Tyre Age: Reading the DOT Code on a Low-Mileage Lotus

Plenty of Lotus cars cover two or three thousand miles a year, often fewer. At that rate a set of road tyres can still show healthy tread depth a decade after it was fitted. Tread depth is only half the story, though. Rubber hardens with age whether the car moves or not, and on a light car that relies on grip rather than electronics to keep it composed, that matters. Mid-November, with many cars about to be laid up, is a good time to look.

Reading the date code

Every tyre sold in Europe and North America carries a DOT code on one sidewall. The last four digits, usually inside an oval, give the week and year of manufacture. A tyre marked 2319 was made in week 23 of 2019. If you can only find a long code without the four-digit group, check the other side of the tyre: the date is sometimes only moulded on one face, which may be the inner one on a car with deep wheel arches. A three-digit date code means the tyre was made before 2000 and should come off regardless of how it looks.

The date is when the tyre was made, not when it was fitted, so check new tyres when they arrive too.

What old rubber does

As a tyre ages the compound loses its oils and becomes harder. The car still drives normally on a dry, warm day, which is why the problem is easy to miss. The difference shows in the cold and wet: less grip, slower warm-up and less warning before the tyre lets go. On an Exige S2 or an Elise S1, with no stability control to step in, you feel that directly.

Look for fine cracks in the sidewall and between the tread blocks, a shiny or glazed surface, and any bulges. Cracking that you can feel with a fingernail is a reason to replace the tyre, whatever the tread depth.

How old is too old

UK law does not set an age limit for car tyres, only the 1.6 mm minimum tread depth. Tyre makers generally advise a careful annual inspection once a tyre is five years old and replacement at around ten years at the latest. Many owners of track-biased tyres replace sooner.

When buying a car, check the dates on all four tyres. A mismatched set or ten-year-old rubber is worth negotiating on, and our guide to buying a used Lotus covers what else to look at.

Before the car goes away

If the car is being stored, pump the tyres up to the upper end of the recommended pressures to reduce flat spots, and note the date codes in your records. Then in spring you will know whether to book a new set before the first trip, rather than finding out on a cold, damp morning. The road trip preparation guide has a fuller checklist.