Tire sealants are often included in emergency mobility kits, but leave a mess

Many drivers bemoan carmakers’ move away from supplying spare tires with their products. For most mainstream passenger cars, the cheaper modern substitute is some type of compressor and sealant kit. The reasons given are lighter vehicles with more usable cargo space, but there are a few pros and cons to keep in mind. While tire chemistry, design and manufacturing have improved their reliability and puncture resistance over the years, the general degradation of our roads and the volume of tire-shredding debris we encounter have kept pace with those improvements to flatten the score, so to speak.

Adding a spare tire to a vehicle that wasn’t built for one involves more planning than just finding a rim and tire. If it’s to be mounted inside a vehicle without a bulkhead protected cargo area (think open SUVs and minivans), it has to be secured strongly enough to stay in place during an impact to prevent it from becoming a lethal projectile. Of course, many drivers of these types of autos carry their own loose collision torpedoes every day in the form of sports gear, tools, and recyclables they’ve been meaning to drop in the bin. Some vehicles without spares can be modified to carry them underneath by purchasing original equipment holders and winches. SUV tailgate mounts may also be available, providing the existing gate hinges are appropriately reinforced to hold the carrier.

Spray sealants typically come in two types: pressurized aerosol cans, and 12-volt compressors with replaceable sealant containers. The latter has more benefits, allowing you to fill a tire to its pressure limit where aerosol cans come up short, top up pressures without sealant, and even for things like water inflatables and air mattresses.

All of these sealants have one thing in common: they’re for temporary use only. Yes they can seal simple small punctures, but the majority of that liquid stays liquid. This means that it doesn’t stay in one place, but sloshes around with the movement of the wheel — a tire imbalance that can never be corrected until the liquid is removed by breaking down the tire. Most passenger car tires will vibrate at highway speed if balance is off by as little as 30 grams, so consider what impact 150 grams of sealant will have. Most sealant makers recommend getting a permanent repair and their product removed within a 100 km of a treatment.

When tire pressure sensors first became common there was concern that liquid sealants could affect or damage them. That hasn’t proven to be the case, but don’t press your luck by leaving it in too long.

And unless you want to lose any working relationship you have with your tire shop, when you bring a sealant-treated tire in for its permanent repair, make sure that the presence of that sealant is well noted on the work order for the technician. Unless the tire has been completely depressurized before it’s removed (and even in some cases when it has) there can be a large, technicians and their workspaces can be caught in an explosive shower unpleasant sealant goop.

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