Dashboard

I borrowed my neighbour’s Honda CRV yesterday when my car was in for a service. It has automatic transmission with an overdrive on/off button at the end of the shift lever. As I started driving, I noticed a light on the dashboard telling me that the overdrive was off. This got me thinking about the buttons, levers and switches in various cars that should be labeled “waste petrol/save petrol” but are instead given other, less clear labels that drivers may not understand. It did turn out that the owner of the CRV had very little idea what the overdrive on/off button was for. (It also turned out that the overdrive was off because I had inadvertently bumped the button, but I won’t let that get in the way of an informative rant.)

Overdrive switches on automatic transmission cars are far less common than they used to be, but in many makes of cars their replacements have been even more frightening. Overdrive is simply the highest gear on an automatic car, the one at which the wheels are turning faster than the engine. The point of optimum fuel efficiency is the slowest speed at which your car can comfortably drive in this highest, overdrive gear. (Or the highest gear on a manual transmission car.) Losing that gear by turning overdrive off increases petrol consumption by 20 percent or more for highway driving. The only legitimate reasons to turn overdrive off is for engine braking when heading down a steep hill on a highway, or if the automatic is temporarily shifting back and forth repeatedly between top gears, but many people leave overdrive off for extended periods.

In some cars, turning the overdrive off also tells the automatic transmission to let the engine rev higher before shifting into 2nd and 3rd gears as well—and so fuel efficiency declines at all speeds. This is the approach used today in many cars that have a switch, button, or lever for “sports mode.” At this setting, the transmission will delay shifting up at every gear, though they will eventually reach the highest gear. The higher revolutions-per-minute will make the engine noisier and less fuel efficient, and the automatic shifting becomes jerkier. (The car will also accelerate faster, but if your main goal is fast acceleration, I’ve already lost you.)

Volvo mercifully has done away with its hideously labeled “Economy/Sport” switch. To a hormonal male, it might as well have read “Pansy/Tough Guy.” Mercedes labels the switch, “Comfort/Sports,” which at least makes economical driving sound a little bit appealing. BMW and Volkswagen have a Sports mode on all of their automatics.

Toyota has done away with Overdrive-Off without replacing it with a Sports mode, and the other manufacturers should follow their lead, in my opinion. I’m generally a timid guy, not suited to the life of an eco-saboteur who would ram a whaling boat or dynamite a logging truck, but if I’m driving someone else’s car, I do them a favour and switch Sports mode off. See if they notice.