Motorcycle tyres: reading the sidewall, the DOT date and choosing a compound

A motorcycle tyre carries more information on its sidewall than any other part on the bike: its size, its construction, what it can carry, at what speed, where it was type-approved and which week it came out of the mould. Most buyers read one line of it — the size — and take the dealer's word for the rest. That is a shame, because the two markings that do most to stop you making a bad buy are exactly the ones nobody looks at: the load and speed ratings, and the date code.

The whole lot takes thirty seconds to read, with no tools, on a fitted tyre. Here is what each block of characters means, and what you do with it when you are choosing.

The size line, character by character

Take a typical sports front marking: 120/70 ZR 17 M/C 58W.

• 120 — the nominal section width in millimetres, inflated and fitted to its reference rim. It is not the width of the contact patch on the road, which is smaller.
• 70 — the nominal aspect ratio, as a percentage: sidewall height is 70 % of the width, so 84 mm here. Drop that number and the sidewall stiffens and the bike sits lower.
• ZR — construction, plus an indication of speed. R means a radial carcass; a dash, or no letter at all, means cross-ply. The Z in front of the R flags a tyre designed to go beyond 240 km/h.
• 17 — rim diameter in inches. It is the one dimension with no room for negotiation: it has to match the wheel exactly.
• 58W — the load rating, then the speed rating. This is the part everyone skips.

Alongside it you will find the direction of rotation as an arrow, TL for tubeless or TT for tubed, the M/C marking that identifies a motorcycle tyre, and the European type-approval mark: an E in a circle, the number of the country that granted it, then the approval number. That mark is what makes the tyre legal on the road.

Load and speed: two standardised scales

Both ratings map onto standardised tables that are identical whatever the brand, and the bike's manufacturer sets minimum values you will find in the handbook or on the machine's data label.

Two simple rules: you can go above the rating specified, never below. And the load rating has to be worked out two-up with luggage, not solo and empty — that is precisely where the margin vanishes, on a loaded adventure bike with a pillion and panniers. An under-rated tyre does not let go all at once: it runs hot, the carcass works, and the wear pattern turns abnormal.

The DOT code: four digits that date the tyre

Look on the sidewall for the letters DOT followed by a string of characters. The last group, set apart from the rest, is the one you want: since 2000 it has been four digits, the first two for the week of manufacture, the last two for the year. A 1224 marking means the twelfth week of 2024, so late March. Pre-2000 tyres carried three digits; you will hardly ever meet one now.

Two classic traps. First, the full code is only moulded onto one sidewall: if you cannot find it, look at the other side of the wheel. Second, that date is the date of manufacture, not of sale or of fitting. A tyre can spend a year or two in a warehouse without anything being wrong, provided it was stored properly — out of the light, away from ozone sources such as electric motors, and not squashed under a stack.

So the useful habit is to read the DOT before the tyre goes on, at the dealer's. A tyre that has already sat three or four years in stock costs the same as a fresh one while having used up half its calendar life. That is either a bargaining point or a reason to walk away.

A tyre ages even standing still

Rubber is a living material: plasticisers migrate, chemical bonds change, ozone and UV attack the surface. A tyre with plenty of tread left can therefore have lost a good part of its wet grip, and show fine cracking at the bottom of the grooves or at the base of the sidewalls.

The five-year figure comes up everywhere, and it is sensible as a marker. It just has to be described for what it is: a rule of thumb accepted across the trade, not a legal limit. No general regulation stops you riding on an older tyre as long as it still meets the minimum tread depth, which sits around a millimetre for a motorcycle depending on the country — check the rule that applies where you ride. Tyre condition and tread depth are among the items looked at during the annual MOT, which a motorcycle takes once it is three years old. Conversely, a three-year-old tyre that has sat behind a south-facing shop window can be dead early. So the honest method cross-checks three things: the DOT date, the look of the rubber under a raking light, and how it actually behaves in the wet.

Sport, road, adventure: what the compound changes

The marketing name tells you very little; the structure of the compound tells you a lot. Three families cover almost every road use.

• Road and touring: a single compound or a mild dual compound, with a carcass built for load and mileage. Several thousand kilometres more than a sports tyre, quick to come up to temperature, well behaved in the rain. The default choice for most bikes.
• Sport and sport-touring: dual or triple compound, hard in the centre for wear and soft on the shoulders for lean. Excellent when hot, far less forgiving over the first few miles on a cold morning.
• Adventure: the road/off-road split is quoted by the maker, from a very road-biased 90/10 to a heavily knobbled 20/80. The more open the tread pattern, the more wet tarmac grip and high-speed stability suffer. Pick the compromise on what you actually did over the last twelve months, not on the riding you dream of doing — the adventure tyre comparison sets out what each pattern gives you on the road.

A new tyre needs scrubbing in: allow a hundred kilometres or so, building lean angle gradually, while the mould release agent wears away and the surface takes on texture.

Mixing makes and models: why it is discouraged

A set of tyres is developed as a pair. The front profile and the rear profile are drawn together so that the bike turns in progressively, with no sudden step or surprise mid-lean. Putting two different models or two different brands together changes that pairing, and the fault does not show itself in the car park: it turns up on turn-in, as a bike that drops in faster than you expected, or resists and then goes.

Some tyre makers publish combinations they have validated, and some manufacturers specify approved fitments listed in the handbook. Outside those documented cases, running a different model front and rear is a bet you get no feedback on until you are already leaned over. Same logic for wear: if the budget only stretches to one tyre, the rear is what goes first in most riding, and you accept that the front will follow soon after.

Pressure cancels out or validates everything else

The best tyre in the world, badly inflated, does less well than an average tyre at the right pressure. Three points, and they are not up for debate.

• Cold, always. Check before riding, or after two hours parked. A hot tyre reads 0.2 to 0.3 bar higher, and correcting it hot amounts to under-inflating it.
• The figure is the bike manufacturer's, not the tyre maker's, and it is often different solo and two-up with luggage.
• Gauges need checking. Two workshop gauges can differ by 0.2 bar; keep yours as your single reference.

Being 0.5 bar down is enough to overheat the sidewalls, wear the shoulders and make the bike feel vague in corners. Cold-weather behaviour is covered in the article on pressure and warm-up in cold weather, and the wear markers in the guide to motorcycle tyre pressure and wear.

Before you buy, in order

Note the full size and both ratings on your current tyre, then compare them with the handbook: a previous fitment may already be out of spec. Decide on the compound family from your real use, wet mileage included. At the dealer's, read the DOT on both tyres before they go on the wheels. After fitting, check the pressures cold the next morning, then ride a hundred kilometres without chasing lean angle.

For the values specific to your machine — original fitment, minimum ratings, solo and two-up pressures, wheel spindle torque on reassembly — the L'Atelier technical assistant pulls them up from the make, the model and the year.