Mountain Driving

I spent 10 days in southern Colorado last summer close to Wolfe Creek Pass, South Fork, Creede
and surrounding area. My Blizzard Pearl handled very well and I didn't have problems with the climbs or the descent. I was very happy when I saw the wonderful mileage I got on the trip!

 

I think it depends on the state of your battery systems and other factors such as the load you are putting on the vehicle.

Without those details, no one can tell you if the small ICE can generate enough power. The Gen III ICE is bigger than the Gen II but is still small compared to ICE only vehicles.

 

Just a few questions for some of you:

1) If you ran downhill with the windows open, would this increase drag a lot to help with B-mode?

2) Similary on an extended downhill, assuming the battery is fully charged, you could then keep the windows all open and then run the A/C on full blast. This should divert some electrical energy to allow for a little bit more regenerative braking capability, and help in braking. Since the battery is full anyways, the regen is providing the electricity (energy is free in essence). This is using the AC compressor for braking.

3) Conversely, going uphill, you want to switch off A/C and direct all available power to driving the wheels. Also you want to turn cabin heat on full to remove heat from the engine and prevent it from overheating. At least, I was told this advice for a non-hybrid. I suppose in a Prius this may not even be an issue due to its efficient ICE, or a waste of energy to run the fan.

PS - If I understand correctly, in B-mode, regen is limited to 30% of normal level. I read this in a Toyota technical document for the Gen I & Gen II.

Appreciate any feedback. Thanks.

 

Battery SOC has nothing to do with it. Even the GenII ICE is fully capable of powering itself + a few hundred kilos of weight up a 8% grade at 80mph with 0% assist from the battery. On long grades, you will deplete the battery. No worries, it is made to do that. The ICE has enough umph to move you.

You are overthinking this WAY too much. The Prius drives exactly like a normal car. A properly functioning Prius has a cooling system for the engine that will keep it cool under extreme operating conditions. Likewise the brakes in the Prius are no more likely to overheat than any other vehicle with similar weight. And there are very very few places that will overheat brakes.

As mentioned before, the decent from Pikes Peak is long and dangerous. They have at least added guard rails in some locations. There are mandatory brake stop checks and coolant checks where water hoses are available to cool down and top off if needed. This is an extreme that almost nobody will encounter on a drive even through Colorado.

If you just drive your Prius like you knew nothing about the car, it will be just fine. The only reason to "drop it into B" is to save your brakes. But your friction brakes will stop the car by themselves and won't overheat on any standard roads in Colorado excluding the Pikes Peak Highway.

The car automatically takes car of the SOC of the battery. When it is full at 80% (all bars) the car automatically spins up the engine and wastes energy. Faster you go, the faster it spins. You could open the windows and turn on the AC, but it is all unnecessary. The car manages itself, let it do its thing.

If you do come to Colorado, I do suggest Pikes Peak and Garden of the Gods (both located in/around Colorado Springs). But I-70 through the mountains will be no issue. I routinely travel this into "ski country" at 80mph with a couple passengers and all our gear. The battery drains completely (40%) and recharges completely (80%) multiple times, but it is doing what it was designed to do.

 

I agree that it is a bit of overthinking, but that's the point of this forum (imo?). I mean hypermilers overthinking every little aspect.

There's no expectations that my methods are practical in any sense of the word (like pulsing & gliding from 40 km/h to 20 km/h in my commute would get me killed) -- but perhaps in an extreme situation, it may help. Though I don't mind you knocking it from a sensibility point of view, I just want to know if anyone agrees it makes sense from a logical standpoint.

Thanks.

 

This has not been my experience:
1963 Ford Falcon 2.4 liters 84 HP (gross HP)
1972 Mazda Mizer 808 1.3 liters 69 HP
1977 Mazda GLC 1.3 liters 69 HP
1986 Ford Escort 1.9 Liters 80 HP
1989 Toyota Corolla All-Trac 1.6 liters 105 HP (AWD made the HP seem much lower, more friction)
2009 Toyota Prius 1.5 Liter 76 HP

 

Your questions seemed directed in a way that there exists a situation where any of them would make a difference.

Logically:

1) Yes the windows open will increase drag and the car will transfer more excess energy to overcome air drag then before. So more energy is needed. In B mode, it would mean less RPMs in the engine. How many less? I doubt it would be measurable.

2) Correct.

3) If your goal is to minimize battery strain, then switch everything off. This allows the battery to assist the ICE longer on an uphill slope. But any real hill will deplete the pack rather fast anyways, so you are just prolonging the inevitable. Turning cabin heat on full and opening the windows a crack is basically making the cabin an extension of the aircool system of the radiator instead of it hitting the firewall and forcing it to go down under the car and out. Now it can go through the car and out too. This is commonly done in old cars with bad cooling. On the same stretch of I-70 I had an old Subaru with a blown headgasket. It would constantly overheat, but I carried 10 2L pop bottles full of water with me and turned the heater on full blast. I was able to traverse the range each time. Strategy was to lightly accelerate up the hill, and accelerate more aggressively down the next hill to save momentum. If you are going less than 52mph, running the heater at full blast will force the engine to run even if it doesnt need to. So potentially more time the engine is on.

As for B-Mode, what is "normal level" that the 30% is referring to? You can regenerate fully up to 80% full charge.

 

Based on first hand experience there, if the load does not exceed the vehicle's rating, I am telling him that it generates enough power.

