Correct Procedure for going up and down mountain grades?

If you set your cruise control for the speed limit, on the downgrades, engine braking will engage to slow you down. Don't be alarmed to see the HV battery icon full - this is normal. You can also "tap down" the set lever for more control.

 

Go like hell on the downhill to gain a run at the uphill

 

I set the cruise control at the posted speed limit and let do it's thing. It will easily keep a steady uphill speed if you just let it alone. On the down hill it will also take care of itself provided the grade is not so steep as to disengage the cruise. If that happens it will go into "B" mode and you will want to gently apply the brakes to maintain a steady speed.

 

On interstate highways I just set the cruise control and let it take care of the speed.

 

I don't expect that the car will have any problem doing this though the engine will be noisy and fuel use will correspond to the hard work.

 

My procedure

Up the hill floor it
Down the hill enjoy it

 

The car climbs the I-70 grades no problem at 80 miles per hour. Those are the steepest interstate grades in the country.
If you set it to cruise control you are going to be sorely disappointed. You need to punch it up the hill and B mode down.

 

I normally back off on the speed when going up a steep hill (10 to 15 mph below the speed limit). That's because I like to keep my engine power output somewhat constant and use a lower gear ratio so to speak (even though CVT has no gears) to climb hills. In some places, a truck lane is available for trucks climbing at a lower speed. I normally would hop on to that lane and get behind a semi but not following too close. This would reduce some air resistance as well.

I do not recommend using cruise control in landscape where the slope is too unpredictable. The car has no eyes so it's better for you to take control. Whether you floor it or take it easy while going up a hill depends on if you care about the mpg. If you decide to floor it, I'd suggest do it before you get to the hill and not after you started to climb. If I'm not mistaken, by flooring it you'd drain your traction battery much more and that would give you room for regen while going down the slope at a later time. You probably should do some experimentation on your own and decide which one is best for you.

 

My technique resulted in a 52.4 MPG average over the coarse of a 2,400 road trip. This included elevations of over 8400 ft. and some BSL. The OP begs some au contraire responses. So, as g4_power suggests, it would be best if you formed you own conclusions on what is best for you. In the long run I think the MPG average is a good measuring stick.

 

If you are truly going up and down mountain passes, without being aggressive from the get go you will not maintain speed and will have to move over into the climbing lane. I dislike perpetrating the stereotype that Prii are slow and always in the way. The Prius when driven properly up steep grades at high speeds works better than most vehicles with 4 times the power because of the awesome "gearing" of the PSD.

If you do not plan to climb the hill at 80mph, then by all means back down, but over long grades your battery will deplete (normal) and when you need to punch it you will have no power. The car has enough power to maintain your speed up the steepest slopes, but it does not have enough power to accelerate to speed up the steepest slopes because you cannot rely on having any available power coming from the battery.

I live in the Rocky Mountains and I-70 and other back road passes are the normal for this Prius half of the year. When they aren't covered in snow, the Prius has no problems.

If you want to drive for max mpg there is only 1 correct technique but you will be killed by road rage drivers. You accelerate down a hill lightly, do not allow regeneration. You pick up enough speed so that on the way up when you crest the hill you are barely moving, like single digit mpgs. Rinse wash repeat. We know this to be the most effective in theory because of math and physics on how the Prius maintains efficiency, but it is demonstrated by the high mpg rollers like Ken@Japan with his 100mpg+ tanks, some over hilly terrain.

 

If you baby it up the mountain, there will come a point where you will have to floor it. You are just prolonging the inevitable. And when this point comes, if you are doing 50mph in the right lane, you will forever be doing 50mph in the right lane unable to accelerate until you crest the hill.

If you drive into it knowing this will happen you can maintain speed at 65mph, 70mph, 80mph, or even 85mph. When the power drops out you can then maintain this speed until you crest the hill. The speed limit on most of the road is 65mph, traffic flows between that and 90mph. If you are going half that speed in the crawler lane even the 18-wheelers will get pissed off at you.

 

I have found that cruise control results in a loss in mileage of about 10%. That being said, long trips on flat roads are survivable only with cruise control. I just finished a 1500 mile trip to Victoria, BC. I got just over 61mpg on the way over (state highways, 60mph speed limits, no CC, but a 5000' pass). Coming back was freeway all the way with three lower passes and I got right at 55mpg. I used CC for about half of the return trip, but not on the passes. There is a lot of info on PriusChat and some of it is even accurate. You need to see what works for you.

 

The faster you go up the hill the worse your gas mileage will be. You can not change the laws of physics. Better to back off up the hills and go faster down. Try to build up speed before the climb and use momentum to get you part way up the climb.

Galaxy Nexus ? 2

 

Hmmm, lets see, $500++ average for a speeding ticket (++ for the increased cost of insurance and "driver ed" due to the ticket(s) ). How much fuel could that buy and would speeding down the mountain be fuel efficient at that rate?

 

Get a PiP and enjoy the extra EV miles you get for all that downhill.