Questions driving in the mountains

I will try all this out next week--- Elsie and I are touring Colorado next week, all over it. We will cross several different of the passes, probably, I will just stay in ''D'', we'll see. I perhaps will try one of the pass descents in ''B'' just to get a handle on it.

 

In either case, when the engine braking starts you will hear a counter intuitive effect, the harder you brake, the faster the engine roars. This is planed and is nothing to worry about, but not what you expect.

 

I just went from Phoenix AZ to Rifle Co, Yellowstone, Glacier, Minneapolis and am now a few miles south of Green Bay. While going from Phoenix up to Flagstaff, I didn't have to use "B" mode or the brakes at all on the 6% downslopes while using cruise control. The Prius kept speed stable going up and kept it in check going down. Fortunately, no one pulled out to slow me down, so it was smooth sailing, quite unlike my Montana van where I was always on the brakes going down. However, when it came to the Beartooth Highway (212) from Red Lodge MT through North Yellowstone, "B" mode was a necessity to have braking kick-in right away and avoid overusing the brakes through the hairpins, etc. The same was true going through Glacier NP, then over to Fairchild AFB and on I-90 east to Bismarck ND. I got fairly good at judging when I needed "B" mode vice letting cruise control take care of things. There were a lot of back roads too where I'd come over a hill and have to drop from 65/70 to 45 very quickly, so "B" mode got a real workout. The roads in Montana were also notorious for 70 mph speed limits, but not recommending speeds for curves and many curves were uncomfortable at 70 mph, so "B" mode was use a lot there too.

I didn't try to manage MPG, so mine went from a low of 39.8 (actual) between Phoenix and Flagstaff running 65/75 to a high of 54.0 once we got well east of Bismarck and flatter land running a combination of 75 and 60/65. Between the 2 of us and luggage, I estimate we were carrying around 700 lbs. Average for the trip so far is 46 mpg over 4,500 miles, 90% in mountains or hills and almost none in cities other than passing through.

 

The PiP is not for everyone. If you do lots of short trips around home it has a significant advantage. If you do longer trips in hilly/mountain areas it has a modest advantage. However, if you do lots of trips on flat highways its pretty much the same as the standard Prius but without a spare tire.

 

Ha, thanks for responding, Double D, I was wondering how your trip was going. I also will hit Rifle, as family is there-- and for years I went there every year elk hunting, with family... I have made it fine in 2 Cadillac's, Trans-am, a Corvette [ duh! ] and several, several trips pulling 4-wheelers in Ford 4WD trucks... Elsie has been to Aspen, Snowmass on ''private jet'' and to Denver on commercial jet, she wants to ''sight-see'' and have a ''road trip''-- my favorite. John Madden and Lester do not fly anymore......I do not foresee any problems--- I am an old campaigner.... [ read ''road lizard'' of many, many years] Here's hoping you guys have a safe, un-eventual trip-- enjoy the road and scenery as we will.

 

Hi Lester, we're having a great time and the Prius has worked better than I expected. I had no problems going up or down grades, using "B", etc. I also haven't had any problems with it slipping backwards when starting on grades.

 

On occasional mountainous road trips I prefer to use cruise control and let the computer do the work for me to maintain my desired speed. On the downgrades I will let the car run 10 or 20 over the speed limit by pressing on the accelerator pedal with the cruise control still engaged. Otherwise, without my intervention the prius will first use regen to slow the car to desired speed, and when that is not enough and the battery reaches capacity for regen, it will begin engine braking automatically. Usually that is enough to prevent going too fast down any grade i've encountered at highway speeds. I have yet to hear of any prius "warping" brake rotors from overheating down a mountain road, something that "will happen" on normal cars if engine braking/downshifting is not used. If cruise control is not enough to control speed on the descent, use B mode or just push on the brake pedal. The beauty of regen braking on your hybrid is your "friction" brakes will rarely, if ever, be stressed or overheated to the point of permanent damage. From my understanding, using B mode will just transfer wear from the brake pads to the engine/transmission. So, my opinion, only use B mode if you fear your brakes will melt on the road you are about to descend.

 

It will start revving the engine up once you hit 80% in D, but more or less, it's just replacing the simulated "engine drag" that would normally charge the battery when you let off the accelerator. If you switch to B, the engine will run even faster, and provide additional drag. Conversely, if you switch to B before the SOC is at 80%, then it will not rev the engine to full speed, instead using the motors to siphon off some power to the battery (more than you would get from being off the accelerator in D, but less than you can get by pressing on the brake).

I don't believe this is correct - from my experience, the brake pedal has no effect on the speed of the engine while in B. The only things that really matter are battery SOC and vehicle speed. The faster you go, the more the engine will rev up to give you drag. And if the battery has hit its max SOC (or is warm enough that charging has been curtailed), then the engine will also rev faster. It does take maybe 2 or 3 seconds after shifting into B for it to get up to speed though, by which point you might've started braking harder. And also, for obvious reasons, it may be that you're braking harder because you started going faster.

 

In Montana, the speed limits were 70 mph and downgrades were full of curves. Many curves had a recommended speed of 45 mph and there wasn't much leeway. Other curves didn't even have a recommended speed (or I missed them), but couldn't be safely negotiated over 55 mph or so, and I'm not afraid of high speeds in the mountains. There was often just no way to let the car exceed the speed limit by 10, much less 20, mph safely. And that doesn't take into account the highway patrol.

 

The only thing I noticed was shifting into "B" resulted in more braking sooner than letting the car figure things out. I don't recall the engine speed changing when I also had to hit the brakes. When I did try to wait for the car to decide, I had to hit the brakes because we were approaching a curve too fast. I don't know if using "B" is better or worse than using the brakes "hard" to slow the car, but there were so many times when we would come over a rise at 70+ mph only to find the speed limit drop suddenly to 45 mph. I likened using "B" to downshifting the 4-speed manual transmission on my '70 GTO back in the day. Eventually I learned to assume a speed limit drop and slowed the car sooner without using "B" or hitting the brakes hard.

 

I seem to remember the ice rpm increase when applying the brake when ice is eating up surplus regen. H