I'm new to the Prius forum but used to be a member on the Tundra truck forum. I lost my password via a new computer and email address and had to rejoin.
I purchased a 2007 Prius last week and have a question. I live in the Orange county Ca. area; my wife and I decided to drive to Ventura last weekend just to put some miles on the car and enjoy it. It is IMO sensational in a lot of ways like 54.5 measured MPG, almost too good to be true! Now my question, while coming down the pass at Camarillo I tried the "B" gear in order to not fry the brakes. It had little if any effect, is that the way it is? And if it is, how do you keep from warping the rotors etc. on a long downhill? Thanks for your answers....
From what I have read, the "B" gear just uses the engine for braking. This is similar to what semi trucks use when going down a grade and is sometimes referred to as a "jake brake". Basically, the Prius uses the internal mass of the engine as a way to bleed energy from the drive train, thus slowing the car.
The downside to the "B" gear is that you lose most of the energy that would otherwise be routed into charging the batteries. From what I understand, there are only a few instances where it makes any sense to use "B" gear and most of them are situations where you are going to be decending a long grade over serveral miles and don't want to ride the brakes to slow your decent. Other than that, you are better off staying in "D".
But what happens to the brakes when you are going down a steep grade several miles long and are frorced to ride them? It seems to me if they are like any other vehicle you are going to warp the rotors or something. I know they are different because they are regenerative but does it harm the car in any way I guess is my real question.
Remember, the Prius does not have a normal transmission, so you cannot downshift into a lower gear to reduce your speed when going down a hill. The Prius is going to try to coast downhill to convert your momentum into energy to charge the batteries. The problem is that you have a speed limit to obey, so you ride the brakes. If you are going down a long grade and riding your brakes the entire time, you are going to cause your rotors to heat up to the point that they might warp.
That is the purpose for the "B" gear. It lets the engine do the braking rather than your braking system. Like I said, there are some very limited times where you will ever need to even think about doing this, but it is there if you need it.
I was in that exact situation last weekend and had to ride the brakes a bit to keep under the speed limit as well as maintain a safe speed. I used the B gear, it did next to nothing! I don't know the car that well but we have lots of long descents out west and it has me a bit concerned. It seems like you shouldn't have to fry your brakes to maintain control. I am probably worried about nothing because I am sure this was taken into consideration in the design of the car.
Regenerative braking mode.... whereby the car behaves more like a manual-transmission in the sense that when you lift your foot off the accellerator the car slows. (rather than freewheeling)
Regenerative braking mode.... whereby the car behaves more like a manual-transmission in the sense that when you lift your foot off the accellerator the car slows. (rather than freewheeling)
This recaptures more energy for the batteries.
Yes, I know but, it's not nearly as effective as dropping down a gear on a long grade which forces the use of the brakes. My issue is I don't want to warp the rotors if I need to ride the brakes. Although after reading the referenced link above it doesn't seem like I will if done properly.
Prius "B" gear on shift selector
Linear Mode
