Key takeaways
- Sidewall damage, a tyre run while flat, and tread at the 1.6mm legal limit all end a tyre outright.
- Mobile vans carry the common car, SUV and 4x4 sizes; unusual sizes can normally be sourced, which is a timing question rather than a no.
- Tyres on the same axle should match closely, so occasionally one damaged tyre means replacing two.
- Run-flats and staggered fitments are worth mentioning on the call, because they narrow what will fit.
Most punctures are repairable. The ones that are not tend to announce themselves badly, at the roadside, at the worst hour, and the immediate worry is rarely the tyre itself. It is whether anybody can actually turn up with the right one. This guide covers what forces a replacement, and what determines whether it can happen where you are standing.
When does a tyre need replacing there and then?
A tyre needs replacing immediately when its structure is compromised or it is no longer road legal, because neither can be restored by a repair. The clearest cases are damage to the sidewall, a tyre that has been driven on while flat, and tread worn to the 1.6mm legal minimum across the central three-quarters. In the UK, driving on a tyre below that limit carries a fine of up to £2,500 and three penalty points, per tyre.
A blowout almost always falls into this category. The sudden failure that empties the tyre usually shreds the internal structure on the way, so even where the visible hole looks modest, the casing beneath it has gone.
Will a mobile fitter have my tyre size?
For the great majority of cars, yes. Vans carry a working range of the common sizes fitted to cars, SUVs and 4x4s, which is what turns up on the roadside most nights. Where a size is less common, it can usually be sourced rather than refused, which makes it a question of when rather than whether.
The way to get a straight answer quickly is to read the code off the sidewall when you call. It looks like 205/55 R16 91V and every part of it matters.
| Part of the code | Example | What it tells the fitter |
|---|---|---|
| Section width in mm | 205 | How wide the tyre is |
| Aspect ratio | 55 | Sidewall height as a percentage of the width |
| Rim diameter in inches | R16 | Which wheel it has to fit |
| Load index | 91 | The weight each tyre is rated to carry |
| Speed rating | V | The speed the tyre is rated for |
If you cannot get to the sidewall safely, your registration is the next best thing. Our guides on what the numbers on your tyre mean and finding the right tyre size go through the code in more detail.
Do you have to replace more than one tyre?
Not usually, but sometimes. Tyres on the same axle should be a close match in type and condition, because a large difference in grip or tread depth between the two changes how the car brakes and steers. If the surviving tyre on that axle is nearly worn out or is a very different type, replacing the pair is the safer call.
On four-wheel-drive vehicles the tolerance is often tighter still, because a significant difference in rolling circumference puts strain on the transmission. Some manufacturers set a maximum permitted difference. It is worth checking the handbook rather than assuming. Our guide on replacing two or all four tyres covers the reasoning.
What about run-flats and specialist tyres?
Run-flats are designed to carry the car a limited distance at reduced speed after losing pressure, which buys you the option of moving somewhere safer. That distance and speed are set by the manufacturer and should be treated as a maximum, not a target. Once a run-flat has been driven on deflated, it is generally replaced rather than repaired.
Mention it on the call if your car runs run-flats, a staggered fitment with different sizes front and rear, or unusually low-profile tyres. Each narrows what will fit, and saying so up front avoids a wasted visit. Our run-flat tyres guide explains how they differ.
What happens to the tyre pressure sensor?
If your car has a tyre pressure monitoring system, replacing a tyre disturbs it, and that is worth understanding before the light comes on afterwards. Most systems use a sensor mounted at the valve inside the wheel. The sensor itself is normally reused, but the small rubber and metal parts that seal it, the service kit, are consumable and are often renewed as part of a proper fitting.
Once the wheel is back on, the system may need a relearn so the car recognises the sensor position again. On many cars that happens by itself after a short drive; on others it needs a tool. Either way the warning light should not still be on when you drive away, and if it is, say so before the fitter leaves.
This matters beyond the dashboard: a TPMS malfunction warning is an MOT failure on cars first used from 2012, so a light left lit becomes a test problem later. Our guide on the tyre pressure warning light explains the difference between a genuine low-pressure warning and a system fault.
What happens to the old tyre?
It goes with the fitter for recycling. You should not be left holding it, and you should not be asked to dispose of it yourself. This is routine and it is part of the job.
Getting a replacement fitted where you are
If the tyre is beyond repair, the fastest route back onto the road is almost always to have the new one brought to the car rather than to move the car to the tyre. That removes the drive on a damaged wheel, which is where the additional damage usually happens.
Read us the code off the sidewall, or just the registration, and we will confirm what we can put on the car before anyone sets off. Fitted and balanced where it stands, the old one taken away. Typically 30 to 60 minutes across London and the nearer Home Counties, longer further out, and you get a real arrival time on the call.
New tyres are covered by the manufacturer's warranty, typically two years against manufacturing defects. If you are still weighing up whether the tyre is finished at all, start with what can be fixed on the spot, or see mobile tyre fitting.
Frequently asked questions
Mobile fitting inverts the question: rather than finding somewhere open near you, the tyre and the fitter come to the car. Give your postcode and the size from the sidewall and you will be told on the call whether it can be done and roughly when.
It is moulded into the sidewall and reads like 205/55 R16 91V. A phone torch usually picks it out. If the tyre is on the traffic side of the car, do not go round to read it; give your registration instead and stay behind the barrier.
On the same axle, tyres should match closely in type and condition. Across axles a different brand is normally acceptable. A fitter will tell you if what is on the car makes that a problem.
It can usually be sourced. That changes the timing rather than the answer, so it is worth giving the size early in the call so the availability check happens before anyone travels.
Yes, it leaves with the fitter for recycling. You are not left to dispose of it.