A look at the tyre wall numbers
For the most part, when the time comes for a rider to put some new road or track tyres on their machine there is little thought into what the size and shape of the tyre actually does for them. I would guess this is because the last pair worked perfectly fine, so why would they need to know?
The answer is they don’t really, but the size and profile of a tyre can actually alter the way your motorcycle rides and handles, and some riders might actually benefit from a little change up.
Before we look at what different motorcycle tyre sizes can do, lets first take a look at what all those numbers and letters mean on the side of the tyre. Not all the of characters determine the size of the tyre, but even so I think it’s worth a little lesson in what they all mean.
As an example, here’s what’s on the side of my Metzeler Racetecs:
180/55 ZR 17 M/C (73W) TL
The first number indicates the width of the tyre in millimetres, taken from the widest point of the tyre.
The second number indicates the aspect ratio (or height) of the tyre. This is represented as a percentage of the width of the tyre. In this example then, the height of the tyre is 55% of 180mm, which equates to 99mm.
This is the first of two speed ratings found in the code. It indicates what speed the tyre is capable of being taken over. In this example ‘Z’ means that the tyre is suitable for speeds over 149mph. However it doesn’t tell us the maximum tolerable speed for the tyre; that comes later in the code in brackets.
Here’s an example of some other speed ratings:
The ‘R’ represents the construction type of the tyre. When you see ‘R’ on a tyre it means it has a radial construction. Here’s a brief explanation of radial tyres and the other most common construction type:
Radial – A tyre that has its cord plies arranged perpendicular (at a 90 degree angle) to the direction of travel.
Belted (‘B’) – A belted bias tyre starts life as a normal bias-ply tyre, then stabilizer belts are placed on top of the existing plies at different angles. This improves performance over non-belted, bias-ply tyres (also called cross-ply).
If it has neither of these letters, it will be a bias-ply tyre.
This next number represents the size of wheel that the tyre fits measured in inches. In this case the tyre will fit a 17 inch diameter wheel.
This simply means that the tyre is suitable for motorcycle use.
The number portion of the characters in brackets represent the load index of the tyre, which specifies the maximum load the tyre can carry. To find what weight this number corresponds to you will need to refer to a load index table. As you can see, the number 73 means the tyre can carry a load up to 365kg.
The ‘W’ in brackets is the second speed rating found on the tyre. Put simply, the load you put on a tyre has an effect on its maximum capable speed. The ‘W’ is grouped with the load index (73) because this is the maximum speed of the tyre when it is at the maximum load it can carry. So in this case, if you load the tyre to 365kg then the speed rating of the tyre becomes 168mph as per the above speed index.
TL means it is a tubeless tyre. If you see ‘TT’ then it is a tubetype tyre, so it must have an inner-tube.
That’s everything in the code explained, but what do the different sizes and profiles of tyre do for you as a rider? Read below to find out how the size and profile of the tyre can help or hinder you.
Tyre Size: The 180 vs 190 debate
You often see the question coming up, which is best out of a 180 vs 190, or 190 vs 200 width tyre? The answer is neither is ‘best’, just that each is going to give you a slightly different feel.
The general rule of thumb is that the wider the tyre, the wider your footprint on the road – for the most part. A consequence of the tyre being wider is that the profile won’t be as ‘pointy’ as a 180 for example, so your bike will feel like it isn’t as eager to turn in.
Many would agree that a 190+ width tyre is only really worthwhile on 1000cc bikes and up, but again there is no right or wrong answer as it is mainly down to personal preference. Assuming of course the bigger tyre fits your smaller capacity bike.
If you’re ever thinking of going up to a 190 on a smaller bike such as a 600 or 750, please know that many 190+ width tyres are designed for 6 inch wide rims, where as many smaller bikes have 5.5 inch rims. People still fit them and get on just fine, but it’s not always recommended.
Generally it is the width and height of a tyre (e.g. 180/55) that determines its profile. However, some manufacturers such as Bridgestone and Dunlop are known to be more pointy than other brands like Metzeler and Pirelli.
As hinted to above, the pointier the tyre, the quicker it is going to feel like it wants to turn in. A 180/60 tyre for example is going to give you a quicker turn rate over a 180/55.
Another benefit of a pointy tyre is that it will give you a greater contact patch when leaned over and on the edge of the tyre, promoting higher lean angles and faster cornering speeds.
The downside to a pointy tyre is that it will feel more unstable going in a straight line and almost twitchy. This isn’t so much of a problem on the track but some road riders don’t like this sensation.
It’s All About You
The size and profile of the tyre you opt for should be down to how you like to ride and what you want from the tyre. Do you like the slower more stable feeling of a wider, less pointy tyre? Or do you like the bike to fall into the corner more, and you aren’t worried too much about little wiggles on the straights? Only you can really decide which size and profile of tyre is best.
It has to be said though that many of the differences in feel that these tyres will give you are small and would take a fairly skilled rider to notice them, and an even more skilled rider to make best use of those differences, so try not to get too hung up on them and just go with what you feel is right for you.
That’s your motorcycle tyre sizes and profiles explained. I hope this has armed you with a little more knowledge on the differences in motorcycle tyres so you can now more confidently make the decision on what type of tyre you want to go for next.