Will a motorbike turn just by leaning into the corner?

The most effective way to turn a motorbike is using counter steering. Riders do this without thinking and, to explain it, takes much more time than the action of doing it.

To turn left, a rider initially applies a small amount of right turn using the handlebars (i.e. pushing the left handlebar forward or pulling the right handlebar backwards). This tips the bike to the left due to centrifugal forces. As this happens, the handlebars catch the fall by also turning to the left naturally, and the rider balances the g-forces in the corner by leaning.

Counter steering is effective from around 15km/h and is the quickest way to initiate a turn. It’s especially useful in an evasive manoeuvre where you need to turn very quickly.

The rider doesn’t think about how this process works while they are doing it; the action is completed as one seamless manoeuvre.

Can you turn a motorbike without turning the handlebars, just by leaning the bike over?

Both wheels on the bike have a gyroscopic motion: they want to continue moving in the same plane while they are spinning. There’s a strong resistance to them changing the plane which is why if you take your hands off the handlebars, the bike will continue to travel in roughly a straight line. It won’t be a perfectly straight line while the rider is on it, though, because the rider can influence the direction of the bike by shifting their weight, and the bike can be moved by imperfections in the road’s surface.

By leaning, the rider can influence the direction of the bike a small amount due to a change in the radius of the tyres. The rider can’t negotiate tight turns using weight shift, though.

Can you lean a motorbike without it turning?

If the leaning force is balanced by another force, you can lean a motorbike without it turning. That other force could be a strong side wind, or it could be the rider countering the lean. This is often done by trials or dirt bike riders when negotiating tricky sections.

Can you steer a bike using the brakes and throttle?

When in a racing or off-road situation, motorbike riders use the throttle and brakes to steer the bike.

There’s a good discussion on fast turning with supermoto bikes here.