Tires are the only part of your car that touches the road, and a mistake can be costly or dangerous. This guide shows how to read a tire's size, check how old it is, decide when to replace it and choose where to buy.
Key takeaways
- The size, load index and speed rating are printed on the sidewall: match your car's recommended size.
- The last four digits of the DOT code show the week and year the tire was made.
- Tires age even when they are not used, and you cannot tell by looking, so check the date code.
- Replace tires that are worn, damaged or too old, and replace them in sets or at least in pairs.
In this guide
How do I read the size on the sidewall?
A tire size looks like 225/45R17 94V. In that example: 225 is the width in millimetres, 45 is the height of the sidewall as a percentage of the width, R means radial construction, 17 is the wheel diameter in inches, 94 is the load index and V is the speed rating. Your car's recommended size is on a sticker in the driver's door jamb and in the owner's manual. Use that size unless a professional advises a change, and check that the load index and speed rating are at least as high as the original.
How do I find out how old a tire is?
Look for the DOT code on the sidewall. The last four digits are the production date: the first two are the week and the last two are the year. For example, 0308 means the tire was made in the third week of 2008. A tire sold as new can still have been made some years ago, so check the date before you buy, and ask for tires made recently.
NHTSA's tire buyers' guide recommends checking this date when you buy tires.
When should I replace tires because of age?
Rubber hardens and cracks as it ages, even on a spare or a car that is barely used, and you cannot see this by looking. NHTSA notes that some vehicle and tire manufacturers recommend replacing tires that are six to 10 years old, regardless of tread wear, and some tire makers set a stricter limit. Check your owner's manual and the tire maker's advice, and replace older tires, especially if you see cracks in the sidewall or tread.
How do I check the tread?
Healthy tread grips in the wet and resists aquaplaning. Check the depth with a tread gauge, or look at the wear bars that sit across the grooves: when the tread is level with them, the tire is worn out. Also look for uneven wear (a sign of alignment or pressure problems), bulges, cuts and nails. Check the pressure monthly, when the tires are cold, using the figure on the door-jamb sticker, not the maximum printed on the tire.
Should I replace all four tires?
Ideally yes, or at least in axle pairs, with the best tires on the rear axle for stability. Mixing very different tires can change how the car handles. On all-wheel-drive cars, differences in tire circumference can strain the drivetrain, so follow the manufacturer's advice and ask a professional.
New, used or part-worn: what is safe?
New tires from a reputable seller carry a warranty and a known age. Used tires are a gamble: you cannot know how they were used or repaired. If you buy used, check the date code, inspect the inside and outside for repairs, and avoid tires with sidewall damage or old age. Never fit a tire that has been repaired on the sidewall.
Where can I buy and fit tires?
Browse tire and wheel suppliers in the Tires and Rims category on Motor Mania Club, and ask for the date code, the price fitted and the warranty before you order. For fitting, balancing and alignment, see garages in the Service Garage category, and use our guide on finding a reliable mechanic.
Sources and further reading
This guide gives general information and is not legal, financial or mechanical advice. Rules differ by state, so check your state agency for the exact requirements.
About the author
Elie Haddad, Founder, Smart Net 360 and Motor Mania Club. Elie Haddad is the founder of Smart Net 360 and of Motor Mania Club, the US automotive marketplace and directory that connects dealers, parts suppliers, garages and car enthusiasts. 15 years in business management and a car enthusiast.
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