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Flat Tire? 7 Reasons Not to Repair It With Fix-a-Flat or Slime Tire Sealant

Almost a third of new vehicles don't come with a spare tire, but that's no reason to pick up this problem-causing goo.
flat tire

You might get it because a tow feels too expensive. You might get it because it seems easier than changing a tire. You might get it because you don't have a spare. But no matter why you're picking up that can of tire sealant, our advice is: don't!

If you're tempted to replace your spare tire with a can of Fix-a-Flat, Slime, or some other tire sealant, read on to see why stop-leak solutions are a terrible idea for tire repair.

Why You Shouldn't Repair a Flat Tire With Tire Sealant

Cleanup Is a Mess

These products inject a sealant into your flat tire to seal the leak, and a gas to fill the rest of the tire. But sealants leave goo inside the tire, and it's a real hassle for tire shop employees to get all of it off the wheel when they do a tire repair — especially if it's dried on. That could cost you when it's time to replace the tire; worse, the substance could even damage an otherwise repairable tire.

Tire sealants can potentially damage an otherwise repairable tire.

Sure, Fix-a-Flat's FAQ says its product "will not cause harm to most tires when used as directed." But which tires aren't included in that "most tires" caveat? Are your tires the wrong ones? Who knows! It's better to carry a spare tire — or opt for roadside assistance, which will cover more than just flat tire issues.

It's Unsuitable for Colder Regions

Tire sealant can freeze, making it unsuitable for most winters in the U.S. If it freezes in the can, you'll have a heck of a time defrosting it — time you could be waiting for a tow truck instead. Even if you thaw the tire goo out, it could still refreeze inside your tire, knocking your wheel out of balance.

You Can Use Run-Flat Tires Instead

Run-flat tires exist. According to research from AAA, 28% of 2017 model year vehicles didn't come with a spare. If you drive one of those cars, you can bet dollars to donuts there are run-flat tires either on or available for your car. Depending on the tire type, they can allow you to drive cautiously on a flat tire for up to 100 miles without damaging your wheel. Nearly every new BMW, many Cadillacs, plenty of Mercedes, and even some Toyotas come with run-flats — just to name a few.

SEE ALSO: Which Motor Oil Is Best for YOUR Car?

Sealant Won't Fix Major Flat Tire Issues

Tire sealant is only useful if you've got a slow leak in the tire or a small hole. If you suffer a more serious encounter — say, with construction debris — the tire goo will not save you. But you won't know if your tire is beyond repair until it's spewing slime all over itself on the side of the road — and maybe all over you.

It Could Ruin Your TPMS

Every new car sold in the U.S. in the last 10 years has a tire pressure monitoring system, which can alert you to a leaking tire before it becomes a critical issue. Tire sealants can clog your TPMS. If it's not cleaned promptly, this could ruin a sensor.

Tire sealants can clog your tire pressure monitoring system. If it's not cleaned promptly, this could ruin a sensor.

A clog isn't the only thing to worry about. If you leave some sealants in the flat tire for too long, this could also damage a sensor. Still, some tire sealant companies insist their product is TPMS-safe — and some car manufacturers specifically say not to use tire sealants.

Motorcycles Can't Use It for Flat Tire Repair

If you're a motorcycle rider, tire sealants definitely aren't for you. Tire sealants like Fix-a-Flat and Slime are intended for use in the tubeless tires found on cars and trucks. Some motorcycle tires still have tubes, and the goo won't even seal a tube leak, much less keep it closed. Further, throwing a motorcycle's wheel balance out of whack is more dangerous on a motorcycle than a car.

Even sealant brands such as Fix-A-Flat warn against using their products on motorcycles.

Tire Sealant Requires Immediate Action

If you're too busy to deal with and fix a flat tire properly, you're definitely too busy to deal with a costly car repair.

When you fill a tire with goo, you're supposed to proceed directly to a tire repair professional. But sometimes it's Sunday, the shop is closed, and you can't get there until Monday evening because you still have to go to work. But then you have just one more errand to run, and then it's time for dinner.

SEE ALSO: How Often Should You Do Car Maintenance?

Whatever the reasoning, if the sealant sits for too long, it can harden and corrode your wheels. Maybe it'll freeze, or dry funny, and now your tire is severely out of balance. Maybe it takes out your TPMS sensor. Suddenly that cheap repair costs hundreds of dollars.

Good News! Tire Sealant Won't Explode Now

Manufacturers once used dimethyl ether for the gas in Fix-A-Flat, which is highly flammable. Road debris stuck in your tire could create sparks, potentially igniting that compressed gas. Luckily, this isn't the case anymore.

Any canned compressed gas is dangerous if you throw it into a fire. But manufacturers have generally switched to using HFC-134a in tire sealants, which is nonflammable. If you've got an ancient can of sealant lying around, dispose of it carefully. But if your tire sealant uses a nonflammable gas like HFC-134a, there's no need to worry about explosions.

