The AC22 Performance Meter

Accelerometers have been used to measure car performance forever, but it's only over the last 10 years or so that digital electronic performance measuring equipment has become widely available. The Vericom was first, followed by the G-Tech Pro - and now UK company Race Technology has released the AC-22 Performance Meter. A small box (40 x 125 x 65mm), the AC-22 can measure a whole range of performance parameters - acceleration (over distance or between speeds), braking deceleration, lateral (ie cornering) acceleration and power at the wheels. The AC-22 is simply placed within the car, set to measure the required parameter, and the car is driven.

Using the Analog Devices ADXL202JQC electronic accelerometer chip, the AC-22 is able to measure plus/minus 2g with a resolution of 0.01g. What does that mean? It means that the AC-22 will be able to accurately measure any acceleration that you are able to get in any road car - unless you hit a wall, that is....

In Australia the AC-22 costs A$370.

The Menus

The instrument uses a 2-line LCD dot matrix display (not back-lit, unfortunately) and three press-buttons. Two are marked with up and down arrows, while the third (red) button is marked with a dot and is called in the handbook the 'select' button. Pressing the red button turns the instrument on, with 'Race Technology' being displayed on the screen. You can then use the arrow keys to scroll through the main menu options - 'Display g-Force', 'Acceleration Timing', 'Configure', 'Switch Off'. The last is obvious, but let's have a look at the others.

The 'Display g-Force' menu option has several sub-options, which are accessed by pressing the red button and scrolling with the arrow buttons. The first option is 'Acceleration g-Force', followed by 'Cornering g-Force', 'Vector g-Force', 'G-Circle', and 'Go to Main Menu'. If you select 'Acceleration g-Force' (ie by pressing the red button), 'Ready to Start' appears on screen. Press the red button again (or wait a few seconds) and 'C=0.00g M=0.000g' appears. This is the actual measuring display, with the left-hand side showing instantaneous g-force and the right-hand side showing the maximum reached. Below this display is a bar graph showing instant g's. If the AC-22 is positioned with excessive tilt (note that it does not need to be dead level during the measuring process) a 'Tilt Error' display will occur.

However, while certainly useful, displaying instantaneous and peak g's isn't something that most people will use. Instead, what about more traditional performance measurement? Returning to the main menu and selecting 'Acceleration Timing' gives you the options of: 'Time Between Speeds', 'Time Over Distance', and 'Time Quarter Mile'. For example, you can select 'Time Quarter Mile', wait a moment and then away you go. It is possible to set the AC-22 to record a heap of data during the run - 60ft, 330ft, 660ft and 1320ft g forces and times, for example.

In addition to all of this, the 'Configure' menu allows the altering of the 'Set-Up Time Between Speeds', 'Set-Up Time Over Distance', 'Set-Up Time Quarter Mile', 'Trigger Value', 'Vehicle Data' and measuring 'Units'. For example, in the 'Set-Up Time Quarter Mile', the 'Rollout' can be enabled or disabled, and for 'Set-Up Time Between Speeds' the unit can be set to record the time taken to accelerate from a rolling 60-90 km/h.

This is really only a brief overview of some of the functions - but how about using it?

Using It

Firstly, it needs to be said that the multiple menu structure isn't terribly intuitive to use. The vast majority of people are going to carry out only two or three performance tests frequently - quarter mile, 0-100 km/h and perhaps an in-gears time. This means that the two functions most often required will be 'Time Quarter Mile' and 'Time Between Speeds'. However, the way in which the menus work mean that each time you wish to use these functions, you need to scroll through three of four things that you don't want - and if you go the wrong way, it's easy to find yourself off in the 'Configure' menu or some other menu that you will very rarely ever even need to see. One way to overcome this problem would be to change the function of one of arrow keys (you don't really need and up and down arrow keys - just one would do) so that pressing it activates just the more obscure menu items.

In our main testing we used as a guinea pig car a Mitsubishi 3.5 litre Verada. The first test that we completed was a 'Time Between Speeds'. In our case the 'Start Speed' had been set (via the 'Configure' menu function) to 0 km/h and the 'End Speed' to 100 km/h. We'd also said yes to 'View Intervals?' and 'View Maximums?'

The 0-100 km/h sprint was completed by the Verada in 9.72 seconds (heading west), 9.95 seconds (east) and 9.80 seconds (west). However, since we'd asked to see as much info as possible, each run also gave us data like this:

10.0kph	0.6s	0.45g
20.0kph	1.21s	0.44g
30.0kph	1.99s	0.35g
40.0kph	2.83s	0.33g
50.0kph	3.63s	0.35g
60.0kph	4.43s	0.34g
70.0kph	5.31s	0.31g
80.0kph	6.57s	0.20g
90.0kph	8.05s	0.19g
100.0kph	9.50s	0.19g

In addition, the distance travelled at each split was also listed - but since we didn't write it down as we were scrolling through the displays, it isn't here. That's a downside - there's no apparent way of recording any data; in fact it seems to disappear as soon as you move to another menu!

