Is the tire pressure different for a different brand of tire, but same size?

May 29, 2005 3:45 PM

I have a 2001 Honda Accord and I am in the process of purchasing new tires. The inside tag inside my driver's door tells me that tires shoud be inflated to 32 PSI or so. Does this rating only apply the OEM tire or any brand of tire? Also, I've noticed that my dealership has been overinflating my tires to 37 PSI. Is there a reason for that?

Does overinflating a tire or underinflating a tire offer any performance difference?

posted by huy_le to grab bag (15 comments total)

The U.S. National Highway Traffic Safety Administration (NHTSA) has a nice web site on automotive tires, including a tire pressure FAQ:

When I get replacement tires, do I still follow the pressure and loading guidance on the vehicle’s tire information label?

A:No matter which manufacturer makes your replacement tires, you should always follow the tire pressure and loading guidelines of your vehicle manufacturer. You’ll find these numbers on the tire information label on your vehicle or within the pages of your vehicle owner’s manual.

Lowering your tire pressure below the recommended pressure may result in a smoother ride or better traction, but significantly increases the possibility of tire failure. Increasing tire pressure may improve gas mileage as well as improving handling under heavy loads, but also carries a heightened risk of tire failure.

I'm not sure why the dealership has been overinflating your tires to 37 PSI instead of 32 PSI. Have you checked to see if your tire pressure gauge is inaccurate? Perhaps they are confusing a 2 with a 7?
posted by RichardP at 4:25 PM on May 29, 2005

Like RichardP said, follow the instructions on the car. Service outlets habitually overinflate for whatever reason; this is pretty universal.

Further, for best tire life, if your tire is wearing more in the middle than the edges, let some air out, and if it's wearing more on the edges than the middle, put some air in.
posted by trevyn at 4:50 PM on May 29, 2005

Also, take a look at the discussion in this earlier AskMefi thread on tire pressure.
posted by RichardP at 4:52 PM on May 29, 2005

Consumer-grade pressure gauges are not very accurate. Also, are you measuring the pressure when the tires are cold? Tire pressure increases significantly when the car's been driven a few miles. The recommendations are for cold pressures.
posted by Kirth Gerson at 5:32 PM on May 29, 2005

Get a decent tire pressure gauge and check the tires while cold if you want to make sure things are at manufacturer spec.

Additionally, if you know anybody with a tire pyrometer, borrow it and go for a drive, then check temperatures across the tire to see if they're heating up evenly.
posted by mosch at 5:51 PM on May 29, 2005

I've been measuring the tires when they are cold. I purchased my gauge at Wal-Mart. I don't want to spend too much on a gauge, but a cheap digital one would be great. Any suggestions?
posted by huy_le at 6:19 PM on May 29, 2005

You can at least check your Wal-Mart gauge by asking a garage to compare its reading to theirs.
posted by Kirth Gerson at 7:22 PM on May 29, 2005

There are two reasons for overinflating:

1. If there is some leakage over time, it takes longer to get dangerously underinflated.

2. There is some people who swear you get better mileage with higher pressure (in my experience, this effect is minimal).

In most cases, inflating tires to up to about 40 psi is perfectly safe. Much more than that, and you risk a blowout (a high school classmate of mine who got a job in a tire shop was killed by an exploding tire).

I might also add that while retail pressure gages are notoriously inaccurate, tire shop gages often are as well. They may be putting a little extra in because they think their gage is reading high.
posted by Doohickie at 8:16 PM on May 29, 2005

Does anyone pump their own tires at home with a bike pump? 35 PSI should be no problem given that bike tires go up to 130 PSI, though the much greater volume might be a bit tedious to fill. A floor pump with schraeder valve adapter should do nicely, no?
posted by randomstriker at 8:46 PM on May 29, 2005

2. There is some people who swear you get better mileage with higher pressure (in my experience, this effect is minimal).

The effect is noticeable when you go from seriously underinflated (say 20psi) to properly inflated (mid 30's). You can lose as much as 2-3mpg because of underinflated tires. If your tires are wearing out down the center of the tread, then you are probably overinflated. Like everyone else said, follow the car's manual.

