On the PBW, and some other folding bicycles, there is no good place to mount a full size pump on the frame. My solution is to put it inside the seatpost.
The first six pictures below show how I did this with a Zefal Lapize frame pump. The flared section of the pump handle had to be cut off, and I used a rubber O-ring around the pump body to hold it tightly in place. I've also made modifications to the pump hose and my tire valves to make it work better. Details of those modifications are on my valve page.
This is basically the same kind of pump I had on my first touring bike 30 years ago, maybe even the same model. Farther down on this page are some pictures of, and comments on, other pumps I've used in the meantime.
(The remaining pictures below are approximately to scale with each other)
This is a nice pump. It's what I started out using with the PBW folding bike. A problem with the PBW and other folding bikes is that there's no good place to mount a conventional full size frame pump. And I basically don't like mini-pumps. This was a compromise. It still won't fit on the PBW frame, but it's the longest pump that will fit comfortably inside a saddlebag, pannier or shoulder bag. It can reach higher pressures than other pumps of its size because it can be braced against the ground like a floor pump. Topeak's similar Road Morph model is a little longer and slenderer and will reach even higher pressures, but I managed to get 130 psi into my air shock with the Mountain Morph. That's plenty - half again as much as I need in the tires on the PBW.
I got this as a companion to the Mountain Morph, for inflating the air shock rear suspension on my PBW. I thought it was kind of neat that they use the exact same thumb lock pump head (The internal parts of the pump heads were originally different but I changed them so they are now the same). This is about the same overall length as the Mountain Morph, but a lot skinnier, so it pumps much less volume per stroke to reach higher pressures more easily. I normally run the air shock at about 125 to 135 psi and the PBW's 20x1.75 tires at 60 to 85 psi. The shock pump can also be used to inflate a tire in a pinch, but it takes a few hundred strokes. I've been carrying both pumps when I go on tours, though I've never had occasion to pump up the air shock while out on the road. The Topeak shock pump has gotten some bad consumer reviews because of inaccuracy of the built-in gauge, but I found that it just needed to be initially calibrated (there's an adjusting screw), and one can't expect too much precision from this type of gauge.
This gets my vote for all-time best frame pump. I carried one on my old touring bike for about 25 years. Lately they are superseded in the US market by the Zefal HPX which has a "frame fit" handle and a device for locking out the spring in the handle while pumping. I like this original model better. The handle is more comfortable, and the spring lock-out function seems to me like more of a marketing gimmick than a real improvement. Last I knew the Zefal HP was still being made.
I am not certain that this is the correct name of this pump. If you know, I'd appreciate hearing from you. This is the pump I've been carrying on my 1976 Jim Redcay for the last couple of decades. I wanted a lightweight frame-fit pump on that bike. I started out with a Silca Impero, which was the pump of choice for high class bikes in those days, but it was too difficult for me to hold the non-locking pump head on the valve and reach adequate pressure. Next I made a hybrid using the body, head and piston of a Zefal HP with the handle from the Silca. I called it the Zefilca. That worked okay but it looked a little weird and the HP body was a little too short for my frame size. Finally I found the above pictured model. I guess it wasn't made for very long because I can't find any information about it on the internet. It's all plastic, including the locking pump head, so it's lighter than the HP and seems flimsier, but it hasn't failed me yet.
Modified November 21, 2003