Vehicles

Getting to Know Your Tires

Wayne Blanchard
Posted on May 1, 2008

MOST PEOPLE BUY TIRES without ever knowing what the data on the tires mean. When we see a size of 235/70 R 16 101 S, most of us are lost. How do these numbers affect your vehicle? Why are they so important? How do you know that the tire you’re being sold is actually the correct tire for you? Here’s the tire data simplified.

1 • SECTION WIDTH: This (235) indicates the distance (in millimeters) across from the widest point of the sidewall exterior to the widest point of the inner sidewall when mounted on the proper rim. A tire that is too thin may not inflate properly on the rim, and one that is too wide may damage the rim and wheel well.

 

2 • ASPECT RATIO: This means that the (70) indicates that the height from the sidewall to the tread is 70% of its section width. Basically, the higher the number, the taller the sidewall, and the lower the number, the shorter the sidewall. Too short a sidewall can cause rim damage and create a poor ride. One that is too tall can “rub” and cause damage to surrounding body panels.

 

3 • TYPE OF CONSTRUCTION: An R indicates that the tire is a radial, which means the tire’s body plies “radiate” out from the center of the tire.

 

4 • RIM DIAMETER: This (16) is the measurement of the rim from inner bead wall to inner bead wall. Only tires of like size will fit your rims.

 

5 • LOAD INDEX: This (101) is the maximum weight capacity of your tire. When multiplied times four, you get the total weight of your vehicle and passengers the set of tires can carry. Example: load index of 99 = 1,709 lbs. per tire x 4 = 6,836 lbs. total. For load ratings, see chart below.  

 

    LOAD INDEX        LOAD (LBS)         LOAD INDEX         LOAD (LBS)    
65639851135
66661861168
67677871201
68694881235
69716891279
70739901323
71761911356
72783921389
73805931433
74827941477
75852951521
76882961565
77908971609
78937981653
79963991709
809921001764
8110191011819
8210471021874
8310741031929
8411021041984

 

6 • SPEED INDEX: This (S) indicates the top speed your tires are rated for. An S rating, for example, indicates a maximum of 112 mph.

 

Tires that have a higher rating are generally made with a stronger compound and contain a reinforced sidewall. Any tire that is high load rated will most likely have the word “REINFORCED” imprinted into the tire sidewall.

 

Related Topics: tires and wheels, vehicle maintenance

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