Cycle computer vs GPS

So as not to hijack the Loas threads, I'll start a new one. I'd been
thinking of getting some sort of cycle-computer, but then I saw
Nathan's graphs from his Forerunner GPS which have speed, heartrate and
altitude. Whoa!

Does it measure speed accurately? Because, holy cow, it would be cool
to see all the data that Forerunner hacks up when you finish a ride!
Why bother with a cycle-computer at all?

Cycle-gadgets are cheaper, right? And I suppose if one prefers the
device on the machine rather than the wrist.

Please discuss.


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Hello Stevyo,
I have the Garmin Foretrex 201 which I'm happy with. I chose the
Foretrex because it has WAAS which is more accurate than the forunner.
It often say's 19 feet accuracy. I think elevation is less accurate on
these devices, but I don't how what the elevation accuracy is.

It's handy on your wrist, you can check the display and change the
settings easily.

There is a lot of function to these devices that I haven't used.

I wish I always wore it. 2 weeks ago, I wondered from the park into a
neighborhood, got turned around and came out 5 miles from the park. It
was 38 degrees F and I had not worn a coat, just a T-shirt and jeans. I
had left the unit in the car. I was freezing. I'm sure I could have
back-tracked on the map to find my way back if I had it.

The computer interface isn't documented well, you'll need to track that
down. I got the interface to work once, but the trial software I used
expired and I didn't want to spend the cost $50. Maybe someone will
recommend a good cheap, or free program.

I'm no expert on this device.

Amazon had the best price I could find.


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Chrashing

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Ken
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I just noticed, 'Garmin has introduced the next generation 205 an 305
units.' (http://tinyurl.com/afta7)


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Chrashing

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Ken
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The new GPS units that include heart rate monitoring and other fitness
features are cool. Something like that is going to be on my want list
sometime soon.

But GPS does have limitations. It will only give you decent accuracy
for speed and distance when it can get good reception. At times it
will not be able to get any reception at all which means that it is
only guessing or not displaying speed or distance at all while it is
out of reception.

Things that affect reception and accuracy are satellite geometry in the
sky (which is of course constantly changing), buildings nearby
(reception in a downtown area with skyscrapers will be more difficult
than in areas with lower buildings or no buildings at all), trees
overhead, how many leaves are on the trees, how much rain is on those
leaves, fog, rain, snow, how the GPS antenna is oriented, you body can
even block the signal. Putting your hand over the antenna can be
enough to block the signal. So there is lots that can affect accuracy
and even whether or not you'll be able to get a lock on the
satellites.

If you're really interested in instantaneous speed readings and
accurate speed readings then a traditional cycle computer that has a
magnet on the wheel will give better results.

If you're looking at GPS units now it is better to go with one of the
new models that includes the newer and more sensitive GPS chips. They
have better signal reception and better battery life. For Garmin units
that new chip technology is by SiRF. Here's 'Garmin's Press Release
about the SiRF chip'
(http://www.garmin.com/pressroom/corporate/083005.html). You'll have
to dig around to find out which of the newer Garmin units are using
that chip.

For accuracy the number that the GPS units report as accuracy (like say
20 feet of accuracy) is just a guess based on satellite geometry in the
sky and not anything to go by. The actual accuracy could be very
different. Again, that number is just a guess and not something that
you should go by.

GPS units don't always do a good job by themselves for altitude or
elevation info. Their first priority is to get the 2D location right.
The 3D info (elevation) is secondary. 2D location is going to be more
accurate than the elevation. So if the unit says you've got 52 feet of
accuracy you can figure that the elevation accuracy is going to be
worse than 52 feet. 2D location requires a lock on at least 3
satellites. 3D location requires a lock on at least 4 satellites. If
you want more accurate elevation readings you should get a unit that
includes a barometric altimeter that supplements the GPS calculated
elevation readings. The barometric altimeter will continue to get
readings even if there are no satellites in view and its accuracy is
also better.

Garmin has a good description of 'GPS technology'
(http://www.garmin.com/aboutGPS/).

