Everything you need to know about… tyre markings
Bryn Phillips knows just about everything there is to know about tyres. Having worked for Bridgestone, Dunlop and Continental, he is now the technical manager at the UK’s largest tyre distributor, Cambrian Tyres.
A tyre has a shelf life of about six years ...”
T yres are crucial elements of a motorcycle as they are the things that basically stop you falling over. So it’s worth ensuring they are kept in tip-top condition and that the tyres are not only suitable for your bike and are inflated to the correct pressure, but that they aren’t past their sell by date. Yes, tyres do have a best before date…
Most people know if their bike has a 120/70 front tyre or a 190/50 rear, but what do these numbers actually mean? A modern sportsbike’s rear tyre will have something like 190/50ZR17M/C on the sidewall. This means the tyre’s section width, which is the width of the tyre, is 190mm and its aspect ratio, or height, is 50 per cent of its width, so 95mm. However, tyre manufacturers are permitted to vary the width by +/-4 percent of the stated size to allow them to tune its handling characteristics.
After these numbers are two letters, usually ZR on a sportsbike. The Z is the tyre’s speed category, in this case Z means above 149mph. The R simply means the tyre is of a radial construction. If it was a cross-ply there would be a hyphen in place of the R. The 17 denotes the tyre’s diameter, 17-inch, while the M/C means it is for a motorcycle. Hopefully this was obvious! After the numbers there is a figure (73W) and these are the
load and speed indexes for the tyre. The 73 means the maximum weight the tyre is rated for at maximum pressure is 365kg while the W represents 168mph, but there are loads of other letters. H, for example, is up to 130mph while L is a maximum of 74mph. The load indexes run from 20 right through to 90, which is a 600kg maximum weight for very large tourers that get loaded up with a pillion and luggage. On the vast majority of tyres for sports bikes there are also brackets around the load and speed indexes and these tell you that the tyre is capable of more than 168mph. Without brackets means up to 168mph.
Alongside, or somewhere near these numbers, on the sidewall is the DOT code. This code indicates that the tyre conforms with the United States Department Of Transportation regulations. Following the DOT code will be four digits moulded in a separate rectangle and these show when it was made. A tyre marked 3613 was built on the 36th week of 2013. This is a crucial piece of information because tyres do ‘go off’ over time. A tyre has a shelf life of six years or so, although this can vary depending on how it’s stored and is affected by temperature, humidity, ozone, etc.
Tyres are made in a variety of places as manufacturers have plants all over the world, so each tyre is stamped with a ‘Made in’ location. Most original equipment tyres (OE) on Japanese bikes are made in Japan, while European bikes mostly use European built tyres. Replacement tyres, although identical in their markings, are also likely to be built in Europe rather than Japan to save shipping costs, although Bridgestone, for example, still builds their radials in Japan. Finally we have the tyre’s actual name and its model. In this case Bridgestone’s Battlax S20 – with a letter ‘F’ after it. Sometimes manufacturers make model specific OE tyres and in this case a different letter may appear after the name to signify it is a special or specific tyre. When Bridgestone sell replacement S20 tyres they will not have the letter as they are a general tyre suitable, and tested, on a variety of different models. However, you can order a manufacturer-specific tyre, although it isn’t normally necessary as the non-OE has been thoroughly tested by Bridgestone. The same is true for other firms. Sometimes, however, the front tyre simply has an F and the rear an R, you can probably work out this code…