CLICK & CLACK : How About Prius's 'B' Button?

Sunday, January 4, 2009

Dear Tom and Ray:

We recently bought a 2008 Prius and just love it, love it, love it. But we're having a bit of a discussion about how to use the "B" on the gearshift. I say it's like a downshift, and you should use it only temporarily, while going down a steep hill or coming to a stop. You use it to save the brakes, then return to "D." My husband thinks it's fine to drive most of the time in the "B" mode, since it regenerates electricity and recharges the battery. Who's correct? And if "B" is the gear to use all the time, why didn't Toyota just call it "D" and forget the separate braking option? -- Gayle

TOM: Gayle, you're 100 percent right, and your husband, unfortunately, has his head up his brake line.

RAY: When you shift into the "B" mode, you increase the drag created by the regenerative portion of the brakes. And while that extra friction does produce some electricity to help recharge the battery, the "B" mode's primary purpose is to simulate downshifting, or engine braking, when you're going down a long, steep hill.

TOM: The "B" mode's secondary purpose is to give guys something to fiddle with while they're driving. And after THAT comes creating more electricity to recharge the battery.

RAY: In any car, hybrid or not, when you go down a long, steep hill, you run the risk of overusing your brakes. If the brakes overheat badly enough, the brake fluid can boil, and cause the brakes to fail completely. So it's always recommended that you downshift in those circumstances, rather than ride the brakes, to keep the car at a safe, reasonable speed.

TOM: But since the Prius has an unusual propulsion system and transmission, they've essentially "faked" a downshift mode for just that purpose.

RAY: So unless you're driving under conditions where you specifically need the equivalent of engine braking, just leave it in "D," Gayle. But try not to rub it in too much. Remember, husbands have fragile egos.

Dear Tom and Ray:

My boyfriend is a great guy but is prone to procrastination and is accumulating LOTS of cars. Here's the inventory of vehicles: a VW bus, two Saabs, an Isuzu Rodeo, a Subaru Forester, his Subaru Legacy, an engine for the Rodeo sitting in the garage and a BMW R1100RT motorcycle in the garage. All of the cars in the driveway are in various stages of repair. Don't get me wrong, he is an amazing mechanic. But how can I help him finish some of these and make room for MY car? -- Beth

TOM: Gee, Beth, it sounds like a pretty harmless hobby to me. I mean, some guys use their free time to go out drinking or carousing.

RAY: But it's perfectly acceptable for you to set some limits on it. For instance, where he does it. See, this guy needs to do this professionally. He needs to go into the junk business.

CONTINUED     1        >

© 2009 The Washington Post Company