When it comes to motorcycle maintenance, one crucial aspect that often gets overlooked is understanding the markings on your motorcycle’s tyre sidewall. We’ve all encountered those rows of numbers and letters while shopping for replacement tyres, but do you know what they actually mean? Fear not, because we’re here to demystify these markings and help you make informed decisions about your motorcycle tyres.
Size Matters, But There’s More!
Sure, you’ve noticed the string of numbers indicating the size of your tyres. But what does it all mean? If you’re looking to change your tyres yourself (which is easier than you think if you have the right tools) you will need to know what you’re looking at! Let’s break it down step by step:
We will look at this tyre as our example:
200 / 55 ZR17 M/C (78W)
1. Width (200)
The first number signifies the nominal width of the tyre in millimetres. So, in this case, the tyre is 200mm wide from sidewall to sidewall. This is measured at the widest point of the tyre. Some manufacturers might have different widths for the same size tyre, this is how they can tune for different handling characteristics, usually by +/- 4%.
2. Aspect Ratio (55)
The aspect ratio is the height of the tyre, expressed as a percentage of its width. Here, the aspect ratio is 55%, which means the height of the tyre is 55% of its width, resulting in a height of 110mm. Again, different manufacturers may vary aspect ratio by +/- 4%.
3. Construction and Speed Rating (ZR)
This is where things get interesting. The “Z” denotes the speed rating of the tyre, indicating that it’s suitable for speeds above 168 mph. The “R” indicates radial construction. If you don’t see the “R,” the tyre is not radial and could be an X-ply or bias construction. Most modern sports and sports touring tyres are ZR rated, meaning they can handle high speeds.
If you have a dirt bike, dual-sport, or older cruiser bike, you won’t find the “R” on the tyre, so don’t worry!
The list of speed ratings are as follows:
|Speed Symbol||Miles Per Hour (mph)||Kilometres Per Hour (kph)|
|V||Over 130||Over 210|
|W||Over 150||Over 240|
|Z||Over 168||Over 270|
4. Diameter (17)
This number is the diameter of the wheel (rim) which the tyre fits on, measured in inches.
5. Usage (M/C)
The “M/C” indicates that the tyre is designed exclusively for motorcycles.
6. Construction (Radial | Tubeless)
This section tells you about the tyre’s construction and compatibility. “Radial” means it’s a radial construction tyre, which is common for modern motorcycle tyres. “Tubeless” indicates that it’s designed to work without an inner tube. However, some tyres may be marked “Tubed” or “TT,” indicating they require an inner tube. There are also tyres marked “TT / TL,” which can work with both tubeless and tubed setups.
7. Load & Speed Index (78W)
Here, “78” is the load index, indicating the maximum weight the tyre can carry. In our example, it can handle up to 425kg per tyre. The “W” is the speed index, signifying the maximum speed at which the tyre can carry its load. For instance, this tyre is rated for speeds over 150mph, and up to 168mph with the given load capacity.
This might be quite confusing as we already covered speed ratings with the “Z”. However there is an important difference between ‘speed rating’ and ‘speed index’. There is a reason the “W” (speed index) is stuck to the “78” (load index).
For our example: The maximum speed you should ride while carrying 425kg at maximum inflation pressure is 270 km/h.
Note that the brackets around “78W” means the tyre can go faster than 270 km/h (provided you’re not carrying 425kg, of course).
Speed and Load Index is as follows:
|Load Index||Kilograms (kg)||Load Index||Kilograms (kg)||Load Index||Kilograms (kg)||Load Index||Kilograms (kg)|
8. DOT Certification
The “DOT” marking stands for the US Department of Transportation. It signifies that the tyre conforms to the regulations set by transportation departments in the USA and Canada.
An arrow on the sidewall indicates the direction of rotation the tyre should have when mounted on your bike. You need to make sure this is correctly done as your bike will fail its MOT if wrong! – So make sure to have a quick look when getting new tyres fitted or if you are buying a new bike.
10. Production Date
A crucial but often overlooked detail, the series of four numbers indicates the tyre’s production date. The first two numbers represent the week of the year it was manufactured, and the last two indicate the year. This information provides insights into the tyre’s age, which can impact its performance. While fresh tyres are ideal, properly stored tyres can remain effective for a couple of years.
Motorcycle Tyre Size Conversion
Various motorcycles have different size requirements, depending on age, style and market etc. Combine this with the fact that motorcycle tyres are manufactured in numerous different countries all over the world – each with differing requirements in terms of load, dimensions and speed ratings.
This has resulted in various size markings (Metric, Inch and Alpha numeric) that can sometimes make life confusing. The below chart it designed as a guide to help you understand the relationship between various size markings**.
**(Please note, these are not direct alternatives in size, but designed to give a steer on comparisons between sizes)
|2.50 / 2.75||80/90||MH90|
|2.75 / 3.00||90/90||MJ90|
|3.25 / 3.50||100/90||MM90|
|3.75 / 4.00||110/90||MN90|
|4.25 / 4.50||120/80||–|
|4.25 / 4.50||120/90||MR90|
|5.00 / 5.10||130/90||MT90|
|4.50 / 4.75||110/90||MP85|
|4.50 / 4.75||120/90||MR90|
|5.00 / 5.10||130/80||–|
|5.00 / 5.10||130/90||MT90|
|5.50 / 6.00||140/80||–|
|5.50 / 6.00||140/85||MU85|
|5.50 / 6.00||140/90||MU90|
|6.00 / 6.25||150/80||MV85|
|6.00 / 6.25||150/90||MV85|
And that’s it! Understanding motorcycle tyre sidewall markings and size conversion goes beyond just knowing the size. Each piece of information serves a purpose, from load capacity and speed ratings to construction details and production dates. Armed with this knowledge, you can confidently choose the best tyres for your motorcycle, ensuring safety, performance, and a smooth ride every time. And remember, if you ever find yourself uncertain, reaching out to experts can help you navigate the world of motorcycle tyres with ease.
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