Classic car tyres: crossply or radial, the law on mixing, and what to fit

Tyres are one of the few parts of a classic where the original specification and the modern reality genuinely pull in different directions, and where getting it wrong is both a safety problem and, in one specific case, against the law. A 1960s saloon left on the tyres it wore in a barn for thirty years is not roadworthy, however good the tread looks, and the right replacement is not always the obvious one.

This is what to fit, what the law actually says, and why the date on the sidewall matters more than the tread on a car that barely turns a wheel.

Crossply or radial

The big decision is construction. Most classics built before the mid-1960s were designed around crossply tyres, where the casing plies run diagonally across the tyre. From the 1960s onward the industry moved to radial tyres, where the plies run across the tyre and a belt runs around it, giving more grip, longer life, and a different feel. By the 1970s nearly every new car wore radials.

For an owner, that leaves three honest options:

• Period crossplies, for originality. A pre-1960 car set up for crossplies handles the way its designers intended on them, and a concours or strictly original car wants them. They give a softer, vaguer feel and wear faster than radials.
• Period-correct radials, the common everyday choice. Specialists make radials in the old narrow sizes with period-looking tread, so the car gains modern grip and life without looking wrong.
• Modern radials in the nearest size, the cheapest route, fine for a car used as transport but more likely to look slightly off and, in some sizes, to foul arches or rub at full lock.

There is no single right answer. A show car wants crossplies; a car you actually drive in the wet is safer on radials. What you cannot do is treat the two as interchangeable on the same axle.

The law on mixing tyres

This is the one tyre rule on a classic that is a legal offence rather than just advice. Under the Road Vehicles (Construction and Use) Regulations 1986:

• you cannot fit crossply and radial tyres on the same axle, and
• you cannot run crossply tyres on the rear axle with radials on the front.

Put simply, if a car carries both types, the radials must be on the rear and the crossplies on the front, never the other way round, and never side by side on one axle. The reason is handling: a mismatched axle behaves unpredictably at the limit, and front radials with rear crossplies can make a car dangerously prone to swapping ends.

Mixing different brands or tread patterns of the same construction is not illegal, but fitting matched tyres across each axle is strongly advised. The safest and simplest answer on a classic is four matching tyres of one construction.

Size, profile, and speed rating

A classic’s original tyre size is usually moulded into the handbook and often onto a plate on the car. Period sizes use the old systems, such as the inch-based crossply sizes (5.20-13, 5.60-15) and the early metric radial sizes (155R15, 165R14), rather than the modern width and profile format. The specialists translate between the original size and what is available now, which is the main reason to buy from them rather than a high-street fitter who will only have the modern equivalent if one exists.

Two things matter beyond the bare size. The profile, or sidewall height, affects both the look and the ride: too low and the car sits wrong and rides hard; the period profile keeps the proportions and the comfort the car was designed for. The speed rating of a period tyre is often lower than a modern one, which is almost never a limit in practice on a classic but is worth knowing if the car is genuinely fast.

Why age beats tread on a classic

The single most important tyre fact for a classic owner is that age, not tread, is usually what kills the tyre. These cars cover very little distance, so a set of tyres can keep almost all its tread for twenty years while the rubber quietly hardens, cracks, and loses grip. A tyre that is legal on tread can be unsafe on age.

Every tyre carries a four-digit date code on the sidewall giving the week and year it was made. Most tyre makers and classic insurers advise replacing road tyres at around ten years from that date regardless of tread, and a car that has stood for years almost always needs new tyres before it is safe, even though the originals look barely used. Check the date code before trusting any classic’s existing tyres, and look for fine cracking in the sidewall and between the tread blocks, which is the visible sign of perished rubber.

Where to buy

Proper classic tyres come from specialists who carry the period sizes and patterns. Longstone Tyres, Vintage Tyres, and Blockley are the established UK names, and they stock genuine crossplies, period-correct radials, and the older sizes in stock rather than to order. The mainstream makers, Michelin, Avon, Pirelli, and Dunlop, all run classic or heritage ranges in the original sizes too.

The reason to use a specialist is the matching. A general tyre shop can fit a tyre that is the right diameter; only a classic specialist will get the construction, the profile, the period tread pattern, and the correct size designation right for your exact car, which is the difference between a car that looks and drives as it should and one that looks slightly wrong on shoes that do not suit it.

Related

This guide is part of owning and running a classic car, the practical side of classic ownership, alongside number plates, road tax and historic status, fuel, storage, and security.