# 11

**~** Recommended Practice

RP 239A VMRS 017 

# COMMERCIAL VEHICLE TIRE INFLATION AND/OR MONITORING SYSTEMS GUIDELINES

PREFACE The following Recommended Practice is subject to the Disclaimer at the front of TMC's 

### Recommended Engineering Practices Manual

. Users are urged to read the Disclaimer before considering adoption of any portion of th is Recommended Practice. 

### PURPOSE AND SCOPE This Recommended Practice (AP) covers current capabilities and basic operation of tire inflation and pressure monitoring systems. 

### It is designed to help fleets select tire inflation and monitoring systems for commercial truck tires. This RP applies to tire pressure equalizers, electronic and mechanical tire pressure monitoring and maintenance devices as well as central tire inflation type systems. 

### INTRODUCTION Maintaining proper tire inflation will maximize tire life and casing durability. This results in reduced overall tire costs, downtime, tire replacement, irregularwear, wheel replacement, road debris and the natural re sources required to manufacture tires and retreads

. Correct inflation will increase benefrts such as fuel efficiency, safety, driver retention and uptime , all of which have a direct effect on cost per mile.
The following sections will explore the basic characteristics of the most common types of systems currently available. Whilethese systems may reduce tire labor, it is still necessary to periodically inspect tires to ensurethey are serviceable, properly inflated and the systems are working correctly. All of these systems needto be properly installed and maintained to deliver the benefits they provide. 

### I. Equalizing SystemsDual Tire Pressure Equalizers Basic System Operation Tire pressure equalizers are designed to maintain the same pressure between two tires of a dual assembly and indicate the state of inflation pressure in the tires. Byequalizing tire pressure overall individual

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- TMC/ATA tire performance and cosVmile are optimized. As a result improper load distribution and consequently irregular tire wear may be reduced

. Tire pressure equalizersystems monitorandequalize tire pressure by allowing air to transfer from one tire to another. This is accomplished by the use of two hoses that are plumbed to a check valve and each attaches to the valve stem of a dual tire. The check valve opens to allow airflow between the tires but closesand shutstheairoff in case of an instantaneous air loss, which prevents bothtires from going flat. In a slow leak situation, the valve isolates both tires after a pressure drop of approximately 1 0 psi. Since a central valve is located in these devices, a single airing point is provided that eliminatesthe need to remove the hoses to add air to the tires. These systems also provide a visual indicator of air pressure conditions. They do not provide actual inflation pressures but provide different types of go/no-go gauges that can indicate whether the tires are underinflated, overinflated or atthe correct pressure. The operating pressure of equalizers is set at the factory. 

### Typical Maintenance Requirements This equipment should 

### be inspected to ensure hoses are intact and attached to valve stems and that the valve and display are also intact. Periodically pressures should 

### be checked with a calibrated airgauge to ensure the equalizer is still operating accurately. 

### Training Requirements Drivers and technicians must 

### be trained to read and understand the displays on the axle end. 

### II. Tire Pressure Monitoring System (TPMS)- 

### A. Mechanical Basic System Operation All of these systems attach to the valve stem and monitor tire pressure through a mechanical device



### RP 239A-1 Issued 

### 312007 Revised 512014

### that works much like an air gauge. They provide indicators orvisual displays on the valve stems. There is no display or alarm in the 

### cab since these devices do not have the capability oftransmitting information. The pressure range the monitor operates in is set at the factory.
The primary difference between mechanical devices isthe displayonthe valve end. Some products provide a dial gauge that indicates exact pressure, others provide a valve cap type of package that ind icates the tire's pressure or pressure range. Maintenance Requirements It is critical to periodically check tire pressure with a calibrated air gauge to determine if the monitors are working correctly. These devices must be replaced 

### if found to be out of calibration. Training Requirements Drivers and technicians must be trained to read and understand the displays on the valve stems.


### B. Electronic Electronic tire pressure monitoring systems utilize electronic sensors that monitor tire temperature and/or pressure. These sensors can be mounted on the wheel, at the external end of the valve stem, at the base of the valve stem, or on the tire innerliner. They use radio frequency to transmit tire data to the receiver included in the system. Vehicle application and the number and types of users of the tire data must 

### beconsidered when selecting aTPMS. Thetype of data transmission also needs to be considered. There are three types of electronic TPMS: a. 

### Basic TPMS

- Basic electronic TPMS provides an in-cab displaywhich delivers audible and/or visual alerts to the driver when a tire problem occurs while the vehicle is in motion. Basic TPMS alerts can be as simple as illumi

nating a warning light or as sophisticated as providing the driver with a schematic of the vehicle's tires and pressure and temperature values. The driver or technician can see the current tire inflation pressure on the display when the ignition is turned on, eliminating the need to manually check tire pressures before the trip. Some systems that monitor tire temperature may provide cold inflation pressure, but not all systems do. (See TMC RP235A, Guidelines tor Ttre Inflation Pressure Maintenance Guidelines.) 

