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
versus the brakes, which were designed to slow down and stop the
South Elgin, Ill.
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
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.
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?
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.