Class 1 Practice

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#1. In large commercial vehicles, most air brake systems use automatic valves to

increase air pressure at the drive wheels.

increase air pressure at the front wheels.

reduce air pressure at the front wheels.

reduce air pressure at the drive wheels.

Most modern tractors are equipped with an automatic front axle ratio valve, which supersedes the manual front brake limiting valve in older tractors. In light-to-moderate braking, the ratio valve automatically reduces air pressure (and hence braking force) to the front wheels to reduce the chance of front-wheel lockup (which could result in a skid) on slippery roads.