"The steeper you go, the better throttle control must be"

[Motofool]

The centripetal acceleration is what the lean of the bike compensates.

However, the angle of lean is not directly proportional to that acceleration and its reaction: the friction force or lateral grip of the tires.

The proportion goes like this:

10 degrees: 0.18 g
20 degrees: 0.36 g
30 degrees: 0.58 g
40 degrees: 0.84 g
50 degrees: 1.19 g
60 degrees: 1.73 g

At extreme angles, forces escalate quickly and things may go out of control soon; hence, proper throttle control there becomes more critical.

"A motorcycle becomes potentially less stable as lean-angle increases......as we have seen, throttle-control plays a huge part in stability; the steeper you go, the better throttle control must be." - K. Code in TOTT2

[csmith12]

Love this stuff!

[alex.s]

you make me feel all warm and sciencey inside.

[Rexbo]

Pin it to win it, duh

[csmith12]

[Motofool]

Yes, proper throttle control is a basic skill to be learned by those who dream of becoming fast "cornerers".

Also, the g-forces that your butt and legs feel are an accurate indicator of the angle of lean and lateral stress on your contact patches; much more accurate than your built-in-your-Homo-erectus'-brain "safe angle perception."

Studies show that leaning our bodies 16 degrees out of the vertical line triggers a mental alarm for an imminent fall.
It is just non-natural for us to lean so much beyond that mental limit without inducing some sort of panic reaction, which can only be overcome with practice.

If you feel 90% heavier than normal, you are close to the limits of your Ninjette; otherwise, push that inside handlebar a little harder and leave that turn behind.

[Toly]

Yes, at higher lean angles, the G forces build up faster. But, your whole body gets proportionally heavier. So, it is getting proportionately harder to move arms/feet around, as G forces build up.

For that reason, you are not likely to make sudden / jerky movements (you can't be very twitchy with extra 5-10-20 lbs strapped to your arms). It's possible but will require real physical effort to overcome the weight.

This really shows at 3-5 Gs and above... but the principle is the same.

[choneofakind]

I like that feeling at the track when my head and chest get heavy and I really squish into the edge of my seat and dig into the outside foot peg; it means my knee is on the deck and I'm going fast It feels like I'm flying.


Hernan, interesting that only 16 degrees cause us to feel like we're falling. That explains why very slow/tight u-turns (like at the MSF course) make us so uncomfortable. That must be right around 15-20 degrees lean, and at such a slow speed, we feel like we will fall. Cool!

[Motofool]

Originally Posted by choneofakind

..........Hernan, interesting that only 16 degrees cause us to feel like we're falling. That explains why very slow/tight u-turns (like at the MSF course) make us so uncomfortable. That must be right around 15-20 degrees lean, and at such a slow speed, we feel like we will fall. Cool!

Tell me about it !!!
That is one of the things that makes MotoGymkhana maneuvers look so easy and feel so hard to do.

[alex.s]

can you modify the graph to include changes in body position? cause with good body position you'll still be doing high Gs but the bike will be at less of an angle right?

[Motofool]

Originally Posted by alex.s

can you modify the graph to include changes in body position? cause with good body position you'll still be doing high Gs but the bike will be at less of an angle right?

Correct, Alex.

If the rider does not hang-off, his CG and the CG of the rider are located over and aligned with a line coming from the line between the contact patches (green line in below picture).

The angle that that line forms with the vertical is the lean angle that corresponds to that speed and radius of turn.

If those speed and radius remain unchanged, nothing can change that lean angle or the lateral forces acting on the contact patches (trying to skid them out of the turn), not even an extreme hang-off: that is what the graph represents.

Hanging-off is for pushing or rotating the bike out so the suspension of the bike re-aligns onto a more vertical position.
In order to be able of doing so, the only thing the rider can do is pushing his body in, moving the CG of the bike and the CG of the rider far apart from that unalterable line coming from the line between the contact patches and forming the unique lean angle.

The picture below represents CG location of an imaginary CG, which is the resultant of the combination of those two real CG locations: bike and rider.

[alex.s]

so the "lean angle" is the angle between the surface normal and the vector between contact patch and the bike+rider CG? not the bikes actual lean angle of the rear tire for example.

[Motofool]

Correct, Alex !!! ......except that the reference is not the surface normal but the vertical gravity.

The surface could be non-horizontal and exactly the same angle will happen for the same speed and radius (as long as the tires have some grip, which does depend on the surface normal).