down shifting on a downgrade

Real mountains have grades that vary. You don't go down 30 miles of Donner at 18mph just because it has one 7% section. So yes, you do need to know how to shift, both up and down, when on mountain roads...

 

Only one of the instructors made us do it, and I hated him. I said every single little thing that I did, including "gas", "brake", "reaching for shifter", "putting hand back on wheel". I was impressed, he managed to either deal with it for the entire 15 minute trip, or he was able to just completely tune me out.

 

Yes sometime its better to shift on a downgrade. If you are a rookie make sure you know what you are doing. My gear selection was always based on the grade the speed limit, my loaded weight and my experience with the hill. If I was empty or lightly loaded I might allow the truck to go a bit faster then normal. No two situations are 100% alike.

 

You need to know how to down shift in a critical situation such as a decent. It's not a matter of "if" you find yourself in too high a gear going down a long grade, it's a matter of "when" will this happen. It will happen. Practice it anytime the opportunity presents itself and it's safe to do so on lesser grades on quiet roads. You need to know how to down shift in traffic and the situations, downshifting on a hill as not much different, just much more critical that you don't screw it up.

Also, engine brakes (engines) seem to have a "sweet spot" where they are most efficient at "braking" (in terms of RPM's) so you'll need to downshift to get the enhanced braking effect of the engine brake (higher RPM's) to continue down the grade. An engine brake will perform much better at 1700 RPM then it will 1300 RPM

 

Every hill and weight and environmental factor combination is different. And like was mentioned many have varying decent rates. You have to find the right speed and the right gear (RPM) that keep you comfortable with reduced brake application requirements and reasonable speed. Descending long grades while heavy, like flying and engineering aircraft, is all a matter of compromises to get a a rate of descent that makes sense, in terms of safety and being able to make an emergency stop in a safe amount of distance if need be, but not going down any slower then necessary. Experience is your best teacher.

It's nice to be able to descend without ever touching your brakes, and this is ideal in terms of safety. However, it's not necessarily "practical" to do so in every scenario. You have brakes, and they are there to use, but they have to be used in a "smart" manner, and conservatively and should never be relied upon too heavily.

 

Shifting on a downgrade is not much different than shifting on level ground, except you will gain some speed.

If you have to down shift going downhill, make sure you get about 5 MPH below what you would normally shift at.

For example, when up-shifting from 9th to 10th it would be done at 55-56 MPH in my truck.
If I need to down shift on a downgrade I would slow to about 50-52 before I started the down shift.
Just make sure you are not burning your brakes before you decide it is time.

I was told the same thing when in school - NEVER down shift while going downhill.
And my mentor shot that to #$% when he asked me... What if I was in the wrong gear and had to use the brakes too much? They would burn, and me along with them.
So he taught me the proper way.

Grades change, and sometimes the proper gear at the top of the hill won't be the proper gear a mile down.
What then?
You need to know how to do it, and when.
If you have to apply brakes more than 2-3 times per minute you will be in danger of a fire. In that case, slow down and shift down.

 

I think you're better off paying attention to what you are doing instead of trying to tell somebody else what and why. Sounds goofy to me...