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This is a message board Sir , where everyone can have an opinion right or wrong and post it up. Thank You.
I think you have to take into account the CG.
When the spinning wheel stops, it’s not lifting or lowering the wheel directly. It is causing the whole motorcycle to rotate around the CG because of torque. The speed at which it stops will greatly affect the severity. Since both tires are spinning the same direction, the rotation around the CG will be the same direction, so the rear will rise and the front will lower.
Chase was lucky. As stated above, his front brake was just dragging, not locked up, so when airborne it slowed somewhat gradually, instead of immediately, which would have made the effect more drastic.
I think the front wheel being high was a result of the slower deceleration of the wheel, and that he was on the gas leaving the jump.
But, as always, I could be wrong.
Forces are acting across different axes here. It seems to me unlikely the spinning mass of a front wheel and inertial rotation when stopped is enough to overcome the mass of the rest of the motorcycle behind it and significantly rotate the motorcycle over the front wheel. A spinning rear wheel will contribute to dropping the rear wheel, not bringing it over the top of the bike, I think largely because of the ways bikes squat and release suspension. Isn't that why a brake tap works to lift the rear end, and why you panic rev when the front drops too much?
Again, I'm just trying to logic my way through this, it's interesting to read the different takes.
That was hard hit, glad he walked away from it.
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I may not have explained it well.
I’m not saying the spinning rear wheel raises it, but the sudden stop when you tap the brake. Think of it as a negative torque. Just like accelerating the wheel will lower the rear.
The force of stopping the spinning front wheel isn’t moving the whole weight of the motorcycle, it is rotating it around the CG.
Think of a teeter totter with the same weight on each side, it doesn’t take very much force to raise or lower it, no matter how much weight is on it.
Acceleration and deceleration of a spinning object will have a larger effect than most people would think.
In a single engine airplane, ( like most, with a counterclockwise rotation of the prop looking from the front ) adding power for takeoff you have to add a bunch of right rudder or you’d run off of the left side of the runway. It’s called the P- factor.
In a plane like a Russian Sukoi, with a clockwise rotating engine, it’s the opposite.
With the front wheel, you’ll of course, get no acceleration in the air, but a quick deceleration would have the same effect as a light brake tap, I would think.
It may seem somewhat counterintuitive but in kinetics what is called a pure moment, that is a pure twisting force or torque in plain English, has exactly the same effect on a body no matter where on the body it is applied.
Consider a dirtbike that has just left a jump face with both wheels spinning. The wheels have a rotational energy and let’s assume that it’s the same for each. When you tap the brake that energy is transferred to the bike in the form of a pure moment which means there’s no other up, down or sideways forces involved. That results in the bike itself gaining rotational energy and starting to rotate around its centre of mass.
It turns out when you resolve all the math that the rotational effect is the same on the larger mass (the bike) no matter where the moment is applied. So in our case, again assuming each wheel has the same rotational energy, you will get the same rotational effect on the bike whether you tap the front or rear brake.
Now I’m a C grade MX rider at best and briefly dabbled with brake tapping years ago but I’m guessing that the rear brake is preferred because (a) you can use throttle to get it spinning again and (b) it’s easier for the rider to use a foot control that is otherwise not doing much while in the air bs the right hand which is also trying to control bars and throttle.
Rear wheel is much heavier than a front wheel, plus you get stability with front spinning and as you say you can get rear moving again but you can for front, its not revokable. So all cases for using front to bring down front end is BS.
I was around a weekend warrior that tried to implement front wheel locking to bring down front end and convince everyone it was much better because they do it in MTB world 🙄😂 A bike is a bike.
Yes, but when the opinion is so idiotic that it probably shouldn't have been posted, like the post @Shred was referencing, it's going to get called out as such. Opinions are one thing, idiotic posts are something completely different.
As you’ll know a brake tap or panic rev is enough to change the direction of the bike by a few degrees which is enough in most cases to get you out of trouble. If the bike was hypothetically floating in space the wheel tap would start the whole bike rotating but much slower than the wheels were.
Motomike,
I have been trying to contact Ronnie from South Carolina who I've met at the MXDN two different times.
Did his phone number change?
Have him call me.
Thanks
I will PM you.
Edit
It says you do not accept private messages.
Any time I see "hidden due to downvotes", I know someone put more than sufficient effort to proclaim their stupidity. But hell, I'm impressed on this one
"no finger over the brake lever"...
Have you even watched the video?
