CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2017 BMW 340i tire pressure dilemma

Tire pressure gauge dilemma!
when I check the tire pressure I get three different readings from three different sources. When the tire pressure from the car system reads 32psi, the TIRETEK air pump reads 36psi and the old fashioned tire gauge I have reads 29. I usually follow the care system. Which one should I believe. On my last check, the garage temperature was 45, the outside temperature was 30 and the tires were warm.

Go to a tire store and they will set all 4 tires at the proper pressure and then see what your vehicle read out is and what your tire gauge reads. You will then know just how close they are.

Tire pressure can vary up to 5 p.s.i. from cold to after driving for awhile. Always check tires when cold, before you drive anywhere. Other than the ones at a gas station with the gage on the hose I have never had problems with tire pressure gages being inaccurate, which does surprise me . If you are concerned find a reliable tire gage and use that.

Both are notoriously inaccurate. I’d believe the car’s gauge before the others. Buy yourself a decent tire gauge if you want proper readings. Amazon has a number of them. Cheaper is not better.

Thanks. I agree. I tend to go by the car’s number. I find it curious that there is that much difference when all three readings were taken at the same time.

Poor quality gauges will show that much difference. It may only be 10% (3 psi) but that is too much.

I like these type gauges myself.

Thanks. I will check them out.

Thanks. I will check a few out. However, I will primarily just rely on the car

Oh? Which tire store is that one?

I’ve never known a tire store that would/could set tires to the “proper” pressure.

I do that when I’m at home. I have found that nobody cares as much about my cars as I do.
CSA
:palm_tree::sunglasses::palm_tree:

What type of tire gauge do you have? My understanding is that the mechanical dial-type gauges are most likely to be accurate. I have several such Accu-Gage gauges that all match perfectly.

I agree with the other comments that the air pump is the most likely one to be wrong.

While you sort this out, remember that underinflation is generally less safe than overinflation.

1 Like

+1 to all of lion9car’s comments.
:+1:

A man with 2 watches is never sure of the correct time.

Sometimes the most important thing is balance. Use the same gauge on all the tires so they all have the same pressure, or at least both tires on each axle match in case your vehicle calls for different pressures front v. rear.

The tire pressures should at least be close. 29 vs 36 is too much of a gap. If the placard calls for 36, then they should be within 1 or 2 psi of that so you need at least that much accuracy.

If you’re a bit anal (like I am, just a little), you will want one of these along with an IR non contact thermometer.

Use the IR thermometer to measure the tire temperature and make adjustments to your desired temperature by adding/subtracting 0.1 psi for every degree above/below 68F or 20C.

German made Moto-Meter dial indicator mechanical gauge with genuine leather pouch.
CSA
:palm_tree::sunglasses::palm_tree:

Not expensive and fairly reliable. I will just rely on the car readings and go from there.

Thanks