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4:18 pm EDT        87°F (31°C) in Bluffton, IN

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At the moment, I am in between loads — I just finished with a delivery here, and I am waiting on dispatch to send me some load offers. This comes on the heels of a tough 540-mile (870 km) trip that I didn’t even get to start until about this time yesterday afternoon; I ran through basically every bit of my available hours to pull this one off.

In this update, I’m going to do a little bit of “public service” that was partially inspired by a thread I recently found on the USENET newsgroup Some residents of the eastern United States, making their first road trips to the Mountain West region of the country, may be surprised or even horrified (“Oh, shit! I just really fucked up my car!”) when they notice the octane ratings on many gasoline pumps in that region. This would be particularly true of motorists who are familiar with the contents of their vehicle’s owner’s manual, and in particular its specification that fuel with a minimum octane rating of 87 (assuming it merely requires regular unleaded) must be used.

In the eastern part of the country, and even in many parts of the West Coast states, the three gasoline grades one will usually find are 87 (regular), 89 (mid-grade), and 93 (premium). However, in some areas of the West — I would think especially in Colorado, Wyoming, New Mexico, Utah, Nevada outside Clark County (Las Vegas), Idaho, northern Arizona, and the western two-thirds of Montana — regular is 85 octane, mid-grade is 87, and premium is 91. Why, you’re asking, are the grades all two points lower — are they trying to screw up your car, or to “force” you to buy the more expensive mid-grade?

Actually, it has to do with how your engine works at the higher elevations (generally above 4,000 ft./1,219 m) in these areas. The air at higher elevations is thinner than it is around sea level, and this has a number of important effects on physical and chemical processes; one non-automotive example of this is that water boils at 203°F (95°C) in Denver, CO, instead of at 212°F (100°C) as it does at sea level. What this thinner air does in your car is reduce the absolute compression that is produced in each cylinder, which in and of itself reduces the chances for knocking (sometimes called “pinging”) and obviates some of the need for octane. (Octane, chemical formula C8H18, is one of thousands of hydrocarbons obtained from crude oil; it is used in gasoline because of its resistance to the self-ignition under pressure that we call engine knocking or pinging.)

(Wait a minute, car buffs are thinking, are you saying car makers are lying about their compression ratios? Not at all — this is where the difference between absolute and relative compression comes in. If your car’s compression ratio is, say, 9.5:1, that’s a measure of relative compression, i.e., volume at the bottom of the piston’s travel vs. volume at the top of its travel, and that never changes. Absolute compression is a measure of what kind of pressure the air-fuel mixture can exert on the cylinder walls, and that varies with outside air pressure, which itself is inversely proportional to elevation.)

For this reason, your engine doesn’t need quite as much octane in fuel at higher elevations. This is why you’ll find 85, 87, and 91 octane fuels as the three gasoline grades in the Mountain West, despite car makers’ usual specification of 87 octane (if the car only requires regular) or 93 octane (if it requires premium, like my friend Marc’s new Evo does). These lower-octane fuels are perfectly safe for your car, as long as you’re going to be staying at higher elevations (above 3,500-4,000 ft./1,067-1,219 m) until you have to fill up again.

That said, if you’re headed into lower terrain, make sure to fill up with your usual 87/89/93 octane gasoline at some point before you get into the lower-elevation area(s). Some of the lower-elevation parts of the West include most of California outside the Sierras; much of western Oregon and western Washington outside the Cascades and/or Olympic Mountains; most of southwestern and south-central Arizona, including the Interstate 8 and Interstate 10 corridors, Phoenix, and Tucson; and the Interstate 15 corridor through most of Nevada and into Arizona and extreme southwestern Utah, including Las Vegas, the incredibly scenic Virgin River Gorge, and St. George, UT. If you’re going there, or leaving the high country to head back east across the Plains, don’t let yourself get too far below 3,000 ft. (914 m) without putting some higher-octane gas into your car.

Thinking about this deal with gasoline octane ratings in the West has sort of gotten me on another (totally unrelated) automotive “public service” kick: the sales pitches by tire retailers encouraging you to “Nitro-Nize your tires!” or some similar line. These tire shops make a number of spurious claims about the use of nitrogen gas to inflate tires in lieu of air, chief among them that it increases fuel economy (lie), makes tires last longer (minimal evidence at best), and holds pressure and prevents leaks better (lie). They also make claims that, while true, have no bearing on the regular operation of passenger-car tires; for example, they always keep pointing to the use of nitrogen in tires on airplanes and race cars.

All of this is just marketing hype designed to get you to spend as much as $50 to have the perfectly good air in your tires vacuumed out and replaced by nitrogen. Let’s face it: the relationship between tire inflation and fuel economy has to do with vigilantly maintaining proper pressure, not what you fill the tire with, and a tire with a leak is a tire with a leak, regardless of what you put in it. Pure nitrogen’s lack of water vapor vis-à-vis compressed air may help to reduce inside-out corrosion of wheels/rims and the tire’s steel belts, but (a) this is really not a problem with most modern wheel and tire designs, and (b) only minimal evidence exists to support this hypothesis. You’ll probably wear out the tire from driving it long before corrosion could really become an issue.

As for the race-car and airplane statements, we’re talking about tires that are subjected to far more cruel and unusual punishment than a passenger car could ever hope to dish out. Race-car tires may have to run in excess of 200 mph (322 km/h) for more than an hour at a time, without stopping. Airplane tires are repeatedly taken from the ground to 35,000 ft. (10,668 m) altitude, where the outside air pressure is one-fifth that at the ground, and back; and upon landing, they are accelerated from a standstill to well in excess of 100 mph (161 km/h) almost instantly. I mean, if you regularly subject your car to such treatment, then by all means fill your tires with nitrogen — but I somehow doubt your tires will ever see anywhere near that kind of stress.

I have a much better idea for keeping your car’s tires properly inflated than spending $50 on nitrogen. I suggest you instead spend $1.69 on a tire-pressure gauge at AutoZone, Pep Boys, NAPA, or whatever your favorite auto-parts store is, and take two minutes to check your tire pressures at least every other week. If your pressures are a little low, find your nearest gas station with an air hose and fill it to the recommended pressure with air — which is already 78% nitrogen by volume anyway. This will do everything the nitrogen-pushers claim you need nitrogen to do, and it will save you a shitload of money relative to falling for their sales pitch.

(It occurred to me after originally posting this that many people may not be aware of how to find the proper recommended pressure for their tires. Do NOT go by what is stamped on the sidewall of the tire — that is the absolute maximum cold inflation pressure the tire is designed to handle, and unless you’re regularly packing your car with so much heavy shit that it is loaded well over its gross vehicle weight rating (GVWR), your tires will be seriously over-inflated at this pressure. Over-inflation is almost as bad as under-inflation; with over-inflated tires, you’ll wear out the center of the tread well before the edges, and your handling will go all to hell because your contact patch with the road is reduced.

To find your correct tire inflation pressure(s), open your driver’s door and look on the pillar behind the door opening for the “tire placard.” Usually, this will be a white sticker that will list your original-equipment tire size, a front tire pressure specification, and a rear tire pressure specification which may or may not be different. I’ve found in my experience that it’s not a big deal to ignore different front and rear specs and inflate all four tires to the higher spec (usually the front); but I would caution against going much more than 3 psi (21 kPa) above that specification in any tire.

Finally, when you’re checking your tire pressures, DON’T FORGET about your spare tire as well. I know it’s inconvenient to get to in a lot of cars, pickups, and SUVs, but the last thing you want to do is find that your spare is dangerously low if and when you have a flat. If you have a “donut” spare, like most cars do, you’ll find its recommended pressure on your tire placard; if you have a full-size spare, like most trucks and SUVs do, inflate it to the same pressure as the other four tires.)

Let me note for the record that putting nitrogen in your tires is not dangerous or unsafe in any way. You’re certainly not going to harm your car at all to put nitrogen in your tires; the only harm, which as I have shown is a completely unnecessary one, is to the contents of your wallet. It’s just a marketing gimmick — just another way for tire shops to make money off the unsuspecting, gullible hordes. Hopefully I’ll prevent somebody from wasting their money by posting this.

Well, it took dispatch a while, but it looks like they’re sending me back to the suckiest place in the universe — Columbus, OH — to get my next load. With that, I’m off to go drive the 140 miles (225 km) from here to there.