Tyres are the only part of your classic car that actually touches the road. Everything else, the steering, the brakes, the suspension, can only work as well as the four contact patches that connect the car to the tarmac will allow. A classic with excellent brakes and worn tyres will stop less effectively than a car with average brakes and good tyres. That is not a figure of speech. It is physics. This guide covers the legal requirements, how to check your tyres properly, and the specific considerations that apply to classic cars which are often overlooked in general tyre safety advice. Tyre condition should also be one of the first things to check when bringing a car out of storage — our guide to bringing a classic out of storage and our pre-season safety check both cover tyres as part of the full inspection routine.
The law on tyres
UK tyre law is straightforward and the penalties for non-compliance are significant. Each offence carries a fine of up to £2,500 and three penalty points, applied per tyre. A car with four illegal tyres is theoretically liable for fines of up to £10,000 and twelve penalty points. In practice enforcement is through MoT failure and roadside inspection rather than automated cameras, but the penalties when caught are real and the safety implications are more real still.
It is illegal to use a motor vehicle on a public road with any of the following:
- Tread depth below 1.6mm across the central three-quarters of the tread width around the entire circumference of the tyre
- A mix of radial and cross-ply tyres on the same axle
- Tyres that are significantly over or under-inflated
- Tyres with cuts, lumps, cracks, bulges or tears in the sidewall or tread
- Tyres of the wrong size or load rating for the vehicle
- Tyres with exposed ply or cord
For classic cars used on a standard MoT, these rules apply in full. For vehicles over forty years old that are exempt from MoT testing, the same standards apply on the road. MoT exemption does not mean roadworthiness exemption. A police officer can still pull over and inspect any vehicle and issue fixed penalties for unsafe tyres regardless of whether an MoT is required.
Checking tread depth
The legal minimum of 1.6mm applies across the central three-quarters of the tread width and around the full circumference of the tyre. Most tyres have moulded tread wear indicators, small raised ribs sitting at the base of the main tread grooves, usually marked with a small arrow or TWI marking on the sidewall. When the tread surface wears level with these indicators the tyre has reached the legal minimum and must be replaced.
The legal minimum is not the safe minimum. At 1.6mm a tyre’s wet weather performance is significantly compromised compared to a new tyre. Most tyre safety organisations and motoring groups recommend replacing tyres at 3mm, and many professional drivers use 4mm as their personal threshold. On a classic car used in mixed conditions this is sensible advice. The tyre is the last line of defence between the car and a loss of control. Saving money by running to the absolute legal minimum is not a worthwhile economy.
A tread depth gauge is a worthwhile investment and costs very little. Check the depth at multiple points across the tread width and around the circumference, as uneven wear reveals other problems including incorrect pressures, misaligned tracking, or worn suspension components.
Checking tyre pressures
Tyre pressure should be checked at least every two weeks and always before a long journey. Check the pressures when the tyres are cold, before the car has been driven more than a mile or two. A tyre driven even a short distance will have increased pressure from the heat generated by flexing, which will give a falsely high reading. If you have driven to a garage to check pressures, add around three PSI to the recommended figure to compensate for the heat, or wait for the tyres to cool before checking.
The correct pressures for your classic are in the owner’s handbook. They are specified as cold pressures and may differ between front and rear. Some classics specify higher pressures for motorway or high-speed use. If the handbook is missing, the DVLA or your marque club can usually provide the correct figures for your specific car.
Under-inflated tyres wear at the outer edges of the tread and run hotter than correctly inflated tyres, which degrades the rubber and reduces tyre life. They also increase rolling resistance, slightly reducing fuel economy. Over-inflated tyres wear in the centre of the tread and provide a smaller contact patch, reducing grip. Both conditions compromise the tyre’s ability to perform its job and both are illegal if significantly outside the recommended range.
Sidewall inspection
The sidewall carries the tyre’s load and absorbs the lateral forces of cornering. It also tells you a great deal about the tyre’s history and condition if you know what to look for. Inspect both sidewalls of every tyre carefully and regularly.
Cuts and abrasions on the sidewall from kerbing are common and should be assessed carefully. A superficial scuff on the outer rubber is generally not a structural concern. A cut that has penetrated through the outer rubber to the cords beneath is serious and the tyre should be replaced. You cannot always tell by looking whether a cut is superficial or structural, and if there is any doubt a tyre specialist should inspect it before the car is used on the road.
