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I have a 2012 Mazda3 that I recently discovered has a leaky tire. The pressure light came on yesterday, and we located the low pressure and added 10-15psi. This morning I drove to work, but the pressure light didn't turn off. I checked the pressure when I arrived and the bad tire had dropped back down again. The leak isn't bad enough to completely flatten the tire, but it also isn't slow enough that a refill will last me a week.

I haven't had a chance to try and locate the leak itself yet, but when I do, I have a couple options for handling. I have both a fix-a-flat and a spare donut in my trunk, as well as a portable air compressor. It seems that using the fix-a-flat would be much easier than changing the tire out. Reading this answer on another question, it sounds like fix-a-flat also would last quite a while, long enough for me to get the car to my regular mechanic on the weekend.

My spare is the one that came with the car 6.5 years ago, so it's also reaching the age where it should maybe be replaced. However, I understand that it may be far safer to just change out the tire, even if it is a pain on a 90-degree day.

So, to bring it all to a question:

If one has the option for both fix-a-flat and a spare tire, in which situations would each be recommended?

  • Take it to a tire shop and have the tire patched properly. – Moab Jun 18 '18 at 14:24
  • Does the car have alloy wheels? I've known a number of Mazda alloy wheels become leaky with age because they corrode and go porous. – Steve Matthews Jun 18 '18 at 14:29
  • @Moab But there is still the matter of getting to the tire shop. – David K Jun 18 '18 at 14:30
  • @SteveMatthews I have no idea. I've had tires replaced, but the wheels are the basic manufacturer originals. – David K Jun 18 '18 at 14:32
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    @DavidK if you can get the car to work, you can get it to a tire shop - they will even (good ones) lend a car or take you to work or train station etc – Solar Mike Jun 18 '18 at 14:35
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I highly recommend never to use Fix-A-Flat (or the like) unless it's absolutely a necessity. There are several reasons for this:

  • Fix-A-Flat has the tendency to ruin your tire pressure sensors if your car is equipped with sensors which read directly. Most sensors of this type are tied to the valve stem, which means the Fix-A-Flat has to pass through and around them in order to do it's thing.
  • As was stated in the comments, tire shops hate the stuff. It's a big gooey mess which they get to clean up.
  • Fix-A-Flat will work for the small leak or even punctures. It won't help with a blowout. Only a replacement, whether it's the spare or a new tire, can cure this ill.

IMHO, a spare is always more desirable than Fix-A-Flat unless you have no other choice. Obviously getting to where you can get things fixed may not leave you any other choice. To not use the spare option if it is available is just being plain lazy.

Riding around on a nearly flat tire (or down 10-15 lbs like yours) is a very poor option.

  • As the tire gets lower, it has more rolling resistance. This rolling resistance creates heat within the rubber of the tire. Too much heat build up causes the tire to degrade. This usually starts by chewing up the inside of the tire sidewall. The reason this is so dangerous is you cannot see it happening. If it were to happen, you'd be running around with a tire which is ready to self destruct. It doesn't mean much at 25mph residential speeds, but at 70mph highway speeds it becomes very dangerous to you, your passengers, and those traveling around you. Very easy to lose control of your vehicle if you were to have a blowout.
  • Low tire pressure means you have less control of your vehicle. The sidewall isn't able to support the lateral loads exerted while the vehicle is in a corner.

If you have the three things available to you (portable air pump, spare tire, Fix-A-Flat), I'd use them in this order and here's why/when:

  • Portable Air Pump: Use to pump up your tire to get you to the shop to get your tire fixed or replace. Don't use if the air is coming out faster than you can put it in, or if it will leak out before you can get to your destination.
  • Spare Tire: Use if the air pump isn't an option. Don't be lazy. Change out the tire and be done with it.
  • Fix-A-Flat: Use only as a last resort. If the air pump fails you and the spare tire is flat or worn out, then use the gooey green stuff.
    • Even then, I'd be tempted to take the tire off the car and take it to the shop rather than using the stuff.
  • Thank you for the detailed answer! I hadn't considered the air pump on its own as a suitable quick fix for a slower leak. – David K Jun 18 '18 at 16:05
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    You should bold the recommendation to pull the tire and get it fixed separately. That's an option that almost no one will think of. And, of course, properly secure the now three wheel car so it isn't a kid killer.... – Bob Cross Jun 18 '18 at 21:41
  • To add about the fix-a-flat, the shop I used to work at will not even repair a tire if they find that stuff in it, they claim it's a liability thing, and it is, since they're the ones liable for it if it fails I suppose... Use as a LAST RESORT ONLY! – user38903 Jul 10 '18 at 13:56

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