Papa Tom

Don't judge me. I've been getting along fine with a certain Schwinn-branded frame pump for quite some time. It takes a little bit of elbow grease to get about 45 psi into a Specialized Nimbus 26" X 1.5" slick that rides best at around 60 psi, but I eventually get to the point where it's rideable in an emergency.

This season, I am experimenting with a new set of Schwalbe Big Apples, which people have recommended that I run at 40psi or even less. The Big Apples are 26" X 2.35".

So here's the question: When I'm out on the road and I do need the frame pump to repair one of these Big Apples, will it involve about the SAME amount of work to get 40psi into a 2.35" wide tire as it does to get 40psi into a 1.5" tire, or will it be easier/more difficult/????

Taking only this information into consideration, am I going to be sorry I did not upgrade my pump?

FBinNY 

Air pumps work according to a simple formula, similar to how leverage trades force for distance.

The volume of air delivered per stroke is equal to the volume of the cylinder. More precisely, it's equal to the displacement, or the difference in volume at the top and bottom of the stroke.

The force needed to push the air into the tire is equal to the pressure times the cross section area of the cylinder or piston (they're the same). This is where the leverage analogy cuts in. A fatter pump will deliver more air per stroke, but may be come too difficult to push when the pressure gets higher. A thinner pump is easier to use at higher pressures, but moves little air per stroke.

It's a simple calculus of volume vs. pressure, and it's up to you to find the optimal balance. IMO, you want the highest volume pump that you can operate up to the desired final pressure (or two pumps, a high volume starter pump, and a high pressure top off pump).

Not, that there's no drawback to more pump length. It moves more air with no pressure/force penalty. OTOH you are limited by what fits on your frame. This is why folks who use pumps more often, like tubular riders who top off daily, generally pass on mini pumps and use the longest pump that fits their frame.

Retro Grouch 

It's all about pressure and volume. 2.35" Big Apples have a lot more volume than 1.5" Nimbus tires so they'll take that much more air and that much longer to pump up. The last pump stroke needed to get either tire to 40 psi will take exactly the same amount of effort.

hueyhoolihan

ask yourself this question, an exaggeration, but fundamentally the same.

will it involve about the SAME amount of work to get 40psi into a 20mm wide bike tire as it does to get 40psi into a 12" wide truck tire?

i think we would agree on the answer .

Bill Kapaun

But there's going to be a lot more going from X PSI to 40 PSI.

FBinNY 

It's important to keep terminology straight. There's the effort of pumping against resistance or force, and there's the effort of pumping 3x the number of strokes to get the job done.

It's easier to keep on point if you avoid the nebulous "effort" and talk about force needed for the final stroke, and the total number of strokes needed.

Think about hill climbing. You can say it's a difficult hill, but that doesn't tell anyone much. Better to talk about how steep, or how long, and of course the height.

AnkleWork

Maybe try pumping them up from empty once? Count the number of strokes.

fietsbob

Science ? The air pressure created by the hand pump has to be greater than the air pressure in the tube already.

Little pumps like the Master-blaster will take more strokes than a Long Frame fit pump .. obviously.. (?)

Floor pumps FTW.

Papa Tom

From the OP: I'm not a big fan of sarcasm, but in this case, the responses from anklework and fietsbob really gave me a good laugh.

I realize I over-complicated the question, so I can't complain that I got some very complicated answers. I guess the simplest way to ask is: Is 40 psi 40 psi regardless of the space it has to fill? I think that has been answered.

All said, I think I will take ankleworks' suggestion and, as soon as I recover from this crappy Vertigo attack, I will try pumping one of my Big Apples with my Schwinn frame pump. If it takes too much out of me, I will invest in a better pump.

Thanks, all!

AnkleWork

Very revealing of our era that simple, practical, direct answers might be considered sarcastic.

dwmckee

Same force per pump, but a lot more pump strokes.