Around Once More on Tire Rotation
Question: Will you please explain for us one more time how rotating tires on a vehicle can extend tire life? Granted, the switching makes four tires wear out all at once, but how can it reduce overall tire wear? All other factors remaining equal--including tire pressure, alignment and driving habits--it would seem that total rubber loss per mile of driving should remain the same.--J.S.
Answer: Tire rotation can add mileage to your tires by interrupting wear patterns that are caused by mis-alignment, poor wheel balance, weak shocks and worn-out suspension parts. Wear patterns, such as cupping or baldness on one edge, can render a tire useless long before its normal life would have expired.
It’s important to interrupt these wear patterns before they become entrenched. For example, if a tire is worn badly along one edge because of an improper alignment, it may be impossible to stop that accelerated wear by simply fixing the alignment.
If you never permit the tire to become worn out severely in any one area, you are more likely to keep the tire in service until it is uniformly worn out. Sometimes, these wear patterns don’t occur, because a car is perfectly aligned and has a good suspension. Unfortunately, by the time you find out if this is the case with your car, a tire may be ruined.
But I think the assumption underlying your question is a good one. A very important aspect of tire rotation is to wear out both tires in a set of two at the same time. A cardinal rule of auto safety is to have virtually identical tires on the left and right wheels, though mixing tires types between the front and rear is sometimes accepted practice.
When one tire in a set of two wears out, you face the choice of discarding the one good tire or buying a second tire that matches. Either choice is not economical. So tire rotation can help make sure that two tires are replaced at the same time.
Finally, most service garages include tire rotation as part of the normal service that most cars should receive every 7,500 to 15,000 miles.
Q: I have a 1965 Mustang with a 289-cubic-inch engine. My dashboard light does not come on for night driving. I was told at two different times to try two different fuses, which I did, but each time it seemed to run my battery down. Is this possible? Is there a certain numbered fuse I should use?--I.D.
A: The fuse block under the dashboard has numbers printed next to each fuse slot, indicating the amperage rating for each fuse. The typical current limit on each circuit is 10 amps, though the headlight circuits are usually rated higher. Once you have identified which fuse is burned out, you should note the amperage rating and purchase a fuse with that rating only.
The drain on your battery indicates that you could have a short somewhere in the circuit that services the small lights that illuminate the dashboard. If you are using the correctly rated fuse, the short would have to be a fairly high-resistance one to not burn out the fuse.
The problem could be in the wiring, which in older cars is troublesome. As wire insulation ages, it becomes brittle and can fall off, causing shorts. Finding these shorts can be a nightmare. I suggest you find a mechanic who is familiar with electrical systems and let him go at it.
Q: I own a 1986 Honda Accord DX with automatic transmission. When I depress the accelerator, the transmission automatically shifts down into a lower gear and the car jerks. The dealer says the transmission of the car is very sensitive and has to work like that. But my other cars never did that. What’s your opinion?--M.K.
A: All automatic transmissions depend on two bits of information to determine what gear they should be operating in. One piece of information is the speed and other other is load. Determining speed is a fairly straightforward matter of measuring the speed of the shaft that comes into the transmission. The second factor, load, is a little trickier.
If you are on a level road and suddenly start climbing a hill, you have increased the load on the engine and transmission. To help the car accelerate, you want the transmission to shift to a lower gear. In the Honda, the transmission senses the increased load by a “transmission throttle cable” that runs from the accelerator linkage to the transmission housing.
When you hit the accelerator hard, the transmission, depending on the speed of the car and the gear that transmission is using at the time, may decide to downshift. The problem comes when the transmission makes the wrong decision, such as when you barely increase the speed and you still get a downshift. The transmission throttle cable is adjustable on the Honda Accord, so it may need to be checked.
As for the jerky sensation, Honda automatic transmissions have a unique design that resembles a manual transmission. The result is that the shift points are felt more firmly than the soft changes that many Americans are used to in domestic cars.
