The iPhone 3G, with its accelerometers and GPS chip, has spawned a unique category of programs in the App Store: automobile performance measurement tools. These programs use the iPhone's GPS chip to measure your vehicle's acceleration and speed (and via this data, horsepower), and the accelerometers to measure the g-forces applied while turning and braking or accelerating. If you're an auto enthusiast, the opportunity to measure these things using your iPhone and a relatively cheap piece of software is quite appealing--dedicated performance monitoring tools can be quite expensive. Since there are now quite a few programs in this niche, varying in both cost and feature sets, I set out to find the best of the best.

At least, that was the intent heading in. Unfortunately, my request to rent Portland International Raceway for a week was summarily rejected without discussion--it seemed perfectly logical to me, but alas, it was not to be. All kidding aside, this class of applications is really not something that can be safely or thoroughly tested on public roadways--many of them measure quarter-mile speed and time, for instance, and even the most pedestrian of vehicles will be well in excess of the posted speed limit at the end of the quarter-mile. Beyond the speed issues, though, there's simply no safe way to evaluate all of these programs' features on a public road.

The other problem in evaluating these programs is that in order to judge their accuracy, I'd need a suite of test equipment similar to what you've find at Motor Trend or Car and Driver. Unfortunately, neither of those fine publications shares lab space with Macworld, so the best I'd be able to come up with is a stopwatch (while someone else was driving, obviously) to compare acceleration measurements--but only up to posted speed limits on deserted back roads. This would, however, leave the key features of many of the programs--G-force and horsepower figures--unconfirmed.

Given these limitations, I felt it wasn't fair to these programs to attempt to review them in a traditional manner--I lack both the track facility and the equipment needed to accurately gauge their performance. As such, I don't feel it'd be fair to assign mouse ratings, because I can't accurately test these programs. Instead, I thought I'd provide a brief overview of the programs that seemed to offer the most interesting and/or useful feature set--so that if you're thinking of plunking down your money, you'll have at least some sense of the programs that seem to stand out from the rest, and can use that information in making your purchase decision.

For more Mac news, visit Macworld. Story copyright Mac Publishing, LLC.