LQ-5 Valve

The axle that locks up first in a hard-braking situation is the lightest loaded axle. If you utilize a lift axle, it will be this axle in most cases. Ever since the Reduced Stopping Distance (RSD) testing of 2011, there has been no option for sensors/modulators on lift-able axles (manually raised and lowered pushers or tags). 

There is an air-proportioning valve that can help, however. Designed for tractors in bob-tail applications,

it reduces air pressure to the service brakes, and can be plumbed to help prohibit lift axle brake lock-up.   This valve may not be available through the factory.  If your customer is interested in reducing flat-spotted tires, you might ask your shop or body builder if they would be interested in adding to LQ-5 valve manufactured by Bendix.  

This valve drops the application air pressure (approximately) in half to the lift axle.  For example, with a 40-psi foot pedal application, the lift axle brakes get 20-psi.  Full application pressure is passed though at full pedal pressure, so they will lockup regardless.  This valve would only be recommended on axles in the 8K-13.5K range, pusher or tag axles rated at 20K usually are loaded to 20,000 lbs.

The manufacturers don’t give away tires, so control costs where the opportunity exists.