The 3 and 5 Rule for Descending Grades

Professional drivers should not have the habit of lightly riding the brakes for long distances as a way to control their speed.  Most heavy vehicles have additional braking devices like engine retarders which can help control speed and you should know how to use the devices on your vehicle.

But regardless of your use of your engine brake, there is a good way to use your service brake without causing unnecessary wear and tear and while delaying the onset of brake fade.  The technique is called the 3 and 5 rule (also sometimes referred to as snub and roll), and the basic principle is that you apply your brakes hard enough for 3 seconds to reduce your speed by 5 miles per hour.

This isn’t a rule that needs to be followed exactly, but the reason why these short, firm brake applications are better than riding the brakes is because they engage all of the vehicle’s brakes at once to more evenly distribute heat.  Brakes, even if well-adjusted, do not apply perfectly-evenly throughout the vehicle, so if you gently apply brake pressure the first brakes to start to apply are doing most of the work.  They heat up quickly and will lose effectiveness before other brakes do, leaving fewer effective brakes for an emergency stop.  The 3 and 5 brake method allows all brakes to engage quickly and do their part evenly to slow the vehicle, and by applying the brakes and then releasing after about 3 seconds, the brakes are given a brief opportunity to cool.