Tire pressure monitoring: a brief introduction to the system by our Dipl.-Ing. Michael Schröttle
Part 1:
1) System types:
Indirect measuring systems (differentiation of wheel speeds; principle: determination of the tire radius as a function of the air pressure)
Problems:
a) No pressure reading, as this quantity cannot be measured. Therefore, any potential savings (fuel consumption, tire mileage) are inherently impossible.
b) Systemic blind spots with simultaneous pressure loss on two or more wheels; this case is statistically unlikely but relevant for the safety function.
c) Warning thresholds are at 15 – 20% pressure loss; this is too high for practical purposes, i.e., the systems tend to warn too late.
d) There is no tire pressure monitoring system here, as the tire pressure is not measured. It is more of a "flat tire warning system," meaning that at best the user receives a warning in case of pressure loss, usually without specifying the affected wheel position.
e) System is not suitable for retrofitting
Advantages:
cost-effective
Direct measuring systems with internal sensors:
Problems:
a) For installation, the tires must be removed and then reinstalled.
b) The sensor batteries are potted inside the sensors and are not replaceable, meaning that at the end of the battery life the entire sensors must be replaced – cost: expensive sensors and installation effort (see a)
c) A vehicle needs two sets of sensors, one each for summer and winter tires (cost!).
d) Sensors can be mechanically damaged when the tire is removed (tire change).
e) depending on the system type, additional effort and costs for automatic wheel position assignment/detection.
f) Tires must be balanced with sensors fitted.
g) expensive in acquisition and follow-up costs
Advantages:
a) Anti-theft protection is not required as the sensors are located in the tire.
b) Measured temperature usually correlates well with tire pressure
c) high measuring accuracy (typically better than 0.1 bar)
d) Practical warning thresholds of 0.2 bar (usually predefined or input of the cold filling pressure/target pressure)
e) no blind spots, as each tire has a separate measuring device
f) in principle suitable for retrofitting
Direct measuring systems with external sensors (design as a valve cap):
Problems:
a) Sensors can be targeted for theft or vandalism. This can be prevented by installing the anti-theft device that is usually included, but this then makes refilling the air more difficult.
b) If the installation instructions are not followed (valves that are too long), the sensors may be damaged if they come into contact with the curb.
c) Tires must be balanced with sensors installed.
d) Measured temperature usually correlates poorly with tire pressure
Advantages:
a) Only one set of sensors for summer and winter tires
b) Batteries can usually be replaced
c) Simple wheel position assignment via sensor numbering
d) only minimal assembly effort
e) cost-effective in acquisition and maintenance/follow-up costs
f) high measuring accuracy (typically better than 0.1 bar)
g) Practical warning thresholds of 0.2 bar (usually adjustable by the user)
h) no blind spots
g) can be easily retrofitted
These systems offer TireMoni
TireMoni, like the ADAC, recommends short metal valves.