"Little angle, try hard braking... rear not too much up"

Alright nerds, riddle me this.



In this video, Toprak describes how if you're straight up-and-down and brake hard, you'll lift the rear - but if you're slightly leaned over, and brake hard, you won't.

I'm normally the physics nerd but I'm struggling to understand this one. Take your shot.

 

Possibly because the center of gravity shifts rearward as the lean angle increases ?

 

I do this all the time by instinct, in surprise-Hard-braking (backroad) moments, ... i was going to make a most/question about why I quickly lean my bike when I slam on the brakes going straight, because I catch myself doing it all the time lately, now that I am riding every day.....Now I know why.
TY

Edit.... i just read the OP, and i felt/thought/felt I was doing it cause it was giving me more front tyre contact patch or something, i was doing it w/out thinking, but am doing it (everytime), and feels like i am getting better front trye feel or something.... I dunno why i doing it, but i am. I feel i can brake harder. Whatever the reason, you can 'feel' it....

 

I've been thinkning about it, (not much, minute here/there) but thining lately, cause I cathc myself doing it, now that i am reiding again. another thing i thought it might be was i thought pushing it over into a lean, gave the tyre some resistance, if that makes any sense.
Anyways.

 

Does it? I wouldn't have thought so. Would love an explanation if you're thinking that's it.

The CG definitely does shift lower... which would have a similar effect... interesting thought. But, he also doesn't seem very dramatically leaned over in the photo they use (nor in the videos I see), so it wouldn't shift much. But.. interesting.

 

I think that just lowering it would make mass up high (rear end of bike) less likely to go upwards, so yeah.

 

As you lean you are adding another dynamic which is the intended curvature radius of the turn path itself and as such braking forces are dispersed over a larger area of energy dissipation and not as linear , kinda like a roundhouse versus a straight jab / curve ball versus fast ball or hammer thrower versus axe thrower etc .

 

When a wheel is spinning in a vertical plane, it is easier to move up and down along that vertical plane than whenitn is tilted from that plane? Maybe? Guessing? Hell if I know

 

He laughs when he says Redding

 

He doesn’t lift the rear when he’s leaned over because he finds a rider to use as a berm

 

I'm going with, it has to do with the wheels spinning

 

First, I'm no physics guy. Would the center line of the front axle be called something like the roll center? If the axle isn't horizontal anymore there's not a perpendicular line down to the ground. You no longer have a good pivot point around the axle if it isn't horizontal.

 

I swear I see Marquez at all angles braking, and the bike swinging all around him.

 

The centrifugal force of a spinning wheel is resistant to being moved from its plane. It would be interesting to see what effect locking the wheel would have on rear end lift, but in the real world the likely result would be near earth orbit for the rider.

 

Yes, because as the bike leans it adds cornering force to the CG to help keep the rear down. More load at CG equals more braking force….
At least until it overloads the front contact patch.
Same thing works for acceleration. You can accelerate more while leaned over without the front wheel lifting than while straight up
And down… till it exceeds the tires limits anyway.

 

The pivot point is probably the contact patch of the front tire.

 

Dirt bike stunt guys use the rear wheel all of the time to either raise or lower the front in the air, to me the effect on the rear would be opposite if the front is on the ground. (gas/brake).

 

Straight up and down the only thing resisting the back of the bike going up is gravity.

When you're arcing a turn leaned over, the rear of the bike now has gravity (reduced due to the angle at which the bike is, the tail wouldn't be going straight up, but at an angle) AND centrifugal force resisting it. The more the lean and speed, the more centrifugal force there is.

 

Perhaps the centripetal (or centrifugal, I can never tell) force involved in turning is pushing the rear down (outside the curve) ?

 

I can't wait to have to explain this one to a bunch of students

Interesting video, maybe there's something there at the pointy end