Quote:
Originally Posted by Thegreatescape
If this is indeed true, then how do many manufacturers (including some Ford models) utilize the ABS sensors instead of actual air pressure sensors to operate their TPMS systems?
For example, this was taken from from the 2002 Windstar shop manual section 204-04:
"The Low Tire Warning (LTW) system detects differences in inflation pressures in one or more tires. The system uses the ABS wheel speed sensors to monitor the rolling radius of the wheel and tire assemblies."
A few other vehicles that use this approach include 2001 to 2003 Ford Windstar, 1997-2002 Buick Park Avenue, 1999-2003 Buick Century & Regal, 2002-2003 Buick LeSabre, 2003 Buick Rendezvous & Aztek, 2000-2003 Chevy Impala & Monte Carlo, 1999-2002 Chevy Alero, 1999-2002 Pontiac Grand Am, 1997 - 2003 Pontiac Grand Prix, 2000 - 2003 Pontiac Bonneville, and 2001-2003 Oldsmobile Aurora. Source: http://www.aa1car.com/library/tire_monitors.htm |
So maybe I was right and I gave up too soon.
Its been rolling around in my head for a while now. Even with a steel belt the MIDDLE of the flat belt can likely bow in or out changing the diameter of the tire slightly.
As for the tank tread comparison.... um.. tank treads aren't Pnuematic. Clearly as you fill a balloon with air the diameter around the ballon increases. A rubber tire is like a ballon except for the fact that its thicker and has a steel belt. from the info above it appears that even a steel belt will give some. 40PSI provides a significant amount of force when you multiply 40 times the area of the inside of the tire in square inches! All that force is pushing outward against the tire rubber trying to maintain shape.
If you can measure (even inaccurately) tire pressures using the speed of rotation, the distance around is not constant with air pressure.