Motorcycle Tyres: The Need-To-Knows – Part Two

When you consider the amount of work motorcycle tyres do and the responsibility they have, you may wonder how they cope. The material they are made of provides the grip that allows you to lay down large amounts of power and torque, lean over at extreme angles at speed, and stop safely with the brakes applied hard. That grip is the difference between pleasure and pain and needs to work well in a whole variety of conditions.

Without good tyres the abilities of the engine, suspension and brakes are irrelevant. Tyres are massively important, and thankfully a lot of them are good, really good, especially when you consider how much of each one is actually in contact with the road. Makes you wonder – how do they cope with that?

Here in part two of our three-part feature on tyres we look at tyre selection. In part one we look at tyre construction, compounds, and tread patterns, and in part three tyre use and maintenance.

Tyre selection:

Motorcycle manufacturers put a lot of effort into making sure that the tyres they specify for a particular bike are the best choice from what is available at the time, and work in conjunction with tyre manufacturers to achieve this. So when it is time to fit new tyres it is often best to stick with the specified ones, especially if you are happy with their performance. But if you’ve had a couple of sets of the same tyre and then read some reviews about another tyre that suits the bike better you may feel the urge to change.The difficulty in making an alternative choice comes from who you believe, whether it is the marketing spiel from the manufacturer or the opinion of the forum. Independent reviews are often the best source of information, but only if different reviewers come to the same conclusions about a particular tyre. If they don’t it just adds to the confusion. What doesn’t help is when a manufacturer uses phrases such as “innovative tread design and nano technology compound”. What does that actually mean? Nothing that is useful for making an informed decision.

Tyre manufacturers upgrade their tyres and launch new ones, and if you keep a bike for a while the ones you originally had may no longer be available. This leaves you with no choice but to change, though a new version of an old tyre should suit the bike just as well if not better. Tyre manufacturers offer search facilities by bike and by tyre size and will list all their suitable tyres. Online suppliers such as Oponeo and Pneus-online are a useful source of information and reviews, carry huge stocks from the majority of brands, and are usually competitive on price. Just factor in the extra cost of fitting the tyres.

When it comes to selecting new tyres, most importantly, and obviously, the tyres must be the correct size for the wheels. Tyres must also be of the correct construction and have the correct speed and load ratings for your bike and for the riding that you do. Most manufacturers will give all the required specifications in the handbook and will give the recommended brand, and sometimes a few optional brands to choose from as well, though ultimately brand choice can be personal. 

It is a general rule of thumb, and a very good one, that you fit tyres in matched pairs. You should never mix cross-ply and radial unless you have one of the bikes where the manufacturer recommends it. Avoid mixing tyres from different manufacturers as they use different construction methods and materials that could affect handling. Avoid mixing different types of tyre from the same manufacturer, again unless it is recommended by the manufacturer. And don’t fit a wider rear tyre just because it looks better because not only it will upset the handling, it could also rub against the swingarm.

But you must also consider your own riding style and how you use your bike when making a choice. A normal road tyre will probably have better grip at its normal operating temperature than a sports tyre not at its normal temperature, so it is pointless buying the stickiest sports rubber for your R1 if you use it to commute year-round in an urban environment. Similarly, you should not choose an all-weather commuting tyre to save money if you only ride hard and fast on dry roads. Sometimes one tyre is available in different load ratings, so if you always ride solo you can select the lower load rating, and if you often ride two-up with luggage you can select the higher rating.

Unless you really know what you are doing or are confident in the advice you are getting it is best to stick to the tyres recommended by the bike and tyre manufacturers.

To tube or not to tube? Do you tube?:

Why do some tyres have tubes and some don’t? A good question. All tyres used to have tubes, but that was when all wheels were spoked, and spoke heads leak air quite well, making a tube essential. One of the main problems with a tube is that if it is punctured it will lose its air rapidly, which is not good. When cast wheels came into being it was possible to take the tube out and let the tyre itself form the seal. But tyres are slightly porous and will constantly leak a small amount of air, and this was overcome by moulding a layer of butyl rubber, from which a tube is made, to the inside of the tyre to seal it. Tubeless tyres can of course get punctures, but when they do their deflation is often slower than a tube, mainly because there are no spokes for the air to leak past, and the object that has caused the puncture will usually stay stuck in the tyre, partly sealing the hole it has made. Not always the case though.