Quit explaining it.
Go to the track, have your mrs or buddy film, and send a good one with the front brake locked off the take off in 3rd or 4th.
Then you'll know exactly what happens and you can compare it to Chase' result. In sure he'll appreciate the research.
It’s really not your place to tell people not to post or what to post here. That’s what the Mods do here.
Yes sir. Sorry if I bothered you.
A couple things to consider.. if the front wheels was locked or high resistance before leaving the jump (likely), little to no conservation of momentum would occur (gyro effect) in the air due to accidently grabbing the front (wheel is already not spinning). At the speed he was going, it wouldn’t throw him forward on take of either, more likely to bind and wash on take (which looks to happen).
Regardless, CS haters will pile on and say it was all mental/his mistake. CS fans will see it has a bike failure. Personally, I think the latter is most likely, but people will see what they want as evidence of this thread.
Now for nerding out. My BS in MechE and physics has me really questioning what I know lol. My experience has always been a dead front/front high effect from a front brake tap. But that could be a lot of factors, like if you blip the throttle when you pull the lever… Conservation of momentum of a single rigid body says the front should go down. However, thats an oversimplification of the problem. A bike is best modeled by a rigis multi-body problem, with forks and swingarm having fixed pivot points to the frame body. Much more complex dynamics there. Im a systems engineer of 5 years so I’m far removed from using math to solve those problems… but looking at it as a single rigid body isn’t quiet right. Also, the rear wheel has much more MOI, you would expect a more drastic impulse from locking that up. Would love to hear LuxonMx chime in, they are typically spot on in applying theory and reality with physics and engineering for moto.
With all due respect to your BS in Engineering, if you lock your front wheel up in the air, your nose picking for sure.
I couldn’t care less about your opinion of my post…. You should try a little of your own medicine. Here you are telling me what I shouldn’t post.
Pit Row
Got me man, why you think I went into engineering and didn’t take racing any further!
Definitely don’t recommend it as a tool in the toolbox, but stuff happens.
all this vitalengineering/astrophysicistiology is f'n entertaining. he crashed. his front rotor got bent somewhere. he dnf'd. he stomped back to the semi. it was 110° so i'll give him a pass. f' that heat
All the squabbling reminds me of the "SEAT BOUNCE" theory only the OG's will remember that one. 😃
Chase just went hard af into that face and his bike couldn’t handle it and something weird happened and locked his front brake up, no way that was on Chase at all. The way his body reacted said it all, something he wasn’t expecting. The wheel was still locked up when he got up, if he grabbed the front brakes then that wouldn’t have happened.
That's exactly what I saw
Another person who hasn't watched the video.
His front wheel was rotating when he left the face of the jump, it stopped rotating in the air, his finger was visible on the front brake lever, the front wheel started rotating when he landed.
During the crash the right side of the handle bars were driven into the ground, the front wheel was locked after the crash.
We will never know the truth, KTM will not admit failure unless it is so obvious they can’t hide it. My guess is they are using ceramic bearings and a ball came apart. Once he got the front wheel rolling it rolled fine than locked up again. A rock, bent rotor or mud would not do that.
Ok fair enough. Continue in your way Sir.👍🏻
That shitty WP suspension couldn’t handle what Chase was doing before Chase grabs the front brakes in the air 🤡🤡🤡
I think your last paragraph is what I'm trying to get at. There are many forces at play and the front wheel is not isolated. It's not a pure "action/equal reaction" hypothetical like the old "how do you get off a frozen lake with a perfectly frictionless surface" thought experiment. It seems that the inertia of a low mass spinning or suddenly stopped front wheel has a lot of other counteracting forces - including engine internals, suspension unloading - acting at different axes and with much more mass in the rest of the bike rider to offset front wheel dynamics in this situation. Maybe the effect of the spinning wheel has more influence over the span of a jump than the momentary force of suddenly stopping the front wheel does when it tries to rotate the rest of the bike over the front axle.
If the front brake tap stopping the front wheel lowers the front, why do a rear wheel tap with having to massage the clutch to not stall the bike it the air? Seems like a tap of the front brake would be much simpler and less risky. Genuine question.
You need to watch again. His front wheel wasn't locked after the crash. It rolled a bit, then locked up. After he dumped it again, picked it up, and tried one more time to move, it rolled a short distance before again locking up.
Statement came out today from ktm about what happened after they looked at the bike and then went in and looked at the data:
Post a reply to: Sexton’s crash