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GregGorman

Catching A Slide With Your Knee

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I keep thinking about how hard it is to hold up a bike when stopped if it gets leaned over too far, or how hard it is to pick up after a fall - it takes everything bit of muscle I've got plus a bit of technique to lift up a sportbike, and I can't do it while straddling the bike. So if a bike truly loses traction in a turn enough to cause a fall, that's what the rider would be faced with, 400 pounds of bike, and holding that up with their knee in an awkward position with no leverage? I'm still very skeptical, but maybe it's just something one has to experience to believe. Why couldn't it just be a temporary loss of traction, due to some surface or tire irregularity, and the traction comes back later because the surface or tire improves, or due to a throttle change, but the rider thinks they've done it with their knee? For example in the video, the detergent is there, then it's not, and the bike recovers, what's so unusual about that?

 

H,

 

It isn't the full 400+ lbs of weight that one has to hold. We are talking the times a rider has saved it, when it has just gone over the edge of traction, but the tires are still in contact with the ground. How much does one have to "hold" a correctly set up bike, when it is in the turn, and the bike is moving? AND let's not forget no lean angle change (otherwise the rider would have some pressure on the bars).

 

Any of the physics guys up here have a an idea of how to calculate this?

 

CF

Cobie,

Not sure it is a trick question.-- my guess will be none. No force is needed to "hold' a correctly set up bike in the turn if not trying to change its line. If I do not need to put the $1250 deposit on the school bike, I shall let both hands off the bar in the lean to prove it during my next school session. :lol:

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Cobie,

Not sure it is a trick question.-- my guess will be none. No force is needed to "hold' a correctly set up bike in the turn if not trying to change its line. If I do not need to put the $1250 deposit on the school bike, I shall let both hands off the bar in the lean to prove it during my next school session. :lol:

 

OK, see here who are the real die hards: in Twist 1 DVD, see if you can find the shot of Keith holding a CBR 1000 with ( 2 fingers on the throttle only.

 

CF

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OK, see here who are the real die hards: in Twist 1 DVD, see if you can find the shot of Keith holding a CBR 1000 with ( 2 fingers on the throttle only.

 

CF

Cobie,

Thanks a lot for info. Another new school exercise now--- 2-finger drill. :lol:

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I keep thinking about how hard it is to hold up a bike when stopped if it gets leaned over too far, or how hard it is to pick up after a fall - it takes everything bit of muscle I've got plus a bit of technique to lift up a sportbike, and I can't do it while straddling the bike. So if a bike truly loses traction in a turn enough to cause a fall, that's what the rider would be faced with, 400 pounds of bike, and holding that up with their knee in an awkward position with no leverage? I'm still very skeptical, but maybe it's just something one has to experience to believe. Why couldn't it just be a temporary loss of traction, due to some surface or tire irregularity, and the traction comes back later because the surface or tire improves, or due to a throttle change, but the rider thinks they've done it with their knee? For example in the video, the detergent is there, then it's not, and the bike recovers, what's so unusual about that?

 

H,

 

It isn't the full 400+ lbs of weight that one has to hold. We are talking the times a rider has saved it, when it has just gone over the edge of traction, but the tires are still in contact with the ground. How much does one have to "hold" a correctly set up bike, when it is in the turn, and the bike is moving? AND let's not forget no lean angle change (otherwise the rider would have some pressure on the bars).

 

Any of the physics guys up here have a an idea of how to calculate this?

 

CF

 

Yeah, it isn't the full 400 pounds. Even lifting a bike from a standstill is not the full 400 pounds, because we are leveraging it around the contact patches as a pivot.

 

Normally when the tires have traction it doesn't require any force from the rider at all to hold it up. It's held up because gravity and inertia are balanced, and traction is providing the turning force. So once the traction goes away of course the balance is lost and it starts to fall. I get what yur say'n, the tires are on the edge, just starting to lose it, but still contributing somewhat to keeping the bike up and then you theoretically only have to provide that last little bit of force with your knee to bring it up.

 

But it seems to me like when you grind your knee into the ground to try to save it, that would take downforce/weight (and thus traction) away from the tires. Just like when pegs drag the ground. And so grinding the knee into the ground could make the situation progressively worse instead of better.

 

It seems it would also create some torque steer effect as your knee drags backward, trying to pull you off the bike, and twisting the bike as you try to hold on, further destabilizing the situation, but I dunno maybe the pucks are slick enough not to create this problem. Then again maybe that torque steer effect is part of what's pulling the front wheel back into line.

