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I've been looking for a type of tire sealant like Tireject/Slime that will prevent flats, not the emergency repair kind. Both of these companies sell the preventative goop, but they specifically state that they are only to be used on offroad vehicles like ATVs and farm equipment, not street cars.

With the given that any damage that happens at highway speeds probably can't be helped by goop, and still following the normal usage and replacement instructions, is there any reason the preventative products wouldn't work for normal driving purposes?

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    Even if your tire was still intact, having a big weight of sealant inside it (apparently Slime needs up to 32 ounces per tire - compare that with the size of a typical wheel balance weight) could screw up the wheel balancing to the extent of making the vehicle uncontrollable at normal road speeds. And an uncontrollable vehicle tends to kill other people as well as the fool trying to drive it. – alephzero Jul 13 at 22:57
  • The centripetal forces that stress a tire at 80 mph are massively higher than at 15 mph. – whiskeychief Jul 14 at 11:34
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For the product to provide long-term preventive sealing, it needs to remain in a fluid state. Driving a car on the highway with a tire full of liquid is dangerous.

Fix-a-flat style repairs are intended for emergency use only, just to get the car to a place where a real repair can be done, and usually are intended to solidify, not stay liquid. You're supposed to drive to a shop and get a plug or patch right away.

Other possible reasons for the difference:

The off-road sealant may have ingredients which could cause deterioration of the tire over the long term, something that might be acceptable for an off-road vehicle but not on the highway.

It could be a legal restriction, such as a chemical which is legal for off-road use, but not on highways, or some sort of tax or fee being included in the price of the on-road product, just as off-road diesel is cheaper due to not including taxes.

Most modern cars have some form of TPMS, and companies advertise their on-road products as TPMS-safe. I doubt the off-road goop has that assurance. Aside from TPMS, using a product not intended for highway use could void the warranty on your tires, or even affect the warranty on the car itself.

The whole idea of tire sealants for automotive use is that you use them as a temporary repair in an urgent situation just until you can get a proper plug or patch done.

The manufacturer also has to be careful of liability. If they don't state that the product is for off-road use only, and something bad happens on the highway as a result of their product, they're in trouble. At least this way they have the defense that the customer used the product incorrectly.

I strongly recommend you avoid using a preventive sealer for a street automobile.

The sealer either works or it doesn't.

If it works, you could get a hole and not even know it. Now you're driving on a tire that needs a repair, but you don't realize it. Your tire could be structurally unsound without you even realizing it, because it never leaks.

If it doesn't work, then you've still got a leak, but now you also have a mess, and the tire shop will be annoyed when they remove the tire and get that goop everywhere.

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  • Interestingly, Michelin is now (2020) introducing this technology into wide production but you can count on them having done plenty of engineering and testing to validate it as being safe for on-road vehicles. 1 2 – whiskeychief Jul 14 at 11:32
  • @whiskeychief, lining a tire with a sealant isn't a new concept, but Michelin's got a new twist. Most self-sealing is done by using liquids which flow into the holes, or soft substances that sqeeze together. Michelin is using new polyers which actually have the ability to form new bonds between surfaces. Basically, you cut it and it reconnects to itself, actually healing the cut, not just closing it up. Since it's built into the tire and is not a liquid, balance isn't an issue, and it's going to be very thoroughly tested before being accepted for street use. It's a far cry from Fix-A-Flat. – barbecue Jul 14 at 17:51
  • Correct correction! It is not “this” technology as I had said, you’re absolutely right. – whiskeychief Jul 14 at 20:07

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