928 S4 V8-4957cc 5.0L (1987)
Tires: Technical Service Bulletins
Tires - Use of Accurate Inflation Pressure Gauge
October 30, 1990
Subject:
Tire Pressure/Gauge
Model
Group
928 S4/GT
4
Part Identifier
Number
4437
9008
ATTENTION: Service Manager/Service Technician
This bulletin replaces Technical Bulletin Group 4, Number 9008, dated October 9, 1990.
Models Affected:
928 S4/GT with Tire Pressure Warning System (RDK).
Concern:
Use of accurate tire inflation pressure gauge.
General Information:
The tire pressure warning system monitors the correct tire pressure more precisely and reliably than tire pressure
gauges in the tool kit or at most workshops.
The system also takes the effect of temperature into account. Driving style, load, roadspeed, outside temperature,
sunlight and heat radiated by the engine affect the temperature of the air in the tires.
Influence of Tire Air Temperature on Tire Pressure
The inflation pressure increases by approximately 0.1 bar (1.5 psi) per 10~C (18~F) increase in tire air
temperature. Even after a short drive, the pressure values can rise to 2.7 bar (39 psi) for the front axle and 3.2
bar (47 psi) for the rear axle. Once the tires get warm, the correct current pressure value always exceeds the
specified inflation pressure value of 2.5 bar (36 psi) front and 3.0 bar (44 psi) rear. Never reduce this inflation
pressure. Refer to chart below.