As the author noted, sometimes when you need air, you’re not near a gas station.
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Good catch, rjcjr is going to edit the piece for clarity. Here are a couple of references for that math.
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If you’re driving around with tires underinflated by 10-20%, you’re doing it wrong.
The numbers aren’t “hyper-inflated.”
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Clever turn of phrase in this context, though.
Can anyone recommend a pump that plugs into a house plug that would be good for a scooter? My Vespa rear tire has the plug in a super awkward spot, and I hate sprawling at a gas station to tweak my air pressure.
Something that had a built-in gauge would be really sweet.
TIA.
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Agreed. But if you’re driving on a beach, you’re also doing it wrong. Does awful damage to beach ecology:
http://lakehuron.ca/index.php?page=Protecting-Our-Beaches
Actually I think they are, or the article is very confusingly/incorrectly worded. And I think I see where the error is.
Working backwards using their numbers, 12,242 miles per year at an average of 22.3mpg is about 548.97 gallons of gas for the average, ideally performing car. Then they claim 144 extra gallons for the underinflated cars, so that would be 692.97 gallons. If we divide the average miles per year by this number we get about 17.67mpg. Coincidentally perhaps this number is approximately 20% lower than the original mileage number. The 20% that appears in the article however is talking about being 20% underinflated, not 20% under-performing in milleage. In order to have a 20% drop in fuel efficiency based on their 1%/2PSI estimate, you’d need to be 40PSI underinflated, which for many typical cars would be a negative PSI.
So either the article is misreporting what the 20% number was, or maybe they calculated things wrong for the final value.
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One more note - I understand the fun of driving “boat” type American cars, but if you’re figuring this $430/year savings based on improved gas mileage, you’d save a lot more money by choosing a different car with better gas mileage.
The link you cite for your 2005 Crown Victoria says it gets 18mpg city, 25 mpg highway - in LA I’m going to guess you get closer to 18 mpg. My 2002 Corolla after 13 years is still getting about 27mpg actual city mileage, despite my lackluster maintenance; driving newer rental cars (not hybrids) I’ve seen actual average mileage of 34mpg and up.
Assuming you used the 20% savings estimate from the CMU study, you’re paying about $2150/year for gas; guesstimating $3.00/G in Cali, that’s around 717G/year or at 18mpg, about 12,900 miles which seems a reasonable number. At 27 mpg, that would be 477G or $1433, saving you almost $720/year; at 34mpg it would be 379G or $1138, saving you over $1000/year.
Your bet has paid out one Quatloo.
I’ve always just made a point to ask the tire guy/gal or the dealership gal/guy. Pretty sure it’s in the manual too. Door sticker - that’s totally news to me.
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Hi, thanks for pointing out the confusion with the numbers. The savings estimates are not hyper-inflated, and are referenced in a 2005 Carnegie Mellon University study found here–>Carnegie Mellon: Save Gas, Money, Environment with Properly Inflated Tires. From the article:
If you do the math to calculate the extra fuel cars consume due to under-inflated tires, consider the Environmental Protection Agency standard that a 1% loss of fuel efficiency occurs for every 2 PSI of air under the maximum level. Add to that the 2003 Department of Energy report that states that vehicles average 22.3 miles per gallon and 12,242 miles per year, and you find that each of the 81 cars burned 144 extra gallons of gas due to under-inflated tires. At $2.25 per gallon, each car owner is spending $324 for gas each year that they really don’t need.
With my Waze showing gas right now are between $3.99 and $5.59 per gallon by me, my savings on 144 gallons per year is around $576.
I came to the comments to say exactly this. When I bought my latest bike pump, I deliberately bought one that said it was also good for topping up car tires. Mine has a built-in gauge, and is totally manual. A power cord wouldn’t do me much good since I park in a communal lot under my apartment building with no wall plugs available.
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I think I spend about $500 total on fuel last year, so this “one weird trick” must be pretty great.
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It’s definitely in the manual. I didn’t know about the door frame sticker (might have different regs in Canada), but I know I learned the right tire pressure from my car’s manual.
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Just to say “don’t forget the spare” when you pumping up tires. Doughnut spares require higher pressure. I had to get my reseated once and the regular tire store couldn’t do it because they couldn’t reseat the narrow rims… had to go to a motorcycle shop to do it.
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The savings estimates just don’t work out.
U.S. Dept of Energy: Under-inflated tires can lower gas mileage by 0.3% for every 1 psi drop in pressure of all four tires.
My car gets 36 mpg (above average) and I drive 12,000 miles per year (below average in my part of the USA)
12,000 miles at 36 mpg = 333 gallons.
333 gallons at $3.00 = $1,000.
Using the DOE number, If all four tires are under-inflated 10 psi (22 psi instead of 32) I’d get 3% less mpg (10 x 0.3%)
36 mpg - 3% = 35 mpg
35 mpg x 12,000 miles = 343 gallons, or 10 gal. more ($30.00)
If I drove a gas hog that got only 18 mpg and drove 18,000 miles per year I’d save $ 90.00
Even if we assume that DOE numbers are too conservative, and figured double the loss, it still looks as if it would be unlikely to save as much as $ 200.00 per year in a gas hog.
When gas prices go beyond $ 7.00 per gallon though . . .
YMMV
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Why do you want to drive around in a car that makes people suspect you’re an undercover cop?
Biiiiig comfy seats. Huge ol’ V8 with massive performance potential. Bombproof reliability. Can be fixed by most anyone. Also, lulz.
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It seems you can get even more miles per gallon by over-inflating your tires, but you sacrifice safety by doing so.
For the record, inflating your tires above the car manufacturer’s recommended pressure doesn’t mean they’re actually over-inflated.
For instance, my Prius rides on Bridgestone Ecopia’s (not a fan of these tires, actually), which have a maximum pressure of 44psi. Toyota’s recommended pressure is 35 front, 33 rear. I run my tires at 42/40 for improved handling and fuel economy. This does have the cost of harshening the ride and resulting in more road noise at speed. It might also be a bit harder on my suspension elements, but they’re still going strong after 125k.
The car is probably very slightly less safe on loose surfaces with these higher pressures, but braking performance is probably actually a bit better on pavement.
General tire pressure safety rule: The rear tires should always carry less pressure than the fronts. You want the front tires to skid first. This also means that if you have a choice, you put your best tires on the back.
There’s much more tire lore to be discussed here, but I’ll stop for now.
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