Tire School

Tire Inflation Pressure

Tire air pressure decreases naturally (little by little)


      It is generally accepted that air pressure in tires on a passenger car decreases by 5–10% (10–20kPa) every month.Air pressure decreases naturally

Tire size:195/65R 15
Starting pressure:220kPa(100kPa=1.0kgf/cm2)

(A) Air pressure(kPa)   (B) Decreases by 10-20kPa a month

Impact of low air pressure on fuel consumption

      According to material released by The Energy Conservation Center, Japan, fuel consumption increases by around 2% in urban zones and 4% in the suburbs when air pressure drops 50kPa (0.5kgf/cm2) below the appropriate level. Please check air pressure once a month to ensure environmentally friendly and safe driving.
      Adequately managing air pressure is important not only to maximize the tire’s feature but also to avoid an increase in fuel consumption.

Pressure down 50kPa from appropriate level (In case of a 2000cc passenger car)

(A) Increasein fuel consumption(%)  (B) Driving area

Urben zone  Suburbs   Expressway

      Measured in a controlled setting using a 2000cc passenger car Driving speeds (average speed including stoppages): Urban zone 15km/h, Suburbs 38km/h, Expressway 78km/h Source: The Energy Conservation Center, Japan

Lowers Fuel Economy

      If the tire pressure is only 155kPa (1.55bar, 22.5psi), 30% lower than the specified pressure of 220kPa (2.2bar, 31.9psi)…

A loss of fuel consumption is around 2%

Cause of Abnormal Wear

      If the proper inflation pressure is not applied, abnormal wear, as shown below, may occur. In the worst case, the tire could burst due to underinflation.
Shoulder Wear

 If the inflation pressure is too low, it causes excessive wear on both sides of tread.

Center Wear

If the inflation pressure is too high, it causes excessive wear on the center part of the tread.

Lack of proper tire maintenance (e.g. underinflation) causes problems

About 21% of cars do not have properly maintained tires.78% of this is due to improper tire inflation pressure

  (A) Survey results of improper car maintenance(2007)  (B) Improper maintenance of tires

  ① Other 7%                  ② Driving over a nail or similar 4%        ③ Injury by obstacles 2%   

  ④ Abnormal wear 7%  ⑤ Worn-down tire grooves 2%              ⑥ Improper tire inflation pressure 78%

Check your tire inflation pressure once a month

How to check the inflation pressure

  1.   Remove the valve cap on the wheel,attach the inflation pressure gauge to the valve, pressing firmly to avoid escaping air, then check the number.Don’t forget to put the valve cap back on when you have finished.*Please check the valve base for damage and air leakage.

  2. The recommended inflation pressure is written on a label stuck in one of these places inside the driver’s door. You can also refer to the vehicle owner’s manual for the recommended inflation pressure.

  3. The inflation pressure should be measured when the tire is cold. When driving, the temperature inside the tire rises causing inflation to expand and the inflation pressure to increase. As a result, measurements taken immediately after driving will be inaccurate.

  4. Go to a tire shop when your tires need to be inflated.

Not sure what your tire pressure should be? There are several places you can find it in your vehicle:
  1.       On the fuel filler door
  2.       On the door frames of the driver’s and passenger’s sides
  3.       Your vehicle’s manufacturer’s handbook

Using a bicycle to illustrate the relation between tires and air pressure

The more air you put in a bike tire, the easier it is to peddle and the faster you can go. Conversely, peddling is more difficult when air pressure decreases; you waste energy and get tired quicker. Although the same phenomenon applies to cars as air pressure changes, you feel the link more with a bike as you are expending your own energy.
When air pressure is too low:

  ・The ride may feel cushy but it is by no means comfortable

  ・The larger ground contact area results in increased energy loss

When air pressure is too high:

  ・Energy loss is low, giving a feeling of buoyancy

  ・It is easier to skid since there is less ground contact area

  ・The ride is less comfortable since shocks are not absorbed

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