by Sam Dillinger (comments: 0)

A quick memo on tire pressure

correct tire pressure

I’ve noticed over the years that I’ve been fixing cars, sometimes I lose touch with what other people do and don’t know about the vehicles we all depend on for so much of our every day lives. Recently my wife called me to tell me that one of her tires was low on air and she wasn't sure how much to put back in to make it safe to drive on. I tend to take things like this for granted because I’ve had to put air in a tire probably 100,000 times in the last 20 years, so it’s absolutely second nature to me. Taking her call reminded me that sometimes the things I take for granted can be essential information that other people might not know. So in the interest of helping people in every way I can, let’s go over the basics of tire pressure, and related problems. You might be surprised at what you didn’t already know about it! (Editing note: after writing the article I realized I didn't say anything about how to check tire pressure. See the attached video).

First let’s cover how to find out how much air to put in your tires. There are several sources to find this information. General consensus will tell you that 35 PSI (that’s pounds per square inch) is what’s used on most regular passenger vehicles. There are variations to this that everyone should be aware of though. For trucks it can be up to 70-80 PSI and for some specialty tires it can be 32 PSI. Other vehicles may require a different PSI than what I have listed here. So how do you find out what’s right for your car? Simple: there’s a sticker on the door jam of the drivers front door that has the factory installed tire size and the factory recommended tire pressure for your car. That’s all there is to it, as long as you still have the factory installed brand, and size of tires. You’ll also be able to find this information in your owner’s manual.

But what if you don’t have the factory tires installed anymore, or the other 2 methods are no longer available to you? That’s an easy one too. The maximum tire pressure for every tire is cast into the side of the tire. It’s written very small and not easy to see, but it’s there. The tire sidewall only lists maximum acceptable pressure for each tire. It’s cast in the rubber very near to the rim the tire is mounted on, and with a flashlight it’ll be relatively easy to find. This goes for factory tires as well, but it’s easier to see and to read on the sticker from the door jam, or in the owner’s manual. Once you've found the max acceptable pressure, you’ll want to inflate the tire to about 5-7 PSI less than the maximum. A good rule of thumb is to never let pressure go lower than 30 PSI.

Other than if your tire gets too low to drive on safely, you may be wondering why else it would be a big deal to know your tire pressure and to check it regularly. That’s an easy answer as well: gas mileage. See here for my article on gas mileage (the part about tire pressure is towards the bottom if that’s the only part of the article you'd like to see), and why tire pressure is so important. If you don’t have time to read that, the gist of it is that lower tire pressure will make your tires less efficient at moving your vehicle and will cost you gas mileage.

One last note about tire pressure- the pressure in your tires will fluctuate slightly in response to temperature. Cold air condenses and will drop your tire PSI by 1-3 pounds depending on just how cold it gets where you live. If you drop more than that, you’ve got a leak in your tire and this is a serious safety concern that should be addressed immediately!

As always, for my members, feel free to drop me a line from www.mycheckenginelight.net with any questions!

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Meet Sam Dillinger

My name is Sam Dillinger. I've been a professional, dealership technician for 18 and a half years. My first introduction to mechanical repair was when my own vehicle broke down in the fall of 1995. I was 18 and couldn't afford to pay to have it fixed. So I borrowed tools and asked a ton of questions and, eventually, was able to replace the clutch on my truck by myself. During the course of that project, I found that I really enjoyed having a wrench in my hand and figuring out the puzzle of disassembly and reassembly of a motor vehicle.

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