I see MotoGP riders lean so much that their shoulders can touch the ground. How is this possible?
In: Physics
When it’s leaning, it’s turning. When it’s turning, momentum wants the motorcycle to keep going in the direction it was going (straight: objects in motion tend to stay that way), but the wheels are making it turn.
From the perspective of someone sitting on/in the vehicle, you feel that “wants to go straight” against the turn as a force towards the outside of the turn.
The way to counteract that force on a motorcycle without tipping over is to be leaning into it. The faster you go and sharper you turn, the more lean you need. Without it, you tip over.
It’s kinda like how in a stiff wind you need to lean into it to not fall over. In a tight turn you need to lean into it to not fall over.
“Center of gravity” is a funny thing, and when you add velocity, it may actually be nowhere near the object itself.
At significant enough velocity, in a turn, the center of gravity shifts *opposite* the turn, and that shift makes it possible for riders to lean pretty close to the ground.
It uses the gyroscope effect. A motorcycle and bicycle want to stay upright while the wheels are spinning.
When you run fast and turn you feel like you are pulled on the outside.
It’s the same for the bikes except they go much faster so the are pulled even harder on the outside.
Hold a bicycle wheel in your hands in front of you by the axles. Have someone make it spin fast, then try to tilt it from side to side. Gyroscopic effect will try to keep it upright.
The lean provides exactly the necessary force into the turn to make it turn. So it balances.
But there is a limit to how tight it can turn and that’s the wheel friction with the road. If the wheels lose grip and skid then the leaning rider falls over because the balance of the lean against the turn stops being balanced when the motorcycle fails to actually be turning because it’s skidding straight instead. When a motorcycle loses grip with the road in a turn the rider usually falls in the direction he was leaning and then scrapes along the road on that side.
Moto GP bike tires are engineered such that the contact area of the tires with the ground kind of remains the same while the bike is upright vs while the bike is leaning. Hence it is easier for the biker and in fact more efficient to lean during turns.
From the point of view of the motorcycle rider, he is upright and the ground is tilted, not the other way around.
If he didn’t lean inward, he would fall over towards the outside of the curve.
Think about what it feels like to be riding in a car going around a curved highway ramp at high speed, where you feel as if you are being pulled towards the car door on the outside of the curve.
It’s the same thing, except the rider deliberately tilts his bike right or left so he *doesn’t* feel pulled left or right.
I believe you are indeed falling sideways, but because you are turning, the bike is also moving sideways so it continually moves in front of your fall and catches you out of it?
Amateur motorcycle racer here. This is actually exactly why the tires are rounded instead of flat like a car.
When you turn a car, you know how your body moves a bit to the left or right? Those are what we call “lateral G’s”, or horizontal forces of gravity.
Same thing happens to a motorcycle, but because the tires are round, there’s always some rubber to resist that force and hold grip even at high speeds and high lean angles. Sportbike tires are designed to have a wide footprint at any lean angle so there’s lots of grip even at high lean angles.
This is of course a gross oversimplification, but you asked for ELI5 so there you go.
Motorcycle tire engineers are some very smart people and the grip on those tires is actually insane. You would not believe how rock steady they feel leaned over that far at those speeds, it’s a surreal feeling.
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