Q: My friend was telling me how he went down a mountain using only engine braking on an automatic transmission car. Is that wise? Seems like a lot of stress is put on a lot of expensive transmission and engine parts vs. the brakes, which were designed to slow down and stop the car.
R.C., South Elgin, Ill.
A: Actually, engine braking saves wear and tear, especially on the brakes. When the brakes are constantly applied, they get very hot — in some cases hot enough to make the brake rotors glow red. Engine braking, on the other hand, turns the engine into a pump that operates not unlike a storm-door closer. Air is pumped into the cylinders and out the exhaust and, above a predetermined throttle-off speed, no fuel is injected. The transmission remains in a lower gear so the clutches suffer no wear. Modern, multispeed (eight, 10 or more) transmission cars even use engine braking to maintain the cruise control.
Q: A couple of years ago I remember reading one of your columns where someone asked you whether it was better to slow down a car by putting it in a lower gear or by using brakes. Your response was that brakes are much cheaper, so use the brakes. I've never seen any studies that show that trans braking has an effect on the life of a transmission. Have you? If you live where there are serious hills or mountains, you can overheat your brakes and they'll stop working. Going down a hill of more than a half-mile, it's always a good idea to use both the trans and brakes.
B.S., Wilmette, Ill.
A: As you may have noted from the previous item, you're right. In traffic and stop-and-go situations, we suggest using the brakes only. You may need to stop suddenly. Although we have not seen any studies on transmission wear, we have seen it firsthand back in the days when we were turning wrenches for a living. A brake job is far cheaper than a transmission job. However, modern electronically controlled transmissions are far more robust.
Q: Back in the '90s many Dodge Caravans and other Chrysler minivans seemed to have rear tires that were not perpendicular to the road. The lower part of the tire splayed outward and the top of the tire/wheel was a bit inward. Just saw it again on a foreign sports car. Is that my imagination or an optical illusion or not? And if I am accurate, do not such tires wear off on the inside very, very fast?
C.K., Williamsburg, Va.
A: The condition you refer to is called negative camber — inward tilt of the top of the tire. There are plenty of discussions about negative rear camber for performance driving, but for those of us schlepping the kids from school to practice to violin lessons there is a safety concern. In a turn, the vehicle body rolls and, when it does, negative camber increases the tire's contact patch — the amount of rubber touching the road. This helps stabilize the vehicle and reduce oversteer. Excessive negative camber does wear the inner shoulders of the tires, but some think it looks cool.
Bob Weber is a writer, mechanic and Master Auto Technician.