Q&A: Replacing small outside mirrors

Q: My wife and I purchased a new 2009 GMC Acadia crossover SUV, trading in a 2006 Buick Rendezvous. The problem with the new vehicle is that the outside mirrors are much smaller than those on the Rendezvous. We feel this is a safety hazard. We were in error not discovering this at the time of our purchase of the Acadia. How can we find out if GMC has outside mirrors that are larger than those on the Acadia on a different model and if they exist, if they're interchangeable? We could pay to have a body shop change the mirrors if we knew what GMC model mirrors to purchase. Do you have an address at GMC we could write to with a request for information about the possibility of changing out the mirrors?

A: I think you should take the easy way out, which is to go in and visit the folks at the parts department where you bought the vehicle, tell them what you want and ask them to research it. They have access to all sorts of possibilities that the regular consumer does not and they're motivated because they've got a local customer who wants to spend some cash with them.

If the parts person is at all reluctant to make these two calls for you (and I really doubt that will be the case), speak with the salesperson from whom you bought the car and ask him or her to have a little chat with the reluctant parts person.

Although parts are rarely interchangeable from model to model, you are not, believe or not, the first person who ever got home with a new car and hated a mirror or some other replaceable piece on a vehicle. The parts folks have, over the years, had to come up with all kinds of alternatives and workarounds. In fact, the GMC parts gurus have probably been confronted with your very same complaint before, and they can quickly tell the parts folks an approach or two that will resolve it. And even if they have not tackled this particular issue, they should be able to come up with a solution quite easily.

Feedback: "I constantly hear from multiple sources," a reader wrote, "that reducing your speed by five to 10 miles an hour will save fuel. I had a 2001 V6 Mustang that got better mileage on trips from Ohio to Tennessee driving 75 mph than at slower speeds. I got nearly 28 mpg at that speed compared to 25 mpg driving at 65 mph. We also get better mileage at higher speeds in my girlfriend's Ford Fusion. Probably on many cars there is an advantage to slowing down, but definitely not on all cars. The efficiency of the particular engine at a specific rpm makes all the difference."

I definitely agree that high-performance cars often get better mileage at higher speeds than at lower ones. But regular vehicles like the vast majority of us drive almost always (and I'm willing to say almost) get better mileage at slower speeds.

That said, I don't necessarily put huge value on whatever mileage the reader might have gotten on a couple of long-haul trips. There are too many variables. Was the tire pressure identical in each case? When was the last time either car had gotten a tune-up? And how much did the passengers and luggage they were hauling weigh? And was the load identical each time? Any of those three factors can affect a car's mpg by three or four points.

Moreover, so can something as simple as a gradual gain in elevation. I remember I was surprised the first time I drove from Denver to Louisville that the mileage was so much better traveling in one direction than in the other. I'd been on what I thought were flat-as-a-pancake roads going and coming and I didn't quickly understand what was going on. What I hadn't taken into account is that although I wasn't climbing any obvious steep hills when I was headed west, I was putting the car through a gradual elevation gain of nearly 5000 feet. That'll change a car's mpg significantly; even though you're not sensing an elevation gain, the vehicle definitely is.

All that said, there's no denying that a few vehicles may get better gas mileage at somewhat higher speeds (although I sure wouldn't break the law to get two miles per gallon better mileage). I just wouldn't jump to the conclusion that comparing one trip to another months later would necessarily be absolute evidence of that.