Air_Pressure_vs_Wet_Performance.doc

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					Most drivers realize that tire load capacity is determined by tire size and inflation pressure.
Larger tires and higher inflation pressures provide more load capacity, while smaller tires and
lower tire pressures provide less.


An underinflated tire will tend to wear the shoulder areas of the tread faster than the center. This
is because there is insufficient air pressure to allow the center of the tread to carry its fair share
of the weight. A correctly inflated tire receives appropriate support from the contained air
pressure to provide an even distribution of load across the footprint. And while most drivers
recognize that this has a significant impact on tire wear, rolling resistance and durability, only a
few realize it also has a noticeable influence on how effectively the tires can resist hydroplaning
to maintain wet traction.


As they taught us in physics class, you can compress and move a gas quite easily, but you
cannot compress liquids and it requires significant energy to move them. Our tires easily push
air around and through their tread designs as they roll. However, when water pools in highway
ruts and builds up on the road surface during rainstorms, the vehicle's speed and weight, as
well as the tires' tread designs, tread depths and evenness of their footprint pressures
determines if and when the tires will be forced to hydroplane.


One of the ways tire manufacturers evaluate their products' hydroplaning and wet traction
effectiveness is by driving them over a glass plate covered with a specific depth of water. The
water is dyed for better visibility and to allow high-speed cameras in underground rooms to
photograph the tires from below. Michelin has provided several photographs of its HydroEdge
premium All-Season tire to help illustrate this tech feature.


                                          The first photograph shows a tire properly inflated to 35
                                          psi sitting still in the water on the glass plate. This
                                          provides an accurate idea of the tire's footprint size and
                                          shape.


                                          The black area is where the tire's rubber compound is
                                          pressed on the glass, and the green areas identify

View larger                               water in the tire's circumferential and high-angle lateral
                                          grooves, and on the remainder of the glass plate.
                                          A properly inflated tire will have enough pressure in the
                                          center of its tread to resist collapsing.



                                          The next picture is of a tire properly inflated to 35 psi,
                                          driving across the glass at 60 miles per hour. If the
                                          glass plate were dry, the footprint size would be
                                          virtually identical to the first picture because air does
                                          not prevent the tread from contacting the plate.
                                          However with standing water on the plate, the tire's
                                          tread depth and tread design must evacuate the water
View larger                               as the tire rolls across the plate at 88 feet per second.
                                          You will notice that the footprint still shows good
                                          contact with the plate, but is slightly smaller than the
                                          static tire's footprint.

A tire that is slightly underinflated will apply less pressure to the center of the tread and it will
become slightly concave.



                                          The next picture is of a tire inflated to only 30 psi, again
                                          driving across the glass at 60 miles per hour. With the
                                          same amount of standing water on the plate, the center
                                          of the tire's tread is lifted as the tread design
                                          unsuccessfully attempts to evacuate water as the tire
                                          rolls across the plate. You will notice that the actual
                                          footprint shows poor contact with the plate and is
View larger                               significantly smaller than the footprint in the photograph
                                          of the properly inflated tire.

A tire that is significantly underinflated will allow the center of the tread to collapse and become
very concave, trapping water rather than flowing it through the tread design.
                                          The final picture is of a tire inflated to only 25 psi,
                                          driving across the glass plate at 60 miles per hour. With
                                          the same amount of standing water, the water lifts the
                                          center of the tire's tread as its footprint rolls across the
                                          plate. You will notice that the actual footprint shows
                                          little contact with the plate and has been virtually
                                          reduced to the shoulder areas.
View larger


Members of The Tire Rack team had the chance to experience the affects of air pressure on
wet performance at Michelin's Laurens Proving Grounds. Drivers were given the opportunity to
compare identical cars on a wet-handling course with the exception of one car having four
properly inflated tires (35 psi) and the other car having significantly underinflated tires on the
rear axle (25 psi).


While driving at the edge of a tire's ability in wet conditions is challenging, the car with the
properly inflated tires provide handling that was predictable. Driving the car with the
underinflated rear tires proved to be much more difficult to drive and forced the driver to slow
down to retain control, producing lap times that were several seconds slower than the properly
inflated car.


While tire manufacturers can develop tires with great hydroplaning resistance and wet traction,
poor maintenance of tire inflation pressures can make a great tire awful.


Adjust your tire pressures as indicated on the vehicle tire placard or in the owner's manual.
Check you inflation pressures at least once a month and before highway trips.




