Junior Member
Registered: 10-30-08
Posts: 2
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During initial testing Adam held up the failed spokes and made the assumption this would detract from a viable test of this myth. I contend that this factor is the one that makes the myth possible!
Why you ask? Well, let's take a look at what would happen if a pole were to cause catastrophic failure of the front wheel:
1. The forks detatch from their support mechanism moving downward and burrowing into the soft dirt. This acts like a fulcrum.
2. The center of gravity moves both forward and downward as the front forks drop.
3. The passenger continues moving forward at a constant velocity as the bike slows beneath him/her.
4. As the passenger leaves the seat, the sudden decompression of the rear suspension starts the rear wheel on an upward trajectory.
5. The passenger impacts the handlebars with a force equal to their mass times the difference in velocity. The bigger the rider, the more leverage applied to the fulcrum.
6. The torque applied to the fulcrum acelertes the rear wheel both forward and upward.
7. The bike arcs skyward, finding itself in translational and rotational equilibrium until gravity brings it back to the ground.
OK - it all depends on the forks burrowing into the ground. If the forks get a good grip the result is pretty scary. I did it in slow motion over a bicycle handlebar when I hit a pothole.
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Member
Registered: 10-30-08
Posts: 6
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YEA!!! What he said!!
We want a DO OVER!!
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Senior Member
Registered: 11-02-07
Posts: 4016
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Just the stoppage of the rotation of the front wheel will create the flip. The wheel need not seperate from the forks, the pole and spokes will stop the wheel, but not the bike.
Then comes the face-plant.
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Senior Member
Registered: 02-09-07
Posts: 56
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quote: Originally posted by fysicsisfun:
During initial testing Adam held up the failed spokes and made the assumption this would detract from a viable test of this myth. I contend that this factor is the one that makes the myth possible!
Why you ask? Well, let's take a look at what would happen if a pole were to cause catastrophic failure of the front wheel:
1. The forks detatch from their support mechanism moving downward and burrowing into the soft dirt. This acts like a fulcrum.
2. The center of gravity moves both forward and downward as the front forks drop.
3. The passenger continues moving forward at a constant velocity as the bike slows beneath him/her.
4. As the passenger leaves the seat, the sudden decompression of the rear suspension starts the rear wheel on an upward trajectory.
5. The passenger impacts the handlebars with a force equal to their mass times the difference in velocity. The bigger the rider, the more leverage applied to the fulcrum.
6. The torque applied to the fulcrum acelertes the rear wheel both forward and upward.
7. The bike arcs skyward, finding itself in translational and rotational equilibrium until gravity brings it back to the ground.
OK - it all depends on the forks burrowing into the ground. If the forks get a good grip the result is pretty scary. I did it in slow motion over a bicycle handlebar when I hit a pothole.
Bad News Guys it is not a myth and he is right busting out the spokes is the key My uncle was doing wheelies on an old dirt bike when the front axle came apart I watched him flip the bike and himself over. When the front forks hit the ground it pole vaulted him and the bike. Sorry I didn't have a camera with me. He wasn't seriously hurt,but the bike was wiped out. |
