Re: Getting old is not for sissies

Frank Krygowski <frkrygow@sbcglobal.net> wrote:

On 3/1/2025 12:53 PM, Roger Merriman wrote:

Frank Krygowski <frkrygow@sbcglobal.net> wrote:

 
I'm puzzled by the video's advice to avoid pulling up on the pedals "as
it's bad technique." I'm pretty sure I do pull up when jumping the bike.
What's bad about it?
 
And more on that video. In slow motion as they showed, the physics is
pretty obvious. The rider gets his body mass moving upwards, then
essentially pulls the bike up with him. That's where I think I pull up
using the pedals.
 

In theory it’s better to have the bike rider spring up, than being pulled
up by foot attachments also slight risk of unclipping.

 
I'm not sure I understand your phrasing. On my road bikes, I "spring up"
- that is, jump my body upward. I then pull upwards with both hands and
feet. Since I use toe clips instead of clipless, I don't think I've ever
unclipped while doing that.
 

 

What's less obvious, I think, is how a skateboarder with zero foot
attachment can bunny hop a skateboard. It's interesting to think about.
 
 

Lot of folks who jump is a focus do run flats so aren’t pulling up.

 
I run flat pedals on my mountain bike and my about-town 3 speed. Yes, I
can jump them, but not as high. On the other bikes, I think the toe
clips help.
 

I’d refer you to the Don who is a ex downhill racer, and rather technical,
to explain why!

<https://youtu.be/F7LO1qnm0Xs?si=0p3ONupQJCKONsR4>

But certainly all of the sane advice for bunny hops are not to being
pulling up with your feet, it can be done but it’s poor technique and will
limit how much you can do.

As with the skateboard "ollie" (linked in another post) getting the
rider's mass up high is easy and obvious, by jumping. Making the bike or
skateboard levitate is what's tricky.
 
I think the physics goes this way: You lift the front of the machine,
raising the machine's center of mass. On the bike, that's by pulling up
on the handlebars. On the board, that's by kicking down on the tail.
 
Once the machine center of mass is elevated, then rotate the machine
about its center of mass. That's  by pushing down on the handlebars or
by kicking down on the nose of the board.
 
That rotational action about the center of mass is what causes the rear
wheel(s) to lift into the air.
 
 

You shouldn’t be lifting either the bar or pedals, it’s about as with all
MTBing weight positions and movement and timing ie push hips back so your
arse is almost brushing the rear tyres.

And the front will come up, scooping the weight forward to drop the front
down and the rear up.

Roger Merriman