Advantages of Correct Tire Inflation


Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy.
Correct tire inflation pressure allows drivers to experience tire comfort, durability and
performance designed to match the needs of their vehicles. Tire deflection (the tread and
sidewall flexing where the tread comes into contact with the road) will remain as originally
designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be
managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes
the tire's structure, blending the tire's responsiveness, traction and handling.


            Can you easily identify which tire is 30% underinflated? Here is what
                  they would look like in the morning parked in your garage.


             (Roll your mouse across the pictures to find out if you were right.)




          Tough to tell; isn't it? Tire pressure must be checked with a quality air gauge
             as the inflation pressure cannot be accurately estimated through visual
                                             inspection.




Disadvantages of Underinflation


An underinflated tire can't maintain its shape and becomes flatter than intended while in contact
with the road. If a vehicle's tires are underinflated by only 6 psi it could weaken the tire's internal
structure and eventually lead to tire failure. Lower inflation pressures will allow more deflection
as the tire rolls. This will build up more internal heat, increase rolling resistance (causing a
reduction in fuel economy of up to 5%) and reduce the tire's tread life by as much as 25% while
increasing the probability of irregular treadwear. Drivers would also find a noteworthy loss of
steering precision and cornering stability. While 6 psi doesn't seem excessively low, it typically
represents about 20% of a passenger car tire's recommended pressure.


Disadvantages of Overinflation
An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is
reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when
encountering potholes or debris in the road, as well as experience irregular tread wear. Higher
inflated tires cannot isolate road irregularities as well causing the vehicle to ride harsher and
transmit more noise into its interior. However, higher inflation pressures reduce rolling
resistance slightly and typically provide a slight improvement in steering response and cornering
stability. This is why participants who use street tires in autocrosses, track events and road
races run higher than normal inflation pressures.




Most drivers realize that tire load capacity is determined by tire size and inflation pressure.
Larger tires and higher inflation pressures provide more load capacity, while smaller tires and
lower tire pressures provide less.


Correctly inflated tires receive appropriate support from the contained air pressure to provide an
even distribution of load across the footprint and help stabilize the tire's structure. And while
most drivers recognize that this has a significant impact on tire wear, rolling resistance and
durability, only a few realize underinflation also has a noticeable influence on how quickly and
precisely the tires respond to the driver's input.


In order to evaluate the influence of inflation pressure on response and handling, The Tire Rack
conducted a Performance Test Track Drive, comparing properly inflated tires to purposely
underinflated tires. We used 2003 BMW 330Ci coupes, and installed P225/50R16 tires on
16x7.5" wheels. We tested new, full tread depth tires.


We chose Goodyear Eagle GT-HR High Performance All-Season radials that were developed to
blend good treadwear, responsive handling and dependable traction. One of the Eagle GT-HR's
highlights is its internal construction that features Goodyear's RaceWrap Construction
Technology developed for the Eagle Race tires used in NASCAR competition. RaceWrap
Construction Technology brings a casing ply down the sidewall at a slight angle, wraps around
the bead and returns it all of the way up the sidewall until it ends under the edge of the steel
belts. This slightly angled, two-ply sidewall enhances steering response and handling stability.


The tires installed on one of our BMW 330Ci test cars were inflated to the vehicle
manufacturer's recommended inflation pressures of 29 psi front and 33 psi rear, while the other
car had its tires inflated 30% lower (20 psi in the front and 23 psi in the rear). We chose 30%
underinflation because it was the percentage of loss initially established by the US DOT at
which passive pressure monitoring systems must warn the driver of low inflation pressure on
future cars.


The first part of the test was visual. We asked the drivers to look at the tires and decide which of
the two vehicles was equipped with the underinflated tires. While perhaps this visual test might
have been easier with taller tires of the past, today's low profile tires fitted to the BMWs
demonstrated how difficult it has become. The drivers agreed that the tire appearance alone did
not provide irrefutable confirmation of the tire pressure contained inside. You can't use your
eyes as a tire pressure gauge.


          Can you easily identify which tire is 30% underinflated with your eyes?
          Here is what they would look like in the morning as you walked to your
                                         car in the garage.


                 (Roll your mouse across the pictures to confirm you were right)




The next test was run on our test course to confirm the influence of tire pressure on the tire's
performance at its limit. While the drivers thought that the properly inflated tires provided
responsiveness and predictable handling, they quickly realized that the same tires in an
underinflated state left a lot to be desired. The underinflated tires required more steering input to
initiate maneuvers and were slower to respond. The underinflated tires also felt out of sync
during transitions; instead of moving in unison, the rear tires' reactions lagged behind the front
tires, resulting in a detached sensation being transmitted to the drivers.
The underinflated tires delivered acceptable steady-state cornering force once they stabilized
on our test track's skid pad, but the car was uncooperative anytime it was asked to change
directions. It proved to be over 2 seconds slower around our test course (2 seconds represents
about a 7% loss of handling performance).


