Quote:
Originally Posted by RidingOnRailz
Tire Pressure and Speedometer Calibration
Curious question:
In a new build vehicle, what pressure are the tires maintained at for calibration, or at least verification of correct operation of, the vehicle speedometer -
the maximum cold pressure according to tire sidewall, or, vehicle manufacturer OEM specified cold tire pressure?
The reason I ask is because if I drive, IE, 56mph in the right lane of a 55mph zoned highway, other drivers are either zooming up to my trunk, or, warping by me in the lanes to my left. My tires are kept at, or at 1psi above, cold pressure specified on the vehicle OEM door pillar decal.
|
Speedometer calibration is done at the placard pressure. But the RPM (revs per mile) value is given to the OEM by the tire manufacturer - AND THEN the vehicle manufacturer makes adjustments - and they tend to have the speedometer read a bit low, because if the speedo reads high, the vehicle manufacturer could be legally liable for someone getting a speeding ticket!
But on a more practical note: People tend to speed, so judging your speedometer accuracy based on the traffic around you isn't a good idea.
A better idea is to use the Interstate mile markers. They are at least reasonably accurate. But use several over a long distance. I like to use 10 miles, although it is sometimes difficult to maintain a steady speed for 10 minutes - even with cruise control!