Silca 2-Step Mini-pump ?

Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.

RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.


but that's all mini pumps are for - to get you home. otherwise you'll
carry a frame pump. think about it - how are you going to compress the
same air in a 20cm long barrel as you can in a 50+cm long barrel? and
2-stage pumps are next to useless because the "high pressure" stage
always compresses before the low pressure one. as long as you can get
100psi from your current mini, it's doing its job and you won't need to
call the sag wagon.

On Sun, 13 Jul 2008 09:38:05 -0700, RS wrote:

Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.

Dear RS,

Depends on what you mean by a mini-pump.

The Topeak Road Morph is often listed as a mini-pump, but it's 13.7"
long and is basically a miniature floor pump, with t-handle, hose,
gauge, and foot-stand. RBT regulars repeatedly recommended it, so I
finally got one a few years ago. Mine works fine (and often) for
inflating 700cx25 to over 100 psi--wish I'd been smart enough to get
it sooner.

$25 at Nashbar in the mini-pump category:

http://www.nashbar.com/profile.cfm?c...20Mini%20Pumps

But you may have shorter pumps in mind, what could be called micro or
pocket pumps rather mini (not that there's any standard nomenclature).

Maybe if you specify a length, you'll get some specific
recommendations for smaller pumps.

Cheers,

Carl Fogel

In article ,
RS wrote:

Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely
work? I mean most minis I've tried will get enough air into a road
tire to get you home but that's about it. And certainly not 100lb or
so of air. I've used Carbone mini, SKS race-day, various Topeak
(poor quality). thanks.

The Silca mini-pump has been recommended as being a decent item by
several people whose judgment I trust. A frequent riding buddy uses the
Crank Bros pump which has some sort of an adjustment for low
pressure/high volume to get the tire fairly full and then a high
pressure/low volume setting for topping it off. I've seen him use it
and it seems to work fine, but have never used it myself.

gratuitous rant I use old Silca frame fit pumps with Campy heads,
since all my bikes are old enough that those sorts of pumps fit easily,
so I haven't tried this one. Modern road bikes seem to be becoming
increasingly useless- no room for fenders, fatter tires, pumps, easily
adjustable stems, Q factors around 160 mm (ouch), ass hatchet saddles
requiring Depends-like padding in shorts and fart slots, breakable
frames and forks and stems and handlebars, non-repairable major
components like brifters... no wonder I haven't bought a new bike since
1998./gratuitous rant

On 2008-07-13, jim beam wrote:
RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.


but that's all mini pumps are for - to get you home. otherwise you'll
carry a frame pump. think about it - how are you going to compress the
same air in a 20cm long barrel as you can in a 50+cm long barrel?

In theory if the bore is the same diameter you should be able to get to
the same pressure, just with more strokes.

Ben C wrote:
On 2008-07-13, jim beam wrote:
RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.

but that's all mini pumps are for - to get you home. otherwise you'll
carry a frame pump. think about it - how are you going to compress the
same air in a 20cm long barrel as you can in a 50+cm long barrel?

In theory if the bore is the same diameter you should be able to get to
the same pressure, just with more strokes.

indeed. in practice though, the unswept volume at the business end is
about the same on both types, thus compression is actually lower with
the shorter stroke. the unswept volume should be proportionately
smaller for the shorter stroke pump for it to achieve the same pressure.

On 2008-07-13, jim beam wrote:
Ben C wrote:
On 2008-07-13, jim beam wrote:
RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.

but that's all mini pumps are for - to get you home. otherwise you'll
carry a frame pump. think about it - how are you going to compress the
same air in a 20cm long barrel as you can in a 50+cm long barrel?

In theory if the bore is the same diameter you should be able to get to
the same pressure, just with more strokes.

indeed. in practice though, the unswept volume at the business end is
about the same on both types, thus compression is actually lower with
the shorter stroke. the unswept volume should be proportionately
smaller for the shorter stroke pump for it to achieve the same pressure.

I was thinking about that sort of thing, and whether it was compression
ratio (total volume:unswept volume) or just bore diameter that mattered.

I kind of thought bore diameter is the main thing because you're pumping
the air into the tyre. If you block the end of the pump off then yes
you'll get a higher pressure in the business end with the longer higher
compression ratio pump.

But it's very hard to squash any pump right down with the end blocked
off. And it isn't blocked off in use-- it's connected to the tyre and
the unswept bit at the end is just an extension of the tyre really. I
don't think it matters much how big or small it is.

A floor pump has a long piece of hose that adds quite a bit to the
unswept volume, but I don't think its length reduces the pressure you
can achieve.

When you put the pump on, air comes out of the tyre into the pump.
There's a check valve or something (Fogel explained it once) that stops
the handle pinging out and giving you a bloody nose, but the pressure in
a small chamber near the end is now the same as in the tyre, say 80psi.