You still shouldn't use it, though.

Readers, do you carry a can of tire sealant in your car? Or do you opt for a spare tire and/or roadside assistance? Let us know how you fix a flat tire in the comments below.

Contributing Writer

Sean is a freelance writer and photojournalist working in the Hampton Roads region. He has been a writer, adventure motorcyclist, drag racer, data nerd, shade-tree mechanic, and tornado chaser. Recommend good beers to him on Twitter at @wxgeek.
DealNews may be compensated by companies mentioned in this article. Please note that, although prices sometimes fluctuate or expire unexpectedly, all products and deals mentioned in this feature were available at the lowest total price we could find at the time of publication (unless otherwise specified).
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Cat Gynt
My 2017 Kia Forté 5 comes with a canister of a sealer and a 12vdc compressor. The user manual strongly recommends only using the brand of sealer provided by the manufacturer. I purchased a full sized spare and had it mounted on a comparable rim ~ $780.00 Within a week of purchasing this vehicle I removed spare and went through a dry run of removing and replacing a tire, augmented the tools with an extension pipe for the lug wrench and practiced tire r&r.
Try TireJect Tire Sealant. Its much easier to use than other brands
Are there any that you'd recommend @maydepot?
Instead of a Fix-a-Flat, I carry a Tire Repair Kit (~$5) along with pliers and air compressor as I can repair most flats on the road and its usually permanent while Fix-a-Flat is temporary and requires a trip to the tire shop. Learned how to do it watching how-to's on Youtube and have repaired about 5 flats (caused by nails) this way, saved about $50.
@boilers. That seems oddly specific. How would you rank your care levels of arguments from human doings, human-ish, humanoids, lizard people, and the closely related hypnotoads.

I would love to see airless tires become mainstream. Any idea how much they would need to cost to become available to consumers?
We have jugs of Slime at my parents farm, but only use it on the tractors, trailers, hitches... etc. Never in our personal vehicles.
I put fix a flat in all my family's cars. When the tire goes flat, it's the most convenient to get them on their way. I don't care about ANY other human being's argument against this practice.
There is a place for a product like Slime- I use it in my garden tractor's tires, my chipper's tires, and my generator's tires.
Damn... and to think I didn't want to be the first to post a comment
I agree with pmurray63 on the run flats. I have a 2015 Infiniti Q50 that had Bridgestone Potenza run flats. Just replaced all 4 tires at 21K miles due to tire wear. And let me clarify I drive 90% highway - not winding side roads.
No surprise I chose new tires that are not run flats. They ride is better, quieter and the tires were less than half the cost of the run-flat option. I have roadside assistance and road hazard as well as a can of fix-a-flat.
I have switched to an emergency kit which includes: tire patch kit, pliers, box cutter, and the air compressor that came with the slime kit. Youtube videos on how to do a patch without taking the wheels off. It's a 5 minute procedure.
I've never used it because I suspected it would cause balance problems. You story confirms my suspicions.
Sure if your 50 miles from nowhere and you have a flat and I have a can of fix o flat I'm going to use it. I don't care if tire guy gets mad.
Back in the 70's I used fix-a-flat and the tire shop told me that my rim rusted from the sealant and he couldn't reseal the tire bead to the rim. I had to pay to replace the rim. Never used that stuff again.
I drive a 2013 Chevy Volt and it doesn't come with a spare tire, but instead it comes with a nifty slime and air pump in one device the GM seems to be putting it in on their recent vehicles. So far, I've been to number of junk yard to search for a compatible spare donut to no avail...
Buy a tire road-hazard warranty and then carry this stuff around.

The guy at the shop would rather just give you a new tire under your road-hazard warranty than clean out the old repairable one.

Ask me how I know.

Yes, we carry a can. Car came with runflats and no spare. It is better than nothing.
"Run-flat tires exist."

Yes, but they're not as good at being tires:

- Reduced tread wear
- Blowouts are still possible
- Hard to tell if it is low on air
- Harsher ride
- Cost
- Less on-shelf availability
I've used it on motorcycles that had brand new tires, that had leaks at the rim bead and it worked great.
Many, many years ago I used this stuff for a flat just to tide me over to get me to the shop, and when I did get there the repair guy was highly annoyed that I had used it. As is stated in the article, the stuff makes quite a mess. That was the last time I ever used it.
I've long carried a tire inflator (a portable compressor) instead. Many leaks can be aired up sufficiently to get somewhere to get the tire fixed (especially in town), and if I encounter one that it can't handle, my car insurance includes road side assistance, including towing if necessary.

The current inflator I use is the Ryobi model that pops up from time to time on DN, and works with one of my tool batteries. Before that it was one built into a jump start pack, and before that a standalone model that plugged into my vehicle's 12 volt accessory port.