14

I measured the PSI on my rear driver tire (using a gauge pin - push it into the needle and a stick pops out with a reading), and I got a reading of 22 PSI. My tires are supposed to be anywhere from 30-34 PSI. The thing is, the rear driver tire (the tire in question) doesn't look flat at all. It looks just as good, if not better than the other tires.

Should I fill the tire with air? I don't want to over-inflate the tire, if my gauge is giving me a bad reading. However, at the same time, the gauge seems to be working fine for the other tires, so one would be reasonable to assume that it's working well for the tire in question as well.

Another note to consider - my front driver side tire looks flatter than the rear driver side tire, but it's PSI is 32.

What should I do? Should I go with how the tire "looks" or what my $4 (from Advanced Auto) gauge says?

kmarsh
  • 2,169
  • 12
  • 37
semore_1267
  • 243
  • 2
  • 7

4 Answers4

18

Yes, you should fill your tire. The fact the other tires all are nominally correct means you should trust your gauge.

Modern tires often have reinforced sidewalls that mask the appearance of low pressure. Waiting for a bad wear pattern is not a good plan, as then you'll have an unevenly worn set of tires.

Pᴀᴜʟsᴛᴇʀ2
  • 165,084
  • 32
  • 259
  • 508
kmarsh
  • 2,169
  • 12
  • 37
7

Because you have verified the gauge is working reasonably by trying the other tires, go with the gauge. Your owners manual will have the inflation pressures for your car. Just make sure that the recommended pressure in the manual is less than the maximum tire pressure imprinted on the sidewall of the tire. If it is, just fill it to the manuals recommended pressure.

Hope that helps!

cdunn
  • 9,326
  • 8
  • 44
  • 76
6

Generally speaking any time your tire pressure is more than 10% over or under the ratings I would definitely correct the pressure ASAP and check the tread wear too. In your case 10% is 3 or 4 pounds and you are seeing the tire is low by about 8 pounds (20+%) which is way too much discrepancy. Pump it up and keep a close eye on it for a week or so to be sure you don't have a slow leak. If it drops again go see your local mechanic / tire guy.

Also, @corsiKa makes an important point above ... the temperature when you measure is also a factor. Extreme cold will temporarily lower the tire pressure a couple of PSI and extreme heat will similarly raise it temporarily. Plus long drives can heat up the air in a tire from friction even on a cold day. Keep these issues in mind both when measuring and when adding air to tires.

O.M.Y.
  • 161
  • 4
4

Your description "front driver looking flatter" suggests that the front driver and rear passenger tires could be carrying more load than the rear driver. If the front driver and rear passenger are on higher pavement than the other two they will carry more load and could appear "flatter". Is this a possibility?

Andy
  • 71
  • 2