I have become slightly obsessed with the idea of using an iPhone as a bike computer. What follows will be of little interest to anyone except gadget-nerd cyclists.

Current status

The iPhone has a lot going for it as a bike computer: it has built-in GPS and accelerometer features, wireless and wired connectivity, and a big screen that can display a lot of useful information. And there are a lot of apps out there for just this purpose. These typically rely on GPS for main functionality (although MotionX also uses the accelerometer as a cross-check, and can use the compass on the 3GS), and produce “tracks” representing each workout that can be used to log and analyze performance after the fact, as well as show instantaneous performance. Some apps emphasize a display of instantaneous performance, some emphasize mapping. Ascent hints at what’s possible—it has a desktop app and an iPhone app; unsurprisingly, the desktop app supports kinds of information that the iPhone app can’t gather.

Limitations and solutions

The iPhone also has some limitations, either unavoidable or arbitrary, that limit its utility as a bike computer. These are:

  • Battery life: certainly the main limitation. Keeping an app running with regular GPS updates can burn through the batteries in about 2 hours, and a lot of rides are longer than that.
  • No backgrounding: Once you launch the bike-computer app, you can’t do anything else. Many of the apps in this category are compensating by building in functions that let you do a lot of the things you’d want to break out for anyhow, such as shooting pictures, controlling music playback, and twittering (!). None let you accept a call. I’m guessing that although Apple has opened up access to features nominally controlled through its Camera and iPod app, it’s keeping access to telephony features walled off.
  • Lack of ANT support: ANT is a wireless standard used for heart-rate monitors, bike computers, and workout-oriented GPS receivers. It doesn’t have much use outside the world of gadgets for endurance athletics, and apparently requires a custom chip that operates in the unlicensed 2.4 GHz band (the same band used by Bluetooth and wifi, which the iPhone does support).
  • Tolerance for hostile environments.

Battery life is an unavoidable problem with any pocketable device that does as much as the iPhone does.

Backgrounding is a knottier question: it’s technically possible (and in fact some of Apple’s own apps can run in the background), but there are legitimate reasons to limit it.

ANT support would require new hardware, likewise a ruggedized case. Currently the only way to get ANT signals into an iPhone is via a product called a smheartlink which rebroadcasts the ANT signals over wifi and acts as a server; there are a few apps on the iPhone that support this, but this is an inefficient approach that not only requires carrying a separate gadget, it also requires that the phone have wifi enabled, shortening its battery life. This product was developed before third-party apps had access to the accessory port: it was a necessary kludge at the time, but now it’s just a kludge. And there are ways to synchronize GPS tracks (as recorded on the iPhone) with data logged by ANT devices after the fact, on the desktop, but this would prevent some of the more interesting potential uses for a bike computer. It’s not inconceivable that Apple might want to add ANT support directly to the iPhone—their previous collaboration on the Nike+ suggests they’re interested in fitness applications, and in fact the chip inside the foot pod for the Nike+ is made by Nordic Semiconductor, the creator of the ANT standard. For all I know, the iPhone could gain ANT functionality with a firmware update.

A ruggedized housing isn’t in the cards, but is trivial to add.

What could be

All of this suggests that in order to make the iPhone into the be-all, end-all bike computer, it needs additional hardware. I envision a bike mount that includes 4 AAA batteries to extend battery life, an ANT chip that passes along signals via the accessory port, an enclosure that covers all the phone’s openings, and a porthole and mirror allowing the camera to take pictures while the phone is in the mount. (Taking pictures en route, especially at key waypoints, is useful for sharing routes, aside from just being a desirable feature in general. What I’d really like is for the phone to continuously buffer the last minute of video, and save the recording if I crash, which would be easy to detect thanks to the accelerometer. That would probably chew through the batteries though)

Ideally, the phone’s operating system would also be updated. The most obvious change would be to allow third-party apps to run in the background (which is possible on jailbroken phones). This is also more battery-intensive. Apple’s partial solution to this—which only works for apps like instant messaging, where a persistent Internet connection is desirable—has been to create an Internet “delegate” that the app hands off its Internet connection to when it quits. For the mooted bike computer to really work, Apple would need to create a GPS delegate and an accessory-port delegate to continue accepting telemetry from them when the app is not running. If Apple really wanted to support athletic uses of the phone, it would build in ANT support and possibly an inclinometer (as I understand it, the accelerometers in the phone get thrown off when the whole phone is in motion).

Assuming that these changes were made, what possibilities would that open up?

Right now, electronic training gadgets fall into three broad categories:

  • Displaying your current stats (speed, distance, cadence, altitude, etc)
  • Logging your workout for later analysis. These will take frequent snapshots of your stats and let you slice and dice the data when you get home, post workout details online, etc
  • Dictating your pace. These act a a sort of workout metronome, indicating whether your speed, or heartrate, or whatever is above/in/below a target zone, counting off intervals, etc.

Many of the more sophisticated gadgets handle all of these functions to some extent, and we’re starting to see an interesting combination called “ghost racing” where you pace yourself against a previous performance (your own or a friend’s). This is a step towards one of the ways I can imagine the iPhone would act as a coach, not just rigidly pointing out whether you’re on pace, but continuously analyzing your performance in terms of your history, using multiple variables and helping you to find weak spots.

With adequate telemetry, a bike computer can measure speed, cadence, heart rate, hill incline, and altitude. Something with Internet connectivity could also pull in weather reports to take winds and temperature into account, and could even ask the user before the workout about the most recent meal eaten and subjective sense of fitness. In short, it would be a full-bore dataporn machine. With all this data, a rider going over the same route multiple times—or even similar stretches of terrain on different routes—will generate a body of data that might allow for an analytic engine to find that a rider is shifting too late on certain hills, or could dig deeper at the end of a certain ride, etc. The gadget could provide this kind of information in real time, perhaps offloading some number-crunching to a desktop computer when off the bike, or to a cloud-based computer. The iPhone’s bluetooth support means that a rider could wear an earpiece to receive spoken cues like “downshift now” rather than needing to watch the screen (I can imagine an entire market springing up for different voices—train with Eddy B!), and also let the rider issue spoken instructions to the iPhone: aside from the obvious benefit that riders wouldn’t need to distract themselves by messing with the display, I’ve also found that the touchscreen is unresponsive when my fingers are sweaty.

Update: Apparently someone at Wired is thinking along similar lines.
Update: Looks like Pedalbrain read my mind.