GPS-enabled cycling computers can record where you've been on your ride, logging your speed and other data every second or so, and providing you with a rich and complete log of each bike trip.
That's useful whether you're training and want to track effort and hills against speed, or whether you're exploring and want to know where you've been. There are probably as many ways of using GPS on a bike as there are cyclists.
GPS-enabled bike computers work by picking up signals from a network of satellites that orbit the earth at an altitude of about 20,000km. These Global Positioning System satellites use atomic clocks to transmit time and position very accurately. A GPS receiver uses the signals from several satellites to work out its position to within five metres.
US-based company Garmin dominates the field of GPS-enabled cycling computers, partly because it has a wide range of good quality products, partly because it was first to market with the Edge 205 and 305 models in 2006.
As GPS receiver chips have become more widely available in the last few years, more manufacturers have entered the market. GPS-enabled computers are available from traditional bike computer makers such as CatEye and Sigma, as well as new players like Lezyne, Bryton, and Mio.
If you have multiple bikes, a big advantage of GPS computers is that you can swap them from one to another without faffing changing set-up.
There are two types of GPS bike computer. Less expensive units use GPS to replace the sensors of a traditional bike computer and display data such as speed, trip distance and time, as well as recording your ride for later analysis.
More expensive GPS units have full satellite navigation functions, with map display and turn-by-turn navigation of a preset route, or one the computer generates on the fly.
Some GPS units are able to pick up signals from heart rate monitor straps and on-bike sensors to log additional data such as heart rate and cadence.
You can get started with on-bike GPS logging for as little as £50 if you shop around. Mapping GPS units start around £200 because of the larger screen and battery and more sophisticated electronics.
For this price we don't expect it to be amazing, but Memory Map's base model on-bike GPS is a bargain if what you want is a simple bike computer and data recorder without bells or whistles. If very long rides are your thing, it'll go 28 hours.
Either this GPS unit with ANT+ for your heart rate and cdence sensors, Bluetooth to talk to your phone and an altimeter is an incredible bargain, or someone has stuffed up and set the wrong price. We suspect the latter as it's also listed for £79, in which case if a data GPS is what you need, grab one of these quick before they notice.
If you want a bigger screen that displays more data at any given time, this inexpensive unit could be just what you're looking for.
Unusually for a budget GPS, the Memory Map 270 has a barometric altimeter for an accurate indication of how much climbing your rides include. It's ANT+ compatible too, so you can add a heart rate sensor or speed/cadence sensors. This isn't a bad price, but shop around: Amazon has previously listed it for as little as £50.
Another good-value base model from one of Garmin's competitors, the Rider 100E has a decent-sized, customisable screen, and works with Bluetooth and ANT+ sensors so you can add heart rate and speed/cadence measurement. There's also a version — the 100T — with a heart rate strap and cadence sensor for about £100, but we've not been able to find any retailers who claim to have it in stock.
If you just want to log your rides then this GPS watch from French sport store giant Decathlon provides a basic set of GPS functions, has a built-in heart rate monitor (and works with a Bluetooth Smart heart rate strap), communicates with your Android or iOS phone and outputs GPX files so you can upload to Strava or your other favourite activity website.
If you're one of those strange multi-sport types, you can use it for running too.
The base model in Garmin's GPS range seemed decent but a bit expensive at £110 when it was first launched, but you can now find it for around £90. Given you can get an Edge 25 for around the same price (see below), we'd get that instead.
The Edge 20 logs your route and standard bike computer speed and distance data, and lets you race yourself against previous rides on the same route.
It's otherwise fairly basic. It can't connect with a heart rate or wheel sensor, unlike more expensive units with ANT+ or Bluetooth connectivity. But it's easy to set up and use and works with Garmin's excellent Garmin Connect website, with which you can set goals, plan rides and track your training.
The Lezyne Mini GPS computer is an easy-to-use option that gives you basic ride information on your handlebar along with the ability to upload, store and analyse your rides on Lezyne's GPS Root website.
If you're a bit of a technophobe or you just aren't interested in masses of ride measurements, the Lezyne Mini GPS might be a good choice for you because it's very simple to use.
The 2017 version adds turn-by-turn directions and some mapping functions.
This Garmin 200 competitor is compatible with ANT+ sensors and is straightforward to use.
Its use of a USB cradle instead of simply plugging in a cable is a bit old school and it can take some fiddling to get the accompanying CatEye Sync software to work with a PC or Mac. For the price, though this is a decent little computer.
The Edge 25 is Garmin's smallest ever GPS computer, and along with its diminutive size, Garmin has nailed the user interface, which is a dream to use.
If you don't need route mapping and navigation and just want to track all the important metrics like speed, distance and elevation, the Edge 25 does everything you need.
It's light, just 25g, and takes up very little space on the stem using the supplied quarter-turn mount that Garmin has been using for years. The 128x160 pixel display is small and grayscale, but it's pin sharp and the new lighter font makes it easy to see at a glance how fast you're riding.
As far as we know this is the cheapest bike-specific GPS with map display, and unlike some other inexpensive mapping GPS units it will also work with heart rate and other sensors and some power meters. It has a touchscreen too. For £174.50 you can get it with a heart rate strap.
It uses Open Street Map files for its mapping, which helps keep the cost down. This open source mapping effort has improved in leaps and bounds in the last few years, but it's still not quite as good as Ordnance Survey maps. For this price, though, you really can't grumble.
Since its launch, which was greeted with favourable but not gushing reviews, the V650 has acquired lots of functions via firmware updates. Riders who've had recent versions are generally very happy with the ease of use, bright screen and features.
One downside is that the V650 uses Bluetooth Smart to communicate with sensors rather than the more common ANT+. That means you don't have quite the range of options as with an ANT+ device like a Garmin, but there are still plenty of options. The only power meters that will work with the V650 are those made by Look, PowerTap, Stages and the Wahoo Kickr.
Oddly, the V650 doesn't work with the cheapest power meter we're aware of, the £350 4iii Precision, but its cheaper kid brother, the M450 does (£123.50 with a heart rate strap). That means the cost of entry of training with power is now under £500.
Our official grumpy Northerner, John has been riding bikes for over 30 years since discovering as an uncoordinated teen that a sport could be fun if it didn't require you to catch a ball or get in the way of a hulking prop forward.
Road touring was followed by mountain biking and a career racing in the mud that was as brief as it was unsuccessful.
Somewhere along the line came the discovery that he could string a few words together, followed by the even more remarkable discovery that people were mug enough to pay for this rather than expecting him to do an honest day's work. He's pretty certain he's worked for even more bike publications than Mat Brett.
The inevitable 30-something MAMIL transition saw him shift to skinny tyres and these days he lives in Cambridge where the lack of hills is more than made up for by the headwinds.