Letting the speed increase going downhill and then braking, snubbing, puts more heat into the brakes than maintaining a safe speed at all times. The amount of heat or energy the brakes need to get rid of can be calculated by a simply formula that considers the mass of the truck, which does not change while going downhill, and the speed. Lookup the formula for Kinetic Energy. Ke = 1/2 Mass multiplied by velocity squared. So ANY additional speed is multiplied by itself and increases the kinetic energy much more than expected. Say you let speed increase by 5 mph the speed portion of the formula goes up by 25, 5 times 5, not five. There is also the consideration of what steady speed should be used. A too-high steady speed will also introduce too much heat into the brakes. I was taught and drove my first 3 years to use the snubbing technique and all of my trucks had NO JAKE. After that I had trucks with jakes and experimented because I would travel the same roads, at the same times, for 2-5 years at a time. I was able to prove to myself what I expected to not work worked better than what I wanted to work.
Anyone can use the online Kinetic Energy calculators and input their own numbers for the mass (weight) of their truck and speeds. If you usually let your speed increase by 5 or 10 mph before slowing down, use those speeds and see the raw numbers. It never is less kinetic energy to let a vehicle speed up and the amount of kinetic energy that must be converted to heat by the breaks doesn’t increase a little bit for a little bit of speed increase. The Kinetic energy/heat increase a lot for a little increase in speed. The math is not even close. Light steady pressure and maintaining a constant speed produces less energy/heat than the alternative. If I used brake pressure I would only use just enough for it to register on the brake application gauge, not enough brakes to even feel their application.
