DIY – Checking and adjusting tire pressure

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September 22, 2012 by quirkyuncle

Checking the pressure in your tires, on a regular basis, is important for your safety. It also will help your tires wear longer and can give you better fuel economy.

Properly inflated tires will help your car handle better and more predictably. Tires that are inflated to the correct pressure will also give you better traction in adverse weather conditions.

Tools: Tire pressure gauge and tire pump (or other air source)
Time: 15 minutes
Difficulty: Easy

You can purchase a tire pressure gauge or from Amazon.com.




Air vs nitrogen
A number of tire dealers are now inflating the tires with nitrogen gas. Using nitrogen gas in tires is great, because it is much more stable than air over a broad temperature range. This means your pressure will stay consistent in hot and cold weather. Nitrogen molecules are also bigger than many of the molecules in regular air, so tires filled with nitrogen will seep less air and hold their pressure longer.

The only problem is that if your tires are filled with nitrogen, you should not mix regular air in, unless the tire is very low – it is better to mix than damage your tire and wheel by running it with low pressure. It does not hurt to mix regular air with nitrogen, it’s just that you’ll lose the benefits of nitrogen when you mix.

So, if your tires are filled with nitrogen, your best bet is to go back to your tire dealer to have their pressure checked.

How often should I check my tires?
Obsessive folks will check their tire pressure weekly. This is a bit excessive, for most people. Checking them once a month is good, several times a year at seasonal changes is adequate. You need to check them more often if you notice a tire that looks low, if the car is handling oddly, or if your area has gone through a significant change in temperature. If any of these conditions occur, spend a few minutes checking your tire pressure.

You can include checking your tire pressure as part of a routine maintenance check that you perform on your vehicle. We’ll talk about that in another posting. Check back soon!

Where do get my air?
While we all know folks who are full of hot air, this is not the kind of air you can use to fill your tires.

If you own a tire pump, you can use it to inflate your tires. The other alternative is to see if your local gas station provides compressed air. Many stations do this, especially if they also perform mechanical work. Some gas stations provide the air for free, as a courtesy to their customers. Others will make you pay a nominal fee, like 25-cents. If you are paying for air, the pump is usually on a timer, so check all the tires first before you start putting air in them – this way you won’t have to switch between checking and filling and potentially end up needing to pay for air twice.

How much air should I use?
In the USA, tire pressure is measured in pounds per square inch (PSI). Other parts of the world can use different units of measure. The process followed here applies everywhere, but you will need to make conversions to your local units of measure.

Your owners manual lists the manufacturer’s recommended tire pressures for your car. These pressures are also listed on a label that is typically on the driver’s side door frame. It looks like this:
Pressure specs

The manufacturer’s recommended tire pressure takes many factors into account. It is a balance of ride quality, the handling characteristics they want the car to have, and fuel economy. You can’t go wrong following the the manufacturer’s recommended tire pressure, but a lot of us like to make some adjustments.

Personally I run all my tires, front and rear, on all the cars in our family at 36 PSI. While this is a pressure that is typically higher than the manufacturer’s recommended tire pressure, it is still well within the maximum pressure specified by the tire maker (you can find this written on the sidewall of any tire, if you care to check).

A car does ride more firm at 36 PSI, which is something that we actually like. 36 PSI will make a car handle more responsively, and is the pressure that a lot of sports car racers use on the track. Running at 36 PSI also increases your fuel economy, as a tire with higher pressure presents less rolling resistance. I have also found that 36 PSI makes tires wear more evenly and therefore last longer.

Give it a shot. Since 36 PSI is usually higher than the pressures listed on your car’s door frame, if you don’t like the way the car rides, just let some air out.

Note: Like revenge, tire pressure is best served up cold. You need to let a car sit for a few hours before checking its tire pressure. If you plan to do this procedure at a gas station, pick one that is really close to home, and let the tires cool before you drive there.

Let’s check ’em!
Before you begin, have your tire pressure gauge and a source of air. Try to check your tires in a safe location – doing this in the street is never good, unless it is an emergency. If you need to check tires in the street, be very careful and try to move the car to a safer location, if at all possible.

  1. Remove the tire valve cap.
    Remove/install valve cap
    Try not to lose the cap, as it keeps the tire valve clean and prevents corrosion and leaks. If you do lose it, you can usually get them for free or for a few cents from a tire dealer. The nicer metal caps are more expensive, but some can fully seal the tire in the event of a tire valve leak.
  2. Measure the pressure. The following photos show how to measure using two common gauge types. Reset the gauge to zero and press the open side of the gauge onto the valve to take a measurement. If you do this correctly, you will hear a brief rush of air (Pfttt). If the gauge is misaligned, you will hear all sorts of hissing. Stop immediately and realign the gauge – all you are doing is letting air out of the tire and will never get an accurate reading.

    Here is a dial gauge. Most of these will hold their reading until you reset them by pressing the button on the side.

    Check with dial gauge

    Here is a pencil gauge. These will hold their reading until you reset them by pushing the slide back in.

    Check with pencil gauge

    You need to read the pencil gauge carefully, as the numbers can be small.

    Read pencil gauge

  3. If the pressure is high, bleed some air out of the tire. Press the post on the end of the gauge into the valve, depressing the little pin inside the tire valve. If you do this correctly, you will hear air hissing out. You do not need to let a lot of air out to make a minor pressure adjustment!
    Bleed excess pressure
  4. If the pressure is low, add some air to the tire. Press the open side of the air line, from your pump or gas station air line onto the valve.
    • If you are using an electric or manual pump, the air line end will have a means to lock the line onto the valve to hold it in place while you are pumping. Lock it and pump. If you hear crazy hissing before you pump, it means the line is misaligned on the valve. Remove it and try again.
    • If you are using an air line, like you find at a gas station (shown below), there is no lock. You need to hold the line in place as the air goes in to the tire. If you do this correctly, you will hear air slowly hissing into the tire. If you hear crazy hissing, it means the line is misaligned on the valve. Remove it and try again.

    Inflate tire

  5. After adding air to or removing air from a tire, check its pressure again, adding or removing air as needed until the desired pressure is reached.
    Check pressure - good
  6. Replace the tire valve cap.
    Remove/install valve cap
  7. If you have a newer car with a tire pressure monitoring system (TPMS), you will need to reset the TPMS system after all four tires have been adjusted. See your owners manual for instructions. Typically, these systems are reset by turning on your ignition key and pressing the TPMS button until the TPMS light goes on and off.
    Reset TPMS
  8. You’re done! Take a ride and see how it feels!

    Some things to look at when checking your tire pressure

    • Tire wear – if your tires have little or no tread remaining or are worn unevenly, they might need replacement. See your local tire dealer.
    • Damages wheel – If your wheels appear damaged, they might need repair or replacement. See your local tire dealer or mechanic.
    • I’ll cover some other cool things to inspect in another posting. Check back soon!

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