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Racing » Products » Data loggers » » FAQ

AP22 Frequently Asked Questions

How does the performance meter connect to the car?

The performance meter does not make any direct or indirect connections to the car at all. Just to be absolutely clear it does not require wheel speed, engine speed, connections to power, or anything else. To measure your cars performance you take the performance meter out of the box, attach it to the dashboard or other flat(ish) surface, and away you go...

So how does it work?

At the heart of the performance meters is a tiny silicon "micromachined" accelerometer. This consists of very small weight on a silicon chip, as the vehicle accelerates, the weight moves. You can demonstrate the same effect by suspending a weight on a length of string, as you pull away the pendulum will move backwards, if you brake the pendulum will move forward. By very precisely measuring exactly how much the weight moves, the acceleration can be calculated. 

How does it measure speed and distance?

Once you know has fast your car is accelerating, it is easy to calculate the speed. If you accelerate at 1g from 0mph, you will be travelling at around 22mph after 1 second. If you measure this 100 times per second, then for each 1g of acceleration, your speed increases by 0.22mph at each measurement. Distance is calculated by knowing how fast you are travelling. So if your speed is 60mph, your distance will increase by 10.5 inches each time a measurement is taken.

How big are the performance meters?

The meters outside maximum dimensions are about 126mm x 68mm x 40mm.

How much do the performance meter weigh?

The basic meter weighs in at about 200g.

What software comes with the performance meters?

The AP22 meters comes with a comprehensive data analysis package for detailed analysis on a PC, a live monitor system that allows you to check the meters output in real time and a "reflash" utility that enables the user to update the meter to the latest firmware version.

Why do the performance meters use a 2 axis accelerometer, not a 3 axis accelerometer?

The answer is quite complicated... but the short answer is we don't do it because it doesn't help!

How is the meter powered?

The meter uses 2 "AA" type batteries.

So I've got the meter, what do I do?

Go out and use it! For example, to do a 0-60mph test: 

1. Attach performance meter to the car.

2. To turn the unit on press the select button (marked ·). Race Technology will appear briefly before entering the main menu. Press the up or down button until Summary Timing is displayed.

3. Press the select button.

4. Press the up or down button until Time Between Speeds is displayed.

5. With the car stationary, press select. Wait until the display changes to: "Ready to Start, 0.00g 0.10g" 

6. Accelerate past 60mph. Once past 60mph the display will show the time taken to travel between 0 and 60mph, for example:"0.0 - 60.0mph, 6.46s 370ft". 

7. After pressing select you will then be asked if you wish to store the data, pressing select again will return you to the main menu without storing the data.

What leads come with the performance meter?

All performance meters are now shipped with an "RS232" style serial lead; this lead is required to download the data from AP22 meters as well as reflashing the firmware when required.

My laptop doesn't have a serial connection, what do I do?

The easiest option is to get hold of a USB to serial adapter - these are available either from us at a cost of £30, or from your local computer store.

How is the meter packed?

The meter is supplied in a high quality, hinged black plastic case with a custom foam interior. The system is shipped in a plain cardboard box and protected with foam chips.

What guarantee comes with the performance meter?

The meter comes with a full 1 years guarantee and lifetime email backup service.

I've damaged my meter, can it be repaired?

No problem, we just do repairs at  cost of time and materials. Drop us an email to arrange the details.

How do I change the meters batteries?

Gently squeeze the top half of the performance meter between finger and thumb. You should now be able to prise the top half of the case from the bottom. The front and back panels must remain with the TOP of the case. Inside the unit you should see two AA batteries. With the unit switched off, remove these and replace with two new cells, making sure the correct polarity is observed. Replace the bottom half of the unit and test. This will not affect any of the AP22's settings, or any of the data stored in the internal memory.

Can I use the meter to replace/calibrate my speedometer?

If your are using the AP22 in conjunction with the GPS3, then it can (and is) used for calibration of the speedometer - but it isn't really practical to replace your speedometer! If the AP22 is used in standalone mode then speed can't be displayed continuously, so it isn't really practical to use it for speedometer calibration.

I have to accelerate to about 68mph before the meter registers I've done a 0-60mph test, what's wrong?

This is quite common! The speedometer is normally designed to read about 10% too high at about 70mph.