Does anyone pump their own tires at home with a bike pump?

Yes, this works fine, it just takes a little time. I've done it several times.
posted by knave at 8:56 PM on May 29, 2005

You can at least check your Wal-Mart gauge by asking a garage to compare its reading to theirs.
Except that the garage gauge is at least as likely to be inaccurate, so a discrepancy will tell you absolutely nothing. Better to go to a tyre shop and do this, or buy a good quality one in the first place.

In most cases, inflating tires to up to about 40 psi is perfectly safe. Much more than that, and you risk a blowout (a high school classmate of mine who got a job in a tire shop was killed by an exploding tire).
I have seen a photo of the imprint that a tyre shop worker left in a concrete ceiling after over-inflating a truck tyre, but you would have to go a long long way past 40 psi to risk that. Nonetheless, the correct pressure as specified by the manufacturer is the correct pressure - between car and tyre manufacturers, millions of dollars are spent working out what the pressure should be, so why would you go against that? Not only do over-inflated tyres wear faster, they do not grip as well and under-inflated tyres grip poorly in cornering, wear faster and affect fuel economy badly.

Unless you are an automotive engineer or have the time and inclination to fiddle with adjustments to tyre pressure and measure the changes, just stick to the recommended pressures.
posted by dg at 9:08 PM on May 29, 2005

RE: Exploding tires due to overinflation - When mounting a tire on a rim, you have to overinflate it, to get it to seat properly. That's why they usually leave the valve stem out of the valve when seating the tire; it minimizes the time that the tire is overinflated. Truck tires require much higher pressure to seat, and truck tires are more likely to be recaps. That's why people get killed by exploding truck tires. I have exploded motorcycle and auto tires while mounting them, and while it was not a pleasant experience, I wasn't hurt.

You won't see odd tire-wear patterns from mis-inflation until they've been driven that way for thousands of miles, unless the inflation error is extreme.

Except that the garage gauge is at least as likely to be inaccurate, so a discrepancy will tell you absolutely nothing. Better to go to a tyre shop and do this, or buy a good quality one in the first place.
I can't speak for places that have tyre shops, but around here, garage mechanics take pride in their tools, and would be far less likely to use a cheap pressure gauge.

If you have a dial-type gauge, there may be an adjustment screw, so you can calibrate it to a known good gauge. At least verify that it reads zero when not on a tire. If you're using one of those telescoping-stick type gauges, and it's not accurate, the best you can do is add or subtract a correction factor when using it.
posted by Kirth Gerson at 4:14 AM on May 30, 2005

Of course, I meant "leave the valve out of the valve stem" up there.
posted by Kirth Gerson at 4:34 AM on May 30, 2005

randomstriker writes "Does anyone pump their own tires at home with a bike pump? 35 PSI should be no problem given that bike tires go up to 130 PSI, though the much greater volume might be a bit tedious to fill. A floor pump with schraeder valve adapter should do nicely, no?"

Heck I've seated a bead with one of those stand up style pumps.

mosch writes "Additionally, if you know anybody with a tire pyrometer, borrow it and go for a drive, then check temperatures across the tire to see if they're heating up evenly."

Ya got to be quick with these unless it's the type with the probes that stick into the tire. The best way is to have a second person operate the meter. Otherwise by the time you jump out of the car and point the guage at the tire it has already started to cool.

Cheaper and easier in my opionion is to use some chalk or white shoe polish and a bit of testing. Start at manufacturer static pressure. Make a mark across your tires and go for a short drive. Note where the most polish is missing and ajust pressure up for edges and down for centre. When you have even removal across your in the right inflation range. Check your pressures the next morning so you know what the cold inflation value is. Details

Lots can be done to correct handling problems by adjusting pressures front to rear. All you need is the ability to draw a line and operate a pressure guage.
posted by Mitheral at 10:24 AM on May 30, 2005

I always check my tires after my vehicle has had maintenance. My dealer does a good job but on my old vehicle the oil change guys couldn't even agree on a pressure across all four tires, let alone from visit to visit.
posted by substrate at 1:53 PM on May 30, 2005