BRIDGESTONE | TRUCK AND BUS RIMS
WHEN DOES THE RIM WIDTH MATTER IN RELATION TO TYRE SIZE? seating area (the area where the tyre
It is important to ensure that a tyre is fitted on the recommended rim width. The specifications for a tyre can be found on the tyre standards – if necessary, ask the manufacturer for clarification – while the rim width is displayed on the rim itself (see left). For example, a 295/80R22.5 tyre can be fitted on a rim width of either 9.00 or 8.25 inches.
Rim width measurement
touches and seals against the rim) is formed at different angles. Fitting a tube type tyre on a tubeless
rim will also not work for the same reason. Tyres and rims are carefully designed to work together and it is important that the correct tyre type and size is fitted to the corresponding type of rim.
WHAT DO ALL THE DIFFERENT NUMBERS ON A TYRE OR RIM MEAN? There are usually many different numbers printed on the inside of a rim. Some of them are serial numbers and date of manufacture. The size of the rim is usually represented by two sets of numbers either side of an “X” as per the picture (see left). The numbers give the rim diameter and width measured in inches. The example rim opposite has a diameter of 22.5 inches and a rim width of 9 inches. Tyre sizes are specified in a similar
TYRE SIZE RECOMMENDED RIM WIDTH APPROVED RIM WIDTH 295/80R22.5
9.00 inches 8.25 inches
way. The tyre size mentioned in the table opposite is 295/80R22.5. The first number in the size gives the width of the tyre in millimetres, while the second number is the height of the tyre sidewall as a percentage of the width. This is also known as the aspect ratio and the last number following the “R”, meaning radial construction method, is the required rim diameter for the specific tyre. This is measured in inches.
Rim width
WHAT ARE THE MAIN CAUSES FOR RIM DAMAGE? Rims can be damaged in several ways, most of which can be prevented by ensuring that your truck and bus is properly maintained. Some of the most common damage can occur when driving with loose wheel nuts or when wheel nuts have been excessively tightened, improper use of mounting tools when changing tyres, using oversized tyres, improper inflation pressure and overloading the vehicle.
real QUESTIONS real ANSWERS JANUARY 2012
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