RIDE guide to...
They’re black and they’re round, and they stick to the ground — hopefully...
Tyres and our favourites
SPEED RATING
(73W) A W speed rating shows that the tyre’s tested up to a maximum of 167.8mph at a maximum load of 365kg (73). But the brackets are significant and show the speed rating is unbounded, meaning that the tyre can in fact carry the maximum load at speeds over 167.8mph
SIZE MARKINGS
180 The nominal width of the tyre across the shoulders, in mm. In real life, a 180mm tyre can vary from 178mm all the way up to 190mm when fitted
55 The ratio of the height of the tyre to the width, in percentage terms. So the nominal height of this 180mm tyre is 99mm
17 This is the wheel diameter measured on the rim where the tyre bead sits. It is imperial because wheel manufacturers work in inches
Z The speed rating — a ‘Z’ rating means it’s capable of more than 149mph. That’s only half the story though — see above
R R for Radial construction. If the R isn’t present or there’s a dash, it means the tyre is bias (crossply) and a B means bias-belted
OTHER MARKINGS
E mark A capital E in a circle means it’s been tested and passed for EU and UK use. No E mark, it’s not road legal DOT code The DOT code is an individual number, like the VIN number on your bike. The last four digits are the manufacturing date code, so 4321 would be the 43rd week of 2021
Maximum Pressure The maximum pressure for the tyre at its maximum load. It’s not a recommendation for normal use; it’s for the tyre if it’s being used at its maximum load only
YOUR TYRES ARE arguably the most important part of your bike. They’re the only part that’s actually in contact with the road (crashes and peg-scraping aside) and the way they feel, grip, wear and interact with the bike’s suspension is key to every second of your ride. But few of us really understand what’s going on down there, so we asked tyre tech expert Tony Charlton from Michelin UK to enlighten us all.
Cross-ply, bias-belted or radial — huh?
“It’s all about the way the plies (cords laid side-by-side encased in rubber) which make up the carcass are arranged, and how many layers there are. The cords themselves can be anything from cotton, through rayon, polyester, steel (we rarely use steel though) through to aramid, like Kevlar. Bias (more commonly referred to as cross-ply) is the classic construction. Plies are laid over each other at angles (plies, crossed) and enclose the wire bead,” explains Tony.
“Bias-belted construction is similar but with an extra layer — the belt — around the circumference which makes it less prone to growth at speed but also makes it even stiffer. That works well with heavier bikes that don’t achieve big lean angles — it’s usually seen on big customs for example — but we also use it for some of our retro-style tyres.
“Radial construction sees the plies laid at or close to 90° to the direction of travel — good for stability at speed, doesn’t grow at high speeds, and allows a flexible tread area but still with stiff sidewalls. Within those categories there are wide variables in ply weights, thread counts, and ply angles — even a couple of degrees makes a huge difference to the way the tyre feels.”
How much rubber is in our rubber?
“Not much! The vast majority of rubber used in modern motorcycle tyres is synthetic, but we do still need our own rubber plantations. Latex does still have its place but the amount we use is secret...” And if you’ve ever wondered why tyres are black, that’s due to the use of carbon black powder (soot, basically) which is a good filler that, during vulcanisation, helps transform the rubber from elastic to visco-elastic. If Silica is used instead of carbon black then tyres don’t need to be black at all.
How long do tyres keep?
“We would normally say that so long as an unused tyre’s been properly stored then up to five years after manufacture it will still perform as new. However once fitted — or if poorly stored — the ageing process starts straight away. Older tyres can still last well if they’re used at least reasonably regularly — tyres like to be used, flexed and worked to keep them supple. We suggest that after five years you should have your tyres inspected by a tyre expert at least annually and that at ten years, you should replace them as a safety precaution. And ride more!”