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Decode the numbers on tyres ( 2018-01-10 )

Have you ever wonder what those numbers on the tyre mean? Along with the manufacturer's name and brand (e.g. Continental UltraContact UC6), there's always a smaller print of a set of numbers and letters relating to the size of the tyre as expressed something like this: 245/45R17 93H. If those numbers seem odd to you, continue to read on as MyCarsearch is going to decode and explain what these odd numbers and figures mean.

Continental tyre 225/50 R 17 98 H with number guide explanation

Let’s take an example of the tyre measurement which is 225/50R17 98H. The first combination set of letters and numbers (e.g. 225/50R17) describes the tyre size and measure, and the last combination set of numbers and letter (e.g. 98H) represents the tyre’s service description.

Tyre guide showing tyre width of 225mm

225 (Tyre Width): 

This is the width of the tyre, measuring from sidewall to sidewall, in millimeters. A 225 means the tyre is 225 millimeters, or 22.5 centimeters, wide.

Tyre guide showing tyre width of 225mm

50 (Aspect Ratio): 

Aspect Ratio or Tyre Profile. This is the sidewall's height (or the depth of the wall at the side of the tyre) that takes measure from the inside diameter to the outside diameter. The profile is expressed in percentage of the width of the tyre. A 225/50 means the sidewall is 50% of the tyre width, making it approximately 112.5mm tall. A low profile tyre is commonly found in the high performance vehicles or sports cars with aspect ratio of 50% to as little as 30% with ultra-low profile tyres. As aspect ratios decreases, the tyre's firmness increases. As a result, the low profile tyres are able to provide greater control and better handling on corners, they can also give a slightly harder or bumpy ride. However, as precautionary, fitting a higher profile than manufacturers’ recommended spec on the same size wheels will alter your speedometer reading and may cause you to travel faster than the actual reading as shown on the dashboard.

R (Radial Construction): 

The tyre's type of construction or simply, Radial construction. The Radial design means the cord plies are arranged at 90 degrees to the direction of travel, or radially (from the center of the tyre). All vehicles produced after 1980s use radials.

Tyre guide showing tyre width of 225mm

17 (Rim Diameter): 

This is the tyre's inner diameter, which matches the diameter of the wheel rims, measuring in inches.

98 (Load Index or Load Rating):

The Load index is used to compare relative load carrying capabilities of the tyre (the load index and its relative weight load are shown in table below). A 98 load index means the tyre is certified and able to carry up to 1653 pounds (or ~750 kgs) at its maximum inflation pressure. For example, if a car weighs 1800 kgs, then each tyre handles 450 kgs with no passengers and cargo. A higher load index tyres are required if you intend to load heavy stuffs in the car boot or towing a heavy trailer. Add up all the load weights and divide it by four to find out if you have the right tyre and within the allowable weight limit, and also make sure your replacement tyres have a corresponding or higher load index.

Car tyre load index indicating how much weight a tyre can support.
Tyre load index table

H (Speed Rating):

The speed rating is always expressed as a letter, and it usually match to the vehicles’ top speed as recommended by manufacturers. It is an indication of the ability of the tyre to dissipate heat to avoid a blowout when vehicle is travelling in high speed as heat buildup faster. Generally, the tyres with higher speed ratings are constructed to able to handle heat better. Those letters and the corresponding speeds that the tyres are capable to handle are included in this chart:

Car tyre speed rating recommendation for various cars.
Tyre speed rating table

Now you will never again need to ask the guy in the tyre workshop: “What do the numbers on the tyre mean?” Instead just simply refer to our little tyre guide here.

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