Other Data There are infrared sensors that measure tire temperatures, air pressure sensors for aerodynamic work, and torque-sensing driveshaft yokes. You can find sensors to measure tire pressure, spring load, and force on suspension components. If you have the budget and want to measure anything, there are sensors to do the job.
The Box (Data Logger) Once you have your sensors mounted on the race car, you need a box to record all of the measurements. Data loggers are a lot like stereo equipment. The average user can't tell the difference between the best high-end unit and a very good mid-level unit, but understanding what you need in a box can make a difference of thousands of dollars at the cash register.
For the average racer, there are two main items to understand about data loggers: number of signals and memory. The old phone answering machine had one signal, the microphone. Data loggers can have many signals, often called channels. Each sensor you place on your race car will require a channel. So, in essence, the data logger is like several tape recorders built into one unit.
Box Size Boxes come in many different configurations. There are little four-channel boxes on the low end of the scale that cost around $600. These are basic units and typically are not expandable. Next are the expandable units that all have roughly the same box size, but allow more channels to be added in the box. Adding channels increases the cost, but midsized units (12-16 channels) start around $1,200 and go to $2,000. High-end boxes have 30-38 channels and can cost $2,000-$5,000, depending on other factors.
Once you start using a basic unit, you may find it confining, but midsized units are more than adequate for weekend racers. For example, if chassis setup is your priority, a midsized unit will allow you to record four individual wheel position channels, steering, brake, throttle, engine rpm, two wheel speeds, two g-force channels, and have some open channels. If engines are your game, then you could have engine rpm, wheel speed, driveshaft speed, water temperature, air temperature, fuel and oil pressure, manifold pressure, eight EGTs, throttle position, g-force, and more. In either case, a midsized unit can handle the load at a reasonable price.
Memory Memory in a data logger is like memory in your home computer. It will take more memory to save a 50-lap main event than a 5-lap test run. Basically, more laps equals more data, and more channels equals more data. Typically, a unit comes with a given amount of memory, and you have the option to purchase more memory. Boxes come with as little as 128K or as much as 4 meg of memory. Even for professional circle track racers, 2 meg of memory tends to be a reasonable quantity. However, some midsized boxes come with 2 meg at no extra charge, so it pays to shop around.
Memory influences the length of recording time, but sample rate has a big impact, too. Think of samples such as the individual frames on a movie film. One frame per second makes a real jerky movie, where 10 frames per second is barely jerky. However, the added frames require more film. Likewise, a higher sample rate uses more memory. Data systems typically run between 10 and 100 samples per second, and some units go as high as 400 samples per second. The question of what sample rate should be used will likely prompt a long debate between engineers, suppliers, and data geeks. Just keep data rate in mind and realize it will impact your recording time.
The Beacon Just like the beep between messages on the phone answering machine, a marker is needed in your data. A lap timer beacon is used with data acquisition systems to signal the end of one lap and the beginning of another. Basic data systems use infrared lap timers already used by many local racers. High-end systems use a multi-IR beacon, but work on exactly the same line-of-sight principle.