Originally Posted by SaToX
Looking at the NHTSA there seems to be conflicting info. One spot it states that the system should indicate when any tire including all four drops 25%. In another spot on the site it seems to be referencing a table that states 20 psi is the safety floor.
The federal safety standard uses both in an overall determination. Whichever value is higher is what is applied to the vehicle.
The lowest placard for any car at the time of the ruling was 26psi.
26psi x 75% ~ 20psi. Hence no vehicle following the 25% rule should ever fall below the 20psi safety floor.