transmission B mode WHY?

I use the B gear just about daily doing down from 800 meters to 400 meters in about 7 klm (over 1200 feet drop over 4.3 miles)
I like it a lot
BTW
CC gets disconnected as soon as you shift

 

Thanks for the post Fuzzy, finally someone who gets it that there are more severe roads than Interstates in this country and does more than hand waving about Prius mountain braking capability.

I came down Pikes Peak in a 1983 Camry with 4 speed automatic and didn't strain the brakes at all by using low range to keep it in 1st or 2nd as needed. It sounds like a Prius is less suited for that road than a well driven car with a normal automatic transmission.

 

You could turn the lights on, turn the AC on full blast, plug something into both the aux ports and blast the radio in hopes of draining off the excess regenerative braking as it comes in and still use B mode. So what B mode cannot do, light regen does. What is regenerated gets wasted by cooling the cabin with the windows down or something.

 

I have no idea why you would come to that conclusion, but I can't alter it with facts.

 

Because Fuzzy had to stop and let his brakes cool descending Pikes Peak Highway in B, while I have descended that road in a regular automatic transmission car using 1st and 2nd gear with little brake usage.

 

For what it's worth, I took mine on Mineral King Road in Sequoia National Park; looking at Google Maps, it's not quite as steep on average - 6400-foot drop over 22.8 miles, versus a 6200-foot drop over 18.8 miles; that's 5.3% grade versus 6.2% grade. However, I wasn't in B, since in my experience on that road, it seemed that the car had to be going much faster than I was (15-20 mph, most of the time) to get any appreciable engine drag. I felt no need to stop to give the brakes a rest. My guess is that Fuzzy was being extra cautious.

 

It is a mandatory brake check. You are required to stop, if you did not then you did so illegally

 

It was 1983, either they weren't checking brakes then or the brake checker was on break. I know enough about my cars to know when I need to stop and cool the brakes....never because I know how to drive on mountain roads.

 

Ah yes. I believe it was in the mid 90s when they changed it, not sure. I know it was mandatory in 1996. There were a few too many deaths from people overheating and flying off the side.

There still are a few deaths every year from people using brakes too much.

 

I used the lights, AC, and rear window defroster. Still not enough regen drag.

Due to heavy downhill traffic, I could not select a different speed to best match the car's capability. My previous cars do/did better in this type of situation.

My three stops were voluntary ones at other locations. Apparently I was being cautious, as the checkpoint attendant indicated that my disk temperature was fine.

But the brake odor was the worst I'd ever smelled on any of my own vehicles, even if it wasn't even close to that Florida pickup, or to the profusely smoking almost-runaway tractor-trailer in front of me on the Whitebird Hill on U.S. 95.

Don't mistake the whole road average for the segment above the checkpoint. If it was just 6.2%, they wouldn't have an attendant staffing a go / no-go checkpoint.

 

Fuzzy, here's some numbers to back-up your observation. The source I found says the average Pikes Peak Road grade is 6.7% with a maximum 10.5% grade. That's getting serious when it goes on forever and is twisty enough that you can't go fast enough in your car to get good engine braking.

 

Not trying to disagree (this is just curiosity at the wheel here), but I just thought I'd try Google Maps' terrain feature to pick out a large grade from Mineral King as well - if I'm fairly generous about how much of the road I include covering one particular incline (which both clearly crosses the elevation lines, and appears to be more steep than average), I can get a 25% grade (though only over ~500 feet). If I estimate more on the short side, it comes out to 30%. Granted, lots of inaccuracy here, given that Google Maps doesn't zoom in very far, and who knows how accurate it is at measuring distance on the road, especially such a curvy one.

I searched the web for such information too - and found that somebody counted the curves (698 over 25 miles!), and historically, the steepest grade was 42%, until the road was relocated in 1913. Better hope your horse team had traction control and anti-lock brakes!

 

In some places drivers used a crosscut saw to fell a tree, and a chain to drag it down the hill. At bottom of hill, discard tree and retrieve chain.

In high traffic areas this did lead to serious deforestation of the top of the hill.

 

Here are some plots from toporoute.com. Total drops are similar, but let me pull out some numbers for the steeper long sections.

Mineral King, from about mile 2.5, drops about 5100 feet in 15 miles, or 340 feet per mile, or 6.4%:



Pikes Peak, from Devils Playground at about mile 3.5, drops 3200 feet in 6.5 miles, or 495 feet per mile, or 9.4%:



I wanted to go faster to get better compression braking, but traffic density did not allow for that.

Note also that Pikes Peak elevation, about 6000 feet higher than Mineral King, results in 20% lower air density. This directly reduces engine compression braking and convection cooling of the brakes. Compared to sea level, the top of Pikes Peak has about 40% lower air density.