In other words, the performance that tire manufacturers build in, low tire pressures can take
away.


Adjust your tire pressures as indicated on the vehicle tire placard or in the owner's manual.
Check you inflation pressures at least once a month and before highway trips.




Driving at high speeds certainly helps make a trip go faster; just ask any driver who has gone
"flat out" on the German Autobahn. However with the exception of events like the Silver State
Classic's Open Road Rally or a driver's school on a racetrack, it's difficult to find a place that
allows unlimited speeds! Remember, the tires on the vehicle should be properly sized, inflated
and inspected if you plan to drive fast because the tires will be subjected to tremendous
stresses.


Because of the weight they bear, pneumatic tires' sidewalls bulge and their treads flatten as
they roll into contact with the road. This results in dimensional difference between the tire's
"unloaded" radius (i.e., between the center of the axle and the top of the tire) and its "loaded"
radius (between the center of the axle and the road). The engineer's call the difference between
the two radii "deflection." Increasing vehicle speed will cause the tires to deflect quicker and
increasing vehicle load will cause the tires to deflect farther (if tire pressure isn't increased).


Consider that a 225/45R17 91W Standard Load tire (with a 25-inch overall diameter) will roll
about 835 times every mile. Although the number of tire revolutions per mile doesn't change
significantly as speed climbs, the revolutions per second become daunting. While the
225/45R17 91W-sized tire rolls a rather comfortable 7 times per second at 30 mph, this same
tire will roll about 16 times per second at 70 mph on an American Interstate and an amazing 35
times per second during a 150 mph cruise on the German Autobahn. Thirty-five tire revolutions
per second means that the tire is transforming from its unloaded to loaded shape and back
            th
every 3/100 of a second.


The European Tyre and Rim Technical Organization (ETRTO) establishes the standards for
tires sold in Europe, and recognizes that the tire's deflection must be minimized and controlled
in order to surpass high speed driving stresses. In order to accomplish this, the tire inflation
pressure recommendations and the tire's rated load capacities are customized when speeds
exceed 160 km/h (99 mph) for all tires up to and including a V-speed rating, and when speeds
exceed 190 km/h (118 mph) for all tires that are Z-speed rated and above.


The Autobahn's unlimited speed opportunities explain why many German vehicles identify
alternate tire inflation pressures to accommodate higher than North American highway speeds
and heavier than typical two-passenger loads. In order to accommodate higher speeds, the tire
size and inflation pressure recommendations are tuned beyond what is branded on the tire's
sidewalls. These increases in recommended tire pressure are usually determined by agreement
between the vehicle and tire manufacturers. In the absence of such an agreement, apply the
following:


Beginning with the vehicle manufacturer's recommended tire pressure for normal highway
conditions, tire inflation pressures are initially increased and then the tire's rated load capacities
(branded on the sidewalls) are reduced as speeds climb.


In our example shown below, the vehicle manufacturer's recommended 35 psi for a 225/45R17
91W Standard Load tire installed on a vehicle initially rises in 1.5 psi increments for every 10
km/h (6.2 mph) increase in speed until the inflation pressures max out with an increase of 7.5
psi when the vehicle's top speed has increased 50 km/h (31mph). Then as the vehicle's top
speed continues to climb, the rated load capacity of the tire is reduced in 5% increments for
every additional 10 km/h until the vehicle's top speed has increased an additional 30 km/h (18.6
mph). In this case the 225/45R17 91W Standard Load size's rated load capacity of 1,477 lbs. is
reduced to 1,255 lbs. when applied to a vehicle with a 270 km/h (168 mph) top speed.


                                For W-Speed Rated Tires

                                                                    W-Speed Rated
               Required Tire
  Vehicle                              Tire Load Capacity                   Tire
                  Pressure
Top Speed                            % of Branded Maximum              35 psi O.E.
                  Increase
                                                                        Example

                                      % of value branded on
mph km/h        psi       bar                                        psi           lbs.
                                             sidewall

118    190       0         0                  100%                   35.0          1000

124    200      1.5       0.1                 100%                   36.5          1000

130    210      3.0       0.2                 100%                   38.0          1000
136    220     4.5        0.3                100%                39.5          1000

143    230     6.0        0.4                100%                41.0          1000

149    240     7.5        0.5                100%                42.5          1000

155    250     7.5        0.5                95%                 42.5          950

161    260     7.5        0.5                90%                 42.5          900

168    270     7.5        0.5                85%                 42.5          850


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's
sidewall.




