[buvanshak]

> When you lean to (your) left, the center of mass of you+bike goes left of the plane of the wheels, this causes the front wheel to rotate away

This does not seem correct. Why does it cause the front wheel to rotate away (right) ?

If you lean a stationary cycle to the left, the front wheel will turn left.

[ska]

  Why does it cause the front wheel to rotate away (right) ?

Answer is : "it's complicated" , which is why this subject causes confusion. There are many arguments about the exact dynamics (combinations of gyroscopic effects, torques, center-of-mass motion), but empirically it is pretty clear that two wheeled vehicles like bikes/motorcycles do not turn without counter-steer.

[jonsen]

Not at all complicated. A bike is made so that the front wheel will turn in the same direction as the bike is leaned. This has a simple stabilising effect. Bike leans right, front wheel turns right, increased centrifugal force from the sharper turn will unlean the bike to the left.

[buvanshak]

> Bike leans right, front wheel turns right

Agree. But this is not what the other person is saying.

[ska]

Except, it doesn’t at first. Which is why this is counter intuitive.

[jonsen]

If you lean your body to the left the bike reacts by leaning to the right. Your body can only move by pushing the bike in the opposite direction.

[NLips]

I shouldn't have mentioned 'leaning left'.

If I'm in contact with the top of my bike and not steering the bars, I can either push the top of the bike left or right. I push the top of the bike to the left. The bike and I have separate moments of intertia around longitudinal axis. Without any other forces involved (just my bum and the top of the bike pushing each other), the bottom of the bike i.e. the contact patch would move to the right. However, there's friction between the tyres and the ground meaning that doesn't happen. Instead, the ground pushes the bottom of the wheels to the left. This means the only external force on the union of rider and bike is from the ground pointing leftwards. This pushes the COG to the left.

While the motion of the top of the bike may cause some countersteering in the front wheel if left free, you can resist this by pushing the right side of the handlebars i.e. steering left. So we now have a bike tilting to the left, with the front wheel pointing forwards, and the COG to the left of the contact patches. The front wheel can be gently pushed to point left.

No countersteering involved.

[buvanshak]

That is bullshit. If I just lean to the left, the bike does not "react" by leaning to the right. If I lean to the left without touching the handle bars, the cycle ll start turning to the left.

With counter steering, it can be made much quicker and in a much responsive fashion.

[ska]

The point is that the wheel, which is free, will turn to the right first. The bike will lean to the left as this takes the two wheels out of line. The wheel will follow to the left.

There is nothing magical about countersteering, it’s just the way cornering works with bikes.

Don’t believe me? Set up an angle indicator and video it.

[buvanshak]

A bike is standing straight, completely still, with the front wheels completely straight. According to you, if I lean this stationary bike, to left, you are saying the front wheel will turn to right, right?

[ska]

Counter steering is a property only while it is rolling forward. You’ll have to be moving reasonably fast to notice it easily.

In context this was clear but I should have been more explicit.