An explanation of the use of tyre speed ratings on Bridgestone Motorcycle Tyres.
Bridgestone motorcycle tyres bear a letter "speed rating" designation indicating the tyre's design speed capability. This speed rating system is intended to allow you to compare the speed capabilities of tyres.
When purchasing or replacing speed-rated tyres, you should always follow the motorcycle manufacturer's recommendations, if any, concerning the use of speed-rated tyres and ensure that you are familiar with the speed markings of the tyres that you buy.
To avoid reducing the speed capability of the motorcycle, replace a speed-rated tyre only with another tyre having at least the same speed rating. IMPORTANT: It is the "top speed" of the "slowest" tyre on the vehicle which defines the maximum speed at which you should ride and which, if exceeded, risks tyre failure.
An overview of Motorcycle Tyre Speed Ratings can be seen here:
Actual tyre speed and performance capability also depends on factors such as inflation pressure, load, tyre condition, wear and driving conditions.
These speed ratings are based on laboratory tests under specific, controlled conditions. While these tests relate to performance on the road under those conditions, remember that real-life driving is rarely identical to any test conditions. Your tyre's actual speed capability may be less than its rated speed, since it is affected by factors such as inflation pressure, load, prior alteration or damage, driving conditions, alignment, wear, vehicle condition, and the duration for which high speed is sustained. A tyre's speed rating becomes void if the tyre is repaired, retreaded, damaged or abused, or otherwise altered from its original condition. Thereafter, it should be treated as a non-speed-rated tyre. The tyre's speed rating designation appears on the tyre sidewall with the tyre size.
Examples: 120/60ZR17 55W - 140/70V18 67V
In these examples, the "Z” and "V" respectively, are the speed-ratings ("R" indicates that each of the example tire sizes are radials).
The "55W" and "67V" in these two examples are known as "service descriptions."