Well, after a few rides with the iPhone app Cyclometer I'm firmly of two minds. On the one hand, I like all the features of the app, including the route maps, all the data that's collected, etc.

On the other hand, I miss being able to glance at my handlebars and see how far I've come (I keep my phone in my bag behind the saddle), or how much more it would take to reach a certain amount of miles. So if I'm out there, and I've ridden for a while, I find it a bit motivating to see that I've gone x.5 miles, and if I just keep going for another 3.5 miles, I'd reach Y. With the phone app, I have to dismount, fire up the phone, and take a reading. Other than that, I like the app.

So maybe I'll get me an inexpensive, wired bike computer (not a GPS unit) after all, and use both it and the app.

I think I could make this decision in less than five months, but who knows?

Hope you can Gary, I am a typical engineer (over analysis, and research) I guess and throw in the hard headed Marine thing. At least I purchased the CAAD 10/4 in a week rather than 5 months:twitchy:

Bill

Of course one issue with using your phone as a bike computer is that if you drain the battery and then need to make a phone call you're SOL. With two devices if the GPS battery dies you can still make a call. Or stick a couple of AA batteries in your saddle bag so if the GPS needs new batteries you've got them right there.

DG,

You live on an island! Just how many places can you go that you need a GPS? Trying to figure that one out.

I'll be looking into some sort of GPS unit when my wife retires and we start doing rides throughout the state and the U.S. Right now I just ride the same MUP and mostly the same club rides so having a GPS device isn't a necessity at this point. I have a GPS head that attaches to my old Dell Axim PDA (with software) but that sucks the battery dry in about 40 minutes. I guess I could just turn it on when needed to save on battery life or just break down and get a Garmin.

I wanted the smart phone not so much for the GPS, it is handy and neat to have, bit to use the ANT+ capabilities for data acquisition while I ride. Yep, I am an engineer and a geek, bit it is still entertaining to me.

Bill

As with everyone else, I like what *I* purchased for a similar issue as yours: The Garmin 500. I'm a beginner brevet rider but our needs are similar.

- battery life is excellent and is simple to extend with a battery extender.

- It's not perfect in that it doesn't have traditional maps but you can load your course into it with a slight bit of effort. If I can figure it out, anyone can. My phone stays in my bag and I can always use it as a back-up. I have a very good sense of direction which helps also. Some of our brevets are provided with turn-by-turn directions via the "ridewithgps" site. The Garmin 500 will accept that site's tcx file which does contain turn-by-turn directions. You can see the next ride here and view the various options available for downloads. This, again, is specific to some but not all of our brevets. For those other brevets, I can use a mapping program to create the course and then download it.

- it accumulates data and I haven't had an issue yet. I have a 400-km event in two weeks - we'll see what happens.

FWIW, I also print off the cue sheets, print them and trim them down to something manageable and then laminate them for use in case the GPS goes tits up.

I purchased an Edge 500 off Ebay for $200, free shipping.

I like it a lot. It's a big improvement from the 305.

It's only a bit bigger than the Sigma computer it's replacing.

So does Stapfam.

Here are a few random thoughts, offered after the realization that I haven't been able to follow a lot of this discussion.

First, about using a GPS unit to track mileage. A GPS unit is a sampling device. So is a cyclomputer but with GPS the sampling interval is very much greater. Also a cyclomputer does a linear measurement whereas GPS attempts to localize in 3-D, or at least 2-D. Here's what all this means.

Suppose you ride in a straight line. Your GPS samples at some interval, but also places you as moving sideways by its average positioning error. If your lateral sampling error is half the sampling distance, i.e. evenly distributed between left and right, your "distance travelled" appears to be 11% greater than your forward progress. On the other hand, successive position samples can be such one is some distance from an upcoming turn, and the next is some distance around the turn. The distance travelled will see you as having cut off the corner. So your apparent distance travelled depends on the reliability GPS reading, not always great through trees, and your particular route. It isn't surprising that GPS does not produce readings precise enough for training.

There seem to be many possible goals for a GPS unit. One is to track where you have ridden. Another is to provide instantaneous readouts of current speed and distance travelled. An inexpensive cyclomputer can do that. Yet another is to carry maps, and display them when required. Paper maps can do that, although not as conveniently. Yet another is to show you where you are, either continuously or when asked occasionally.

For riding through unfamiliar territory, especially while touring, the map access and "where am I" features would seem important, which is why I'm interested. I'm not sure maps need to be displayed continuously, which suggests that neither battery life nor display legibility are quite so critical.

Unfortunately GPS-for-bike discussions end up all sounding the same. I'd really like to see discussion driven by the intended uses, and then specific products recommended based on that discussion. Thanks!

My only reason for wanting a GPS equipped computer would be the mapping feature. When my wife and I start cycling in areas of Florida and the U.S. that we are not familiar with, the maps would be nice to get us back to our starting point if we get lost. I don't really care about altitude readings as Florida is pretty flat but my wife's Garmin Forerunner CX405 will have that info in the event we get curious.

Both Florida and the U.S.! Is that an inclusive or exclusive and? :)

I'm working on a migraine and this post just made it worse.

It's not your fault.

A perfect recipe for a tombay. Just sayin'

That might be part of the problem. It's beautiful out there....and I'm in here.

Sorry about your migrane. That's just the way the world works.

Here's a pic to illustrate, purely hypothetical, mind you.
http://bikeforums.net/attachment.php...hmentid=239118
On the left is an example of how lateral errors can increase the apparent distance travelled. The numbers shown assume that for every increment x travelled forward there is a lateral error x/2. This isn't a true picture but one can suppose that there is a "typical" sampled interval both laterally and forward. The forward errors from sample to sample will cancel because for each interval too short the next will be too long. The lateral errors will randomly swing left and right. With the x/2 assumption one appears to travel the hypoteneus of the triangle.

On the right is an example how sampling the course results in corners being cut off. The apparent course from point to point is less than the actual distance travelled. The greater the distance between points, the greater the possible error.

On a real course the apparent distance travelled could be either less or more than actual, depending on how tight the curves were and how precise the GPS positions were. In any case, one would surely like better than +/-6% precision for training purposes.

Good score! You did well.

What you say is correct, but I think my Garmin Edge 500 does not wander laterally nearly as much as your example. The plots of my ride look like the points fall quite close to the actual path, even at fairly high zoom.

Now for altitude, your argument is 100% true. If you use the raw data directly, the total ascent might be twice what is displayed on the unit (which has data smoothing for altitude). It may smooth the distance data too, I never thought of that, but I doubt it is needed.

I have the speed cadence sensor, but I haven't figured out how the data from the sensor is used. I have the unit set to auto stop at speeds less than 3 mph. The unit goes into autopause occasionally on climbs of about 6 mph through tree lined ascents. I am pretty sure it is losing the GPS signal and pausing because it thinks I have stopped.

I would think it would use the more accurate speed sensor over GPS, but it appears to me that GPS rules until the signal is completely gone. Since the plots don't show any sign of the pauses, it may be that the stored data uses the wheel sensor, while the display sticks to GPS.

Oh, I'm sure my example was extreme. After all, it did assume the error was equal to the sampling interval, which is highly improbable. I was merely trying to illustrate how there could be error at all, both high and low.

There is one more source of error I didn't show. That is when you get one or more more bad positions because of momentary poor satellite readings. One bad data point which misplaces you by half a mile can ruin your whole day!