So I see knees down on tarmac in loads of photos and of course on the world superbikes. However what is the physics of it, I mean is it necessary to overall stability, does the knee acheive anything over not having a knee down. I ask this because I get the bike quite low when cornering but have never felt like I've needed to lean off it and scrape my knee accross the tarmac. I feel perfectly stable with my **** on the seat and my knees tucked into the tank.
Yes I see it and it looks cool and I want to do it but am also a little scared, so like I said, is it neccesary?

 

hanging off the bike lets you keep the bike actually more upright - everything else being equal for a corner. so that means the more you hang off, the more speed you can carry. when you hang off, the center of gravity (COG) is more to the inside of the corner, again, allowing you to go faster. as well, most racers feel that the knee on the ground gives them more stability.

if racers are doing it - you can be assured it helps you go faster

oh.... but that doesn't mean it's necessary on the street. you shouldn't be going fast enough to effectively "get the knee down" on your sunday rides. that doesn't mean you shouldn't move around on the bike and lean, but to actually get the knee on the ground - that's just dangerous to be that leaned over on the street as opposed to the track.

 

Dragging knee is a byproduct of proper body positioning, technique and speed. Like Conrice said, hanging off the bike properly will lower the center of gravity, letting the bike turn with less lean angle. Having the knee out like that helps to "square" your body on the bike. You want your body (spine) parallel to the bike as opposed to all crossed up. Try hanging off the bike and keeping your knee up against the bike, all you do is rotate around the tank and end up being crossed up which usually doesn't do much to where you COG is.

Now, is it neccessary? I guess if you look at guys like Mick Doohan who rode completely crossed up, then maybe not. Some of the AMA guys don't drag knee around every corner, but they're every bit faster than any of us on this forum.

There's also the fact that once you get used to it, it'll help you gauge your lean angle while going through the corner. TBH, it still freaks me out every time my knee hits the deck.

If you hang off the bike, your bike won't be using up as much lean angle (will be more upright) which means you have that much more contact patch to use in the corners.

 

Then can you exlpain why the hang their foot off the peg as they are coming to a corner from mach 4?

 

Kind of the same as the motocross technique where you're foot and leg create a downward leverage which adds weight to the front contact patch. They're not putting their boot out past the front axle like the motocross guys but obviously it does add something the front traction wise.

 

so you think the GP teams pay riders like rossi and stoner to showboat and go slower - and not win?

believe me,they wouldn't - it helps them go faster. it helps him with feel and balance. he says it stablizes him on left corners under hard braking

 

Knee down is a by product of proper body position and it helps you feel whats going on threw the corner. MotoGP people hanging their foot off before a corner was a rossi only thing that he probably did to make himself feel better then everyone started copying it.

 

I put my knee down when I'm going straight.

 

Yep. I totally think that.

It just doesn't make sense to me, but I am not anywhere near the level of performance OR skill as ANY of those guys!

 

It's something I aim to do at some point but should I be doing it on the roads though, it seems excessive and pointless but it looks cool.