If a vehicle's horsepower and top speed are increased significantly, confirm that the required
adjustments are made to the tire pressure and/or load conditions beyond the vehicle
manufacturer's recommendations using the following charts.


       Recommended High Speed Pressure & Load Capacity Adjustments
                                For R-Speed Rated Tires

                                                                 R-Speed Rated
 Vehicle      Required Tire
                                       Tire Load Capacity               Tire
   Top          Pressure
                                    % of Branded Maximum            35 psi O.E.
  Speed            Increase
                                                                       Example

                                     % of value branded on
mph km/h      psi        bar                                      psi          lbs.
                                            sidewall

100 160        0          0                  100%                 35       1000

106 170        1        0.06                 100%                 36       1000

112   180      2        0.12                 100%                 37       1000


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.
       Recommended High Speed Pressure & Load Capacity Adjustments
                                For S-Speed Rated Tires

                                                                 S-Speed Rated
 Vehicle      Required Tire
                                       Tire Load Capacity               Tire
   Top          Pressure
                                    % of Branded Maximum            35 psi O.E.
  Speed            Increase
                                                                       Example
                                   % of value branded on
mph km/h     psi       bar                                    psi          lbs.
                                          sidewall

100 160       0         0                  100%               35       1000

106 170       1        0.06                100%               36       1000

112   180     2        0.12                100%               37       1000


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.
                              For T-Speed Rated Tires

                                                              T-Speed Rated
 Vehicle     Required Tire
                                     Tire Load Capacity             Tire
   Top            Pressure
                                  % of Branded Maximum          35 psi O.E.
  Speed           Increase
                                                                   Example

                                   % of value branded on
mph km/h     psi        bar                                   psi          lbs.
                                          sidewall

100   160     0          0                 100%               35       1000

106   170     1        0.06                100%               36       1000

112   180     2        0.12                100%               37       1000

118   190     3        0.18                100%               38       1000


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.


                              For U-Speed Rated Tires

                                                              U-Speed Rated
 Vehicle     Required Tire
                                     Tire Load Capacity             Tire
   Top            Pressure
                                  % of Branded Maximum          35 psi O.E.
  Speed           Increase
                                                                   Example

                                   % of value branded on
mph km/h     psi        bar                                   psi          lbs.
                                          sidewall

100   160     0          0                 100%               35       1000

106   170     1        0.06                100%               36       1000

112   180     2        0.12                100%               37       1000

118   190     3        0.18                100%               38       1000

124   200     4        0.24                100%               39       1000
NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.


                              For H-Speed Rated Tires

                                                              H-Speed Rated
 Vehicle     Required Tire
                                     Tire Load Capacity               Tire
   Top         Pressure
                                  % of Branded Maximum          35 psi O.E.
  Speed           Increase
                                                                   Example

                                   % of value branded on
mph km/h     psi        bar                                   psi            lbs.
                                          sidewall

100    160    0          0                 100%               35         1000

106    170    1        0.06                100%               36         1000

112    180    2        0.12                100%               37         1000

118    190    3        0.18                100%               38         1000

124    200    4        0.24                100%               39         1000

130    210    5        0.30                100%               40         1000


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.


                              For Z-Speed Rated Tires
      (tire manufacturer must confirm speed cabability beyond 149 mph)

                                                              Z-Speed Rated
             Required Tire
 Vehicle                             Tire Load Capacity               Tire
               Pressure
Top Speed                          % of Branded Maximum         35 psi O.E.
                  Increase
                                                                    Example

                                   % of value branded on
mph km/h      psi       bar                                    psi           lbs.
                                          sidewall

118    190     0         0                 100%                35.0          1000

124    200    1.5       0.1                100%                36.5          1000

130    210    3.0       0.2                100%                38.0          1000

136    220    4.5       0.3                100%                39.5          1000

143    230    6.0       0.4                100%                41.0          1000

149    240    7.5       0.5                100%                42.5          1000
                              For Z-Speed Rated Tires
      (tire manufacturer must confirm speed cabability beyond 149 mph)

                                                              Z-Speed Rated
             Required Tire
 Vehicle                             Tire Load Capacity               Tire
               Pressure
Top Speed                          % of Branded Maximum         35 psi O.E.
                  Increase
                                                                    Example

                                   % of value branded on
mph km/h      psi       bar                                    psi           lbs.
                                          sidewall

155    250    7.5       0.5                100%                42.5          1000

161    260    7.5       0.5                100%                42.5          1000

168    270    7.5       0.5                100%                42.5          1000

174    280    7.5       0.5                 95%                42.5          950

180    290    7.5       0.5                 90%                42.5          900

186    300    7.5       0.5                 85%                42.5          850


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.


