Nudging ever so gently back on-topic...
Two "classes" of bicycle-mounted GPS have emerged to cover very different markets:
1) GPS primarily as training aid packed with street maps that allows integration of training and social media via cellphone-upload-assist. These seem to be generally better suited for training and laying out rides in smaller areas closer to home and civilization...a bit more like a GPS-equipped runner's training watch.
2) A full-on "Adventuring" GPS for use on- and off-road apart from (and not integrated) with a smart/cellphone. These can be pre-loaded with maps to allow direct navigation in unknown areas far from one's home ground, and do not integrate any training functions or means for uploading to social media/cellphone integration.
I went with the latter, preferring a Garmin Oregon 400T -- basically a hiker's GPS -- 'cos I could load it with City and Street (Garmin's designations) maps as well as Topos (topographical maps) for most of the world. While it will pair with Garmin's bicycle cadence reporting unit, it is really a field-standalone unit with greater capabilities in route planning and waypoint/track up/downloading provided via Garmin's MapSource and BaseCamp computer software and purchased or homemade maps. By selecting the appropriate maps and "profiles", I can use the GPS in the same way as I would a dedicated car unit -- it only lacks voice prompts but is otherwise functionally the same in that mode. I've also got my hiking trails, cross-country maps, etc. in full contour or with sat-photo overlays as I desire, and can make my own maps to scan and load into the unit. This is really handy if -- like me -- you set out cross-country or don't follow the roads or go on roads too small to have been mapped by the folks at Garmin. It is worth noting Garmin miss a *lot* of roads in the extremely rural/remote Western US -- particularly Nevada, in my experience -- so the topo maps and triangulating position by terrain and compass and paper/homegrown maps are really helpful.
From my previous deep involvement in geocaching, I know the later GPS-equipped smartphones work well even apart from cell-tower signals. However, earlier Assisted-GPS (AGPS) phones depended on a signal to work in a timely manner, especially if they have not been used for GPS work for awhile (i.e. a couple weeks or 20 miles from last location). They used cell-tower connections to download updates to their satellite-tracking algorithms. Such GPS-assist allows a device to predict where the satellites will be located in a given timeframe rather than searching the entire sky -- my camera works the same way for GPS-tagging my photos, downloading satellite orbits a month at a time).
The advantage of a smart phone with a dedicated GPS chip is they use satellites when they can; when they can't they use other methods to approximate location. Newer phones have other tricks as well -- they can use the IP address of your WIFI network to approximate your location. They can also triangulate your position using a cellular connection to spot your location to within a hundred meters or so, depending on how many masts they can see at the time. The downside to the later phones with GPS chips is they do motor through batteries pretty quickly, so if you want continuous tracking, they have to be powered by a dynohub or buffer battery. The same caveat applies to a standalone GPS used continuously, though some (Il Padrone's) have much better battery life than others.
Before selecting a bike-mountable GPS, I think it is worth asking yourself how you'll be using it, and where. Some simply excel at one kind of use and are understandably a bit lacking in other areas. If you're training for fitness and are a recreational rider who ventures in or near cities and wish the camaraderie or competition of tracking and sharing your fitness with or against others, then a GPS biased toward that use will make you happiest. If you're really going back-of-beyond, then perhaps a GPS dedicated to that market would better fit your needs, though lacking in fitness tracking and social-media connections. A gentle reminder in closing: It is always a Good Idea to take a belt-and-braces approach and pack paper maps and a compass and know how how to use them. GPSs -- like any gadget -- can fail, and it is surely nice at those times to still be able to navigate with some certainty. "Getting lost" means failing to know where you are in relation to your goal. Fix that, and you're set.
Best,
Dan. (...who doesn't leave much to chance when touring solo and unsupported in remote territory)
