Q: I always use Top Tier gas from the same brand in my vehicles. But I was wondering, does it make sense to vary the brands to get a variety of additives/detergents, or does it not make a difference?

A: All gasolines are the same until the additives are blended in. So, all Top Tier gasolines have additives that meet those criteria. Short answer: Switching brands is perfectly fine but isn't necessary.

Downshifting explainer

Q: I own a car with an eight-speed automatic transmission and manual shifters. If I am approaching a red light 50 to 100 yards away, am I better off downshifting or gently applying the brakes? Does repeated downshifting do long-term damage to the transmission?

A: You can leave the gear selector in drive and still operate the manual shifters. The transmission will revert to drive without harm. When the cruise control is set, the car may downshift on its own to take advantage of engine braking when descending a hill. The short answer is that yes, you may downshift when approaching a red light without damaging anything. I put my transmission in manual mode and use the paddles exclusively on twisty country two-lanes.

Another reason

Q: Regarding the query from a recent reader about why people leave 20 feet of distance between cars at a stoplight: One reason may be that, with the increase in carjackings in many cities, police departments advise drivers to leave room to maneuver in case someone tries to hem them in.

A: Many readers mentioned this.

Tire rotating

Q: I own an Audi Quattro and a Toyota SUV with all-wheel drive. Both vehicle manuals state to rotate the tires front to back and vice versa. I buy my replacement tires at Costco, and they insist that AWD vehicles have the tires crisscrossed when rotating. Which method is correct for these types of vehicles?

A: Rotating your tires ensures that they wear evenly at the same rate. That's important on all-wheel-drive vehicles because replacing only one or two tires is prohibited. Audi's front-to-rear and rear-to-front rotations meet these needs. But Bridgestone, the brand that Costco sells, recommends that the tires on AWD vehicles be moved diagonally. In my opinion, both techniques are acceptable and infinitely better than neglecting rotations.

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.