What is the "B"?

My reference point is US95, descending into Lewiston Idaho. Top to bottom it is 1975 feet in 7 miles. The steep core is labeled 7% grade, though from toporoute I can justify only 6.8%.

For this descent, assuming a reasonable load, I'm figuring about 28kw at 60 mph, though this includes air drag of the hull.

 

I didn't know about toporoute. VERY cool! Here is an elevation profile of my route:



I didn't remember the two areas of rise on the way down LOL
As you can see though, the steepest grade for over 0.5 of a mile exceeds 10% if I am eyeballing accurately. Too bad the graph does not have more distance resolution.

 

Even though "B" doesn't give enough drag to match the friction brakes (thankfully), it DOES allow you to slow using friction brakes, then coast to allow them to cool.

Do note the Prius NEEDS "B". It's a very slippery car with almost no mechanical drag without it. It takes off down hills!!

Try highway 99 in B.C., heading west (south), from just past Duffey Lake to the IR at Lillooet river. Some places it's 18% grade. Luckily, you don't go too fast on this road. Best part is the 10 km/hr corners and Bailey bridges further east (one lane). Oh, and the switchback at one of the 18% grade parts, where the posted warning is 10 km/hr. Bottomed out the forks on my RZ350 motorcycle slowing for that one!

Had bugs in my teeth after taking the MC on that road. (how do you tell if a motorcyclist is happy - he/she has bugs in his/her teeth!)