We then used the 'Acceleration g-Force' function to record peak-g's on launching the automatic car, with and without the traction control system operating. This gave 0.53 and 0.50 g with the traction system on, and 0.53g and 0.53g with it off.

Braking performance? That can be measured by simply reversing the 'Time Between Speeds'. We set the 'Start Speed' to 100 and the 'End Speed' to 0. We then drove away from a standstill (with the meter showing on the display 'Get to 100kph'), then when we exceeded 100, the display changed to 'Start Braking'. Incidentally, you don't need to start braking the instant you reach 100 - the meter will start its measurement only when you slow below the designated speed.

The results? 100-0 braking - 3.1 seconds, 43 metres, 0.96g.

On another run we asked to see everything, and the following data was available:

90.0kph	0.69g	0.3s
80.0kph	0.81g	0.61s
70.0kph	0.88g	0.92s
60.0kph	0.90g	1.23s
50.0kph	0.91g	1.54s
40.0kph	0.91g	1.85s
30.0kph	0.91g	2.16s
20.0kph	0.93g	2.46s
10.0kph	0.94g	2.75s
0.0kph	0.91g	3.07s

We also threw the Verada around a roundabout, recording a peak lateral acceleration of 0.86g. However, the softly-sprung Verada leans quite a lot in this type of driving, and while the AC-22 has a variable input factor for Tilt, it appears that this applies only to longitudinal acceleration (ie car squat) - not lateral (ie car roll).

The AC-22 also has a power estimation ability. With data on vehicle mass, CdA (drag coefficient x cross-sectional area) and rolling resistance inputted, the AC-22 can estimate power available at the wheels. We did only one test of this feature, where it showed the Verada as having 96kW at the wheels (flywheel figure is 150).

Accuracy?

As with any tool, the accuracy of the AC-22 will depend very much on how it is used. If your performance testing stretch of road runs downhill, well.... But unlike some of its competition, at least the AC-22 self-corrects for some degree of tilt when it is placed in the car - you don't need to level it absolutely accurately before you begin testing. The availability of the user-definable 'Tilt Factor' correction should also allow it to be very accurately calibrated for a particular car's suspension characteristics.

We ran one dragstrip test of the AC-22 on a Suzuki Swift GTi - on that test it proved very accurate, with the AC-22 suggesting 16.98 seconds at 85.4 mph, and the official timeslip being 17.017 seconds at 81.75 mph. Incidentally, at the same time a G-Tech Pro read 16.75 at 85.65 mph.

Conclusion

The number of functions and the way in which they are accessed means that the AC-22 probably isn't for everyone. However, if you want to be able to collect accurate, broad data on the performance of your car, wish to be able to calibrate the device for your specific application, and to perform 'real world' testing, the AC-22 is the best product we have sent to do it.

http://www.race-technology.com/WebPage/Main.html

Comparisons Below is a table (provided by the manufacturer of the AC-22) comparing the features with of the AC-22 performance meter with the G-Tech pro and the Vericom VC2000. Make/Model Vericom VC2000 Race G-TECH pro AC-22 Display Type 20x2 LCD 4 Digit LED 16 x 2 LCD Power Calculations Yes, no compensation for aerodynamic drag or rolling resistance Yes, no compensation for aerodynamic drag or rolling resistance Yes, fully configurable for vehicle mass, CdA and rolling resistance Acceleration between 2 speeds Yes Yes, only 0 to 60mph Yes Brake timing Yes Yes, limited to starting from 60mph Yes 1/4 mile timing Yes, including 8 intermediate timing points, no rollout compensation Yes, including 1 intermediate timing points, no rollout compensation Yes, including 5 intermediate timing points, rollout compensation selectable Measurement of cornering g-force No No Yes Power supply Powered from car cigarette lighter Powered from car cigarette lighter 2 x AA batteries, battery life approx 50 hours continuous use Acceleration over selectable distance Yes No Yes Unit selection Metric/Imperial Metric/Imperial Metric/Imperial individually selectable for each measurement Reaction time measurement Yes No No Maximum g-force measurement during acceleration run Yes No Yes g-force bargraphs No No Yes g-circle measurement No No Yes Maximum measurable g-force Don't know, at least 1.5g 1.27g At least 2g