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i.e. Your front end low or about to endo. You panic rev to bring your rear down or to get your bike to match the attitude of the tranny. (ala Lil Hanny or BamBam) - Not bring your front end up.
Your front end high or about to loop out in the air. You wheel tap to bring your front end down. (ala Uncle Ronnie) - Not bring your rear end up.
The Shop
Sorry, physics.
conversely, the sudden acceleration of the rear wheel and the chainline's interaction with the suspension extend/jack the swingarm. the chainline forces the rear wheel down, it reaches full extension, the bike rotates around the drive sprocket where the force is initiating. the suspension is designed with a certain amount of antisquat to keep the chain from completely compressing the rear shock when you twist the throttle.
if the bike rotated around some CoG, when tapping the brakes, then why is front brake tapping not a thing? you could completely eliminate accidentally stalling with a front brake tap. i dare you to try it, haha.
here is a video of the force a wheel places on a bike during a braking moment. different kinematics, same principles.
https://www.youtube.com/watch?v=cY2j2gDiZQY&ab_channel=andrextr
It’s actually caused by the actual force of pushing down on the brake pedal, pushing the front wheel down. 🤦♂️
In the Stewart gif, the brake is tapped and the rear wheel rises relative to the center of gravity of the bike. This causes the rear wheel to trace a higher trajectory than it otherwise would have.
And no one brake taps the front wheel because there is no way to get it spinning again before you hit the ground. If you’ve ever wheelied until the front wheel stopped, you’ll know why this isn’t desirable.
One more thing…Here’s a quote from Wikipedia about reaction wheels in spacecraft:
“Reaction wheels can rotate a spacecraft only around its center of mass”
Here’s the full article:
https://en.m.wikipedia.org/wiki/Reaction_wheel
re stewart: yes. and at the same time it compresses the rear suspension. in the GIF you do not see the suspension push the wheel back down. that means it has to be pushing chassis up, because of those equal and opposite forces you reference. trajectory is actually fixed by the velocity and angle of departure from the lip of the jump. braking and revving only changes the bikes attitude.
from the 29-42 minute marks of this video, the front wheel isn't spinning. wonder how he made it those 5km without the front wheel spinning? Let alone the front wheel wasn't spinning when he sat it back down at 30km.
https://www.youtube.com/watch?v=zfryxJ5BK0s&ab_channel=TASKMANAGER
tons of folks wheelie far enough for the front wheel to stall and manage to ride away just fine. tapping either brake creats a moment of leverage over the chassis. if it didn't, then there is no way the bike would compress the rear suspension mid air.
Pit Row
In a single engine airplane, you have to add right rudder to counter a strong left turning force as you add takeoff power. It’s called p factor. I won’t get into the FAAs definition of what causes it, but it’s from the acceleration of the spinning mass (crank and prop).
The suspension compressing is a reaction, not the driving force.
- Seat bounce and his trajectory will be steeper, scrub it will be less steep
Once in the air, angular momentum is conserved. If your rear wheel is spinning fast and you hit the brakes, the bike rotates around the CM. The rear wheel rises and the front end dips. The bike rotates more slowly because it has much more mass than just the rear wheel.
There is no net height increase because the CM is floating through the air.
Please see enclosed scientific paper.
In the diagram I can’t tell if he is concussed and should he be allowed to race this weekend though.
The bike in the air has a certain amount of potential energy due to height, and Kinetic energy due to speed (linear speed plus rotational parts).... Lets isolate the gravity for a moment because what is lost in potential energy due to the height and gravity, is gained in kinetick due to the vertical speed lost/gained..
Now if you push the brake, since energy does not dissapears, the kinetic energy due to rotation of the real wheel shoud be converted to potential energy (the bike gains height as a whole), being the rear goin up, and the front going down arround its center of gravity.... but as a whole it actually gains height....
This is not enterely true because the fact that you push the brake, generates heat... an other type of energy so no all kinetic energy lost went to raise the bike as a whole as some of this energy went to thermal energy.
So depending how much energy became thermal, it depends hoy much height was gained, and since the bike in the air can only rotate around it center of gravity..... happens what you see in the video... the rear goes upwards.
Great move by Anderson!!!
(English is not my first language so sorry if my explanation is a bit confuse)
The real question is:
Is that jump a single since there’s no longer a valid landing in the middle due to Chase and his bike?
Don’t ask me how many centimeters it is, my brain hurts.
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