This depends upon one's reference point. Compared to bloated 21st Century gas hogs, yes. But compared to the mainstream 1980s 4-cylinder car that my Prius replaced, or another that my spouse still drives, it is not small.

I've done these on multiple cars, and even turned on the rear window defroster on the Prius, to increase drag. But it doesn't really seem necessary, and only the AC seems to be significant, particularly with the inefficient AC in my remaining nonhybrid.

This works on older cars with compromised cooling systems, but OP's car is too new for this to be necessary.

 

Thanks for the feedback. Perhaps in an emergency this info is helpful. For instance, if you are traveling in a caravan and one car breaks down in the middle of nowhere. Then you have to load everything into the Prius. Then perhaps the Prius is overloaded beyond the 700 lbs designed payload (5 adults + gear).

Or with a roof-rack to store skis and boards.

Or if you are in some scenic back-road, instead of the interstate where maximum grades are standardized. I know there are many worse secondary routes, even here in my locale. Plus it's better if the brakes are cool for an emergency stop, if there were a rock slide for instance.

That's also very good strategy about going uphill slowly and accelerating downhill to carry momentum back uphill. Thanks for pointing that out.

So the thing about B-Mode:

From Toyota Hybrid System / Toyota Hybrid Diagnosis / Section 6-1

That's a direct quote. The first sentence I quoted is some kind of mangled translation because it contradicts the second sentence, at least in the way I interpret it.

Here's a guide to Colorado I-70, if it helps anyone.

 

Yup. But keep in mind us engineers point out the abs max and then marketing and liability slash and hack it into something much safer. You could probably haul a silverback gorilla in the Prius no problem.

And I have 180cm skis (pretty long nowadays) and they fit perfectly in the hatch with the seat folded down. No need for a skirack. They actually fit diagonally just in the backseat as well.

Colorado definitely has some bad secondary roads. But if it is meant for commercial/residential traffic, it is abled to be traversed with enough skill and patience. If you are traveling in the wintertime, one of those chain kits for $100 that you just wrap the tire with and can be put on in 1 minute per tire is worth it. Nice to have for piece of mind. I have a kit in my boot by the spare tire although I have not yet had to use it. Even when there were tire chain restrictions in effect.

lol. If there is a rockslide, you will know it because you wont be moving fast enough to use your brakes. Rockslides are a real danger but they generally try to prevent them before it happens.

Best to just use a reliable car and not a 20 year old subaru with a blown engine. You have a Prius, so you are good to go.

I interpret that as B mode will waste 70% of recaptured regenerative braking spinning an air pump. So if the regen is maxed out recapturing 120A, then 84A are going to spin the engine really really fast with no gas and 34A are going back into the HV battery.

All of I-70 has cell reception even in a blizzard. It is also pretty well populated. The runaway ramps are clearly marked. There are even signs like "you're not down yet, another 3 miles of 6% grade ahead" or "lost brakes? DO NOT EXIT. Runaway ramp X miles ahead". It's not a bad system.

 

^Cool. I've never driven I-70 in Colorado. However, I do drive the grapevine all the time. I can make this no problem in my marginal non-hybrid vehicle, so I'm sure I'd have no problem in a Prius. Pretty much means you are spot on that the Prius will handle itself on I-70.

This is a plot elevation of the grapevine along the I-5, from about the 5/210 interchange, to somewhere in the central valley.

You can see how flat the central valley is. If you imagine going from right to left, which is north to south, you go from 200 ft to about 4200 ft.

In Colorado, it's about 4000 ft to 11000 ft back to 4000 ft in. More or less about 2 grapevines, repeated a few times. Gives me a good idea what to expect.

 

Thank you.

I love Flagstaff. Off roading the cinder dunes is a blast. I always have a steak at the Horsemen Lodge about 3.5 miles north on hwy 89 when we're there. Lots of cool things to do in and around Flagstaff. Walnut Canyon, Sunset Crater, Meteor Crater, Indian Ruins, Sedona, etc.

Back to Colorado. For aspen viewing, a good trick is to call one of the hotels or off road tour companies in Crested Butte at their 1-800 number to get an idea from the locals when the aspens are going to be at their peak color before going. The drive between Durango and Silverton is also beautiful when the aspens are turning. Note, CR12 and Durango are far enough apart that they will be in different stages of color change. Generally, it's late September to early October. Catching them early rather than too late is better if you have to err one way or the other.

There are gorgeous drives (paved roads) all over Colorado and the Prius can handle all of them just fine. Since the OP is going to be in the northern part, the drive up through and above Estes Park is well worth the time. It's gorgeous.

 

I will second the Horseman, we ate there once last summer and will stop there again this summer when we stop in Flagstaff on the way to Mesa Verde and Durango.

For the OP.

People were driving far lower performing cars than the Prius on mountain roads well before you were born. Just drive the thing.

1. The engine is based on a very reliable higher powered Corolla engine. The Prius engine doesn't develop enough power to hurt itself and at 10k foot altitudes it develops a lot less power than it does at sea level. Don't hesitate to just keep your foot on the floor. Just ignore the whiny noise the engine makes, you won't be damaging it.

2. Braking is simple. Brakes are for changing speed, gearing down (or using B) is for maintaining speed. Any time you have to ride the brakes going down a hill to maintain speed, you should be in B.