Tire Pressure / How often do you check?
 

Admittedly, I've been historically bad for checking tire pressure. But, now that I'm driving 82 miles roundtrip to work, I've been a bit more conscious.

After a month found my tire pressure was down 4 lbs across all tires, which is nearly 10%.

How often do you check your pressure? And, is a 10% lose per month normal?

The short answer is no; it is not normal, especially in late Spring when temps are warming up, but there are some variables that could cause two different measurements without the cause being leaking tires; especially if it was all four tires that dropped.

I assume from your post that you had checked the tire pressure in all four tires approximately 30 days apart and you measured 4 psi difference in each tire, so lets take it from there.

My best guess is that one of three things has occurred or a combination.

(1) Did you check the air pressure both times with cold tires? Cold means, did you ensure that you checked the psi before you drove on both occasions? If you checked them the first time when they were hot (after driving), and the second time, when they were cold (before driving), then that would account for the 4 psi difference and you were 4 psi under inflated the entire month. The psi should be checked and adjusted only with cold tires; hot tire measurements are invalid and you should not check and adjust them hot except for an emergency like a flat tire.

(2) If we rule out the first cause, and you did check them both times cold, then my next question would be...what was the air temperature difference between the two measurements, as psi will drop approximately 1 for each 10 degrees drop in air temp? It is my experience that this time of year, the opposite will occur, and once the average morning low temperature comes up 20-30 degrees, I'll usually have to take some air out of my tires; however, it's better to err on the high side than the low side, so I usually wait until I'm at least averaging 3-4 psi too high on my morning measurements before I remove air from my tires.

(3) Lastly, it could be a difference in tire gauges, and either one or both are inaccurate. Did you use the same tire gauge to take the measurements?

If you rule out 1, 2, and 3, then you likely lost air pressure in all four tires, and my advice is to keep a check on them a little closer for just a little while until you figure out what's going on; and also, I'd advise erring on the high side and make sure you're inflating to the pressure recommendation listed on your door panel or owner's manual; not the max pressure listed o the tires.

My pickup so far has TPMS system that seems to work pretty good, so I rarely physically check them, but I set my dash display to show the PSI upon restart of my truck now and then, so I can check them cold (before driving). My wife's 2007 Saturn; an early TPMS adopter, does not work good. So, if I have no TPMS or a malfunctioning TPMS system, then I check once per month, unless my tires are getting very worn or old, or I have one or more that I know is losing air, then I'll check once per week or even more if I need to. Also, if the temps are quickly warming up outside or getting colder; like in Spring or Winter, it's a good idea to keep a closer check on where the PSI is. A 50 degree swing in air temps can cause a 5 PSI difference in tires.

Thanks for your valuable time for your well thought out responses, GregSFC (System File Check?)

I suspect the age of the tires may be the issue.

I read, regardless of mileage, tires have about a 4 year life, due to material deterioration. Ever see cracks in tire sidewalls?

Thanks for the TPMS suggestion!

Yea every car registered after 2014 has tyre pressure monitoring systems as a safety regulation in the UK. Prior to that, I'd usually check mine once a month, 6 weeks maximum.

So, Paul, what pressure change did you notice between month checks?

Decided against installing a TPMS. Too troublesome with having to replace batteries in 4 sensors.

All I need to do is establish the acceptable interval between topping off the air.

After 4 weeks, I lost 4 lbs per tire. Estimate I'll be down 2 lbs after 2 weeks, which is my threshold for more air.

Someone needs to invent a self-inflating tire that, when the pressure is low, the tire will self-inflate with each wheel rotation.

Bumped my bike tires up today, they were at 60, took them up to 80psi. Lap times (2 mile loop) dropped by over 1 minute, from 10 down to under 9.

I have a 30 gallon compressor in the garage, so top offs are a breeze. The OE tires on the Mirage lost little air, easily a month without loosing more than 2 psi. When I swapped out the rims and new tires, the left rear had a slow leak. TPMS light came on after 6 days. I was going to pull the wheel off and dunk it in water to locate the leak, but after another week it stopped loosing pressure.

The rim had been refinished and it had a rough surface on the bead area on that rim. The other 3 were fine and I cleaned the bread area thoroughly before mounting the new tires.

I have one of the inflators with a built in gauge, so topping off is a breeze. Without a wheel leaking down more rapidly that the rest, I'd go monthly on cars, weekly on bikes.

Self-inflating tires are in development. They'll have an efficiency price to pay though.

Certain cars, a particular Mercedes-Benz SUV have the ability to adjust pressures from the cabin via the cars computer, so you can drive across snow/sand without having to exit the vehicle and adjust them manually.