On The Road
by: Bill Oetinger 4/1/2008
Altitude Sickness
One of the first columns I wrote in this space was called Confessions
of a Cyclometer Junkie. In it, I deplored the obsessive-compulsive addiction
to data fostered by those little plastic computer thingies on our handlebars.
I wrote that in October of 1999--way back in the last century!--and I think I
did a decent job of dissecting the dysfunction of data overload. But I avoided
one subset of the topic entirely. In that piece, I said: "Oh lordy...don't even
get me started on altimeters!"
Recently, the topic of altimeters has percolated back up into the conscious part
of my brain again after having lain dormant and mostly unconsidered for most
of the past ten years. We have this little program in our club called April Alpina,
which encourages people to log all their elevation numbers for one month and
enter them in a big, communal graph on the club's website. Personally, I'm not
buying into this program. While I enthusiastically support our Century Challenge
on-line log, which encourages people to list all their century rides, for some
reason the altitude challenge just doesn't capture my interest. Too close to
my old cyclometer data addiction, I think...too much fussing with numbers.
Anyway, like it or not, during the month of April, the subject of climbing becomes
a hot topic in the club. Those who do buy into the April Alpina program flood
the club's ride list with absurdly hilly routes where you can pile up some extremely
gaudy numbers in the vertical sweepstakes. (Running against the grain, I have
listed one of the only rides of the month that isn't stupid-steep...but it is
a century.) Mind you, I do not mind climbing. All else being equal, I would rather
do a hilly ride than a flat one, which is fortunate, considering that I live
in a region that is rarely flat. I just don't feel the need to go out and explode
an aorta or two while hauling my sorry fat ass up a 25% wall, or three or six
such walls run together. Give me a nice 7% climb followed by a nice 7% descent,
and I'm a happy camper.
During the frenzied run-up to April, with so many busy little brains looking
high and low for the hilliest hills around, a thread worked its way along our
chat list for a few days, with the subject being those infamous roads that are
steeper than steep: where are they and just how nasty might they be? Baldwin
Street in Dunedin, New Zealand was mentioned (at up to 35%), as were several
amazingly steep streets within that vast flatness known as Los Angeles (Fargo and
Eldred, both at over 30%). Of course a few San Francisco blocks made the list
(a block of Filbert and a block of 22nd, out in Noe Valley, both at over 31%),
and our own April ride list features a bushel basket full of off-the-wall walls
over in Berserkley. But the winner appears to be Canton
Street in Pittsburgh, Pennsylvania, at a whopping, eye-popping 37%, and the
top half of that bad boy is cobblestone!
The reality check here is that most of these are city streets of only a block
or two in length. They may be ridiculous and mind-blowing in their own way, but
they don't really compare to slogging up six or eight or twelve miles at 12%
on a big alpine pass, or even doing three miles on some of our steeper Sonoma
County back roads, which might vary between 8% and 20%.
One of the things that occurred to me while following this thread is that we
tend to be rather subjective about our climbs, to the point sometimes of bending
the facts and figures to fit the feelings in our legs and lungs, creating a sort
of mythic hyperbole about the nastiest climbs. Gradient numbers have always been
the fish stories of the cycling world. Just as the angler will hold his hands waaaaay far
apart to describe the one that got away, so too will bikers toss out gradient
figures that are little more than tall tales. For the good of our sanity, this
is becoming less prevalent as the use of reliable GPS units becomes more common.
Finally, we're gathering together figures we can trust.
It hasn't always been this way. I have only owned two altimeters, both bike computer
models: the original Avocet 50 and the later Cateye. Both relied entirely on
barometric pressure for their readings, which left some room for error, one way
or another. Given the somewhat unreliable data, the natural human tendency is
to err on the high side when translating the "facts" of those fuzzy figures into
the "fiction" of the anecdotes we pass around amongst our cycling pals. Of course
we want the fish to have been bigger--the biggest!--and so too do we want the
hill to have been as steep as it could impossibly have been. Lord knows it felt
that steep...