If a tyre is marked TT or tubed type it must be run with a tube. If a tyre is marked TL or tubeless it should be run without a tube. Some tubeless tyres can be fitted with tubes if necessary and if the manufacturer says it is OK, for example if the tyre you need is not made in both forms but is to be fitted on a bike with spoked wheels. If the manufacturer does not specify that it is OK, it is best not to use a tube as the inner surface of a tubeless tyre is sometimes ribbed or rough and this can abrade the surface of the tube. Generally, if a wheel has spokes it will need a tube, though there are some spoked wheels that hold the spokes in a separate section of the rim so they are not actually seated within the inflated part of the tyre, allowing tubeless tyres to be used. Adding a tube to a tubeless tyre increases the rolling and unsprung weight of the wheel, which can cause overheating and adversely affect handling particularly at speed – a tube will effectively reduce the speed rating of a tubeless tyre by one rating for ratings above 130mph, so an H rated tyre stays an H, but a V becomes an H, a Z becomes a V and a W becomes a Z.

Tyre sizing, markings and ratings:

Your motorcycle's handbook will specify the tyres you need, and a series of letters and numbers are used to define the exact specification. So what do the letters and numbers all mean? Confusingly three systems are used, as shown in the examples below. The first is an older (but still used) numeric system based on inches that is used for tyres designed for older bikes. The second is the most common system and uses an alpha-numeric system and a combination of inches and mm. The third example is also alpha-numeric and is a system used mostly for cruiser tyres.

EXAMPLES:

3.25-19 M/C 69R TT:

• 25 – the width of the tyre in inches.
• 19 – the size of the wheel in inches.
• M/C – means it is a motorcycle tyre.
• 69 – the load index (see table below). Refers to the amount of load or weight the tyre can handle. Sometimes one tyre is available in different load ratings, so if you always ride solo you can select the lower load rating, and if you often ride two-up with luggage you can select the higher rating.
• R – the maximum speed rating (see table below).
• TT – tubed tyre

120/70-ZR17 M/C (58W) TL

• 120 – the width of the tyre in mm.
• 70 – the aspect ratio. This refers to the height of the sidewall and is expressed as a percentage of the height to the tread width. For this example 120/70 means the sidewall height is 70% of 120, which is 84mm.
• Z – indicates the tyre is safe for use over 150 mph (see table below). This marking is only found on radial sports tyres and is in addition to the maximum speed rating given on all tyres along with the load rating.
• R – means radial. A tyre marked B is bias- belted. Cross-ply tyres have no related marking.
• 17 – the size of the wheel in inches.
• M/C – means it is a motorcycle tyre.
• 58 – the load index (see table below). Refers to the amount of load or weight the tyre can handle. Sometimes one tyre is available in different load ratings, so if you always ride solo you can select the lower load rating, and if you often ride two-up with luggage you can select the higher rating.
• W – the maximum speed rating (see table below).
• TL – tubeless tyre

MT90-16 T 71H TT

• M – means it is a motorcycle tyre.
• T – denotes the width of the tyre. T is 5.10 inches.
• 90 – the aspect ratio. This refers to the height of the sidewall and is expressed as a percentage of the height to the tread width. For this example 90 means the sidewall height is 90% of 5.10 inches, which is 4.59 inches.
• 16 – the size of the wheel in inches.
• T – denotes the rim contour.
• 71 – the load index (see table below). Refers to the amount of load or weight the tyre can handle. Sometimes one tyre is available in different load ratings, so if you always ride solo you can select the lower load rating, and if you often ride two-up with luggage you can select the higher rating.
• H – the maximum speed rating (see table below).
• TT – tubed tyre

LOAD INDEX TABLE

SPEED RATING TABLE

Note that most tyres are made to run in one direction only and have an arrow marked on the sidewall to mark the direction of normal rotation. It is essential that the tyres are fitted the correct way round for them to function correctly.

A lot of other information, sometimes including the construction materials, can also be found on a tyre sidewall, some of it repeating what is included in the coding but without using the code itself.

The circled E symbol denotes a tyre homologated for use in the EU, and the number, in this case 4, denotes the country that made the approval.

Tyres manufactured after 2000 have a four-digit code such as 0917 to denote the tyre was made in the 9^th the week of 2017. Tyres manufactured before 2000 had a three-digit code such as 327 to denote the tyre was made in the 32^nd week of the seventh year of a decade, but it fails to indicate which decade, so it could be any decade from 1907 to 1997. Suffice to say, any such tyre found on a bike today should be considered too old for safe use. Generally, tyre manufacturers say any tyre more than 10 years old should be replaced, because the rubber hardens and deteriorates with age, especially if they live outside and are exposed to the sun or are exposed to anything such as electric motors that produce ozone, which damages rubber. If your tyres are getting on a bit check the sidewalls regularly for cracks and any other signs of deterioration.

To see the full range of tyres available from MPW, along with our selection of tyre accessories such as warmers, inner tubes, tyre levers and pressure gauges, browse the motorcyclepartswarehouse shop.