Space-saver spare or sealant kit: what is in your boot?
8 min readBy Wheel Fit
The short answer: most cars sold in the last decade carry either a space-saver (limited to around 50mph and a restricted distance) or a sealant kit (small tread punctures only). Check which you have before you need it.
Full-size spare
Increasingly rare, usually on estates, 4x4s and vans. No restrictions — fit it and carry on. The one thing to watch is pressure: a spare that has sat under the boot floor for three years is almost certainly low.
Space-saver
The narrow wheel with the bright rim. Designed to get you off the motorway and to somewhere that can fix the real problem.
- Speed limit, usually 50mph, printed on a label on the wheel.
- A distance limit, often around 50 miles.
- Different diameter and grip to the other three, so handling and braking are affected. Some cars will disable or limit stability systems.
- Should generally go on the rear. If the puncture is at the front, many handbooks tell you to move a full-size rear wheel to the front and put the space-saver at the back.
Sealant kit
A bottle of sealant and a small compressor. It injects goo through the valve, you drive gently to spread it, and it plugs a small hole from the inside.
What it will handle: a nail or screw in the tread, roughly up to 4mm.
What it will not handle:
- Sidewall damage of any kind.
- A blowout or a large split.
- A tyre already driven on flat.
- A tyre off the rim.
Two things worth knowing. Sealant has an expiry date — check the bottle, because a five-year-old kit may be useless. And a sealed tyre normally still has to be replaced; the sealant also has to be cleaned out of the rim and the TPMS sensor, which can add to the bill.
Which is better?
| Full-size spare | Space-saver | Sealant kit | |
|---|---|---|---|
| Sidewall damage | Handles it | Handles it | No use |
| Large hole or split | Handles it | Handles it | No use |
| Small tread puncture | Handles it | Handles it | Usually works |
| Speed limit after | None | ~50mph | ~50mph |
| Distance limit | None | ~50 miles | Short |
| Needs you to change a wheel | Yes | Yes | No |
| Boot space and weight | Most | Some | Least |
For getting you moving, a space-saver, every time. It handles any puncture including a destroyed sidewall, where sealant handles one narrow category. The catch is that fitting it means kneeling beside the car — which on a motorway you should not do at all.
Check what you have — now, not later
- Lift the boot floor. Full-size wheel, narrow space-saver, a bottle and compressor, or nothing at all.
- If it is a wheel, check its pressure. Space-savers usually run much higher than normal tyres — the figure is on the wheel itself.
- If it is a sealant kit, check the expiry date on the bottle. Replacing it is cheap.
- Find the jack, brace and locking wheel nut key while you are there — a missing key stops the job entirely.
- Check the spare's age too. A twelve-year-old space-saver is not reassuring — how long tyres last.
Common questions
- Can I buy a spare for a car that came without one?
- Often yes, if there is a well under the boot floor to take it. Make sure the wheel, jack and brace are correct for your car — see flat tyre with no spare.
- Does using sealant write off the tyre?
- Not automatically, but it makes proper inspection messier and some sealants make it difficult. Always tell the fitter it has been used — can a puncture be repaired?
- Why does the space-saver go on the rear?
- Because it has less grip than the other three, and you want the reduced-grip corner at the back for stability. Many handbooks tell you to move a full-size rear wheel to the front and put the space-saver behind it.
- Do I need to tell my insurer?
- No — using the manufacturer's spare or kit as intended is normal use. Driving beyond a space-saver's stated speed or distance limits is a different matter.
Our honest view
Know what is in your boot, check the spare's pressure occasionally, and check the sealant's expiry date. Then, if a tyre goes somewhere genuinely unsafe, you can leave both where they are and call someone to come to you.
Related: what to do with a flat tyre on the motorway and changing a wheel safely.
