In 2022, over 342 million passenger tires were shipped in the United States, according to the U.S. Tire Manufacturers Association. Given that Americans drive over three trillion miles every year, according to the Department of Transportation, those millions of tires are needed to replace worn, damaged, aged or dry-rotted tires. When considering tire replacement for your vehicle, whether they’re winter tires that have been in storage or tires you got from a friend, it’s important to know how to tell if tires are dry rotted. If a tire dry rots, tire components, such as the tread, sidewalls, belts or bead wire, may separate from each other. Tread separation or sidewall blowout at highway speeds could result in a crash. Here’s how to determine if your tires are safe to drive on.
What Causes Dry Rot On Tires?
Tires age as soon as they’re manufactured, ideally lasting up to 10 years, but shipping, handling and exposure accelerate aging and dry rot, shortening their life. Dry rot itself is a condition that affects the material that the tire itself is made of, so it isn’t a foreign substance that can be removed like mold. Obviously age is a major factor for dry rot in tires and cannot be mitigated, but exposure to ultraviolet (UV) light can also dry rot tires. Sunlight (especially if you live in a place with warm weather) is a common cause of tire sidewall dry rot damage. If you ever drive by an RV camp ground you will notice many vehicles with special covers over the tires to help reduce UV tire damage.
While not a direct cause of dry rot on tire materials, a lack of tire maintenance can speed up tire failure. Driving on underinflated tires causes more wear on the tire tread and more flex in the tire side wall. This leads to heat that damages the tire and may speed up tire failure. Hauling too much weight can also damage a tire, so pay attention to tire load ratings. Pushing tires over their limits combined with dry rot will greatly shorten tire life.
A close look at your tires will help you determine whether they’re safe for service or ready for recycling. Cracks on the surface of the rubber, whether on the tread, shoulder or sidewall areas, are a good sign your tires are ready for recycling. These surface cracks are an indication that your tires have deeper cracks you can’t see, such as where the tread or sidewalls bond to the belts. The top layer of rubber will likely be hard but brittle. If any pieces of the tire crumble or fall off it is a sure sign that dry rot has set it and the tire must be removed from service immediately. Color can also be affected by dry rot so if the tire looks more grey than black it may be dry rotted.
Another factor is the DOT code, an alphanumeric string that’s usually eight or twelve digits long, molded into the tire sidewall. A valid DOT (Department of Transportation) code means the tire meets DOT safety standards. The DOT code or tire identification number (TIN) looks something like this: DOT PCTS PWPY or DOT PCTS OMFR PWPY. Here’s what each section of the code means:
- PC: Plant code, identifying which company made the tire.
- TS: Tire size, such as 245/50R16.
- OMFR: Optional manufacturer code.
- PW: Production week (the week of the year the tire was made).
- PY: Production year (the two-digit year the tire was produced).
For example, if the DOT code reads DOT U2LL 5117, the tire was made by Sumitomo Rubber Industries, Japan (U2), size 245/50R16 (LL), in the 51st week (51) of the year 2017 (17). Those last four digits are the most important piece of information. Even if you bought a set of tires brand new, they may have sat in a warehouse for months or longer. Most manufacturers don’t recommend using tires that are over six years old, so these tires should be discarded after 2023, even if you can’t see any cracks. Just because a tire looks fine, the age of the tire has the final say as to whether it is still safe to use. Cars that are rarely driven (like collectible cars) can have tires that look perfect thanks to routine cleaning and treatment, but are not safe to drive with on the streets.
How to Tell If Tires Have Tread Wear
Tread wear is another reason to replace your tires. You might have heard that you can use a coin to gauge tread depth, but nothing beats a compact and easy-to-use tire tread depth gauge. Measure all the main grooves across the tread, but not on the tread wear indicators, which are 2/32″ shallower. If any measurement is below 4/32″, wet braking and snow traction are significantly impaired. At 2/32″ tread depth, wet braking distance can be nearly double that of a new tire.
Inspect tires at least monthly for pressure, age, tread wear and dry rot. Consult your local, trusted mechanic at your next oil change or during seasonal maintenance for a professional recommendation. Lastly there is no way to fix tire dry rot. Once the tire starts to deteriorate there are no magic sprays or treatments that can bring it back. The only solution for a tire that is affected by dry rot is replacement.
Check out all the tire and wheel products available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on dry-rotted tires and maintaining your car tires, chat with a knowledgeable expert at your local NAPA Auto Parts store.
Photo courtesy of Flickr.
Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.