                              For V-Speed Rated Tires

                                                              V-Speed Rated
 Vehicle     Required Tire
                                     Tire Load Capacity               Tire
   Top         Pressure
                                  % of Branded Maximum          35 psi O.E.
  Speed           Increase
                                                                   Example

                                   % of value branded on
mph km/h     psi        bar                                   psi            lbs.
                                          sidewall

100    160    0          0                 100%               35         1000

106    170    1        0.06                100%               36         1000

112    180    2        0.12                100%               37         1000

118    190    3        0.18                100%               38         1000

124    200    4        0.24                100%               39         1000

130    210    5        0.30                100%               40         1000

136    220    5        0.30                 97%               40             970

143    230    5        0.30                 94%               40             940

149    240    5        0.30                 91%               40             910
NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.


                             For W-Speed Rated Tires

                                                             W-Speed Rated
 Vehicle     Required Tire
                                    Tire Load Capacity               Tire
   Top         Pressure
                                 % of Branded Maximum           35 psi O.E.
  Speed         Increase
                                                                 Example

                                  % of value branded on
mph km/h      psi      bar                                    psi           lbs.
                                         sidewall

118   190      0        0                 100%                35.0          1000

124   200     1.5      0.1                100%                36.5          1000

130   210     3.0      0.2                100%                38.0          1000

136   220     4.5      0.3                100%                39.5          1000

143   230     6.0      0.4                100%                41.0          1000

149   240     7.5      0.5                100%                42.5          1000

155   250     7.5      0.5                 95%                42.5          950

161   260     7.5      0.5                 90%                42.5          900

168   270     7.5      0.5                 85%                42.5          850


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.


                             For Y-Speed Rated Tires

                                                              Y-Speed Rated
 Vehicle     Required Tire
                                    Tire Load Capacity               Tire
   Top         Pressure
                                 % of Branded Maximum           35 psi O.E.
  Speed         Increase
                                                                 Example

                                  % of value branded on
mph km/h      psi      bar                                    psi           lbs.
                                         sidewall

118   190      0        0                 100%                35.0          1000

124   200     1.5      0.1                100%                36.5          1000

130   210     3.0      0.2                100%                38.0          1000

136   220     4.5      0.3                100%                39.5          1000
                               For Y-Speed Rated Tires

                                                                    Y-Speed Rated
 Vehicle      Required Tire
                                      Tire Load Capacity                   Tire
   Top           Pressure
                                   % of Branded Maximum               35 psi O.E.
  Speed          Increase
                                                                        Example

                                    % of value branded on
mph km/h       psi       bar                                         psi          lbs.
                                            sidewall

143    230     6.0       0.4                  100%                  41.0          1000

149    240     7.5       0.5                  100%                  42.5          1000

155    250     7.5       0.5                  100%                  42.5          1000

161    260     7.5       0.5                  100%                  42.5          1000

168    270     7.5       0.5                  100%                  42.5          1000

174    280     7.5       0.5                  95%                   42.5          950

180    290     7.5       0.5                  90%                   42.5          900

186    300     7.5       0.5                  85%                   42.5          850


NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall




(공기압, 온도변화)


Your tires support the weight of your vehicle, right? Well they don't! It's the air pressure inside
them that actually supports the weight. Maintaining sufficient air pressure is required if your tires
are to provide all of the handling, traction and durability of which they are capable.


우리들의 타이어가 차의 무게를 지탱하고 있을까? 글쎄. 그렇지 않다. 실제로 무게를
지탱시키는 것은 타이어 안의 공기압이다. 만약 당신의 타이어가 그것이 가진 능력인
핸들링, 제동성, 견고성을 모두 발휘하기 위해서는 충분한 공기압을 유지시키는 것이
요구된다.


However, you can't set tire pressure...and then forget about it! Tire pressure has to be checked
periodically to assure that the influences of time; changes in ambient temperatures or that a
small tread puncture has caused it to change.
그러나, 공기압을 한번 채우고 나서 잊어버려서는 안 된다! 타이어 공기압은 정기적으로
점검되어야 한다. 이것은 시간의 영향 즉 주위 온도의 변화 또는 작은 트래드의 구멍이
공기압을 변화시켰는지를 확인하기 위해서다.


The tire pressure recommended in your vehicle's owner's manual or tire information placard is
the vehicle's recommended cold tire inflation pressure. This means that it should be checked in
the morning before you drive more than a few miles, or before rising ambient temperatures or
the sun's radiant heat affects it.


