bad technique, inexperience, pedal stroke, blah blah blah BOLLOCKS!

Everyone does it, and you can’t help it. Let professor Mike try and explain why, and without the use of pictures to illustrate my point.

TL;DR: conservation of momentum.

Consider two masses, A and B, of arbitrary shape, or if you like, mass A can be in the shape of a person, and mass B can be in the shape of a bike. Mass A >> mass B. For example, I weigh, let’s say 93 kg, and my bike weighs, lets say, 7 kg. Total = 100 kg

The system of two masses are joined by a link. This link pivots about the centre of mass for the system of both A and B. Because mass A is much heavier than mass B, that centre of mass is much closer to mass A than mass B. In fact, it is only 7% of the distance from mass A to B.

So when the rider, mass A stands up, he actually moves forward, relative to the centre of mass of the system. Because mass A has moved forward, mass B MUST move backwards for the whole system to preserve its centre of mass. The bike has to move back a lot to counteract the rider moving forward just a little bit.

I hope that explains it. Basically, the only way you can stand up without throwing your wheel back is to do it very slowly. So slowly that the person behind you doesn’t remember when you started to stand.

Just be mindful that the wheel is coming back on a hill. Leave a gap.