Data Analysis Fundamentals: Wheel Speeds
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Wheel Speeds
03.03
| 00:00 | - Wheel speed data is pretty self explanatory but it does open up the ability to analyse more aspects of the car's performance. |
| 00:07 | Traditionally, getting this information was relatively time consuming and expensive as it required individual speed sensors to be mounted in such a way that they can pick up on a tooth wheel on each hub. |
| 00:20 | If you're dealing with an older car, then this is likely to still be your only option. |
| 00:24 | However, with the majority of modern cars now having ABS, we may have alternative options. |
| 00:31 | While it's very specific to the individual vehicle, often the individual wheel speeds that the ABS computer needs to function are also communicated on the vehicle's CAN bus and this information can be read and decoded by the datalogger system via the OBD2 port. |
| 00:47 | Alternatively, many of the aftermarket standalone engine computers for late model cars, are already configured to receive this information and this can be broadcast to the datalogger. |
| 00:58 | It's important to mention that you can't share the signal from a factory ABS wheel speed sensor between the ABS computer and your datalogger as this will almost certainly cause a fault that renders your ABS useless. |
| 01:10 | Once you've physically got the wheel speed data into your datalogger, there's a lot to be learned from this information. |
| 01:16 | First of all, it gives us the ability to set up driver warnings to visually indicate that wheel is locked on a non ABS equipped car. |
| 01:24 | This might sound like it should be unnecessary and you should be able to tell if a wheel is locked up but that's not always the case, particularly in the wet. |
| 01:32 | Even in the dry it can be hard to know that you've got off the brakes enough to allow the wheel to unlock. |
| 01:39 | Likewise, driver warnings could be used to indicate wheel spin, however this is something that the driver should be able to feel more easily, wet or dry. |
| 01:47 | One of the advantages of having wheel speed data is that it gives you a more reliable channel that can be used for vehicle speed. |
| 01:55 | While GPS is useful to a point, the data for GPS speed is seldom as reliable as a properly calibrated wheel speed input. |
| 02:04 | This becomes critical when you're looking at the speed channel when comparing laps. |
| 02:09 | Wheel speed can also be used in conjunction with lateral and longitudinal G force and a lap beacon in order to provide track mapping if you don't have a GPS antennae. |
| 02:18 | For this sort of input it's not strictly to have all four wheel speeds and usually a single undriven wheel speed is sufficient. |
| 02:27 | If you don't have ABS, then this input is still prone to error due to locking. |
| 02:31 | Although most data analysis packages will provide the option to correct track maps to account for brake locking. |
| 02:38 | This offers a nice segway into another use of wheel speed data which is to analyse brake lockups. |
| 02:44 | Something that can be very helpful in optimising the driver's brake applications as well as the brake system itself. |
| 02:50 | On the flipside of this, the wheel speed sensors can also show the telltale signs of compression locking which is the result of the driver not properly matching revs on a downshift. |
