Low Tire Air Pressure - How to Pinpoint Issues

You fire up the car, coffee in hand, and then that light stops you right in your tracks. Nothing puts a dent in the morning routine and commute quite like a TPMS warning.

As it should – Tire Pressure Monitoring Systems (TPMS) are not commonly faulty, and so if low tire pressure is being signaled, it’s likely that one or more of your tires have slipped into a hazardously low pressure status. You shouldn’t drive until all four wheels and tires have been thoroughly evaluated.

So how does a layperson conduct a check of tires for low pressure, identify the cause of pressure loss, and evaluate road-worthiness? Here’s some guidance.

1. Visually inspect of all four tires.

If your TPMS doesn’t display individual tire pressure but rather signals only for a loss of pressure on one or more wheels, then a visual inspection of all four tires in search of the affected tire is a reasonable first step.

You’re looking for a clearly flat tire or a comparatively compressed and bulging tire sidewall that is characteristic of a tire with low pressure. Also, listen for any “hissing” noise as you inspect the tires.

Note that, unfortunately, low tire pressure is not always visually distinct. Even a substantial 10-20 psi difference between tires won’t necessarily be visible in terms of how the lower pressure tire is interacting with the road surface the stationary vehicle, so apparent consistency between the look of all four tires doesn’t mean “all clear.”

If your visual check unveils no real clues about which tire(s) are low, then the next step is a tire pressure check of all four tires. Tire pressure measuring devices are available at any auto parts store, large retailers, gas stations, and tire shops. (Pressure devices are inexpensive or even complimentary at many tire shops.)

With a tire pressure measuring device, check all four tires and note the pressures. How do they compare to one another? Are there any tires that are measuring low by comparison? How far off are any of the tires from vehicle specification? (For more details and in-depth instructions see Knowing your tire pressure and How to do a quick tire safety check.)

Along with clear signs of tire pressure loss, look for possible structural issues like sidewall bubbles, extreme low tread, bead damage (where the tire meets the wheel edge), or other abnormalities. If any of these issues are present, in combination with a loss of pressure, then the tire is potentially compromised and shouldn’t be driven on. Even the re-inflation of a tire in such condition can be very dangerous and shouldn’t be attempted.

2. Pinpointing the cause of pressure loss on a tire.

If you’ve identified the tire with low pressure, a focused review of that tire could pinpoint the cause.

• Scan the tire tread for nails, screws, or other sharp objects that might be lodged in the tire. Often the item that caused the puncture is still embedded in the tire and creates a gradual but persistent loss of air pressure. If no puncture point is obvious, and there’s still air pressure in the tire, the next step is to spray the tire tread with a solution of soapy water. Coat the tire tread, as well as the base of the tire sidewall where the bead is seated onto the wheel. The escaping air will create bubbling.

• Leaking valve stem. A similar technique can be used to diagnose a leaking valve stem. Pour water or a soapy water solution over the valve stem and check for bubbling. If you see bubbles – typically near the base of the stem – then you’ve identified the leak.

• Loss of effective tire seal. The sealing point at the base of the tire sidewall (where the tire meets the wheel) is fundamental to maintaining tire air pressure and can become compromised. Extremely rough roads, for example, can damage wheels to the point where they’re out of round and no longer able to effectively bond with the tire bead.

As detailed above, a soapy water solution coated at the tire-wheel sealing point will create bubbles if air is leaking. Remember that for a thorough check, both inner and outer tire-wheel sealing points would need to be checked, which requires the safe removal of the wheel.

3. The temperature variable.

What about the “curious” case of all four tires being low pressure? Has a thief in the night absconded with your tire pressures?

Well, probably not. The likeliest cause of a consistent pressure loss affecting all four tires is a drop in temperature. When temperatures drop, and air condenses, there is a predictable corresponding loss of tire pressure.

If tire pressure loss has resulted from a drop in temperatures, then take it easy and drive at reduced speeds. Re-inflate your tires to vehicle specification at first opportunity.

Remember: Safety First

You should only investigate a loss of tire pressure to the extent that you are comfortable and able. For example, if you lack the know-how to jack up your vehicle and remove a wheel for a comprehensive tire review, then get a professional to do it.

Other safety principles to keep in mind:

• Re-inflation is not a solution. Without an understanding of the underlying cause of tire pressure loss, adding more air isn’t an option. Even if after re-inflating the tire appears to be holding pressure, don’t assume the problem has been resolved. Tire blowouts and other catastrophic failures can occur when driving on an inflated, damaged tire.
• Driving on a flat tire is extremely hazardous. Don’t underestimate the potential for a total loss of vehicle control on an underinflated or nearly flat tire. If the affected tire has a slow leak and is holding pressure sufficient drive to a tire repair shop, then that drive should be conducted with extreme caution.
• Consult with a professional as soon as possible. We’ve given you tips to help pinpoint the cause of tire pressure loss, but there’s no substitute for professional tire evaluation and repair.

Overall, the best thing you can do for your tires is to check your tire pressure every month. This will help your tires reach their optimal traction, stability, and durability. Just like a balloon that starts to lose air after a few days, tire pressure changes over time. Even though tires are fairly airtight, there are still microscopic pores in the tire walls that let very small amounts of air escape over time.