Kicking the bike backwards when standing... what's the cause?
 

Shifting ones weight forward? starting your stand with the pedal down (no force)?

/discuss

Physics.

Gravity too

If you have someone on your wheel, warn them you are about to stand.

user error

Naaaaaahhh!

http://snltranscripts.jt.org/77/pics/77rtheodoric6.jpg

http://www.cosmosmagazine.com/files/...618_newton.jpg
I could tell you, but then I'd have to kill you.

In the sense of center of mass (COM), if you're COM is moving up a steep hill at 10mph and you stand, you're probably moving 90% of the bike weight (your body) forward faster than 10mph, meaning the bike itself has to either slow down or go backwards (just for a moment). Now, I suppose you could apply sufficient force just as you started standing up that you keep things moving forward.

Even if all the wheel does is slow down, someone close on your wheel could bump it.

How do you counteract this mysterious and dangerous effect?

/discuss

If it's gravity why does it happen on the flat too?

Because gravity doesn't go away when the road gradient is zero?

It depends on your frame of reference. As the rider who's standing, it appears that you are moving forward when you stand, because your frame of reference is anchored at the bike.

If you're another rider, your frame of reference is your own bike. When the guy in front stands up, his weight moves forward relative to his bike, but his COM continues at the same speed. Since the bike is lighter and the COM didn't move relatively, the bike moves closer to yours.

The effect would be much smaller if we just rode much heavier bikes ;)

It's not so mysterious. When some people stand, the first thing they do is pull themselves forward off the saddle with their arms. When you do this, you are pulling the bike back by the handlebars. If the first thing you do is push hard on the pedals and let your legs raise you off the saddle, then the bike doesn't jump back.

So your saying the reason a bike moves "backwards" when a rider stands on flat ground is because gravity pulls it back?


Is the correct answer.

I didnt say it was mysterious..... just wanted a sanity check.

Sorry wfrogge, the "mysterious" part was a reply to post #9.

Magic

No, I was answering your question.

In my previous post, I said the reason a bike moves backwards when a rider stands on flat ground is because of the law of reciprocal actions.

it's basically the reverse of throwing your bike at the line. If there is someone on my wheel, I make an effort to stand smoothly and without throwing the bike backwards. It takes some effort.

I don't see that post anywhere

http://www.bikeforums.net/showpost.p...62&postcount=7

or do I need to spell everything out?

It has nothing really to do with gravity.

You posted a picture of newton, you didn't specify if you were alluding to his 3rd law of motion or gravity.

Both of you are correct in your observations.

+1