Anderson mid air brake tap to save Sexton

RaceFace58
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Meriden, CT US
2/24/2022 12:39pm
KurtJ99 wrote:
Once Jason takes off, regardless of seat bounce or scrub, the trajectory of the center of mass (CM) of him and his bike is set. -...
Once Jason takes off, regardless of seat bounce or scrub, the trajectory of the center of mass (CM) of him and his bike is set.
- 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.


That diagram is spectacular.
In the diagram I can’t tell if he is concussed and should he be allowed to race this weekend though.
Well clearly he has watermelon rind on his head in the diagram proving he has been severely out of it and thus should not race. I’m sure I’ll now hear that watermelon rind cures concussion. There’s gotta be a study on that!
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thundergoat
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Beverly Hills, CA US
2/24/2022 6:09pm
I was sitting right where this happened. I couldn't believe Anderson went for it. From my view it looked like he had plenty of time to...
I was sitting right where this happened. I couldn't believe Anderson went for it. From my view it looked like he had plenty of time to see chase on the ground and not go for the jump, and then it took forever to get the red cross flag out.
On TV it looked like late flagging, maybe no one in the corner ?, he was laying there for a bit before being jumped over
Yeah people around us were screaming at the flagger, and then questioning why Anderson went for it like he did. It was an extremely foolish move, especially for someone who has been on the wrong end of a similar situation before.
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ToolMaker
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Escondido, CA US
2/24/2022 7:08pm
gti wrote:
The rear wheel would stay in( or also become) the Axis position and the front will drop when the rear brake is applied.
Torque is applied at the CG. Superposition of torque is early statics
RaceFace58 wrote:
This is hilarious. Explain what is applying torque to the center of gravity. The torque is coming from a spinning rear wheel being stopped and that...
This is hilarious. Explain what is applying torque to the center of gravity. The torque is coming from a spinning rear wheel being stopped and that inertia forces the entire bike to pivot at the rear axle. Now for bonus points, who invented the brake tap?
It would only pivot about the rear axle if there was balance. That's why an out of balance wheel hops as you drive down the street. Since the bike itself is only on one side and weighs about 200lbs., that energy (the rear wheel spinning and violently being stopped) that's trying to push the bike down is resisted by the mass of the bike itself, so instead of just the bike being pushed down, the wheel climbs up about the mass of the bike. So as it pushes the front down, it also lifts the back wheel up.
TM
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The Shop

PFitzG38
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Newport Beach, CA US
3/10/2022 10:14am
PFitzG38 wrote:
Broseph wrote:
So from the article, tapping the brakes makes the bike rotate forwards and revving makes the bike rotate backwards. Am I missing anything? I thought that...
So from the article, tapping the brakes makes the bike rotate forwards and revving makes the bike rotate backwards. Am I missing anything? I thought that was common knowledge.
I just thought it was interesting that someone at MXA was thinking along the same lines I was - even explaining the opposing forces. That and I like stirring up shit and watching all the Vitards get wound up! My contention is nothing raises the wheels. Brake tapping lowers the front and panic revving lowers the rear. No one can brake tap over anyone. It’s that gravity thing
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Broseph
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Stevenson, WA US
3/10/2022 10:56am
PFitzG38 wrote:
I just thought it was interesting that someone at MXA was thinking along the same lines I was - even explaining the opposing forces. That and...
I just thought it was interesting that someone at MXA was thinking along the same lines I was - even explaining the opposing forces. That and I like stirring up shit and watching all the Vitards get wound up! My contention is nothing raises the wheels. Brake tapping lowers the front and panic revving lowers the rear. No one can brake tap over anyone. It’s that gravity thing
If brake tapping only lowers the front and revving only lowers the rear, can I do both and prevent an over-jump? You know, ratchet the bike down out of the air with alternating brake/rev/brake/rev?
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early
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OH US
3/10/2022 11:41am
That article doesn't say what you think it does, also, Jody isn't a Physicist or Engineer. He talks about how the rotation of the wheel effects the frame of the motorcycle, this is essentially saying it works on the CG of the motorcycle, not the axis of angular momentum (rear axle).

