How do I use a tyre sealant kit or a space saver spare?

Most new cars no longer carry a full-size spare. Knowing which of the three possible arrangements is in your boot, before you need it, is the entire point of this guide.

Safety

What you'll need

• The kit or spare already in your car
• The handbook
• A torch (optional)
• Gloves (optional)

Step by step

1. Find out now what your car actually carries.A full-size spare, a space saver, a sealant and compressor kit, or nothing at all with run-flat tyres. Look in the boot well this week, not on a dark verge.
2. Get somewhere safe before doing anything.Level ground, away from traffic, handbrake on, hazard lights on. On a motorway, none of this applies — call for assistance from behind the barrier.
3. Assess the damage before choosing.Sealant only works for a small puncture in the tread area. A cut or split in the sidewall, a hole bigger than a few millimetres, or a tyre already driven on flat all need recovery.
4. For a sealant kit, read the instructions on the bottle.Most involve connecting the bottle to the valve, emptying the sealant in, then running the compressor to inflate. Some pump the sealant through the compressor itself.
5. Inflate to the placard pressure and drive gently.The sealant only spreads and seals once the wheel is turning. Most kits ask for a few miles at low speed, then a recheck of the pressure.
6. Tell the tyre fitter that sealant has been used.It coats the inside of the tyre and the pressure sensor. Fitters need to know, and some sealants make a permanent repair impossible.
7. For a space saver, loosen the bolts before jacking.Break each bolt loose by a quarter turn with the wheel still on the ground. A wheel spins freely once it is in the air and you cannot hold it.
8. Use the correct jacking point.The handbook shows reinforced points under the sills. Jacking anywhere else bends the floor or the sill. Never put any part of yourself under a car held only by a jack.
9. Fit the space saver, lower, then tighten diagonally.Nip the bolts up by hand while the wheel is off the ground, lower the car, then tighten fully in a diagonal pattern with the weight on the wheel.
10. Respect the limits printed on the wheel.Space savers are usually limited to 50 miles per hour and a restricted distance, and many manufacturers say not to fit them to a driven axle. They also need a much higher pressure than a normal tyre.
11. Get to a tyre specialist straight away.Both solutions are there to move the car to a place of repair. Neither is a state to leave the car in for weeks.

Tips

• Check the sealant bottle's expiry date. Sealant has a shelf life of a few years and an expired one may not work.
• Check the space saver's pressure when you do the other four. It is almost always flat when it is finally needed.
• Keep gloves, a torch and a mat in the boot with the kit. Kneeling on a wet verge in the dark is unpleasant enough already.

Common mistakes

• Using sealant on a sidewall cut — Sealant cannot bridge a sidewall failure and the tyre will deflate again, possibly at speed. Sidewall damage always means recovery.
• Attempting a wheel change on a motorway hard shoulder — It puts you kneeling beside traffic at seventy miles an hour. This is the single situation where breakdown assistance is unambiguously worth waiting for.

If it doesn't work

Questions people ask