Q: I just bought a pristine 2017 Mercedes-Benz GLA250, only 60,000 miles, with brand new run-flat tires. Love the car! Hate -- I mean hate -- the ride! My teeth jar going over bumps! These tires are just terrible! My mechanic took some air out of the tires but told me if I want a more smooth, regular ride, I need to buy “regular tires.” I only drive about 12 miles round trip to play pickleball and do some shopping and I have AAA, so I’m not concerned about a flat tire.

Thinking about pulling the $1,000 trigger on some new Michelins. Your opinion is so much appreciated.

B.J., Orefield, Pennsylvania

A: See the next question.

Q: What is your opinion on run-flat tires? I understand their value and actually had one save me once when I went over a pothole and got a flat. I was able to drive the 35 miles home on the run-flat. However, I think they ride much rougher and are more noisy than traditional ties. I also think they are actually more prone to getting flats. I ran over a pothole a second time and the entire sidewall came apart, which required a tow. Never once had this happened with potholes on traditional tires.

A.W., West Simsbury, Connecticut

A: My opinion matters less than yours, but for the record, I prefer traditional tires for both handling and riding comfort. You’ve got to base your opinion by weighing safety and security against comfort and handling and cost.

Q: The tire pressure indicator on my instrument panel, I assume, is electronically transmitted. Where are the sensors located in the wheels? If I need new tires, do the sensors also have to be replaced ?

M.M., Des Plaines, Illinois

A: There are two kinds of tire pressure sensing systems: direct and indirect. The direct system is the most common and has sensors mounted in the rims and is part of the valve stem through which air is injected. The second, indirect system relies on the ABS system’s wheel speed sensors. On the indirect system, if a tire loses air, it rotates faster than the other tires triggering the warning light. If they are working, the sensors do not require replacement.

Q: One argument for inflating tires with nitrogen is that it leaks out of tires (fractionally) slower than oxygen does, so that tires inflated with 100% nitrogen won't need to be topped up as often. But that means that tires filled with plain old air will gradually become filled with pure nitrogen, as the oxygen preferentially leaks out. Gotta love science.

G.Z., Chicago

A: Yeah, but they will have lost pressure. Dilemma: Use air or nitrogen? One is cheap and easy to find when you are passing through East Overshoe, Idaho.

Q: I have a 2015 Subaru Forrester. It's been a great car, but I've noticed the gas mileage is consistently lower, about 2 miles per gallon in the winter. This occurs even on long drives when the car should be at temperature. Science indicates engines are more efficient at temperatures. Would it make sense to block part of the radiator to increase the operating temperature in the winter? I've seen this on semi tractor radiators.

S.B., Buffalo Grove, Illinois

A: No. The engine is most efficient at normal operating temperature. Blocking the radiator also blocks the air conditioner condenser as the A/C runs whenever you select the defroster in the climate control. Diesel engines in semis are another story.

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