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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: Getting old is not for sissies
Date: Sat, 1 Mar 2025 13:40:09 -0500
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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.

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.


-- 
- Frank Krygowski