Q Last summer I was looking to replace two of my four P165/70R13 tires. I found some cheap ones at Wal-Mart for $35 each. I asked if they could put them on that day.

The mechanic showed me the recommended tire information on the door jamb of my car, saying that because the recommended tire size was P165/80R13, they couldn't put the on 70s; they could put on only tire sizes specified by the carmaker. I tried to explain to him that it was a "recommended" tire size, but to no avail. I took the car to another Wal-Mart and got the same speech there.

I have purchased a lot of tires for many cars from a lot of shops, but in my 35 years have never heard such a thing. Have you?

A I suspect the issue isn't tire size, rather it's the potential liability of installing tires of a size not recommended by the tire maker. Check with a good tire dealer; a P175/70R13 tire should have about the same rolling diameter and would fit the same size wheel.

Why are you looking for "cheap" tires? No other components on your vehicle are as important to your safety as the tires. Look for inexpensive, quality tires -- your safety rides on them.

Q I recently purchased a used 2003 Ford Ranger with 52,000 miles on it. It's a V6 2WD with an automatic. Recently, while pulling away from a stop sign, it seemed to slip out of gear. The transmission engaged for the first few feet, then the engine revved slightly before it re-engaged with a small clunk. It has happened only a few times since, always while pulling away slowly from a stop. I'm concerned.

A I would be, too. Make sure the fluid looks relatively clean and pink, and the level is up to the "full" mark on the dipstick when the vehicle is fully warmed up. And check for fault codes with a scan tool to identify any type of transmission issue. From a maintenance point of view, have the fluid and filter changed. Even though Ford doesn't have a recommended transmission fluid change interval on this unit, I think this is a logical next step.

Q You have explained "fuel packing" in the past. If I remember correctly, you've explained that while at a filling station a person should not continue to fill the fuel tank -- squeezing more and more fuel into it, even though the automatic shutoff on the fuel nozzle is stopping fuel flow from the pump.

I think you've explained that this is not only potentially dangerous, but potentially bad for the emissions systems on the vehicle as well as the environment.

Would you consider explaining it again? Seems like every time I fill up, about 80 percent of the folks there are packing as much fuel into their tanks as possible. They must not know it's a bad idea.

A Just as you described, "fuel packing" can overfill the fuel tank and force liquid fuel into the vapor storage system and the charcoal canister.

At start-up, some of this fuel can be drawn into the induction system through the purge valve, causing a rich fuel-air mixture and doing the catalytic converter no good at all.

When the automatic nozzle shuts off the first time, wait a few seconds, squeeze the handle again until it shuts off again, then round your purchase off to the nearest nickel. Stop there.

Now they know -- thank you.