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The
sidewall description on the tire "89H" is referred
to as the tire's service description. The "89" is
the load index and the "H" is the speed symbol.
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The load index is an
assigned number that corresponds with the load-carrying
capacity of the tire. In this case, the "89" indicates
a load-carrying capacity of 1279 lb at maximum inflation
pressure. The load index for most passenger car
tires ranges from 75-100.
Speed ratings are determined
by indoor laboratory testing methods which measure
high speed tire durability under controlled test
conditions. These test procedures do not take into
account underinflation, tire damage, vehicle characteristics
or road conditions which can lead to sudden tire
failure or loss of vehicle control at much lower
speeds than indicated by the tire's speed rating.
When a "ZR" appears in the size designation (275/40
ZR17 93Y) the maximum speed is indicated by the
service description - in this case 270km/h(186 mph).
Have you ever wondered why you need a tire speed
rated for 270km/h(186 mph) when you never drive
over 105km/h(65 mph)?
When replacing tires on your vehicle, you should
use replacement tires with a speed rating equal
to or greater than that of the original equipment
tires if the speed capability and handling characteristics
of the vehicle are to be maintained.
Remember, never operate your vehicle in an unsafe
or unlawful manner. Your Toyo distributor or dealer
can provide you with more information on speed ratings.
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