FYI from MCI - Maintenance Matters

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MAINTENANCE MATTERS

Tire Pressure Monitoring Tips

MCI is incorporating several new technologies for the 2006 model year. One of these changes is the tire monitoring system. The SmarTire® system monitors tire pressure and temperature and gives the driver early warning of tire-related problems from the driver's control panel. A small, wireless sensor is mounted on each wheel and collects temperature and pressure data, which is transmitted to a receiver that analyzes this information. If a fluctuation in pressure or temperature occurs, a warning light will illuminate on a display unit located in the driver's area.

With the introduction of this technology comes a realization that tire pressure is affected by ambient temperature. Located in the MCI maintenance manuals and on the coach VIN plate is the recommended tire pressure settings for that coach model. This recommended cold pressure setting is based on an ambient temperature of 65°F. If the ambient temperature is higher or lower than this specified temperature, the air pressure setting for the coach tires must be adjusted accordingly.

Tire Air Temp	Recommended Cold Tire Pressure PSI Settings - Displayed on Coach VIN Plate (based on 65° F.)
	65psi	70psi	75psi	80psi	85psi	90psi	95psi	100psi	105psi	110psi	115psi	120psi	125psi
75° F	67	72	77	82	87	92	97	102	107	113	118	123	128
85° F	68	73	79	84	89	94	100	105	110	115	120	126	131
95° F	70	75	80	86	91	96	101	107	112	117	123	128	133
105° F	71	76	82	87	93	98	103	109	114	119	125	130	136
115° F	73	78	84	89	95	100	106	111	117	122	127	133	138
125° F	74	80	85	91	97	102	108	113	119	125	130	136	141
135° F	76	81	87	93	98	104	110	115	121	127	132	138	144
145° F	77	83	89	94	100	106	112	117	123	129	135	140	146
155° F	79	85	90	96	102	108	114	120	126	131	137	143	149
165° F	80	86	92	98	104	110	116	122	128	134	140	146	152

Please note: This chart only addresses the issue of tire under-inflation due to temperature increases in excess of 65° F.

Using the above chart as a reference, assume the coach you are working on is located in Miami, Florida and you're adjusting the air pressure in the tires to the settings below:

FRONT AXLE	DRIVE AXLE	TAG AXLE
120 psi	90 psi	100 psi

The outside temperature is about 90°F, so the tires need to be inflated to the following pressures to compensate for the higher ambient temperature:

FRONT AXLE	DRIVE AXLE	TAG AXLE
127 psi	95 psi	106 psi

Without compensating for the higher ambient temperature, the tires would be 5-7 psi under-inflated even before the coach is moved. A tire that is properly inflated will run approximately 80° warmer than ambient, but a tire under inflated by 10 psi could run as much as 130° warmer! This results in poorer tire life, a decrease in fuel economy, and a greater potential for tire failure.

If you have further questions about proper operation of the system and proper tire inflation please call the MCI Customer Fleet Support Center at 800-241-2947.