Go faster in autocross: The apps, sensors and traces you need | Articles

What’s Out There?

The options for autocross data acquisition aren’t as numerous or advanced as the options for track use, but there are still some powerful data suites out there. Most prominently, SoloStorm was designed from the ground up as an autocross-savvy data capture solution. Although it works fine for track use as well, the feature package was designed for–and by–autocrossers and their specific needs. 

The basic package starts at $220 and uses an Android device’s internal GPS and accelerometer. But it can be expanded to draw data from more powerful outboard accelerometers, GPS devices, cameras and OBD readers. 

SoloStorm is powerful and flexible, but it does require a bit of knowledge of the Android workspace. If you’ve never used anything but iPads and iPhones, expect an intensive learning period before everything is seamless.

SoloStorm offers a powerful and versatile data suite for autocross, and one of its biggest strengths is its expandability. It can be run with just an Android smartphone or expanded with video, outboard accelerometers, OBD data and high-resolution Bluetooth GPS modules, like this one from Dual. Photography Credit: Courtesy Jesse Waymire (side-by-side video)

Our other favorite plug-and-play data system for autocross is the ApexPro. Like SoloStorm, ApexPro is also a full-featured track data system that can set up a non-looping, point-to-point course with a separate start and finish line–basically, the ability to record an autocross, something not found in many systems aimed at track use.

What makes the $589 ApexPro one of our favorite units is its ease of use and convenient form factor. The entire unit fits in your pocket and works with an external GPS receiver and accelerometer. 

The ApexPro was originally designed for track use, but the option to add custom start and finish lines makes it an exceptional and easy-to-use autocross data tool. Its compact form factor makes it easy to move from car to car, and its simplicity allows for nearly instantaneous setup. Photography Credits: Courtesy ApexPro

Pair it with an iPad or iPhone–Android options are in the works–and you have a powerful, easy-to-use data partner. Anyone familiar with iOS functionality will feel right at home and be up to speed right away. An OBD module is now available as well to add even more car-based channels to the data capture.

And as far as dedicated data systems that consciously cater to the autocross market, that’s about it. But some enterprising drivers have figured out ways to adapt other systems to autocross use. The VCM Suite from HPTuners and the TrackAddict and Harry’s LapTimer apps have all been used to track autocross data with varying success. In some cases, like the phone-based apps, the user typically sets up an autocross course as a segment of a track so the data is gathered from two separate points. 

Finally, GM’s built-in Performance Data Recorder, available in Corvettes and Camaros, can track some important data streams in an autocross situation, although it makes overlaying multiple data streams for comparison difficult.

What Do You Need?

What you need really comes down to what channels you want to monitor, but there’s often a catch in autocross situations: that seriously compressed timeframe for analyzing any data. Autocross grids can recycle in a matter of minutes, putting real pressure on drivers who want to review data. 

For this reason, we put a real premium on ease of use. Being Apple cultists from the days when Macs had mouses with one button and a wire, we tend to gravitate toward the iOS-based ApexPro. Users more comfortable in an Android environment could have better success with SoloStorm for the same reasons.

But what hardware do you need? That depends on the data you want to track and what you want to do with the info. At the most basic level, you should be able to generate, with a few clicks, a speed/distance trace that you can overlay with other speed/distance traces. After that, having a friction circle display is beneficial for analyzing corner entry and exit. 

Just those two channels can pay huge dividends, whether you’re running solo or sharing a car with a co-driver. 

Next, we’d add some car-based channels from an OBD connection. Throttle position is probably the most notable, but brake pressure and steering angle are also useful additions if you can capture them.

What Do You Do With the Data?

Ah yes, the big question. As we mentioned before, autocrossers usually have to analyze their data very quickly–while they’re also checking and adjusting tire pressures, switching drivers, sipping a cool beverage, or doing one of the other dozen things that have to be crammed into the few minutes between runs. 

So your data analysis needs to be streamlined and limited to things you can easily put into action on a subsequent run. That said, we’ll focus primarily on a speed trace. Backing that up, if time allows, we’ll cross-reference that data with a friction circle and a throttle position trace if it’s available. 

Analyzing a speed trace on an autocross course is similar to looking at one from a road course, but there are a few peculiarities. Autocross puts a huge premium on getting on and staying on the throttle, so you want that speed trace to have a nice, consistent upward trajectory from the minimum speed point in a corner. Momentary plateaus in the acceleration graph almost always correlate to throttle lifts, so figure out why you weren’t staying on the gas and take steps to fix it. 

Next, look for any areas of consistent speed. Spoiler alert: Autocrosses rarely keep a car at a consistent speed for very long, so any horizontal areas on the speed trace should be red flags. About the only spots you might see near-horizontal lines are particularly long, sweeping, constant-radius corners–again, rare in most autocrosses–or in the middle of particularly long slaloms. (We’re talking at least six- or seven-pylon slaloms.) 

If you’re seeing horizontal speed traces anywhere but those rare occurrences, give that section a little more attention to determine why you aren’t braking later into the section or accelerating sooner out of it.

Braking takes a bit of experience to properly examine because many autocross situations require brakes to be used in fairly nonintuitive ways–to force weight transfer into a corner or to make a momentary attitude adjustment, for example. 

Whether on a track or an autocross course, you’re looking for a nice, sharp peak at the top of the curve–where you’re transitioning crisply from throttle to brake–as well as a crisp trough at the bottom–where you’re releasing the brake and getting back on the throttle. 

Know your charts. The friction circle cloud is a great place to get a snapshot of an entire autocross run. Are a lot of dots grouped toward the center of the chart? That’s bad and shows periods of inaction or coasting. 

Here, the dip in the speed-versus-distance trace reveals that we entered the first section of a slalom a little slower than ideal. 

What does this dip in the middle of a long, left-hand corner say? Did we get too aggressive on initial throttle and have to back way off to gather the car back up? We spent more than three car lengths of distance to regain our previous speed. 

Unlike on a road course, though, you’ll likely see a lot more non-threshold and very momentary brake applications where your goal is to bleed off a few miles per hour or extend braking while still cornering. So if you see some braking traces that look nonstandard, ask yourself if there’s a way to accomplish the same thing in less time or over a shorter distance–but also realize that the uniqueness of the autocross environment makes for an occasional funky brake trace.

Once you have multiple runs in the data system’s memory banks, you can begin overlaying them and looking for differences. Remember, you’re up against the clock here, so first look for the low-hanging fruit. Usually this means large areas of higher speeds, particularly in places where the speed trace is closer to horizontal–like those sweepers and long slaloms. More speed over more distance means greater reduction in time than momentary speed differences.

However, in many cases, particularly if you’re a driver of higher skill, all you’ll have to work with are those momentary speed differences near the peaks and troughs. And many of these differences will be the result of a compromise–like trading a slower mid-corner speed for a higher peak speed in the following straight. 

When faced with a compromise, favor the path that results in the greater speed differential over the longer distance. If you’re able to hold a 1 mph advantage through the end of a 120-foot straight by dropping the minimum speed through a 30-foot-long turn by just 1 mph, put your energy into the move that has you traveling faster for longer. 

And remember, it’s pretty easy to get overwhelmed with too much data in too short a time, so focus first on things you can confidently change in subsequent runs.

Also, always remember to hit “save.”