Aerosol flat fixers should be used only as a last resort

DEAR CAR TALK:

We were on vacation and got a flat tire that was caused by a screw. A good Samaritan saw our dilemma and offered us a can of aerosol flat fixer and aired up our tire for us so that we could get to a repair shop.

Once at the shop, the mechanic told us that the tire could not be repaired because of the aerosol product that we had used. We had to buy a new tire and were wondering if a tire is really toast once you use this product, or if he just wanted to sell us a tire.

– Rita He’d rather sell you a tire than clean out your old tire, Rita. Products like Fix-a-flat can be helpful in emergencies if you have a small puncture -- like a screw in the tread.

They inject a gooey substance into the tire and then provide some air, from the can, to hopefully give you enough tire pressure to limp to a repair shop. But it’s a temporary solution. That gunk needs to be cleaned out of your tire if you want to repair it and keep using it. The goo gets distributed unevenly, and when it dries, it becomes impossible to balance the tire. It should be cleaned out within about 100 miles of using it.

Cleaning out that goop is a messy, unpleasant job. It’s the tire shop equivalent of changing a diaper after your kid’s been playing in a bouncy house for four hours. And that’s why your repair shop said “no thanks.”

Some shops will do it but will charge you extra for it. Others may just refuse.

Another disadvantage of Fix-a-flat, and its ilk, is that they often don’t work on larger punctures, larger than, say, 2-3 millimeters -- or a fat screw.

The best solution, of course, is a full-size spare tire. That allows you to keep driving indefinitely. But fewer cars provide full size spares these days.

The next best option is a mini-spare, which will let you drive 50 miles and does no further damage to your flat tire.

Next on my list is a tow truck. If you have a car club membership or roadside assistance, you can get towed to a repair shop and possibly have your old tire fixed.

If you’re stranded and none of those options are available to you,