I have an old convertible that I drive mainly in mild, sunny weather. While those days can occur at almost any time of the year around here, there are still times when the car sits idle for weeks, or even months, at at time. Recently, when I hadn't driven it in a little while, I went to take it out for a little exercise and found the front tires were in visibly in need of air. When I re-inflated them, I found an even bigger problem—they were badly dry-rotted. The tread was great, but the sidewalls had significant cracks, where the rubber had dried out necessitating an unexpected expense to replace them.
With this incident in mind, and seeing plenty of cars out there rolling on seriously scary looking tires, I humbly offer the following guide to assessing the condition of your tires, centering on three basic factors: inflation, tread wear, and dry rot, in the hope that your road miles may be safer.
Inflation--The basic question here is whether you have enough air in your tires. Too little air and your tread will wear out prematurely and deliver poor fuel economy. Too much air, and you will have a harsh ride, poor handling, and risk a blowout. So, that begs the question of where the proverbial 'Goldilocks zone' is. Generally speaking, it's around 30-32 psi. You can verify that on a sticker inside the driver's door, on most vehicles, but also check the sidewalls of your tires to see what the maximum inflation is. Usually, it's around 35 psi. If your car does not have a built-in tire pressure monitoring (TPM) system, you need to invest in a good quality pressure gauge (don't worry, they're not expensive) and check your tires at least a couple of times a month. If you find yourself frequently putting air in your tires, you may want to get them checked for road hazards (nails, screws, etc.), damaged or defective valve stems, or rusted rims.
Tread Wear--Too little tread can result in too little traction, which is very dangerous, especially on wet pavement. To determine proper tread depth, you can do one of two things—check the wear bars or measure with a penny. Every tire has wear bars in the grooves. They run perpendicular to the tread grooves, and the tread should be higher than the wear bar. If it isn't, then it's time to start shopping for tires. An alternative method of measuring is to stick a penny in the tread groove, so that Abe Lincoln's head appears to be going in head first. You don't want to see the top of Abe's head. If you do, your tread is too thin. Be aware that you can't necessarily notice uneven tire wear if you are standing next to your vehicle. To check the front tires, you will need to turn the steering wheel so that the entire tread is facing out of the fender well. Turn it all the way to the left, check it, and then turn it all the way to the right to check the passenger side. You will probably need to get down on the ground behind the car to check wear on the rear tires.
Another thing you need to observe about tread wear is whether it is wearing evenly across the face of the tire. You can check it visually, but you can also use the penny method, described above. If, say, the outer tread is more heavily worn than the inner tread, or vice versa, this is a good indicator that your alignment is off. Do not put off getting your alignment adjusted. Left unaddressed, your tires will wear out very quickly.
Dry Rot--Addressed in the introduction, dry rot is a silent killer of tires, especially on cars that aren't driven much. The tread may look great, and even pass a state safety inspection, but the rubber itself will dry out over the course of several years, and cracks will begin to show. If you begin noticing these cracks, keep a close eye on your tires, as they will probably need replacing sooner, rather than later. An increase in the size and number of the cracks, especially if they run the entire circumference of the sidewall, as happened with the tires on my convertible, it's time to replace them, regardless of tread depth.
The hardening of the rubber also causes tires to lose traction, especially on wet pavement. This can happen before you see significant cracks in the sidewalls. For this reason, you should be aware of the age of your tires. All modern tires, manufactured since the year 2000, have a date code stamped on the sidewall. Look for the letters DOT (Department of Transportation), followed by a string of numbers. The last four numerals indicate the date of manufacture; for instance, a date code of 3317 would indicate the tire was manufactured the thirty-third week of 2017. If your tires are more than say, seven years old, keep a close eye on them for indications of dry rot, as it can set in and spread quickly on older tires.
A note on tire sealants. Many newer cars come from the factory with an air compressor and a built-in bottle of tire sealant, instead of a spare tire and a jack. My daily driver was one of these, and I immediately bought a spare and a jack, which I, thankfully, have never had to use. Whether you have a compressor with a tire sealant bottle, or you carry an aerosol can of sealant in your trunk, be aware that the compound, while great for an immediate repair, can soften the rubber of your tire, thus shortening its life. I have had more than one mechanic tell me not to use the stuff, and my personal experience bears this out. Also, my car's owner's manual stresses that it is, at best, a temporary solution, and suggests replacing the affected tire at the earliest opportunity.
If you follow the tips above, you will be safer on the road, while likely prolonging the life of your tires, which will save you money in the long run. That's a win all the way around.
Be safe out there!
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