Motormouth: Run-flat tires run rough

Q: I just bought a pristine 2017 Mercedes-Benz GLA250, only 60,000 miles, with brand new run-flat tires. Love the car! Hate the ride! My teeth jar going over bumps. My mechanic took some air out of the tires but told me if I want a smoother ride, I need to buy “regular tires.” So now I’m thinking about pulling the $1,000 trigger on some new Michelins. Your opinion is so much appreciated.

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 actually are more prone to getting flats. I ran over a pothole a second time, and the entire sidewall came apart, which required a tow. I’ve never had anything like that happen on traditional tires.

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?

A: There are two kinds of tire pressure sensing systems: direct and indirect. The direct system is the most common. It 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: I have a 2015 Subaru Forrester. I’ve noticed that the gas mileage is about 2 miles per gallon lower in the winter. 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.

A: No. The engine is most efficient at normal operating temperature. Blocking the radiator also blocks the air conditioner condenser, which runs when you select the defroster. Diesel engines in semis are another story.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to motormouth.tribune@gmail.com.