WAAS is nice but it is not guaranteed to always make the GPS reading
more accurate. At times it can actually decrease the real (as opposed
to the reported) accuracy. WAAS will only improve the accuracy if the
WAAS satellite is in view. The WAAS satellite sits low on the horizon
so it can be easily blocked by trees, buildings, cliffs, etc. If
you're in an area where you are not likely to be able to pick up the
WAAS satellite it is best to turn that feature off. Out in the ocean
or up in a plane the WAAS works great because it is easy to see the
satellite. In the woods or in the urban jungle, WAAS is less useful.

Knowing what is going on with GPS and how to use it correctly quickly
gets in to technical matters. To use it correctly you need to know how
it works along with where and when it will or will not work.

I have an old Garmin Vista. It frequently loses satellite lock due to
tree cover when I go on muni rides. It also loses the satellites at
times when I go on Coker rides. It uses the older and less sensitive
GPS chip. The new SiRF chip should do better, but I haven't used a GPS
with that new chip yet to compare.


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The "Edge" is supposed to be the sh t for bicycling, from Garmin. It's
new.


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Thanks Ken, JC, and Mike! I've been reading up on these, and I'm still
not sure I want one bad enough to part with the $ yet.

A smaller unit would be my highest priority. When they can get cell
phone, camera, GPS, altimeter, a tire pump and maybe a good juicer all
in one unit, down to a wris****ch size, I'm getting it!


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steveyo

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steveyo wrote:
Thanks Ken, JC, and Mike! I've been reading up on these, and I'm still
not sure I want one bad enough to part with the $ yet.


Yes, they can get expensive. Especially if you get a GPS that supports
mapping cause then you have to buy the electronic maps to load onto the
GPS. Then there is the other gadgets that you'll get for the GPS, a
holster or a pouch, rechargeable batteries, etc.

Then after you get it you'll discover that GPS software on the computer
is generally frustrating to use. Most of the programs use a different
format for exporting and importing data so getting data to and from
different programs is more difficult than necessary. The UI on most of
the software programs is poor and frustrating. I generally end up
swearing and cursing when I have to do manipulation of GPS data on the
computer. I think most GPS software for the computer is written by
apes. Even the commercial stuff is lacking.


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Chrashing wrote:
Maybe someone will recommend a good cheap, or free program.



sport tracks. My favorite non-obvious feature is the "export to google
earth" but it's packed with useful features.



Amazon had the best price I could find.


Cabela's price matched the Amazon price. Other retailers might also.

-mg


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I was tired of breaking cycle computers, so I decided to get a GPS
instead. I got the Garmin Foretrex 101 (around $130 I think).

While I don't regret the decision, it has the following issues:

Since mine doesn't have rechargable batteries, and I only get about
12-14 hours from a pair of AAA batteries. Cycle computer batteries seem
to last forever, and you don't have to remember to turn them on or off.


Doesn't work in heavily tree covered areas or on very overcast days.

Unreliable top speed!! Since I like to go fast, it's a bummer that the
top speed reading is really only an estimate.

Still, its nice having something that's less likely to break since I
wear it on my wrist, and I love all the extra features.


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mgrant wrote:
(computer interface pgm)sport tracks. My favorite non-obvious feature
is the "export to google earth" but it's packed with useful features.

That is cool.


mscalisi wrote:
I was tired of breaking cycle computers, so I decided to get a GPS
instead. I got the Garmin Foretrex 101 (around $130 I think).

While I don't regret the decision, it has the following issues:

Since mine doesn't have rechargable batteries, and I only get about
12-14 hours from a pair of AAA batteries. Cycle computer batteries seem
to last forever, and you don't have to remember to turn them on or off.



so yours weighs 2.6 oz and the 201 (rechargable) weighs 2.75 oz.
Does wearing that weight on your wrist get cumbersome? Can you switch
wrists?


mscalisi wrote:

Doesn't work in heavily tree covered areas or on very overcast days.

Unreliable top speed!! Since I like to go fast, it's a bummer that the
top speed reading is really only an estimate.

Still, its nice having something that's less likely to break since I
wear it on my wrist, and I love all the extra features.


It won't work in your pocket, right?


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steveyo

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