당신의 자동차 주인의 매뉴얼이나 타이어 정보전단에 권고된 타이어의 공기압은 그
자동차의 권장된 찬 공기압을 말한다. 이 사실은 몇 마일 이상을 운전하기 전 매일 아침에
또는 주위 온도가 오르거나 태양열이 영향을 미치기 전에 공기압을 점검해야 하는 것을
의미한다.


Since air is a gas, it expands when heated and contracts when cooled. In most parts of North
America, this makes fall and early winter months the most critical times to check inflation
pressures...days are getting shorter...ambient temperatures are getting colder...and your tires'
inflation pressure is going down!


공기는 기체이기 대문에 열을 받으면 팽창하고 식으면 줄어든다. 이 사실 때문에 대부분의
북미지역에서는 가을과 초겨울이 공기압을 점검하는 가장 중요한 시기가 된다….낮은 점점
짧아지고…. 주위 온도는 점점 추워진다… 그리고, 당신의 타이어의 공기압은 내려가는
것이다.


The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire's inflation
pressure will change by about 1 psi (up with higher temperatures and down with lower).


대략적으로 매 10 도 화씨의 온도변화에 타이어의 공기압은 약 1psi 씩 변화한다. (온도가
오르면 공기압도 오르고, 온도가 내려가면 공기압도 내려간다).


In most parts of North America, the difference between average summer and winter
temperatures is about -50° Fahrenheit...which results in a potential loss of about 5 psi as
winter's temperatures set in. And a 5 psi loss is enough to sacrifice handling, traction, and
durability!


대부분의 북미 지역에서는 평균 여름과 겨울 온도의 차이는 약 마이너스 50 도 화씨에
이른다. 이것은 겨울온도가 되면서 공기압의 약 5psi 의 잠재적 손실을 말한다. 그리고,
5psi 의 손실은 타이어의 핸들링, 제동성, 내구성을 손상하는 데 충분하다.
Additionally, the difference between cold nighttime temperatures and hot daytime temperatures
in most parts of the country is about 20° Fahrenheit. This means that after setting tire pressures
first thing in the morning, the vehicle's tire pressures will be almost 2 psi higher when measured
in the afternoon (if the vehicle was parked in the shade). While that is expected, the problem is
when you set your vehicle's tire pressures in the heat of the day, their cold pressures will
probably be 2 psi low the following morning.


게다가, 북미의 대부분의 지역은 추운 밤 온도와 더운 낮 온도의 차이는 20 도 화씨에
이른다. 이는 아침 처음의 공기압이 오후에 측정했을 때 (그늘에 주차되어 있는 경우) 거의
2psi 가량 올라간다는 말이다. 이 것이 예상되면, 문제는 당신이 타이어 공기압을 한 낮에
조정하면, 그 찬 공기압이 아마 다음 날 아침에 2psi 낮을 수 있다는 사실이다.


And finally, if the vehicle is parked in the sun, the sun's radiant heat will artificially and
temporarily increase tire pressures.


그리고 마지막으로, 자동차가 햇빛에 주차되어 있는 경우, 태양열이 인위적이고 단기적으로
타이어의 공기압을 상승시킨다.


We put some of these theories to the test at The Tire Rack. First, we mounted two tires on
wheels. We let them sit overnight to equalize and stabilize their temperatures and pressures.
The following morning we set them both to 35 psi. One tire and wheel was placed in the shade
while the other was placed directly in the sun. We then monitored the ambient temperatures, tire
temperatures and tire pressures through the day. As the day's temperatures went from 67° to
85° Fahrenheit, the tire that was kept in the shade went from our starting pressure of 35 psi to a
high of 36.5 psi. The tire that was placed in the sun and subject to the increase in ambient
temperature plus the sun's radiant heat went from our starting pressure of 35 psi to a high of 40
psi. In both cases, if we had set our tire pressures in the afternoon under the conditions of our
evaluation, they would have been between 2 and 5 psi low the following morning.


우리는 이 이론을 실재 타이어 랙에서 실험하였다. 우선, 우리는 두 개의 타이어를 바퀴에
장착했다. 그리고 타이어를 밤새 온도와 공기압을 평준화하고 안정화하도록 그대로
놓아두었다. 다음날 아침 공기압을 모두 35 psi 로 조정했다. 한쪽의 타이어와 바퀴는 그늘에
세워두고 다른 한 쪽은 햇빛에 놓아두었다. 그리고 주위온도, 타이어 온도 그리고 공기압을
하루 내내 관찰 하였다. 낮 온도가 76 도 에서 85 도 화씨로 오르자, 그늘에 세워진
타이어는 처음의 35 psi 에서 36.5 psi 로 공기압이 상승했다. 햇빛에 세워둔 타이어는
주위온도 상승과 태양직사광선으로 인해 공기압이 처음의 35 psi 에서 40psi 로 상승했다. 이
두 경우 모두, 만약 우리의 관찰조건에서 오후에 공기압을 조정했더라면, 공기압은 그 다음
날 아침에 2psi 에서 5psi 사이에 낮아져 있었을 것이다.


