DEAR CAR TALK: Will I get better gas mileage with my pickup truck tailgate up or down?
When I try to find the answer, I get mixed messages. — Randy
DEAR READER: Surprisingly, you'll get better mileage with the tailgate up.
Like most of the people whose half-informed posts you've been reading online, my late brother and I once tried to answer this question on our radio show. We puzzled it out for about six seconds and concluded that, of course, you'd get better mileage with the tailgate down! The tailgate is obviously a big wind blocker and a source of drag that lowers your mileage. Obvious, right?
A few days later, we got a letter from a listener of ours — none other than the president of General Motors, Bob Stempel.
I believe the letter started out: "Au contraire, Piston Puss!" Bob — who was an engineer and, crucially, had wind tunnels at his disposal — explained to us that rather than blocking the wind as you drive along, the tailgate actually traps air in the pickup bed. And while that pocket of air stays still, the rest of the wind moves smoothly right over the top of the bed as you drive.
When the tailgate is open, he said, the wind actually creates more turbulence in the bed and reduces your mileage. And as if we didn't feel dumb enough by that point, he also reminded us that the closed tailgate is also an important part of the structure of the pickup.
When the tailgate's open, or removed, the truck is less safe in a crash. It's like removing one side of a cardboard box. It folds more easily, which is exactly what you don't want in an accident.
So, the pickup truck drivers you see with their tailgates removed or open are losing on two fronts, Randy.
Three fronts if you count all the stuff that rolls out while they're driving.
■ ■ ■
DEAR CAR TALK: In a recent article, you wrote about when the batteries in the tire pressure sensors in tires fail and cause the low tire pressure light to come on. You advised replacing the sensors, which you said typically last about seven to 10 years.
I have another question. Is it OK to just ignore the light if I check the tire pressure myself, by hand? Both my cars are older Buicks — 2002 and 2005 — each with just over 100,000 miles.
I found the article very informative but still have this question. — Sharon
DEAR READER: The answer is yes — you can go back to the pre-tire-pressure-sensor days and check the tire pressure yourself with a pressure gauge.
But I don't recommend it. For one thing, you really have to do it regularly. And in reality, most people don't. I'm a mechanic, and even I didn't check my tire pressure regularly in the old days.
I rarely even looked at the passenger side of my car. The tires could have been missing for all I knew.
And even if you are diligent and check the pressure once a week, or once a day, you'll miss one of the real safety features of the tire pressure monitoring system: getting warned if your tire is losing pressure while you're driving.
Let's say you run over a screw, and your tire starts slowly leaking air. Then you're on the highway. The tire pressure warning light will come on once your pressure drops about 10% below recommended pressure.
That usually gives you time to get off the highway and avoid a blowout. Or avoid changing a tire while Tombstone Pizza trucks whiz by you at 70 mph.
The final problem is that on most cars, there's one warning light on the dashboard for all four tires.
So, if one sensor dies and you ignore the light, you'll never know when another tire is low — even if the other three sensors are still good.
So while the answer to your question is technically yes, Sharon, I still recommend you replace the sensors in the tires when they fail. They really do provide an important service. And while they cost about $80 each to replace, it should be a once-in-a-car's-lifetime event, if that.
Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting cartalk.com