast enough so the gyroscopic reactions can be strong enough to orient the front wheel enough in the right direction and generate strong enough centrifugal forces. So a minimum speed must be attained before a 2-Wheeler can be stable WITHOUT hands on the handlebar. But the gyroscopic reactions themselves do not explain why this minimum speed is about twice as low WITH hands on the handlebar. d) As speed increases, the gyroscopic reactions and the centrifugal forces generated by the right-left orientations of the front wheel are increasingly important, even more so since they are proportional to the speed squared. This explains an easily observed fact: WITHOUT hands on the handlebar, the higher the speed, the more stable the 2-Wheeler gets.
A centrifugal force is thus generated towards the right and it adds up to the gyroscopic counter-reaction generated by leaning around axis (5). Thus, both maintain the 2-Wheeler vertical while the torso keeps on leaning right around axis (8).
Thus, whether the 2-Wheeler is leaning or it stays leaning, the rider has the impression that his vehicle is very stable at such speeds, WITHOUT hands on the handlebar. Anyone can observe that on a motorcycle at 100 Km/h WITHOUT hands on the handlebar, a rider can easily turn or lean his head and torso very low to the right or left (and even touch the ground with his hand) and the motorcycle only slightly changes direction towards the side the rider leaned. It's caused mostly by the front wheel gyroscopic reactions.
f) If the hands are put back on the handlebar at such speeds of 40-50Km/h on a bicycle and 100Km/h on a motorcycle, the gyroscopic reactions are still present and continue to stabilize the 2-Wheeler. When the rider leans to his right and pushes on the right handle of the handlebar while pulling on the left, he thus feels the gyroscopic counter-reactions on the handlebar that does not let itself turn easily. So the rider does have the feeling of pushing-pulling on the handlebar and, consciously or unconsciously, he is 'countersteering' the front wheel. So these gyroscopic counter-reactions explain the feeling of pushing-pulling on the handlebar when going into a turn using the known and taught Countersteering technique. The motorcycle wheels are heavier and turn faster than the bicycle wheels. The gyroscopic counter-reactions on the handlebar are thus much larger on a motorcycle than on a bicycle. This may explain that the Countersteering technique is more present in the motorcycle world than in the bicycle world.
Since the front wheel is oriented towards the left around (14), centrifugal forces (16) are generated to lean the 2-Wheeler towards the right or (15). Thus the gyroscopic reactions and the centrifugal forces add up to lean the 2-Wheeler and start it going into the turn according to the Countersteering technique.
These gyroscopic effects thus play an important role in supporting the Countersteering technique WITH hands on the handlebars.
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Ethier. All rights reserved. All information on this site is presented as is for the benefit of readers. Great efforts have been made to cover many aspects of 2-Wheeler steering and make texts and figures as clear as possible, in order to help ride and steer better. But It remains the sole and full responsibility of the reader to apply or test any recommendation, theory, suggestion…made. Thus, Pierre M. Ethier cannot be held responsible for any misunderstanding or any consequences resulting from using this information. Send any question, remark, joke, complaint or suggestion to pierre.ethier@clevislauzon.qc.ca or to Pierre M. Ethier, 2120 Du Foulon, App. 8, Sillery, Quebec, Canada, G1T 1X4 |
In order to observe its reactions, of a gyroscope can be
bought or it can be borrowed from the physics department of a school. But it's simpler to use a bicycle wheel (a
motorcycle wheel is too heavy) supported by its axle while someone else makes it turn forward:
a) If the rider puts his hands on the handlebar and
his 2-Wheeler falls towards his left when going forward on the road, it's now easy to understand the front wheel
gyroscopic reactions:
e) Around 40-50Km/h on a bicycle or100Km/h on a
motorcycle, the gyroscopic reactions are quite strong. If the torso leans progressively to the right around axis (8),
the chassis and front wheel are pushed by action-reaction to lean left or around axis (5). WITHOUT hands on the
handlebar, the gyroscopic reactions thus orient the front wheel towards the left or axis (6).
The rider’s torso may stop leaning at angle (9) to the
right and the 2-Wheeler may stay about vertical. Then, the torso weight to the right generates a torque that acts on the
2-Wheeler and the front wheel around (10), which is the opposite of axis (1) of the gyroscope image. WITHOUT hands on
the handlebar, the gyroscopic reactions thus also orient the front wheel towards the opposite of axis (2) of the
gyroscope image, or around axis (11) here. Thus, adding to the gyroscopic counter-reactions around axis (10), a strong
centrifugal force is then progressively generated towards the left to maintain the 2-Wheeler vertical even though the
rider’s torso still leans to the right.
g) Again when going into a turn using the
Countersteering technique, the rider leans to his right around (12) to go right, and he pushes on the right handle along
(13) while pulling on the left handle. He thus orients the front wheel left around axis (3) of the gyroscope, or (14) of
the 2-Wheeler here. The front wheel and the 2-Wheeler chassis will thus lean towards the right around axis (4) of the
gyroscope, or (15) of the 2-Wheeler here, towards where the rider wants to go. 
h) After starting to go into the turn according to
the Countersteering technique, the rider is leaning towards his right and the chassis of the 2-Wheeler also leans
towards his right. The front wheel follows the chassis and it is thus leaning towards the right or axis (17) here, which
is the opposite of axis (1) of the gyroscope. Even with hands on the handlebar, the gyroscopic effects also act around
the opposite of axis (2) of the gyroscope, or towards the right around axis (18).
Nothing helps predict the final leaning angles of the torso
and chassis (While the Torso-Arms-Handlebar theory predicts them). But due to the gyroscopic reactions and the
centrifugal forces, the torso and the chassis are both leaned to the right with the front wheel also oriented towards
the right (19). This front wheel orientation towards the right generates a centrifugal force towards the left (20) which
counteracts the weight (21) of the rider and 2-Wheeler to hold them and go into the right turn along (19).