Next we evaluated the affects of heat generated by the tire's flexing during use. We tried to
eliminate the variable conditions we might encounter on the road by conducting this test using
our "competition tire heat cycling service" that rolls the tires under load against the machine's
rollers to simulate real world driving. We monitored the changes in tire pressure in 5-minute
intervals. The test tires were inflated to 15 psi, 20 psi, 25 psi and 30 psi. Running them all under
the same load, the air pressure in all of the tires went up about 1 psi during every 5 minutes of
use for the first 20 minutes of operation. Then the air pressures stabilized, typically gaining no
more than 1 psi of additional pressure during the next 20 minutes. This means that even a short
drive to inflate your tires will result in tires that will probably be under-inflated by a few psi the
following morning.


다음으로 우리는 타이어의 사용 중 그 운동에 의해 야기되는 열의 영향을 측정하였다.
우리는 이 실험을 함에 있어 실제 도로에서 경험할 수 있는 변화무쌍한 조건들을
제거하려고 했다. 이를 위해 ‘경주 타이어 열 회전 서비스’를 사용했는데, 이것은 타이어를
그 기계의 회전에 대항한 하중 아래서 타이어를 회전시키는 것으로 실재 상황의 운전의
조건을 만들기 위한 것이다.                   그리고 우리는 5 분 간격으로 타이어 공기압의 변화를
측정했다. 실험에 사용된 타이어는 15 psi, 20 psi, 그리고 30 psi 로 공기압을 맞추었다. 같은
하중아래서 이 타이어들 운행시키자, 모든 타이어의 공기압은 처음 20 분간의 운행 동안 매
5 분에 1 psi 로 공기압이 상승했다. 그리고 나서, 공기압은 안정되었는데, 주로 다음
20 분간의 운행 동안 1 psi 가 넘지 않는 공기압의 상승이 나타났다. 이 사실은 짧은 시간의
주행도 타이어 공기압을 상승시키고 그리고 다음 날 아침에 몇 psi 정도의 공기압을 낮출
있다는 것을 말한다.


Add all of these together, and you can understand why the conditions in which you set your
vehicle's tire pressures are almost as important as the fact that you do set it.


이 모든 사실을 종합하면, 왜 어떤 조건 아래서 자동차 타이어 공기압을 조정하느냐는
타이어 공기압 조정 자체만큼이나 중요하다는 사실이 이해될 것이다.
It's important to remember that your vehicle's recommended tire pressure is its cold tire inflation
pressure. It should be checked in the morning before you drive more than a few miles, or before
rising ambient temperatures or the sun's radiant heat affects it.


당신의 자동차 주인의 매뉴얼이나 타이어 정보전단에 권고된 타이어의 공기압은 그
자동차의 권장된 찬 공기압을 말한다. 이 사실은 몇 마일 이상을 운전하기 전 매일 아침에
또는 주위 온도가 오르거나 태양열이 영향을 미치기 전에 공기압을 점검해야 하는 것을
의미한다.


And by the way, if you live in the North and park in an attached or heated garage you will lose
pressure when you leave its warmth and venture into the real world outside during winter. Add 1
psi cold pressure tire pressure to compensate for each 10° Fahrenheit temperature difference
between the temperature in the garage and outside.


그리고, 만약 당신이 북쪽지역이 살고, 차를 차고나 따뜻한 주차장에 주차할 경우, 겨울에
차를 밖으로 몰고 나가서 차가 식을 경우 공기압의 손상을 경험할 것이다. 차고와 바깥
온도의 10 도 화씨 차이마다 1psi 씩 찬 공기압을 보충하는 것이 필요하다.




(공기압, 시간 변화)




Your tires support the weight of your vehicle, right? Well they don't! It's the air pressure inside
them that actually supports the weight. Maintaining sufficient air pressure is required if your tires
are to provide all of the handling, traction and durability of which they are capable.