How long do the batteries last?

The batteries last for about 30 hours continuous use… that's a lot of acceleration runs!

What is the resolution of the performance meter?

There are two parts to the resolution; the internal resolution at which calculations are done, and the external resolution at which the results are displayed. Internal g-force resolution is 1/256 g. speed calculation resolution is, 54.3 inches per hour. Distance resolution is 0.04 inches, External g-force resolution is 0.01g, speed resolution is 0.1mph or 0.1kph. Distance resolution is 1ft or 1m. Power resolution is 1hp or 1kW.

How accurate is the performance meter?

After a great deal of testing of the performance meter on all sorts of different vehicles, it has proved to be accurate to within 2-3% straight out of the box. Once it has been set up for your particular car (for example at a drag strip), measurements will be within 1%. 

How is the performance meter calibrated?

Each unit is individually calibrated during production. The calibration is stored internally and should never need changing (although it can be reset by the user if required).

How is the performance meter mounted in the car?

The performance meter should be mounted on a flat, level surface in the car, such as the dashboard or centre console. We found that the best way to mount it was either using sticky back velcro or simply blu-tac, both of which are supplied.

What if I can't mount it level?

When timing operations are started, the performance meter checks how level it is, and compensates for any tilt errors. If the tilt is too much it will display a message telling you. If it's within range, the unit will compensate for the tilt using Active Tilt Compensation. This reduces the error for large tilt angles by accounting for not only the offset caused by the units tilt, but also for the reduction in sensitivity caused by the tilt. This extra compensation increases the angle you can mount it at before you get a 1% error from less than 8 degrees to over 23 degrees.

My car squats down at the back when accelerating. Won't this affect the results?

Indeed it will, as the angle of the performance meter changes, two factors come into effect. The first is that the earth's gravity will affect the reading, increasing it. The second is that the sensitivity to the vehicles acceleration will be decreased. The overall result is in optimistic readings from the accelerometer. To overcome this, we have a built in "Tilt Factor", which applies a clever correction algorithm to compensate for the effect. Ideally this would be set by testing against a known timing system such as at a quarter mile strip, and changed until the results are closest. However, typical values for different car types are given in the instruction manual.

What is Rollout?

At the start of a quarter mile strip, there are two sets of timing beams, the pre-stage and the stage. The car must break both beams before it is said to be staged. The timing will start when the stage beam is re-made as the vehicle moves forward. Because of this, it is possible for the vehicle to move some distance before the timing starts. This is called the rollout and can be up to a foot.

What are CdA and Rolling Resistance?

In car specifications, the drag coefficient (Cd) is sometimes quoted. This may be a figure like 0.30 for a sleek saloon car, or up to 0.70 or more for a car like a lotus 7. What they don't usually tell you though is the frontal area of the car. The bigger the frontal area (A), the more drag, as CdA=Cd x A. If you know the frontal area and Cd of the car, you can calculate the drag power.
Rolling resistance is the resistance between the tyres and the road. The power required to overcome this increases in proportion to speed.

How do I calculate CdA and Rolling Resistance?

The easiest way to calculate the CdA and the rolling resistance is to use the Race-Technology Coastdown Calculator Which is available from our website. To use this you need to drive at around 50mph and time how long it takes to coast down to a lower speed.

If the GPS3 is attached, how often do you get GPS speed updates?

The GPS system calculates speed 5 times a second. However, this data is combined with the data from the accelerometers to calculate speed 100 times every second with very high accuracy.

If the GPS3 is attached, how often do you get GPS position updates?

The GPS system calculates position 5 times a second. However, this data is combined with the data from the accelerometers to calculate position 100 times every second with very high accuracy.

If the GPS3 is attached what benefits do I get?

Once the GPS3 is attached, the AP22 automatically senses it and uses the data. The GPS data is combined with accelerometers to calculate speed and position 100 times every second. Using an AP22 without GPS means that the speed/track maps will "drift off". They are only really accurate for about a minute on flat road. With GPS data available the "drift" is eliminated - so for short runs you won't see much benefit, but longer runs the data will still be very accurate enabling whole races to be logged and analysed. 

Are they in stock?

We are normally able to supply the AP22 performance meter directly from stock.