The iPhone has proved to be rather adept at replacing other pieces of hardware. The combination of portability, a big screen that allows it to mimic any interface and an open (ish) App Store means that we are continually surprised at what people can make it do.

Today, it’s the turn of the bicycle. It turns out that many of the geegaws you might buy at the LBS (local bike shop) are already available as downloads from the iTunes Store. Here are our favourites.

CycleMeter

CycleMeter’s hideous interface contrasts with its truly astonishing Rube Goldberg setup. The app works as a cycle computer, showing a readout of your speed, distance, average speed and trip time. It works with any iPhone and also the iPod Touch. That’s right, the GPS-free iPod Touch. How on earth does it do that?

A cycle computer counts the revolutions of your wheels and, because you have already told it the wheel’s circumference, it can work out the rest. Purpose built devices use a magnet on the spokes and a detector on the fork.

CycleMeter uses sound to accomplish the same thing. Put a small plastic tag on one spoke so it hits the fork on every revolution. Then run the cable of your earbuds down the fork and secure the microphone next to this point. The tick, tick, tick of the plastic tab is picked up and the rest is done in software.

A truly heroic hack, we think you’ll agree, and just $0.99 (plus the cost of replacement earbuds after every passing shower). It can’t be long before there is a Bluetooth spoke-widget that can talk directly to the iPhone, though. Combine with proper trip-log software and you’d have a real winner.

Product page [iTunes]

BrakeLights

Just as ingenious as CycleMeter, although slightly less jerry-rigged, is BrakeLights. It adds a brake light to your bike, whether using cantilevers, side-pulls, disk or running a no-braked fixie. Strap it to your bag or back, screen pointing behind you, and ride. The app uses the accelerometer to detect when you slow down and flashes a red light on the screen. $1.

Product page [iTunes]

Back Light

Similar to BrakeLights, the awkwardly named Bicycle Back Safety Flashlight is another $1 lamp, but this time it stays on all the time you are riding. It also lets you write messages to those following you. The suggestion is the word “STOP”, but we imagine that you, dear reader, could manage messages both more creative and abusive.

As an everyday light replacement the battery drain might put you off. But in an emergency, why not? Especially if you have an always-connected iPhone. Imagine: “Damn, I forgot my back light. Wait, I’ll just download a new one.” $1.

Product page [iTunes]

Gear Calculator

Bicycle Gear Calculator is rather specialized, but if you need it, it may just beat doing hard sums in your head. The application works out gear ratios for you, based on crank lengths, wheel sizes and cog/sprocket sizes. It’ll even tell you what ratio you should ride to maximize tire wear based on the pattern of skid patches on the tires themselves. $5

Product page [iTunes]

Speed

Speed is a more practical speedometer, although you’ll need an iPhone 3G or better to use it. Instead of the dangerous sounding wires-and-plastic approach taken by CycleMeter, it uses the iPhone’s GPS to work out your speed. It also has a rather lovely interface, although it might be more suited to a car dashboard than a bike’s handlebars. Works in both kph and the obsolete mph. $1

Product page [iTunes]