Tire overinflation

April 19, 2005 6:51 AM

The sticker in my Malibu Maxx prescribes tire pressure of 30 psi; the sidewalls on the tires list a maximum pressure of 44 psi -- is it OK to run them at 35 psi, or higher, to gain better gas mileage, or will the money saved be nullified by shortened tire life?

Further info: I'm currently getting about 28 mpg at 35 psi, with about 80% highway miles, 20% city. I was getting lower mileage at the prescribed 30 psi, but that was also during much colder weather.

posted by beagle to travel & transportation (14 comments total)

be careful - i've driven a car with overinflated tyres before and it was not pleasant. serious understeer. i thought the steering was failing! i don't know how overinflated they were, but you should probably be concerned about harming the handling of your car.
posted by andrew cooke at 7:07 AM on April 19, 2005

Note very closely your tires - if they start to wear more in the middle, it's too much. Also, *rotate* them with every oil change if you're gonna do this. Andrew's right about the understeer; the vehicle recommended pressure makes the tires have a spring rate that is what the vehicle suspension engineers designed for.
posted by notsnot at 7:12 AM on April 19, 2005

I'm going to suggest you go with the figures on the tire itself rather than the car. If you've changed the tires from those that were on the car from the factory, you'll need to adjust the pressure to suit the new tires.

Get a good tire pressure gauge, though; one of the metal variety with the needle, or a digital one. The plastic pencil-shaped slide-style ones aren't very accurate, and it's important to get the left and right side pressure balanced as well as you can.
posted by odinsdream at 7:14 AM on April 19, 2005

Go with the figure on the car itself for performance as the car was designed. A little overinflation as you seek should not hurt performance and may actually improve your cornering a bit. It will probably also save you a few cents per fill-up. On the downside, the tires are less resistant to road damage from potholes and stuff when overinflated.
posted by caddis at 7:40 AM on April 19, 2005

Do what the car manual says. The sidewall is informing you of maximum safe inflation pressure; the tire company is mandated to put this information on there. However, the car's suspension was designed with certain inflation pressures in mind. If you change these pressures significantly, ride quality, handling, tire life and fuel economy will all be altered from what the manufacturer intended. In most cases these changes will not be improvements.

Don't inflate your tire to the listed sidewall pressure. I can guarantee you won't like the result.
posted by ikkyu2 at 7:53 AM on April 19, 2005

This is a great question, as my car also says one thing and the tire another. I am quite uncertain, and am inclined to think the tire is the better expert on tires. But any ideas I have on this were formed in the dark ages when cars were still mostly made in Detroit (or Flint).
posted by Goofyy at 8:56 AM on April 19, 2005

Do not go with the pressure on the tire, go with the pressure on the door sticker or in the manual for the car.
posted by caddis at 9:25 AM on April 19, 2005

Yes, go with the pressure listed for the car, unless it is greater than the pressure listed for the tires, in which case you need new tires that can handle the pressure.

The inflation pressure is to balance the weight of the car so the tire surface is flat on the road rather than curved in or curved out. The manufacturer of the tire doesn't know how heavy your car is, because the same tire can be used on many models. Thus their number is the maximum inflation pressure that the tire is designed to withstand.

Note that if you ever drive your car in a location that has substantially less gravity than Earth's, you will need to reduce your tires' inflation accordingly.
posted by kindall at 11:01 AM on April 19, 2005

The pressure on the sidewall is certainly the safe maximum and you don't want to go over that, but I'm convinced the pressure on the door-jamb sticker on my car is too low. My wheels have been checked and re-checked for proper alignment, caster, camber, toe-in, etc. etc., and yet the tires aren't wearing evenly. The tread in the center is still OK but the tread on the edges (both edges of all tires) is pretty much gone. Lacking any evidence of mis-adjustment, this says "underinflation" to me just as it would say "overinflation" of the tread center were bald while the edges were not. Next set of tires, I'm definitely going to try upping the pressure a bit, while still keeping it south of the sidewall maximum.
posted by jfuller at 11:11 AM on April 19, 2005

My experience with tire wear is usually similar to jfuller's. Is it possible this happens because, for all the manufacturer knows, you're going to drive the car mainly in a very hot climate, so, if you drive in a cool climate, your tire doesn't warm up as much as expected and the resulting profile is hollow rather than flat? Do folks in Southern California, for example, find that their tires wear out in the middle, rather than the edges, assuming proper alignment, etc.?
posted by beagle at 11:48 AM on April 19, 2005

Shoot for 32-35. It's what I've used for years on several different cars. If you're going on a long trip on divided highways, go for 35 and see what kind of mileage you get; if it's raining, though, you get better traction at lower pressure (for the same reason you get better mileage at higher pressure: contact area).

On Preview: a Malibu Maxx? Yuck. I hope it's nicer on the inside than on the outside!
posted by Doohickie at 2:13 PM on April 19, 2005

a Malibu Maxx
Yup. Had my midlife crisis with a Taurus SHO. Lots of vroom, sexy leather interior, etc. Sucked up money for gas and repairs no end. Croaked at 110,000 miles. Now, I go for practicality, reasonable comfort, economy, and hopefully longevity. Looks be damned.
posted by beagle at 2:38 PM on April 19, 2005

Now, I go for practicality, reasonable comfort, economy, and hopefully longevity.

So you bought an American car? *boggle*
posted by kindall at 3:07 PM on April 19, 2005

beagle: Just for your information, I'm not really one to talk, being the proud owner of a Ford Aspire.
posted by Doohickie at 6:30 PM on April 21, 2005