Are you a pusher/tag expert and know where to get help? Try eLearning and Guru.
- Gary Hey
- 21 hours ago
- 2 min read

Did you know mounting a pusher/tag is only allowed at the factory on tractors, given RSD (Reduced Stopping Distance) requirements? This is because the ABS - ESP/ESC is designed in conjunction with the lift axle. The system can’t be reprogramed after the chassis is manufactured. Straight trucks don’t have this requirement, thus lift axles can be added anytime with any quantity.
The 1st axle (located next to the drive axle) must be more than 96” from the rear rear drive axle, or it carries no weight = 0 lbs. Tandems (40" - 96") are rated 34K federal and most state bridge formulas. With 3 axles at 96”, 34K is still the requirement.
Axles spacing with the drive suspensions at 56" w/one inch increments must locate the lift at 41" min. 55" is 42". 54" is 43". 52" is 45". All equal 97".
Given most all <13K pushers are lightly loaded, the others can be located as close as possible. Rule of thumb is 3” between tires. Seems some DOT inspectors require 40” for these axles, but that’s not the regulation. Some officers assumes the tandem definition is part of the equation, which it’s not. We recommend Vocational experts run a bridge calculation document for each chassis. We have a calculator if you need one.
Adding the LQ-5 Bendix valve reduces brake pressure to the pusher/tag (up to 40 PSI). Since these axles are usually lightly loaded axles, they tend to flat spot tires.
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