Another question would also be what’s the difference between wheel speed and vehicle speed?
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It’s pretty simple honestly. You have a sensor that spins and for however many times it spins there is a corresponding speed. It factors in things like what gear you’re in, what size tires, the transmission gearing, tear end gear all that stuff, but simply put it just spins a sensor that counts the number of spins.
Wheel speed vs vehicle speed is actually a really cool aspect that’s becoming a lot more prevalent especially in racing. It’s goal is to help with traction ultimately. Let’s say you have a Corvette with a big supercharging making 1,000 horsepower, cool stuff! Corvettes are rear wheel drive which means the engines power is delivered to the rear wheels while the front wheels just roll and turn.
Let’s say you want to race someone at a track because street racing is stupid. You know that grip is the key to racing so you turn on traction control and here we go. Now vehicle speed is easy it’s how fast the entire vehicle is moving. Wheel speed doesn’t equal vehicle speed though. Let’s say you take off and the tires start spinning from all that power. Your back tires are going to spinning faster since they don’t have traction and are being powered by the engine compared to your front tires which are just rolling at the speed of the vehicle. The cars computer can see this and regulate power (variety of ways often pulling back timing) to try and keep the front and rear wheels spinning at the same speed meaning you have traction. The same works for braking, you don’t want your brakes to lock up and skid, that’s not the fastest way to slow a car. So while braking the car is looking at each wheel and if one has a rapidly dropping wheel speed the ABS module will cut and reapply braking quickly and as repeatedly as needed to ensure the tire never stops rolling and stays at that maximum strength braking force.
There are other things that can be useful to measure wheel speed but that’s the basic gist. Something like drifting prioritizes the rear wheels spinning much faster than the front wheels to make the car slide on purpose. So you’d see the rear wheels doing 100mph or whatever but the front doing 40mph and the vehicles absolute speed would be the 40mph of the front wheels.
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