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.
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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?
Short answer A size such as 225/45R17 94V means 225 mm width, a sidewall height of 45% of the width, radial construction, a 17-inch wheel, load index 94 and speed rating V. Use the size on the driver's door jamb sticker, with a load index and speed rating at least as high as the original.
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?
Short answer Find the DOT code on the sidewall. Its last four digits are the production date: the first two are the week and the last two the year, so 0308 means the third week of 2008. A tire sold as new can be several years old, so check the date before buying.
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?
Short answer Rubber hardens and cracks with age even when unused, and you cannot see it. NHTSA notes that some vehicle and tire makers recommend replacing tires six to 10 years old regardless of tread, and some set stricter limits. Check your manual and replace older tires, especially if cracked.
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?
Short answer Check the depth with a tread gauge or the wear bars across the grooves, and look for uneven wear, bulges, cuts and nails. Check the pressure monthly with cold tires, using the figure on the door-jamb sticker rather than the maximum printed on the tire.
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?
Short answer Ideally yes, or at least in axle pairs with the best tires on the rear axle. Mixing very different tires can change handling, and on all-wheel-drive cars differences in tire circumference can strain the drivetrain, so follow the manufacturer's advice.
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?
Short answer New tires from a reputable seller have a warranty and a known age. Used tires are a gamble: check the date code, inspect inside and out for repairs, avoid sidewall damage or old age, and never fit a tire that has been repaired on the sidewall.
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?
Short answer Browse tire and rim suppliers in the Tires and Rims category on Motor Mania Club and ask for the date code, the fitted price and the warranty. For fitting, balancing and alignment, use garages in the Service Garage category.
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
How this guide was prepared
This guide is written from official and industry sources, which are listed above, and checked against how Motor Mania Club works. We aim to review our guides every few months and change the date when something is updated.
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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