This SAE recommended practice defines the system and component functions, measurement metrics, testing methodologies for evaluating the functionality and performance of ground vehicle CTIS. Systems of this type allow the driver to select the operational tire pressure set point (TPSP) based on off-highway conditions, and, upon returning to highway operations, maintain the inflation pressure to the vehicle specified level.
These systems are recommended to address all serviceable tires as originally installed on a vehicle by the OEM and/or specialty vehicle manufacturer, and, for the aftermarket (including replacement or spare parts) are recommended (but optional) to address all tire/rim combinations installed after initial vehicle sale or in-use dates.
Systems for use by military and some other very rigorous off-road applications require such extreme performance requirements, particularly at very high and low temperature and other combat-based extremes that such applications may fall outside the recommended parameters of the subject document. In those cases, it’s the responsibility of the procuring customer, vehicle OEM, and applicable component(s) OEM to determine what compromises might be required, and the suitability of design and performance solutions that may be outside of those recommended here.
This document is applicable to all axle and all wheel combinations for the following vehicle types, but does not preclude it’s use on other vehicle types - single unit powered vehicles exceeding 7257 kg (16,000 US lbs) gross vehicle weight rating (GVWR), and multi-unit vehicle combinations, up to three (3) towed units, which use an SAE J560 connector for power and/or communication, or equivalent successor connector technology. For combination vehicles including two or more trailers, the dolly axles are also included. The included vehicles can be newly manufactured vehicles or existing vehicles, fitted with air or hydraulic braking systems.
Special Note: Equipment known as 'dual tire equalizers' are commonly used with this category of vehicles. When installing a CTIS system, dual tire equalizers systems are not recommended as they run counter to the purpose of the management system.
NOTE: The following systems are not being addressed in this edition of the subject document.
1. Tire Pressure Monitoring Systems - these systems have been addressed under SAE J2848-1.
2. Tire Pressure Maintenance Systems - these systems have been addressed under SAE J2848-2.
Within the medium and heavy-duty vehicle industry, the equipment supplier community has responded to the need to manage inflation pressure for greater vehicle operational performance when transitioning from improved roadways to unimproved roadways and back, by developing onboard adjustable tire pressure systems. The central tire inflation system (CTIS) is one such system. Through a CTIS, the vehicle driver from the cab position is capable of selecting a pressure level based on the ground flotation conditions, and the vehicle load, for uninterrupted operations. Because operators will expect these systems to provide the selected level of pressure and to maintain that level of pressure especially as the vehicle returns to highway operations, it is important that all marketed systems respond with a minimum level of performance to assure continued in-service safety.
In the "off-road" or unimproved roadway environment, the driver typically will operate at a reduced vehicle speed and may choose a reduced tire inflation pressure. Under these conditions, it is important to maintain a balance between the tire's flotation performance at high deflection and the tire’s durability. These characteristics are particular to each tire manufacturer's product, and therefore it is not practical to define one universal set of operating criteria nor a singular limiting threshold for the off-road environment. At the same time, when these vehicles return to highway operations, it is expected that tire pressure systems of this category, having survived the harsh environments to which they were exposed, will be able to bring the tire’s inflation pressure back to the specified highway pressure level, and maintain it.
For both SAE document SAE J2848/1 and SAE J2848/2, the system performance and communications to the driver functions have been made coherent and consistent. Under this document, it is essential that the driver communications and performance thresholds, especially when operating to highways conditions, also be consistent with the document series. Each management system must still keep the driver informed of the status of the pressure level and make him aware when the system installed is no longer performing its intended function. This document captures the attributes of pressure management systems while retaining the alerts and warnings so vitally important to the driver.