Understanding the Mechanics of a Car's Speed: Answers to Common Questions

[Averagesupernova]

There are many variations of ABS. Early GM systems that only had rear wheel ABS simply relied on ONE sensor at the output shaft of the transmission that determined how quickly the drive shaft decelerated. As far as I know, there is no method independent of the wheels for the vehicle to know how fast it is traveling.

 

[ray b]

I don't know if it is used
but a simple decelleration detector could be used
like a weight on a string on a micro scale
our GM suburban would kick in ABS at low speed on crossing white lines
as the ABS kicked in at AS LOW as 2-3 mph when stoping at a trafic light
kinda spookie when it happened

a radar system could KNOW speed independent of the wheels
or the quick cycle of the system may defeat creep at a stop

 

[apples]

Apples, sorry for the hijack.

LOL, I asked about the speed of a piston, and it ends up with ABS.

 

[Danger]

And it'll probably have worked its way around to limited-slip differentials by next week.