From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: 2 silly wheel questions
Date: 22 May 2001 15:41:20 GMT

Jon Isaacs writes:

>> The real reason people ask, is that practically no one uses a Silca
>> Impero frame fit pump, most riders being incapable of using such a
>> pump.

> I have a couple of bikes with Silca frame pumps.  The problem with
> them is that the tubes are plastic and can break.  While they are
> light weight, they are less durable IMHO than the HPX Zefals and for
> those who are not weight-weenies, the trade of a few ounces for a
> superior pump that will also work on Schader valves is a good one.

The piston area of the Zefal is about 1/2 that of a Silca Impero and
that is one of its attractions for people without a strong arm.  That
Silca pumps are fragile is apparent but to make up for that they cost
a fraction of the not comparable Zefal.

As I said, the Silca died with the demise of bicycle racers pumping tires.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: 2 silly wheel questions
Date: 22 May 2001 22:23:22 GMT

Mark Weaver writes:

>> As I said, the Silca died with the demise of bicycle racers pumping tires.

> or maybe they died because they sucked, and a superior product came
> along.  actually dozens of them came along. even the $5 plastic pump
> i got in germany is MUCH better than a silca impero. the only thing
> they're good for is so that really old geezers can have something to
> be nostalgic over.  -mark weaver p.s. so how do bike racers get air
> in their tires without pumping them?

Maybe, maybe, but I know how the non racing riders complained about
the difficulty of pumping with these pumps, not having the skill or
arm strength to push that size piston.  This is the same size piston
used on high pressure floor pumps operated with two hands.  I have
several double action pumps that use the leather from these pumps.  I
don't believe there is a pump on the market with that cross section.
Today people would rather pump almost indefinitely with a pump of half
the cross section and a quarter the length to inflate a tire rather
than to put some force into their stroke.  The reason is as I stated.
Not maybe maybe maybe...

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: 2 silly wheel questions
Date: 24 May 2001 15:35:48 GMT

Benz OuYang writes:

> On frame pumps, I don't know why most of them are designed in such a
> way that the rider has to support the pump at both ends.  For
> example, the Silca Impero pump has its outlet hole in such a way
> that the pump, when in use, is perpendicular to the plane of the
> wheel.  Thus, the rider has to support both the valve area and work
> the piston.  This makes it awkward at best to get the tire up to
> pressure.

I think this is the best testimonial to my contention that non-racers
are not able to operate a Silca pump.  The mode of operation is the
natural one for such a pump and is the one that I would choose were I
to design a pump.  The valve and tire is purposely not part of the
pumping force circuit so that the stem and tube are not load bearing,
which they shouldn't be.  That is why some pumps use short hoses,
however, these make forceful pumping even more awkward.

I find gymnastics people use to inflate a tire unambiguous evidence of
the problem.  Arm strength and coordination do not come easily for
many riders.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: 2 silly wheel questions
Date: 24 May 2001 16:38:02 GMT

Lincoln Dickerson writes:

> Have they ever made a pump that clips on the rim our uses the rim
> somehow as the point where the force is applied.  This is kind of an
> off the cuff thought.  Could it be done?

What for?  Tire inflation costs work and energy, and at a reasonable
rate requires force, force that the uncoordinated and weak of arm do
not muster.  For these folks 1:1 gearing on average gradients and
micro pumps are the norm.  Unfortunately they outnumber and out-spend
those who are able and strong and thereby skew the market for useful
products.  Triple chainwheels with ten-speed clusters (30 gears)
pander to this crowd.  I sense you are pressing in that direction.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: 2 silly wheel questions
Date: 24 May 2001 20:34:31 GMT

Sheldon Brown writes:

>>> On frame pumps, I don't know why most of them are designed in such
>>> a way that the rider has to support the pump at both ends.  For
>>> example, the Silca Impero pump has its outlet hole in such a way
>>> that the pump, when in use, is perpendicular to the plane of the
>>> wheel.  Thus, the rider has to support both the valve area and
>>> work the piston.  This makes it awkward at best to get the tire up
>>> to pressure.

>> I think this is the best testimonial to my contention that
>> non-racers are not able to operate a Silca pump.  The mode of
>> operation is the natural one for such a pump and is the one that I
>> would choose were I to design a pump.  The valve and tire is
>> purposely not part of the pumping force circuit so that the stem
>> and tube are not load bearing, which they shouldn't be.  That is
>> why some pumps use short hoses, however, these make forceful
>> pumping even more awkward.

>> I find gymnastics people use to inflate a tire unambiguous evidence
>> of the problem.  Arm strength and coordination do not come easily
>> for many riders.

> I'm pretty coordinated, but don't have a lot of arm strength.  I too
> like the classic Silca Impero.  I have a couple of tricks that make
> it work for me despite my weak arms.

> I work the handle with my right hand. As pressure builds up, I
> finish each stoke by bumping my right wrist up against my chest, and
> use my back for the final push on each stroke.

> I'll commonly use it either crouching, with my left wrist braced
> against the inside of my left knee, or standing, with the end of the
> pump pressing against a tree, fencepost or the like.

That's an elegant way of introducing the way one uses these pumps.
You do it no differently than anyone I know who does it well.  The
fence post is reserved for times when one has already ridden enough
miles for a day.  The trick is to not pump at arm's length, so to
speak, involving unnecessary muscular activity, as pumping vertically
against the ground does better than any method I've seen.  Unless you
are standing over the pump to put your weight on the handle with a
straight-arm push (as with a floor pump) , it's a lot of extra work.

> I only need to resort to these "gymnastics" for the last 30 psi or so.

Maybe last 30 strokes but that ain't psi.  That's the last 5 or maybe
8 psi.  It's a non-linear exercise.  50-60 strokes usually does the
trick for me with a 570mm long pump body.

> Sheldon "Strong Back, Weak Arms" Brown

You could also call that "practical".

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: Is effort to inflate tire to 80psi double  to get 40, or more?
Newsgroups: rec.bicycles.misc,rec.bicycles.tech
Message-ID: <1adZ9.62545$Ik.2448944@typhoon.sonic.net>
Date: Mon, 27 Jan 2003 16:31:57 GMT

TJ writes anonymously:

> Two questions really.  What is the expected MAXIMUM pressure you
> could expect a simple (non hi-tech) bicycle hand pump to inflate a
> tire to?

The simplest pump is probably the Silca frame-fit plastic pump, having
no features other than a piston and pump head with a grommet.  This
pump can get 100psi into a tire for an athletic person as it did for
many years in bicycle racing when racers carried their own spare
tubular tires and had no "spare wheel service".

> Do you have to put in twice as much energy to double the pressure in
> the tire. Say from 40psi to 80psi. Or would it take 3 times or 5
> times (or an exponential amount) more effort to double the pressure?

If you have tried it, you'll have noticed that 30psi is trivial with
the mentioned pump while 90psi is a bit of work and the last 10psi to
100 are as much effort as all the previous.  The Silca has only a
small dead space, that volume of the pump that, when the piston is all
the way in, does not get pushed past the tire valve or pump check
valve.  Bringing dead space up to pressure occurs with every stroke
but it is not part of the useful effort.

Inflation work is a square law by which doubling pressure requires at
least four times the work.  With dead space, that all pumps have, it
is more.  This means that there is an upper limit to the pressure a
pump can deliver when all air in the cylinder is compressed into the
dead space without any going into the tire that is already at that
pressure.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA