Inflate Those Tires

Every time I check the pressure in my tires, it is always below the recommended pressure. Every time! And to be honest, it isn’t something I think about on a regular basis. When I had a car, I did get into the habit of keeping a tire gauge in the car. (I presently don’t have a car, as I live within walking distance of my workplace in the Netherlands, but when I return to the U.S. my intention is to get the most fuel efficient car I can find – and to start experimenting with techniques for improving fuel efficiency).

It seems that my experience with tire pressure is certainly not usual. A feature story today at Yahoo Finance has recommendations for improving fuel efficiency:

The 15-Minute Tip: Err on the Side of More Air

The recommendations are to keep your air filter maintained, and echoing the recommendations from my previous essay – overinflate your tires. The story contained this statistic:

The Carnegie Mellon University Sustainable Earth Club studied 81 random vehicles in a parking lot and found that 80 of the 81 had under-inflated tires. The average rate of under-inflation was 20% — soft tires, indeed.

What does that cost?

The EPA estimates that for every 1 psi of under-inflation, fuel economy drops by 0.4%. That’s not much, but if the tires are under-inflated by 8 pounds, that’s a 3.2% drop in fuel economy. About 1.2 billion gallons of fuel are wasted annually due to under-inflated tires, the NHTSA estimated in 2005.

Hundreds of dollars in savings

So, by changing your air filter and pumping up tires that were under-inflated by 8 pounds, you’re likely to get a 13.2% improvement in your fuel mileage.

Take an average U.S. vehicle driven 12,000 miles at 20 miles per gallon. That’s 600 gallons of fuel a year. At $3.60 per gallon, that’s $2,160 a year.

To put that in perspective, that 1.2 billion gallons of wasted fuel is likely greater than what we currently net from ethanol production (net being BTU output of ethanol minus the fossil fuel inputs).

I wish there was an easy way to make sure all tires were properly inflated. Hey, maybe there is a business opportunity there for enterprising young people: After showing them the data on how much it is costing them, make a deal with your neighbors to keep their tires properly inflated.

16 thoughts on “Inflate Those Tires”

  1. I am totally anal-retentive about checking fluid levels and tire pressure before I go anywhere. It’s a product of growing up running farm equipment, having older vehicles and a doing all of my own vehicle service.

    There are a few aftermarket tire pressure monitors PressurePro is one and the Wikipedia TPMS entry has a bunch of info. Slashdot ran an article a while back regarding security on TPMS systems and this security article has some detail around the unencrypted information that can be picked up from such systems that uniquely identify the vehicle.

    Although the ride would be rougher, heavier ply tires and higher pressure would improve fuel economy.

    Most of the medium duty truck tires run at 65-70psi rating. The 22.5″ rim semi tires are a bit above that. There would be no flex in a 10 ply tire with 70 psi and only passenger vehicle weight on it, but it would be fuel efficient.

    Imagine if you used steel wheels on a steel highway how efficient and smooth that would be! wait… I think someone came up with that before the crackpot idea of rubber tires on asphalt came along.

  2. My car has a built-in tire pressure monitor and a built-in mileage monitor. You’re seeing GPS devices even in modest cars these days, and I’ll bet these monitors will soon be standard equipment.

    If the manufacturer would just do a little tweak, those monitors could show not only pressure/mileage…. but also toggle the estimated cost impact under some assumed fuel cost (maybe driver input?) and driving style.

    Putting dollars on a meter, instead of psi or furlongs or whatever, would get some attention.

  3. Love it or hate it, Oregon still forbids self-serve gas. If we’re going to have pump-monkeys, then we should also have a statute that requires gas stations to HAVE working air pumps and for the pump-monkey to offer to check your tires and fill them up to the minimum spec for your car or the (higher) pressure you specify.

    I worked as a pump-monkey as a kid and for my regular customers I would always make sure their oil was in good shape and their tires were inflated properly; several commented that I had saved them real money just doing those two things.

  4. Oregon’ers must be brain dead.
    Pump up those tires!
    RR: Thanks for this post. I actually have an air compressor on my premises. It will bu used weekly from now on!

  5. Look at what GreenRoad is doing. They build a blackbox that monitors and displays driving behaviour for you – or your boss. They mainly focus on that it improves safety but as their name suggests, its also about fuel consumption.

    Similar to 4Refuel.

    Btw, I was told to over-inflate tyres (to a reasonable degree) in driving school. 🙂 Plus, I have noticed how the geek in me tries to push down average consumption as soon as my car displayed it in the dashboard.

    I want more monitoring, in the shower, next to my computer, my oven etc.

  6. I’ve read lots of articles recommending to keep my tires inflated. What I can’t find in these articles, is where to find out where the recommended level for my tires is listed.

    It’s really hard to get a useful answer on this topic. I know my tires’ MAXimum inflation, and occasionally someone mentions there’s supposed to be a sticker in my door jam or trunk telling me a recommended PSI. But there isn’t.

    Help? Is there a reliable way to find out this inflation level that I’m supposed to be using?

  7. I think the CAFE standards are stupid, but things like this show you there are a lot of simple things that Detroit could do to improve fuel efficiency that wouldn’t cost a lot. Here are some ideas:

    1) Tire inflation monitoring
    2) Fuel efficiency computer
    3) Modified fuel intake “cold box”
    4) Low pressure exhaust
    5) Reduce weight
    6) Built in GPS
    7) Continuously Variable Transmission
    8) Variable valve timing
    9) Idle/stop, electric assist motor
    10)Regenerative breaking, run accessories (A/C, etc. by wire)
    11) Reduce drag
    12) Reduce engine friction
    13) Reduce rolling resistance

    Detroit does make some good engines, I’m looking at the 2.3l Duratec DOHC engine for my next car. I reject the idea that we can’t improve efficiency without giving up safety or convenience.

  8. The Deisel Cummins motor is reputed excellent…”will run forever”…can get 400k easily on it…these can be converted to run on waste vegetable oil…that is my plan…with all the greasy restaurants in the Southwest, and the lack of diesels on the road, this strategy get me several years of “free gas.”

  9. @ouini: As the late Roger Smith (of Roger & Me fame) once said: “If I had a secret I wanted to keep from the Russians or my wife, I’d put it in the owner’s manual. No one ever looks there fore anything.” — JMG

  10. I have an old car, so I had a lower tech way of monitoring the pressure in my tires. I had a set of those tire pressure valve caps that are green when at the right pressure, yellow when it gets a couple of psi below nominal, and red when it gets really low. You buy one that matches the desired pressure in your tires. I used to glance at them before getting into the car to drive, but they got stolen and I haven’t replaced them.

  11. KingofKaty said, “I think the CAFE standards are stupid“.

    I would have to agree the the US CAFE standards are stupid, because they are so much lower than anyone else’s.

  12. I don’t believe other countries have anything like the CAFE regulations. As Robert is saying in this post, instead they use high fuel taxes instead to encourage small, fuel efficient vehicles and less driving.

    Incidentally, replacing the air filter on a gasoline powered vehicle will have no effect on gas mileage, as the air flow into the engine at cruising speed is controlled by the combination of air filter and throttle restriction. Reduce the air filter restriction, and you will simply end up backing off on the gas pedal a tiny bit, increasing the throttle restriction to get back to the same air flow. Diesel engines, which have no throttle valve, WILL benefit from this change.

  13. I reject the idea that we can’t improve efficiency without giving up safety or convenience.
    Amen to that!

    Seems like Detroit (or more precisely, the Big 2.8 [overpayed]management) have this self-defeating attitude of woe-is-us, nothing-can-be-done, it’s-all-the-Japanese’s-fault. What would it take for them to snap out of it?

  14. Bankruptcy and purchase by the Japanese (or Chinese quite possibly) will probably do it.

  15. Replacing the air filter on a gasoline vehicle will improve fuel economy. Partially blocked air filters bias the fuel air ratio in favour of less air, reducing potential power output by not allowing all the petrol molecules to be burnt due to the shortage of oxygen.

    This is ignoring extra power used by the engine to induct air through a restrictively blocked filter.

  16. Anonymous, I’m sorry, but in the case of a modern gasoline engine you are wrong on both counts. All a partially blocked air filter will do is reduce the maximum available power and torque output of the engine. At PART LOAD conditions, any time you do not have your foot to the floor, it will have no effect at all. Any modern automobile gasoline engine has a closed loop, feedback controlled fuel injection system, which measures air flow, and injects the correct amount of fuel to burn completely (stoichiometric mixture) in the air available. It has to do this to enable the 3-way catalyst to work efficiently. Most of the induction work done by the engine is to draw air past the throttle, not past the air filter. And as I stated previously, for a given power demand, the lost power drawing air through a partially blocked air filter will merely be offset by a slightly more open throttle, which brings the air flow, and induction power lost, back to the same value.

    You have a reasonable case for diesel engines, for the few remaining older cars with carburetors, and for small lawn and garden equipment engines, but not for the bulk of modern vehicles.

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