Skip to content 
A puncture rarely happens at a convenient time. Whether you’re on a motorway, a country lane at night, or a car park miles from home, knowing exactly what to do, and how to drive safely on your spare can make an already stressful situation far more manageable.
If you’re driving in or around Guildford, knowing how to handle a puncture safely is even more important, especially on busy roads or motorways where stopping conditions can be unpredictable.
The problem is, spare tyre advice tends to be vague. “Drive carefully.” “Don’t go too fast.” “Get to a garage soon.” That’s not enough. This guide gives you the complete picture, the types of spare, the speed and distance limits, the legal position, what your spare does to your car’s handling, and what to do with the damaged tyre once the spare is on.
First: Do You Actually Have a Spare Tyre?
Before anything else, it’s worth knowing what’s in your boot, because the answer might surprise you.
Around two-thirds of all new cars now leave the factory without a full spare wheel. Manufacturers have been reducing spare tyres since the 1990s to save weight, cut costs, and free up boot space. In their place, you might have one of three things:
| What’s in Your Boot | What It Is | Temporary Fix? |
|---|---|---|
| Full-size spare | Identical (or near-identical) to your fitted tyres | No distance/speed restrictions if same spec |
| Space-saver spare | Thinner, smaller temporary wheel | Yes, 50mph max, ~50 miles |
| Run-flat tyres | No spare at all, tyres have reinforced sidewalls | Yes, 50 miles at 30–50mph max |
| Tyre sealant and inflator kit | Foam sealant + compressor, no spare wheel | Minor punctures only, not blowouts |
| Nothing | Increasingly common on newer cars | You need breakdown assistance |
Check your vehicle handbook now if you’re not sure, it will tell you exactly what your car carries and where it’s stored. Knowing before an emergency is far better than discovering it on a dark roadside.
The Four Types of Spare Tyre Explained
1. Full-Size Spare
The traditional spare. It matches (or closely matches) the tyres already on your vehicle in size, load rating, and speed rating. If you have a genuine full-size matching spare, you can drive at normal speeds and distances, but you should still check it regularly for pressure, tread depth, and condition. A spare that hasn’t been used in five years may have deteriorated without showing visible signs.
2. Space-Saver Spare (Donut)
The most common temporary spare. It is noticeably thinner and smaller than a standard tyre and is engineered purely to get you off the roadside and to a garage, nothing more.
Key restrictions:
- Maximum speed: 50mph
- Maximum recommended distance: 50 miles
- The maximum speed is usually printed on a sticker on the wheel itself. If the sticker is missing, treat it as a 30mph maximum until you can get proper advice.
Space-saver tyres alter your car’s handling in meaningful ways, more on that shortly.
3. Run-Flat Tyres
Run-flat tyres have reinforced sidewalls that support the car’s weight even after a complete loss of pressure. They allow continued driving after a puncture, but with strict limits:
- Maximum speed: 50mph (some manufacturers specify 30mph)
- Maximum distance: 50 miles
Run-flat tyres are common on BMW, Mini, Mercedes, and some Audi models. One critical point many drivers are unaware of: run-flat tyres cannot be repaired after a puncture. They must be replaced. Driving on a deflated run-flat damages the reinforced sidewall, making repair impossible even if the puncture itself looks minor.
4. Tyre Sealant and Inflator Kit
These kits, sometimes called “tyre mobility kits”, are not spare tyres at all. They contain a foam sealant that is injected through the tyre valve, plus a compressor to re-inflate.
They work only for small, clean punctures (typically a nail or screw in the tread). They will not work for:
- Sidewall damage
- Large tears or blowouts
- Punctures near the tyre shoulder
There is also a crucial secondary issue: once foam sealant has been applied inside a tyre, a professional repair is no longer possible. The sealant contaminates the inner liner, preventing the clean surface needed for a proper puncture plug or patch. The tyre must be replaced entirely. If your car comes with a sealant kit, use it only as a last resort and inform the tyre fitter of what you’ve used, so they know before removing the tyre.
Speed and Distance Limits at a Glance
| Spare Type | Max Speed | Max Distance | Can Be Repaired After Use? |
|---|---|---|---|
| Full-size matching spare | Normal (if same spec) | No restriction | Depends on damage |
| Space-saver spare | 50mph | ~50 miles | No, replace after emergency use |
| Run-flat (after puncture) | 50mph (30mph some models) | 50 miles | No, must replace |
| Sealant kit | 50mph (post-inflation) | ~50 miles | No, must replace |
What a Space-Saver Spare Does to Your Car
This is where most guides fall short. Drivers fit a space-saver and assume the car will drive roughly the same, just a bit bumpier. The reality is more significant.
Handling and steering – A space-saver’s narrower footprint reduces contact with the road. Steering may feel lighter or less precise. Cornering grip is reduced, and the car may react less predictably in an emergency swerve.
Braking distance – Because the space-saver is a different size to the other three tyres, the car’s braking balance changes. Anti-lock braking systems (ABS) and electronic stability control (ESC) rely on all four wheels being consistent in size and rolling speed. A mismatched tyre interferes with these systems, potentially increasing stopping distances.
All-wheel drive and four-wheel drive vehicles: a serious warning. If you drive an AWD or 4WD vehicle and fit a space-saver spare, you must consult your owner’s manual immediately. Many AWD systems require all four tyres to be the same rolling circumference. A space-saver, being smaller, rotates at a different speed. This forces the differential to compensate constantly, which can cause serious, expensive damage to the transfer case or centre differential within a very short distance. Some AWD manufacturers explicitly state that a space-saver spare must not be fitted without disengaging the AWD system. If you drive an AWD vehicle and get a puncture, prioritise calling for recovery rather than fitting a space-saver if you are not certain your system allows it.