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H,

 

Good questions, I'm sure some engineer could come up with some facts on this. I look at it more from the perspective of load. Tires normally give when there is too much load placed on them, for the condition (in my case, a hard tire that was not suitable for those conditions). I turned it in got to max lean (not very far over that day), and the front just kept going. My knee was out and reaching for the ground, as the front went, I kept a little pressure on it, took some load off the front, and it came back. No throttle changes. As for how much pressure, not sure how to quantify that. The thigh, pushing outwards (don't think it's that strong), and I wasn't sore or bruised at all later, I'd take a wild guess 30 lbs pressure?

 

A tire can also go from not enough load, anyone ever had the front slide from being on the gas too hard? I have.

 

Does this make sense from the standpoint of load?

 

CF

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I keep thinking about how hard it is to hold up a bike when stopped if it gets leaned over too far, or how hard it is to pick up after a fall - it takes everything bit of muscle I've got plus a bit of technique to lift up a sportbike, and I can't do it while straddling the bike. So if a bike truly loses traction in a turn enough to cause a fall, that's what the rider would be faced with, 400 pounds of bike, and holding that up with their knee in an awkward position with no leverage? I'm still very skeptical, but maybe it's just something one has to experience to believe. Why couldn't it just be a temporary loss of traction, due to some surface or tire irregularity, and the traction comes back later because the surface or tire improves, or due to a throttle change, but the rider thinks they've done it with their knee? For example in the video, the detergent is there, then it's not, and the bike recovers, what's so unusual about that?

 

H,

 

It isn't the full 400+ lbs of weight that one has to hold. We are talking the times a rider has saved it, when it has just gone over the edge of traction, but the tires are still in contact with the ground. How much does one have to "hold" a correctly set up bike, when it is in the turn, and the bike is moving? AND let's not forget no lean angle change (otherwise the rider would have some pressure on the bars).

 

Any of the physics guys up here have a an idea of how to calculate this?

 

CF

 

I don't know how to calculate it, but couldn't you put a sensor on the slide bike, and see how much pressure is being put on the outrigger wheel when it touches down? That outrigger wheel saves slides, right? (or you could measure the amount the outrigger shock travels, and calculate it from that.) Seems like the same principle, it just adds a little upward force on the bike to stop it from leaning over any farther, and that combined with good throttle control can save the slide, right? The outrigger wheel seems a reasonable approximation to a knee slider, since knee sliders do slide easily and I'm sure that little wheel has significant drag, probably would be pretty close to the same amount of friction.

 

Or, how about this, can you gutsy fellas experiment by pushing down a tad with your knee while dragging it and see if it changes your lean angle? It sure seems to me like it would NOT take much pressure to change the lean angle, standing the bike up a little and thereby increasing traction. I'm not reliable enough at dragging my knee to try this myself, although I think I've experienced it a few times when my knee touched down unexpectedly, and a little too hard, bouncing the bike up a little.

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Here's the most extreme example I've seen:

http://www.youtube.com/watch?v=Z_kQWsvRAy8

 

Yeah, he used his elbow in that one!

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And he came back to finish on the podium, 3rd I believe!

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The theory: the front (usually) or the rear starts sliding with your kneed down. To keep from crashing you push down with your knee and hold the bike up until it regains traction.

 

Is it possible? Is it really what is causing the bike to regain traction?

 

Yeah, I saw Colin Edwards and Nicky Hayden at Jerez. My theory is the bike simply slowed down enough for the front to regain traction and/or they rolled on the gas a bit and that's what saved it.

 

 

I would have to say yes. A while back, I was taking a corner and dragging my knee, when I heard something more than just my plastic knee puck scrapping the asphalt. It sounded metallic. Suddenly, I felt my bike tip to the right a bit and the rear began to slide.

 

It was weird; everything went into slow motion... I didn't panic. I simply threw my knee out a little more, felt the rear tire regain traction, and lifted the bike up and out of the turn.

 

Afterwards, I surveyed my bike for damage, and noticed that my right rearset had contacted the pavement and had been grinded down a little. Fortunately, no other part of my bike contacted the asphalt! :D

 

My incident wasn't as dynamic as Colin Edward's recovery, but it just goes to prove that the training received from California Superbike School really paid off as far as enabling me to respond rather than react to this occurrence. :)

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O.K. I think everybody is correct here, you can't lift 400 lbs. with your knee but that is not what is going on. A whole bunch of things are going on at once; throttle control, steering input and on. The knee down gives the rider a touch of stablility and enough drag to reduce speed to regain traction. Too bad we don't have 15 cams to show every little thing that is going on, the slight changes of center of garvity and center of ballance.

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