Seeing as how my own expertise in the altimeter department peaked with that Cateye--which
I still use as my everyday cyclometer--I'm not the one to be talking with any
authority about the current state of the technology, meaning the advent and refinement
of the GPS units. For that, I turn to my club mate Lou Salz, an engineer with
Agilent and an all-around smart guy when it comes to crunching numbers. I asked
him a few questions about this topic, and his replies were so interesting that
I am simply going to turn this column over to him for awhile and let him bring
us up to speed.
I first asked him to refresh my memory about the thinking that went into that
original Avocet 50...
"The following URL points into the rec.bicycles FAQ. This pretty well documents
Jobst Brandt's views and contributions to the Avocet 50 Algorithm. He explains
the 10 Meter (~30 foot) algorithm too...
http://yarchive.net/bike/altimeter.html
"I'll restate this a little and say that barometric altimeters are essentially
measuring air density. The air gradually becomes less dense as you move away
from the center of the earth. Gravity is holding in the air molecules. The effect
is a somewhat smooth function: as you go up in elevation, it gradually decreases.
But there are certain atmospheric conditions that affect air density. Colder
air is more dense. As air cools, the molecules are bouncing around against each
other less rapidly and will more easily fit into a smaller space. So cold air
tends to be more dense and heavier and will drain into low spots, particularly
at night when the air is calm. If you are riding your bicycle along a road that
is fairly flat but is up against higher terrain, this effect can be quite pronounced.
Cooler air draining off the hillsides and down small creek canyons causes the
air to be more dense in some places at exactly the same elevation as other places.
This effect is small, but not completely negligible. Altimeters are designed
with temperature compensation to help correct for this error. The problem is,
temperature sensors do not respond all that fast. Sometimes there can be a short
delay where the barometric altimeter registers a lower number. It is corrected
shortly, or as you leave the cold pocket of air quickly and things return to
normal. But if your cyclecomputer was measuring every little change, it would
have just added 10 or 20 feet to your ride without you having done any climb
at all.
"Jobst defined the algorithm in the Avocet 50 to ignore a climb until you have
climbed more than 30 feet. Then it adds the 30 feet on and continues adding from
there. So if you start a gradual climb it would read 0 after you climb the first
10 feet. It would still read 0 after you've climbed 20 feet. Then at 30 feet
it would read 30. At 40 feet it would read 40. So it isn't taking away from bigger
climbs at all. It is just removing any changes smaller than 30 feet that are
not part of a bigger elevation change. Avocet patented this idea. There are other
ways to solve this same problem, but this is a simple way that works pretty well. The
controversy comes because it doesn't count things like smaller freeway overpasses
and railroad underpasses. Jobst has been clear about what he did and why he did
it. Some don't like it. Many don't understand it. To me it is a logical tradeoff
that produces reasonable numbers. I personally believe the Avocet numbers are
better than the Cateye, but neither is perfect. Such is the nature of just about
any measuring device."
I then asked Lou to revisit a comment I had heard him make once that the amount
of computing power in a modern bike cyclometer is greater than that in the first
space capsule to land on the moon...
"On the computer that put a man on the moon, let me clarify. The Apollo
space capsules had a very limited amount of power and space available. There
were on-board navigation computers. They were designed in the early 1960's and
were very, very primitive by the standards of even computers that were available
by the time the flights were actually flown. Computers were very limited and
took a lot of electricity and generated lots of heat. There were some fairly
powerful land-based computers that were used to compute aspects of the flights,
but that information was generated ahead of time or was relayed up to the space
capsule. These were the sorts of computers that filled whole buildings that had
special air conditioning systems and crews of dozens of technicians to keep them
running.
"A modern GPS like my Garmin Map 60 CSx contains two fairly powerful little computers.
One of the computers does most of the user interface and map calculations. The
second one is part of the chips that receive the signals from the satellites.
Both of these computers are likely considerably more powerful than anything that
was on board the Apollo spaceship. They are both considerably more powerful than
the desktop computers of not that many years ago. This device contains an optional
slot for flash memory where I loaded a small micro SD memory chip (purchased
at Costco for about $25) which is large enough to hold a map of every public
roadway in the entire United States, at the same time. The new Garmin Edge 705
has all these features in addition to the heart rate monitor and normal cyclocomputer
features. I have one on order and it will likely be mounted on my handlebars
on the Seven before you write your article. It is an amazing piece of technology.