This is easy to see in a 10th scale 2wd RC buggy with a fast motor. You can jump it, pull the throttle or jam the brakes, see the buggy rotate about the CG, and crash the shit out of it without getting hurt.
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Sandusky26
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2002
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Eastern, NC US
3/10/2022 12:45pm
PFitzG38 wrote:
I just thought it was interesting that someone at MXA was thinking along the same lines I was - even explaining the opposing forces. That and...
I just thought it was interesting that someone at MXA was thinking along the same lines I was - even explaining the opposing forces. That and I like stirring up shit and watching all the Vitards get wound up! My contention is nothing raises the wheels. Brake tapping lowers the front and panic revving lowers the rear. No one can brake tap over anyone. It’s that gravity thing
Broseph wrote:
If brake tapping only lowers the front and revving only lowers the rear, can I do both and prevent an over-jump? You know, ratchet the bike...
If brake tapping only lowers the front and revving only lowers the rear, can I do both and prevent an over-jump? You know, ratchet the bike down out of the air with alternating brake/rev/brake/rev?
I have seen some guys do that when they over jump. I don’t know who’s correct here, I just know I haven’t brake tapped in a long ass time.
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3/10/2022 1:46pm
Haha. Vital just invented a new form of flight. Seems we don’t need jet engines or wings or rockets. If we just put a dirty big wheel at the back of any vehicle, hit a bump and twist the throttle we can increase altitude.
Falcon
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Menifee, CA US
3/10/2022 3:33pm
You cannot change the net effect of the forces at play, and thus are not raising the bike at all. Not, at least, as an entire package of mass. The bike will land in the spot that the rider, Sir Issac Newton, and God agreed upon as soon as the bike left the ground. However, rotating the entire chassis by brake tapping would technically raise the rear wheel and lower the front as the entire package rotates around its center of gravity. This would do two things: make the front wheel touch the ground a little bit earlier, and allow the rear to remain airborne a little longer. Remember that the front wheel is about 5 feet ahead of the rear and the bike is moving forward.
Jason's actions, if that's what he even intended to do, resulted in his rear wheel touching ground a little farther down the track than it would have had he not applied braking.



*Let's assume the suspension is fully extended at the moment of brake tapping for the purposes of this exercise.
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3/10/2022 3:42pm
Yeah I think maybe we are talking past each other. When people are saying the rear comes up or the front drops, this is not actually changing the trajectory of the CG of the motorcycle, which as elegantly stated above, is determined as bike/rider system leaves the jump by god and Newton.
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SLAPAHO
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Newport Beach, CA US
3/10/2022 4:44pm
This is basically what JA did. tap to get a little more distance.. you be the judge on the rear wheel lifting or not..

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Tdc_worm
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Location
Austin, TX US
3/11/2022 10:08am
We talk about the center of mass of the machine. This made me wonder if the center of mass of the system is not static. That is to say that the rider has mass and quite a bit of range of movement. If this is true, can the rider affect the location of the axis about which the bike rotates?
Sawfish
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Las Vegas, NV US
3/11/2022 11:26am Edited Date/Time 3/11/2022 11:27am
SLAPAHO wrote:
This is basically what JA did. tap to get a little more distance.. you be the judge on the rear wheel lifting or not..
This is basically what JA did. tap to get a little more distance.. you be the judge on the rear wheel lifting or not..

That’s a really good explanation.


I had no idea so much of vital is completely inexperienced with being in the air.
Falcon
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Menifee, CA US
3/11/2022 3:44pm
Tdc_worm wrote:
We talk about the center of mass of the machine. This made me wonder if the center of mass of the system is not static. That...
We talk about the center of mass of the machine. This made me wonder if the center of mass of the system is not static. That is to say that the rider has mass and quite a bit of range of movement. If this is true, can the rider affect the location of the axis about which the bike rotates?
Yes.
When standing, the rider's body weight + bike weight makes the center of mass higher. When sitting, it is lower. If the rider moves rearward, there is a rearward bias to the center of gravity, and vice-versa with forward. Keep in mind, the rider's influence on the machine is not absolute nor perfect.
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