When you start pumping the pressure in that chamber increases, but it
doesn't have to get much above 80psi before it pushes past the valve
(the one on the inner tube). So I think the total volume:unswept volume
ratio needs to be high enough to push the valve open, but no more than
that, and that's not all that high.

Some mini-pumps I suspect don't have such a narrow bore, because it
takes rather a long time to pump up an MTB tyre with such a small volume
pump. But this is a problem when trying to get your road bike to 100psi.

In article ,
Ben C wrote:

On 2008-07-13, jim beam wrote:
RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does
it work slightly better than other mini-pumps, most of which
barely work? I mean most minis I've tried will get enough air
into a road tire to get you home but that's about it. And
certainly not 100lb or so of air. I've used Carbone mini, SKS
race-day, various Topeak (poor quality). thanks.


but that's all mini pumps are for - to get you home. otherwise
you'll carry a frame pump. think about it - how are you going to
compress the same air in a 20cm long barrel as you can in a 50+cm
long barrel?

In theory if the bore is the same diameter you should be able to get
to the same pressure, just with more strokes.

Is that a linear relationship (e.g., in jim beam's scenario it would
take 2 1/2 times as many strokes to fill the tire to the same pressure)?
It seems like it ought to be.

jim is right that mini pumps are designed to be the bare minimum to get
one home. That's why I carry a frame pump- I don't want to spend 2 1/2
times as long pumping up the darned tire.

On Jul 13, 2:12 pm, wrote:
On Sun, 13 Jul 2008 09:38:05 -0700, RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does it
work slightly better than other mini-pumps, most of which barely work?
I mean most minis I've tried will get enough air into a road tire to get
you home but that's about it. And certainly not 100lb or so of air. I've
used Carbone mini, SKS race-day, various Topeak (poor quality).
thanks.

Dear RS,

Depends on what you mean by a mini-pump.

The Topeak Road Morph is often listed as a mini-pump, but it's 13.7"
long and is basically a miniature floor pump, with t-handle, hose,
gauge, and foot-stand. RBT regulars repeatedly recommended it, so I
finally got one a few years ago. Mine works fine (and often) for
inflating 700cx25 to over 100 psi--wish I'd been smart enough to get
it sooner.

$25 at Nashbar in the mini-pump category:

http://www.nashbar.com/profile.cfm?c...category=60001...

But you may have shorter pumps in mind, what could be called micro or
pocket pumps rather mini (not that there's any standard nomenclature).

Maybe if you specify a length, you'll get some specific
recommendations for smaller pumps.

Cheers,

Carl Fogel

I've used a fat frame-mount Hurricane Mini-Max, about 30cm long, well
over a hundred times after the burl-looking handle on Silca stand pump
broke in half. Key to satisfaction with any mini-pump, ISTM, is a hose
which lets you plant one end of the pump against the ground. That
makes repeated strokes at higher pressure pretty easy, even for
routine maintenance.

http://www.performancebike.com/shop/...tegory_ID=4361

Specs on pumps don't necessarily report on the hose. With the above
pump, the hose is hidden in the barrel. You twist and pull the head
twists to lock the hose in place for use.

Harry Travis

Tim McNamara wrote:
In article ,
Ben C wrote:

On 2008-07-13, jim beam wrote:
RS wrote:
Is anyone using one of these: the Silca 2-Step mini-pump and does
it work slightly better than other mini-pumps, most of which
barely work? I mean most minis I've tried will get enough air
into a road tire to get you home but that's about it. And
certainly not 100lb or so of air. I've used Carbone mini, SKS
race-day, various Topeak (poor quality). thanks.

but that's all mini pumps are for - to get you home. otherwise
you'll carry a frame pump. think about it - how are you going to
compress the same air in a 20cm long barrel as you can in a 50+cm
long barrel?
In theory if the bore is the same diameter you should be able to get
to the same pressure, just with more strokes.

Not so. Maximum pressure depends on two design issues: The obvious
one, general seal quality, and the ratio between: (pump chamber volume
with the plunger all the way out),(pump chamber volume with plunger all
the way in). The point is, if there's a lot of "dead space" in the
barrel that the plunger doesn't pump out, you're gonna max out at a
lower pressure. Fortunately, most modern pumps seem to have little dead
space.

Is that a linear relationship (e.g., in jim beam's scenario it would
take 2 1/2 times as many strokes to fill the tire to the same pressure)?
It seems like it ought to be.

Twice the cross-sectional bore /area/ means half as many strokes; and
also twice the force required at any given pressure. This assumes
/zero/ dead space (see above), but that's close enough to true. Well,
that assumes equal chamber /length/, so twice the chamber /volume/ means
half as many strokes.

For example, the Silca (frame) pump has about 1.4 times the bore
diameter as the Zefal HP, and about the same length. That means about
twice the cross-sectional area (area ratio is the square of the diameter
ratio), so the Silca pumps a tire with half the strokes, but you need
twice the arm strength.

Mark J.