### The technician can set the

C> 2014-TMC/ATA 

### target pressure by using the in-cab display in conjunction with adjusting tire pressure. b. 

### Remote-reading TPM5-This type of TPMS is linked to the vehicle databus, telematics or infrared data transfer systems for remote reading. These types of systems send data on all or some of the tires on the vehicle to a telematics system thatcommunicatesthe data via satellite or cellular network to a remote location for analysis. Alerts can then 

### be sent via e-mail and remote access to tire status is obtained through the internet. These configurations may also provide an in-cab display for the driver that provides audible and/or visual alerts. Changes in target pressure may 

### be made overthe internet or may have to 

### be made on the vehicle, depending upon the system. 

### c. Off-boardGate, Lane orHandheldReading TPMS-This system type utilizes off-board gate, lane, or handheld readers that provide interval monitoring of tire pressures and temperatures at staticor lowvehicle speeds. It initi

ates data transmission to the various readers and/or data storage devices. In-cab displays may not be included with these systems. Maintenance Requirements Sensors should always be installed so that they are positioned with the valve stem. Care must 

### be taken when mounting and demounting tires so that sensors attached to the wheel or at the base of the valve stem are not damaged. As a general rule, liquid tire additives (sealants, balancers, coolants) should not be used with TPMS sensors used inside the tire chamber. Check with the manufacturers of other additive products to ensure these products will not interfere with TPMS sensor operation. Most electronic systems self-calibrate and diagnose system problems. Follow manufacturer instructions for maintenance of your respective TPMS. Training Requirements Drivers must be instructed in the company's policy when tire alerts are triggered. This can include continuing travel to the company's yard, stopping at the nearest tire service location, or stopping immediately and acquiring emergency road service. Maintenance personnel should also 

### be instructed on how to respond to alerts and any reports that are generated by the TPMS. lire technicians must 

### be trained to properly install sensors, mount and demount tires, and move sensors so that the TPMS receivers



### RP239A-2recognize the wheel positions on which the sensors are installed. If the ti re p ressure monitoring so l ution includes software applications that must be used in conjunction with theTPMS , then technici ans must be trained to use them as we ll

. Detailed maintenance instructions and training should be provided by the system manufactu re r
. Ill. Ti re Inflat ion Syst ems (Mo nitors , i n f l ates, a n d /o r d efl ates)
Bas i c System Ope ration Tire inflation systems taketh e ai r that is stored in the air tanks on a vehicle and use it to supp ly ai r to the tires. This 

### can be done on demand or automatically triggered through sensors that monitor ti re pressure. These systems can be broken down into two types: automatic and variable

. Automatic tire inflation systems mai ntain tire pressure at a sing le p reset level and a re pneu m atically or electronically activated. Electronically activated systems use an EC U to measure tire p ressures at regular intervals and inflate the tires as requi red

. Pneumatically operated systems keep ti res inflated by maintaining a predetermined air pressure continuously applied to the tires. A warning lamp indicates to the driver when ti re or system service is required. These systems eliminate the need to m anually inflate tires. Automatic ti re inflation systems have no ope rational involve m ent from the driver

. They automatically sense the p ressu re i n the ti r es and inflate as necessary. Variable- or driver-actuated tire inflation systems can raise or lower tire pressures during vehicle operation to compensate for varying load and road conditions in addition to maintaining ti re pressure. These systems allow the d river to interact with the system and change tire pressure on dem and. They are electronically activated and must have battery power to the ECU fo r the m to fu nction and to retrieve fault codes. These systems are usual ly used for onoff road operations.
Tire inflation systems use compressed air from the vehicle's ai r system. They transfer this air to a frame mounted cont ro l unit. Air isthen delivered to a whee l end rotary union that distributes the air to the tire valve stems. Different ai r delivery methods exist in these systems

. Some systems use the axle tube as a p ressure con C 2014

- TMC/ATA duit , some have a dedicated airline in the axle , and othe rs h ave outboa r d p l u m bing.
All ti re i n flatio n systems must be vented to prevent hu b pressurization in the event of a component fail

u re. Some systems vent ai r at the whee l ends while othe rs vent remotely

. One ti re never supplies air to another tire , leaving the systems to maintain correct air pressure set
tings th roug h out

. Current ti re i nflation systems have safety devices built into them

. A pressure protection valve (PPV) is required in these systems to ensure a rapid loss of ti re pressu re will not d rain the ve h icle air system be low a safe p ressu r e required for proper braking

. If a sig n ificant loss of ai r should occur in a tire or the inflation system itself, the remaini ng ti res are protected from air loss by check valves in the air hoses

. Some ti re inflation systems have the capability to communicate to an off vehicle data co l lection station via com m unication devices al ready in service as specified b y the fleet. Th ese off-vehicle signals can 

### be via satellite, cell ul ar o r other remote-based communication systems

. It is the respons ibi l ity of the data collection provider to have the decoding softwa re for integ rating the systems. M a inten ance Requi reme nt s Recommended inspection procedures need to 

### be pe rformed on ti re inflation system equipped vehicles in conjunction with a fleet 's sched u led p reventiv e maintenance inspections

. It is still necessary to pe riod ically inspect ti res to ensure they are service

able , properly in flated and the systems are working correctly. These checks will allow the technicians to determinewhethe rthe system isfunctioning correctly, if tires have leaks or o ther out-of-service conditions , and measure tread depth.
T ra i ning Req u i rements Drivers needto be trained regardingthe mean ing/ope ration of the tire inflation system indicato r /warning light and t heir expected respo n se
. Technicians m u st be trained to set and verify the p roper tire p ressu re target and correctly maintain the system
. Appropriate personnel shou ld be inst ructed on how to recognize four basic items about the system: 

### 1

. Howto inspectthe system for basic component integrity and leaks throughout. 2. How to properly dis m antle and reassemble

RP 

### 239A- 3