우리들의 타이어가 차의 무게를 지탱하고 있을까? 글쎄. 그렇지 않다. 실제로 무게를
지탱시키는 것은 타이어 안의 공기압이다. 만약 당신의 타이어가 그것이 가진 능력인
핸들링, 제동성, 견고성을 모두 발휘하기 위해서는 충분한 공기압을 유지시키는 것이
요구된다.


However, you can't set tire pressure...and then forget about it! Tire pressure has to be checked
period ically to assure that the influences of time; changes in ambient temperatures or small
tread punctures have not caused it to drop.
그러나, 그러나, 공기압을 한번 채우고 나서 잊어버려서는 안 된다! 타이어 공기압은
정기적으로 점검되어야 한다. 이것은 시간의 영향 즉 주위 온도의 변화 또는 작은 트래드의
구멍이 공기압을 낮추지 않았음을 확인 하기 위해서다.


While tires appear solid, the molecular structure of the rubber used to manufacturer them
actually looks like strands of cooked spaghetti stuck together. These molecular strands are
stretched and returned to their relaxed state every time the tire rolls (about 800 times every
mile).


타이어는 겉으로 단단해 보이지만, 타이어 생산에 사용되는 고무의 분자구조는 사실 요리된
스파게티을 한 데 뭉쳐놓은 줄(실) 모양이다. 이 분자의 끈들은 타이어가 운행할 때 마다
늘어졌다가 원래의 상태로 돌아가기를 반복한다 (약 1 마일당 800 회씩).




Since typical tire pressures range from 30 to 35 psi for cars (with light truck tire pressures often
higher), there is a constant force trying to push the air through the tire. This allows some of the
air to escape (called permeation) right through the microscopic spaces between the rubber
molecules. And somewhat like a rubber balloon, the air will eventually escape if it is not
replenished.


보통 타이어의 공기압은 자동차의 경우 30 에서 35psi 사이이다. (트럭은 종종 타이어
공기압이 더 높다. 타이어에는 항상 타이어의 공기를 밀어내는 힘이 작용한다. 이 현상은
타이어의 공기가 고무와 분자 사이의 미세 공간을 통해 빠져나가게 한다. (침투현상으로
불린다) 고무풍선과 비슷하게, 그 타이어의 공기는 만약에 보충되지 않는다면 완전히
빠지게 될 것이다.


All things being equal, a tire's inflation pressure will go down by about 1 psi every month. This
means that if air isn't added for two to three months, the tire's inflation pressures will probably
be 2 to 3 psi low.


모든 조건이 같다면, 타이어의 공기압은 매달 약 1psi 씩 내려갈 것이다. 이 것은 만약에 2-
3 달 동안 공기가 보충되지 않는다면, 공기압은 2 에서 3psi 정도 낮게 될 것이다.


Tires are normally inflated with air (a combination of gasses comprised of about 78% nitrogen
(N2), 21% oxygen (O2) and 1% argon (Ar) along with traces of other gasses) from the local gas
station. Unfortunately, using air permits moisture and the amount of water vapor in the air varies
from place to place, time of the year and due to weather conditions. While air is all around us,
finding a convenient source of compressed air is becoming difficult, and finding a source of
"dry," vapor free compressed air is even more difficult.


타이어는 주로 동네의 주유소에서 주로 기체로 채워진다. (약 78%의 질소, 21%의 산소,
1%의 아르곤 그리고 기타 다른 종류의 기체의 종합이다) 안타깝게도, 사용하는 기체는
습기를 만들고 공기 중에 물이 증발되는 양은 지역에 따라, 계절에 따라 그리고 날씨에
따라 다르다. 공기는 우리주위에 널려 있지만, 압축된 기체의 편리한 공급원을 찾는 것이
점점 어려워 지고 있고, 증발문제가 없는 ‘건조한’ 압축된 기체의 공급원을 찾는 것은 더
어렵다.


In order to help maintain more constant tire pressures we should check them more frequently.
Once a month and before trips is the minimum, once a week is preferred. This will allow us to
refill lost pressure that escapes over time, as well as discover any pressure losses due to slow
leaks caused by minor punctures before significant pressure is lost and the tire's internal
structure is damaged.


좀 더 안정된 타이어 공기압을 유지하기 위해서는 우리는 자주 점검해야 한다. 한 달에 한
번, 여행 전의 점검은 최소한이고, 일 주에 한번이 더 좋다. 이는 시간이 지나면서 손실된
공기압을 채울 수 있게 할 뿐만 아니라, 많은 공기압의 손실 전에 그리고 타이어의 내부가
손상되기 전에 작은 구멍 같은 것으로 인해 점진적으로 줄어드는 타이어의 공기압이 손실되
는 것을 발견하는데 도움을 줄 것이다.