Road noise and vibration – The different tread pattern and compound of a space-saver create additional noise. This is normal. However, vibration that increases over time or at certain speeds is a warning sign to stop and inspect the spare.
Can You Drive on a Motorway with a Spare Tyre?
No law in the UK explicitly prohibits driving on a motorway with a space-saver spare. However, the 50mph speed limit on a space-saver means you must keep to the left lane and drive significantly below the national speed limit. This is legal, but it creates a hazard for other drivers if you are not clearly managing the situation.
If the motorway is the only practical route to safety, use it, but stay in lane 1, drive at a consistent speed, and consider using your hazard lights briefly to signal that your vehicle is moving slower than traffic around you. Get off at the earliest opportunity.
Do not use a run-flat tyre at full motorway speeds. The 50mph restriction applies equally on a motorway as anywhere else.
Is a Spare Tyre a Legal Requirement in the UK?
No. There is no UK law requiring you to carry a spare tyre, a space-saver, a sealant kit, or any puncture repair equipment whatsoever.
However, there is an important MOT-related point that catches many drivers out: if your car presents for an MOT with a space-saver spare fitted in place of a standard road tyre, it will fail the MOT immediately. Space-saver tyres are not approved for normal use, only temporary emergency use. If you’ve been driving on a space-saver and forgotten to replace the damaged tyre, your car is also likely not roadworthy under UK law while the spare is fitted.
How to Check Your Spare Tyre Before You Need It
The worst time to discover your spare is flat, perished, or too old to use is at the roadside. Build these checks into your regular vehicle maintenance; they take two minutes.
Tyre pressure – Most space-saver spares require a higher pressure than standard tyres, typically 60 PSI. Check yours against the specification in your owner’s manual or on the wheel sticker. Pressure drops slowly over months and years, even in unused tyres, so a spare that was correctly inflated two years ago may be dangerously flat now.
Tread depth and condition – The legal minimum tread depth in the UK is 1.6mm across the central three-quarters of the tyre. Check your spare the same way you’d check any road tyre.
Tyre age, the DOT date code – This is something almost no guide mentions. Every tyre has a DOT code moulded into the sidewall. The last four digits tell you the week and year of manufacture, for example, 2319 means the 23rd week of 2019. Most tyre manufacturers recommend replacing tyres over six years old, regardless of tread depth or appearance, due to rubber degradation. Your spare may look perfect and still be structurally unsafe if it is over six years old. Check the date.
Jack, wheel brace, and locking wheel nut key – Your spare is useless without the tools to fit it. Confirm these are present, accessible, and in working order. The locking wheel nut key in particular, is often lost during car ownership changes. Check you have the correct one for your vehicle’s alloys.
What to Do with the Damaged Tyre
Fitting the spare solves the immediate problem. What you do next matters.
Can the original tyre be repaired?
A tyre puncture can often be professionally repaired, but only if:
- The puncture is in the central tread area (not the shoulder or sidewall)
- The hole is no larger than 6mm in diameter
- The tyre has not been driven on while flat (which causes internal structural damage)
- No sealant foam has been applied
If any of these conditions aren’t met, the tyre must be replaced. Bring the damaged tyre with you to the garage, don’t leave it at the roadside. A professional inspection can tell you whether repair is possible, which can save you the cost of a full replacement.
Don’t ignore what caused the puncture. A nail in the tread is usually straightforward. But a blowout, sidewall failure, or rapid deflation at speed may indicate a deeper issue, impact damage from a pothole, a valve fault, or a manufacturing defect. If the cause isn’t obvious, ask the tyre fitter to inspect the wheel and the failed tyre carefully before you assume a simple replacement is all that’s needed.
The Risk of Buying a Used Spare Tyre
If you need to replace your spare or acquire one for a car that doesn’t have one, buying a used tyre may seem like a sensible way to save money. It isn’t.
Research suggests that around 98% of part-worn tyres sold in the UK are non-compliant with the legal requirements for selling second-hand tyres. Structural damage, age-related degradation, previous repairs, and incorrect labelling are common. A tyre that looks acceptable on the outside may have a compromised internal structure that only becomes apparent under load, at the worst possible moment.
Buy new. For a spare tyre that you hope never to use, the cost difference is modest. The safety difference is not.
Frequently Asked Questions
Can I reuse a space-saver spare tyre?
Technically yes, if it’s undamaged and within its age and tread limits, but space-saver tyres are not designed for repeated use. If it has been used once, inspect it carefully before relying on it again, and consider replacing it.
How do I find my spare tyre?
Most commonly under the floor panel in the boot, or sometimes mounted externally under the rear of the vehicle (4x4s and SUVs). Check your vehicle handbook for the exact location in your model.
Does my spare tyre affect my car insurance?
Driving on a roadworthy spare tyre within its rated limits is legal and should not affect your insurance. However, if you were involved in an accident while driving outside a space-saver’s speed or distance limits, an insurer could argue the vehicle was not in a roadworthy condition.
What if I don’t have a spare or sealant kit?
Call for breakdown assistance. Do not attempt to drive on a flat tyre, even a short distance on a deflated tyre causes severe damage to the rim, tyre structure, and potentially the suspension.
Spare Tyre Advice and Fitting at G4 Tyres & Wheels in Guildford
Whether you need your damaged tyre repaired, a replacement fitted, or a new space-saver spare to carry for emergencies, G4 Tyres & Wheels stocks a wide range of tyres and spare wheel solutions for all makes and models.
If you’re unsure what your car carries, what condition your spare is in, or whether your damaged tyre can be repaired, bring it to us, we’ll give you a straightforward, honest assessment.
Don’t wait until you’re stuck at the roadside to think about your spare. Check it now.