"Having been involved in the early development of the GPS system in my days at
Rockwell Collins (in Cedar Rapids), I find it astounding that these things can
be made so small. In 1979, we all speculated that one day the receiver might
be made small enough to fit in a packback-size package that a single soldier
might carry to help his platoon navigate. Little did any of us realize just how
small it would eventually be and that it would be feasible to outfit everyone
with these devices. Cell phones are starting to come out equipped with GPS receivers.
Very shortly every cell phone might be able to carry out these cyclocomputer
functions if the right software is downloaded. Picture a future iPhone that can
play all the music in your library, call all your friends and do all the cyclocomputer
functions at once. It will be possible very shortly and may already be done for
some high end models.
"I also have a slightly older Garmin GPS. It is a Garmin eTrex Vista. It was
a very nice little GPS and worked well on my handlebars. The memory was not that
large. Newer versions of this same model, the eTrex Vista CXs are much more capable
in the same nice little form factor. They keep getting better. About every
two years Garmin completely replaces their product line with newer and better
models. They continue to make their own products obsolete. They can sell them
for big bucks because of all these new features. The 705 model I am buying can
be equipped to read power out of a special bicycle hub. That aspect isn't my
thing, but the racer kids are all drooling to get one. I guess I don't want to
know that much about my pedaling these days. Both of these GPS models contained
a barometric altimeter. The altimeter works much like the ones in the Avocet
50 or Cateye. The GPS signals can also provide some altitude information. It
can be somewhat inaccurate at times, but if you take the strengths of the barometric
altimeter, which is quite accurate in a relative sense, and combine it with the
GPS signals, which are good in an absolute sense, you end up with a self-calibrating
barometric altimeter. The other thing the GPS-based units buy you over more traditional
models is the memory where your track data is stored. You can see exactly where
you went and what the elevation is at each point of data that was collected.
It collects a data point once every 100 feet for so. That is where I capture
the raw data for my map and profile work.
"The real attraction for me is the navigation capabilities these devices bring.
It isn't that big a deal when you are riding the normal roads we ride every day.
We know where we are going and what is coming. Where they are great is when you
are in a new city trying to find your way to your hotel. It was great on my New
Zealand tour. I generally put my hotel or backpacker lodge into the device the
night before. I planned the route the way I normally would. I could look down
and see how far I had to go. As I got into the town, usually late in the day
and tired after a full day of various adventures, I was headed for the barn.
With the GPS map display in front of me, I could see exactly where I was in this
new town and where my hotel was. It left me much more free to explore and sight
see and not need to focus as much on navigating.
"One other aspect of this that many people are missing is that GPS-based bicycle
computers are stealing the high-end cyclocomputer business from the traditional
players like Cateye and Avocet. Both Cateye and Avocet once had fairly expensive
high-end models that did elevation. These GPS-based units have now captured most
of that market. Cateye and Avocet are now relegated to selling the very low profit,
low margin commodity units. There isn't much money to be made in that, even though
the volume is bigger. People like Garmin and Magellan are going to reap the big
profits off the state-of-the-art devices that will fund further R&D and more
types of devices. Polar had been working into this market too with their heart
rate monitor-based units. They have been getting the higher end of the market
in recent years. They will now be squeezed too unless they add GPS features.
I see the GPS-based units eventually completely displacing all but the very cheapest
cyclocomputers. As GPS receiver chips are made smaller and cheaper to fit in
cell phones and the like, companies like Garmin will be able to squeeze even
some of the lower end devices out of the market. They don't need the silly magnets
on the wheels and there is no need to calibrate for various tire sizes. It will
be fun to see how this plays out. Cateye seems to be spending more time on their
bicycle lights. That might be a wise choice. It is another somewhat high tech
area with new types of lights coming out. They are good at it, and as oil goes
up, more people are going to want and need bicycle lights."
Thank you, Lou, for what I at least consider a very informative dissertation.
We've probably gone on as long as we ought to with this for now. I have some
other thoughts on the subject, in particular concerning the creation of elevation
profiles, but I think I'll save that for another column on another day. For now,
take a break from the computer and go outside and climb some hills. Whether you
record all your elevation data is up to you.
Bill can be reached at srccride@sonic.net