Bulges in the sidewall indicate internal structural damage, usually caused by an impact with a pothole or kerb at speed that has broken the internal cord structure. A bulge means the tyre must be replaced immediately. It will not recover and it can fail without warning at speed. Cracking in the sidewall rubber, particularly the fine crazing that develops on tyres that have been stored or aged, indicates that the rubber compound has degraded. See the section below on age specifically, as this is the most important tyre safety issue specific to classic cars.
The age problem: specific to classic cars
This is the most important section in this guide for classic car owners because it addresses a risk that general tyre safety advice rarely covers adequately. Tyre rubber degrades with age regardless of use. A tyre that has been stored for five years without being driven has still aged five years. The oils and chemicals in the rubber compound that keep it flexible and bonded to the cord structure gradually migrate out of the rubber over time, leaving a tyre that looks acceptable but has lost the flexibility and strength of a newer tyre. This process is accelerated by UV exposure, ozone, and temperature extremes.
The tread depth on an aged tyre may be perfectly legal. The tyre may show no obvious external damage. But a tyre that is six, eight, or ten years old is significantly more likely to fail suddenly under load than a tyre of the same tread depth that is two years old. Sidewall cracking is the most visible indicator of age-related degradation, but it can be well advanced internally before it becomes visible on the surface.
Most tyre manufacturers and safety organisations recommend replacing tyres at six years regardless of condition, and no later than ten years from the date of manufacture. The date of manufacture is moulded into the tyre sidewall as a four digit code: the first two digits are the week of manufacture and the last two are the year. A tyre marked 2419 was manufactured in the twenty-fourth week of 2019. Check this code on every tyre on your classic and on any spare tyre carried. Many classics are running on tyres that are well beyond this threshold, particularly if they have been in long-term storage or lightly used.
Flat spotting and storage damage
A car stored on its wheels for a prolonged period develops flat spots where the tyre’s contact patch deforms slightly under the weight of the car. Minor flat spotting usually resolves itself after a few miles of driving as the tyre warms up and the rubber recovers. Severe flat spotting, particularly on older tyres, can be more persistent and may cause a noticeable vibration at certain speeds that does not fully resolve with driving. This is more common on tyres that have been standing in cold conditions, where the rubber is less able to recover its shape.
If the car is to be stored for more than a few weeks, raising it on axle stands to take the weight off the tyres entirely eliminates flat spotting and also removes the constant load from the sidewalls. This is good practice for any classic in medium to long-term storage and significantly extends the usable life of the tyres. Our winter storage guide covers axle stand storage and tyre preparation as part of a full lay-up procedure.
Tracking and balancing
Incorrect wheel alignment, commonly called tracking, causes accelerated and uneven tyre wear and reduces the precision of the steering. A car that has had any suspension or steering work done, or that has had a significant impact with a pothole or kerb, should have the tracking checked before further use. On a classic car with older suspension components, incorrect tracking is also a symptom of worn parts rather than simple misadjustment, so an alignment check should be accompanied by a visual inspection of the steering and suspension components.
Wheel balancing eliminates vibration caused by uneven weight distribution around the wheel and tyre assembly. Classic car wheels can be balanced using the same equipment as modern wheels, though some older alloy or steel wheels require care with the balancing weight placement. A vibration that appears at a specific speed and disappears above or below it is almost always a balancing issue rather than a structural one.
Choosing tyres for a classic car
Matching tyres to a classic car requires some thought that does not apply to modern vehicles. The original tyre sizes specified in the handbook may be in a format that is no longer manufactured, requiring a metric equivalent of the same overall diameter. Fitting a tyre with a different overall diameter affects the speedometer accuracy and the final drive ratio, neither of which is catastrophic but both of which are worth knowing about.
Classic car specialists including Longstone Tyres, Blockley, and Vintage Tyres stock tyres specifically designed for classic cars, including crossply options for the earliest cars and remould options for some pre-war sizes. These specialists can advise on the correct equivalent sizes and on which modern tyres offer the best combination of period appearance and modern performance for a specific car.
Radial tyres fitted to a car designed for crossply tyres will generally improve wet weather grip and tread life, but may alter the handling characteristics to an extent that requires adjustment in driving style. Some classic cars are sensitive to this change and some owners prefer to retain crossply tyres for originality and handling consistency. The choice is a personal one, but mixing radial and crossply tyres on the same axle is illegal and potentially dangerous regardless of the reason.
A quick pre-drive check
Before any journey in a classic, particularly after a period of storage, spend two minutes walking round the car and looking at each tyre. Check that all four look evenly inflated and that none is visibly lower than the others. Look at the sidewalls for any new damage. Look at the tread for anything embedded in the rubber. Check that the spare is in usable condition, inflated and without visible damage. None of this takes any time and it has the potential to prevent a breakdown or worse.