Tuesday, October 02, 2007

Physics and floor pumps

Tuesday, 2 October

I admit I didn't do so well at high school physics--and that class was a long time ago. I'm not sure this subject was covered, though.

When I use a floor pump, it seems that I cannot inflate my tires to more pounds per square inch than pounds of my body weight. Even if I put all my weight on my hands and take my feet off the ground, I still cannot put enough air in the tires for a TT (and barely enough for commuting). Does this reflect how much I weigh, or how little upper-body strength I have?

I know all you 160-pound guys have never encountered this problem, so I'm sure you'll have lots of speculation to offer. Just don't blame me when I can't be a self-sufficient cyclist.


Anonymous said...

The Physics:

F = P * A
(F = force, P=pressure, A=Area)

Or, doing a little handy rearranging, P = F / A

So 100 lbs force on a 1 sq inch pump = 100 PSI.

Your floor pump is probably bigger than 1 square inch, so you would create less pressure (and things like friction, pump efficiency, blah blah blah would make the output even less).

Since you're not filling up giganto MTB tires, use a smaller pump!

STOKED I AM said...

So my frame pump, which provides a better workout than the bike, will allow wimpy little me to get higher PSI in my tires?

Argentius said...

Well, leverage matters too -- that's the prob with frame pumps, etc.

But, yes, you want a floor pump that has a smaller stroke volume. We have two floor pumps, one that will inflate a tire to 100psi in, say, 15 strokes, and one that takes perhaps 25.

The ladyfriend has to really fight the 15-stroke pump to get a tire to 100psi, but does not really struggle with the 25-stroke pump.