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Motormouth: Only 1 tire is bad; why do I have to replace all 4?

Bob Weber, Tribune News Service on

Published in Automotive News

Q: My wife recently hit the curb, ruining the right front tire of her 2016 Lincoln MKS. When I went to replace the tire, I was told that that tire was no longer available and, because the car was all-wheel-drive, all four tires had to be replaced. The car has only been driven about 23,000 miles. The other tires have plenty of tread left. Anyways, the tires were replaced at a cost of $1,200. I had heard that all the tires on an all-wheel-drive vehicle had to be the same. When I asked the salesman why, he said he didn’t know. Also, I asked what would happen if I just replaced that one tire. Again, he didn’t know. Would anything bad have happened to the vehicle if I just replaced the one tire and saved $900?

E.C., Boston

A: Your car has a viscous coupling that links the front wheels to the rear wheels. Usually, it simply does nothing. But if the wheels on either the front or rear start to spin, fluid in the coupling will congeal and redirect the torque. Mismatched tires cause the coupling to engage all the time, which damages it. All wheels and tires must be the same diameter. Replacing the viscous coupling would cost more than the tires. That’s also a good reason to rotate your tires regularly.

Q: I have a Hyundai with the lane-keeping assist feature that gently beeps to tell me I have drifted over the "fog line" as well as reminding me I have crossed a center line. It also gently nudges the steering wheel to correct the action and if I let it, will actually try and steer me back into compliance. It is fairly close to hands-free driving, but not nearly good enough to make that claim. I am assuming it does all of this fancy work via some sort of video sensors that are looking down toward the pavement for the existence (or lack thereof) of some form of painted marking on the road. So, my question is: How does this feature work (and does it work?) on a snow-covered roadway where these painted lines are not visible to the eye? If it is true that it is "looking for the painted lines," then wouldn't that pretty much rule out driverless cars in a climate that even occasionally has snow on the road?

P.L., Bloomington, Minnesota


A: Forward-pointing cameras, usually located in the rearview mirror, look at the lane markers—the lines on the sides (which some people call fog lines) and the center lines. Obscured lines, missing lines and broken lines render the system useless. Even if the lines are visible, though, you can override the system by manually turning the steering wheel. Lines gone? Hands on.

Q: I have a 2022 Ford Explorer with an aggravating warning to keep my hands on the steering wheel. On long drives this warning comes on several times even though at least one hand is on the wheel. It seems to only be satisfied if I keep my hands at 10 and 2 all the time. Can this feature be shut off?

D.P., Wauconda, Illinois

A: There is no simple setting to disable the lane-keeping feature. Try wiggling the wheel from time to time. Driving 72 straight miles of Interstate 80 between exit 318 in the Grand Island, Nebraska, area and mile marker 390 near Lincoln may have you wiggling like a worm.

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