Push backward into backsides?
Talking about bike-maths (Galileo would have built sick rhythm sections): when you manual-pump a roller, should the force be directed vertically (to increase your weight as you suggest in Mastering Mountain Bike Skills), or perpendicularly to the backside (so that all the energy is used to push off the ground)?
Provided that our aim is to get as much speed as possible. This issue has been niggling me for a long time…
Thanks for the interesting question. I too have wondered about this.
Turning vertical anger into lateral love on my beautiful Fox/Shimano/Specialized Stumpy 29.
Here’s my current thinking:
Job #1 should generally be: Balance on your feet. There are exceptions, especially at the top end of the sport, but most of us should focus on light hands, heavy feet. You cannot go wrong.
A proper pump-manual happens when you anchor the bars toward your hips and extend your legs while driving your hips toward your bars. This movement is analogous to gate starts, rowing, power lifting, nordic skiing, lifting furniture and many other forms of human power generation. When you dial in this motion, you can harness a TON of power. But you have to stay balanced and manage the opposing forces through your core.
If you try to push your bike backward into the backside, I think these things will happen:
• You will push yourself forward, off balance.
• You’ll reduce the amount of power you can generate between your hands and hips.
• You’ll be working against yourself. More on that:
If you focus on pushing downward, the slope of the backside will translate some of your downward anger into forward love. Since you just got very heavy, you’re about to get light. That’s perfect, because you can use that lightness over the 2nd roller. Sine wave of love.
More heavy >>> more light >>> more awesome.
On the other hand,
If you push backward, the slope of the backside will push you forward. While you might get a momentary boost in body speed, you’re now on the front of your bike and disconnected from your internal power source. Also, you’ve created less heaviness, so there’s gonna be less lightness … which means you won’t absorb the frontside as smoothly. I can envision lots of ways to handle this situation, but they all seem awkward.
More backward >>> more forward >>> more awkward.
To sum it up:
• Stay in the middle. Crush your feet down while you anchor your bars to your hips.
• Learn more in the book Pro BMX Skills — and in my skills clinics.
Know more. Have more fun!
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The goal is to push directly down, not back. For 2 reasons: first it will keep your weight directly over the pedals so you stay in a neutral position on the bike (minor reason).
Secondly (major reason) if you push straight down, part of your force will be directed forwards (concept of force vectors), and you will gain speed. If you were to push backwards (to remain perpendicular to the grade of the downslope. the vector for the force going forward would be zero, you lose speed due to friction and go slower.
Best example I’ve ever seen of this was watching Aaron Gwin at Windham 2 years ago. He blew his chain coming out of the start, but by catching and pumping every backside on the course he built up enough speed to clear a 65 finish line jump without ever being able to take a pedal stroke. Free speed is a good thing
Nice one Scott!
Through the kind efforts of good teachers, I have managed to learn a few things over the years.
Happy New Year Sensei
Lee, I’m so glad you resonded to that excellent question. Scott has also a great answer.
How about a ‘thought experiment’ as per Galileo? I imagine I am at the back side of a roller with a unicycle. If I hold the unicycle vertically and push it straight down, the wheel will roll forward (Lee’s ‘Good’ graphic). If I hold the unicycle wheel perpendicular to the backside of the hump and push into the hump, the wheel won’t go anywhere (Lee’s ‘Not So Good’ graphic). Just like Scott’s vector analogy.
Chris, well said.
Thanks for an answer, Lee. I focused on the mathematical part so much that I actually forgot about practical aspects 😉
Yes, notice however that pumping backwards would push your bodyweight forward and my concern was whether this wouldn’t be more efficent in some situations (ex. rollers with a steep backside). The steeper a slope is, the less forward speed will it generate from you pushing downwards. But you would have to go slow enough to get a good push and it would be quite awkward to catch the second roller though, as Lee mentioned.
Don’t forget about gravity. On a steep backside that’ll give you some good drive.
Not so much in a manual maybe but in a normal pump situation I feel having a very slight forward bias on the backside feels sweet. Basically just a drop of the heels and wrists and consciously driving the bike mostly down and a little forward with my legs. Like driving in the 5 o’clock direction.
Feels really good in the belly of a berm too!