If you want to know how fast you're going and how far you've been, you need a cycle computer, a small electronic widget that sits on your handlebars and measures your progress. You can get a surprising amount of performance for your money.
How much you pay for a cycling computer depends on the functions you want. You'll pay more for a wireless sensor than for one connected to the head unit by wires, for example, and still more if you want functions like a heart rate monitor, cadence sensor of ability to pair with a smartphone.
We've found the best deals on cycle computers in a range of categories, from brands with good reputations for reliability and usability. Before you wade in, though, you might want to read our general guide to cycle computers.
You can get basic computers from manufacturers you've never heard of for as little as £3 from Amazon, but on the rare occasions they have reviews, they're not exactly rapturous. Our selections are a little more conservative.
French sport superstore chain Decathlon is always worth a look for a bargain, You only get five functions in this minimal unit — speed, average soeed, trip distance, total distance and clock — but for just eight quid what more do you want, or really need?
Just over a tenner gets you this nifty little five-function unit from CatEye. It's supposed to be £14.99, but CRC has it at the price above, and CatEye's reputation for reliability makes it a good deal at that price.
It's a wired unit and tells you speed, maximum speed, trip distance. odometer and time. It comes with a universal mount but the cable is only long enough to reach the front wheel.
If you want a few more functions and a bigger screen with more data, another few quid gets you this CatEye model. You get a stopwatch as well as a clock, and it'll attempt to work out how many calories you've burned. That's really only useful for comparing the amount of work you've done between rides; don't hit McDonald's hard just because it says you'd burned off the equivalent of three Big Macs.
For just £20 this is one of the cheaper wireless computers we've found from a significant brand (though if you're really strapped, the B'Twin 120 is even cheaper at £12.99). It has a big display, with a backlight, and features include average and maximum speed, trip and total distance, clock, stopwatch and speed comparison against the average so far.
We've chosen a lot of CatEye computers in this selection because they're widely available, reliable and easy to use. The Velo Wireless is the company's cheapest wireless computer but gets solidly positive reviews.
In effect, it's the wireless version of the Velo 9, though it lacks that unit's calorie guesstimate function.
If you want something a bit more posh, the skinny version of CatEye's Strada computer is available heavily discounted. It has a bigger screen than the old Strada, and a comes with a slimline sensor so it's less obtrusive on your bike.
As well as a full range of functions, it has a second trip distance meter, so you can, say, measure intermediate sections of a long ride.
Heart rate computers
Cheap computers that also tell you your heart rate are rare, but this super-cheap unit from Argos is probably worth a punt.
You get your usual computer functions, plus current and average heart rate and it even gives an estimate of how many Calories you've burned.
Okay, we have to admit a bit over 60 quid isn't exactly cheap, but the Ciclosport CM4.41A is the least expensive computer we've found that gives you both a heart rate monitor and an altimeter.
There's a decent suite of heart rate functions too, including target zones and heart rate-based Calorie consumption.
Computers that can use the Global Positioning System to find your precise location, and speed without wheel sensors can now be found for under £50 if you shop around. We've saved you the trouble.
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.
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.
This GPS watch from French sport store giant Decathlon provides a basic set of GPS functions, works with a Bluetooth Smart heart rate strap (Decathlon's is £27.99), 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.
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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.