Explaining Motorcycle Tyre Codes
When considering motorcycle tyre replacement, it’s best not to take any chances. If you want to use tyres other than those recommended by your motorcycle manufacturer, there are many options available. But you need to make sure that any deviation from what’s recommended is suitable for your bike, safe and within the law. An important part of the information displayed on the sidewall of every motorcycle tyre is a code that gives details about, size, fit and use. Understanding this code is essential when choosing the correct tyre for your own motorcycle.
MOTORCYCLE TYRE CODE
190 / 50 ZR 17 (73W) TL
Shown above is a typical code for the rear tyre of a larger capacity motorcycle. Below is an explanation of each element.
Width of the Tyre – Measured across its widest point in millimetres
Aspect Ratio – The aspect ratio is the height of the tyre’s sidewall in relation to its width (shown as a percentage). So with this example, the sidewall height will be 50% of 190 millimetres = 95 millimetres.
Speed Rating – In this particular tyre code the ‘Z’ is one of two speed ratings. Although the ‘Z’ indicates the tyre is suitable for speeds over 240 kph (149 mph), it doesn’t tell us the maximum permissible speed. An additional speed rating, shown in parenthesis towards the end of the tyre code, will give this information. Both should be used in combination.
Other speed ratings:
R = 170 kph (106 mph)
S = 180 kph (112 mph)
T = 190 kph (118 mph)
U = 200 kph (124 mph)
H = 210 kph (130 mph)
V = 240 kph (149 mph)
Z = Over 240 kph (149 mph)
W = 270 kph (168 mph)
Y = 300 kph (186 mph)
Construction Type – R = Radial construction. B = Bias-Belted construction.
Note: If omitted, the tyre will be cross ply construction.
Wheel Rim Diameter – This is the wheel diameter the tyre fits, measured in inches.
Load Index – To find the actual weight the number represents, you’ll need to refer to a tyre ‘Load Index’ table. With this example, 73 = 365 kg (805 lbs). Most manufacturers also state the maximum load in kilograms and pounds somewhere else on the tyre sidewall, so eliminating the need for a ‘Load Index’ table. This may be an important consideration when your bike is heavily loaded during motorcycle tours.
Speed Rating – Usually shown in parenthesis with the load index number. The load applied to the tyre has an effect on its maximum speed, that’s why the two are shown together. With this example, the maximum speed for the tyre will be 270 kph (168 mph) when at its maximum load of 365 kg (805 lbs). When not under maximum load the tyre can be safely operated at higher speeds. In the unlikely event you regularly ride at speeds exceeding the speed rating of your own tyres, contact the tyre manufacturer for advice, or refer to the ETRTO guidelines (European Tyre and Rim Technical Organisation).
TL = Tubeless.
TT = Tubetype (an inner-tube must be used).
OTHER TYRE MARKINGS
Direction of Rotation Arrow – The tyre must rotate in the direction of the arrow when the motorcycle is moving forward.
Date of Manufacture – Usually shown as a 4 figure number. The first two digits represent the week of manufacture, the second two digits represent the year of manufacture. Example: 5107 will mean the tyre was produced in the 51st week of 2007 (December, 2007). Example: 0611 will mean the tyre was produced in the 6th week of 2011 (February, 2011).
Note: Tyre rubber will degrade over time, even when not fitted to a vehicle. Although there’s no hard and fast rule about how old is too old, it’s generally accepted that tyres should be replaced 5 or 6 years from their date of manufacture.
TWI (Tread Wear Indicator) – Most motorcycle tyres have wear bars located inside the tread grooves. The wear bars are raised about 2 mm above the bottom of the tread groove and positioned at various places around the tyre. When the tyre has worn level with the wear bars it should be replaced. A small triangle on the sidewall is often used to show their position.
M/C – Suitable for motorcycle use.
MAX. PSI – The maximum pressure the tyre can be inflated to in pounds per square inch.
MAX. BAR – The maximum pressure the tyre can be inflated to in Bar. This is the standard unit of pressure in most European countries outside the UK. If you ride on motorbike tours in Europe, it will be useful to know the PSI equivalent (1 bar = 14.50 psi).
E Mark. – Tyres sold in Europe must comply with European standards and be marked with an ‘E’ code. The number that follows this letter will indicate the country that has approved the tyre for road use. The American equivalent is the DOT code (Department of Transport).
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