Quote:
Originally Posted by KRAM36
Why does what matter? The fact that people on the forums don't know the answer to this or that I want to know how the Boxster determines it's speed?
It matters to me because I am going to change the diameter of my tires and I want to calculate how far off my speed will be if the car judges the speed from the tire rotation speed.
Thanks for not answering the question and being a jackass for nothing.
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You are quite welcome.
I think you will find that I am generally not a jackass, and go quite far out of my way to help people find answers that I often have no other use for. In this case it would have been nice to know the scenario before calling me a jackass for not helping. I don't like spending a bunch of time because someone was "just wondering", hence my comment. This actually piqued my interest last night and I even spent a half an hour of my time looking up exactly how it calculates speed. I looked in the Bentley, the factory (996) 911 Technical Introduction Service Information manual and called a friend that I thought would know as he sets uses this info in 911 and Boxster race cars. Why would such a jackass go to this trouble? Maybe he likes abuse.
Yes, of course the system uses wheel speed to calculate vehicle speed. That is the only way it could. Each "tone wheel" that the wheel speed sensors read has 48 teeth that is read by the ABS module. The ABS module then divides this down by eight and sends it to the appropriate module. The real question is does it use one sensor, does it somehow derive it from all of the sensors, or? Well, the answer, as far as I can tell is a bit tricky. It appears that there are two speed signals sent out. One from the right rear, and one from the left rear. The key is that it seems that the speed is derived from the rear wheels, not the front, so hopefully that answer is good enough. But hey, I am just a jackass.