Tire Size Chart: How to Read Tire Sizes & Choose the Right One for Your Vehicle

Choosing the correct tire size is more important than many drivers realize. The wrong tire size can affect your vehicle’s safety, handling, fuel efficiency, and even speedometer accuracy. This is where a tire size chart becomes essential.

Whether you drive a car, SUV, or truck, this guide will help you understand tire size numbers, use a tire size chart correctly, and confidently choose the right replacement tires for your vehicle.

What Is a Tire Size Chart?

A tire size chart is a reference table that explains tire size measurements and helps drivers identify compatible tire options for their vehicle. It breaks down tire dimensions such as width, aspect ratio, wheel diameter, load index, and speed rating.

Tire size charts are commonly used by:

• Vehicle owners replacing worn tires
• Online tire shoppers verifying fitment
• Mechanics and tire professionals
• SUV and truck owners comparing alternate sizes

Using a tire size chart ensures your new tires match your vehicle’s design and safety requirements.

Why tire size matters

Tire size affects safety, handling, braking, speedometer accuracy, fuel economy and clearance. Choosing the correct tire size (or a safe alternative approved for your vehicle) keeps systems like ABS, traction control and the odometer functioning as designed.

Authoritative manufacturers and regulators recommend following the OEM size or approved alternatives in the owner’s manual or tire placard.

Where to find your tire size (step-by-step)

Finding your tire size is easy — here are the four fastest places to look and exactly what to do.

Check the tire sidewall (best place)

• Look at the side (wall) of any tire on your car.
  
• You’ll see a series like 225/65R17 or P215/60R16. That whole string is your tire size.
  
• Tip: take a clear photo with your phone so you don’t have to copy it by hand.

Owner’s manual (official and reliable)

• Open your vehicle’s owner’s manual and look for a section called “Tires,” “Specifications,” or “Tire Size.”
  
• The manual lists the factory (OEM) tire sizes and recommended air pressure.
  
• If you can’t find the physical book, most manufacturers have PDF manuals online — search for “[your car model] owner’s manual.”

Driver-side door jamb sticker (quick reference)

• Open the driver’s door and look on the door frame (the part the door closes onto).
  
• There’s usually a sticker titled “Tire and Loading” or similar. It shows the recommended tire size and the correct tire pressure for front and rear.
  
• This sticker is great because it tells you the exact size your car came with from the factory.

Online vehicle fitment tools (fast check)

• Many tire retailers and brand websites let you enter your vehicle’s year, make, and model to see recommended tire sizes.
  
• These tools are handy for shopping, but always double-check the actual sidewall or door sticker before buying.

How to read tire size numbers (step-by-step)

Use this example: P225/65R17 102H. Each part tells you something important about the tire.

Tire type — the first letter (P, LT, ST)

• P = Passenger tire (cars, most crossovers).
  
• LT = Light Truck tire (pickups, heavy-duty SUVs, towing). Built stronger for heavier loads.
  
• ST = Special Trailer tire (trailers only — not for cars or trucks).

Tip: Use the tire type that matches your vehicle. Don’t put LT or ST tires on a passenger car unless a professional says it’s appropriate.

Tire width — the first number (225)

• This is the width in millimeters from one sidewall to the other (so 225 mm wide).
  
• How width affects your car:
  
  • Wider tires = more grip (better traction), especially in turns.
    
  • Wider tires = sometimes heavier and can lower fuel economy a little.
    
  • Wider tires can change handling — more responsive, but sometimes harsher ride.

Tip: Match or stay close to the OEM width unless you know why you’re changing it.

Aspect ratio — the second number (65)

• This is the sidewall height as a percent of the width. For 65, the sidewall height = 65% of 225 mm.
  
  • Calculation: 225 × 0.65 = 146.25 mm (that’s the sidewall height).
    
• What it means: A lower number (like 40) makes a shorter sidewall — better cornering, firmer ride. A higher number (like 70) makes a taller sidewall — smoother ride, more cushion.

Tip: Taller sidewalls = more comfort; shorter sidewalls = sportier feel. Don’t change too much or you could affect speedometer reading and clearance.

Construction type — the letter (R)

• R = Radial construction (the most common today).
  
• Bias-ply tires exist but are mostly for certain trailers or older vehicles.

Why radial tires are standard: Radials give a smoother ride, better grip, and last longer for most cars.

Wheel diameter — the number after the R (17)

• This is the wheel (rim) size in inches that the tire fits — here, 17 inches.
  
• Match the tire to the wheel exactly. A 17-inch tire won’t fit a 16- or 18-inch wheel.

What happens if you mismatch: The tire won’t mount correctly, or it could rub, fail, or be unsafe.

Tip: If you want bigger wheels, you must choose tires made specifically for that wheel size.

Load index — the number after the size (102)

• The load index is a code that tells how much weight one tire can safely carry.
  
  • Example: load index 102 is about 1,874 lbs per tire (check a load index chart for exact values).
    
• Why it matters: SUVs, trucks, and vehicles that tow or carry heavy loads need a higher load index. Using a tire with a lower load index than OEM can be dangerous.

Tip: Always choose tires with the same or higher load index than the factory recommendation.

Speed rating — the final letter (H)

• The last letter (like H) is the speed rating, which indicates the maximum safe speed the tire can handle (H ≈ 130 mph).
  
• You don’t need a tire rated for race speeds — just match or exceed the manufacturer’s rating.

Tip: Match or exceed the OEM speed rating for safety.

Practical tire size chart (Common sizes)

Passenger Car Tire Size Chart

Use this table to identify common tire sizes for sedans and compact cars and match your current tire size when replacing or upgrading tires.

Best for: daily driving, fuel efficiency, comfort-focused vehicles.

SUV & Crossover Tire Size Chart

Refer to this chart to find popular SUV and crossover tire sizes and ensure the width, aspect ratio, and wheel diameter match your vehicle’s requirements.

Key note: Always verify load index when choosing SUV tires.

Light Truck (LT) Tire Size Chart

Use this table to compare light truck tire sizes designed for towing, hauling, and off-road use, and confirm the tire type (LT) and wheel size compatibility.

Important: LT tires have stronger construction and higher load ratings.

Metric ↔ Flotation (Inch) Comparison (Examples)

Flotation sizes (e.g., 31×10.5R15) are expressed as overall diameter × section width × rim. Below are practical approximations to help translate:

Note: these are approximations for fitment comparison — always check clearance, load index, and speed rating before substituting.

Quick calculator: How to compare two tire sizes (diameter & % change)

When comparing two sizes, we care most about overall diameter (affects speedometer and clearance).

Formula (digit-by-digit):

1. Sidewall height (mm) = section width × aspect ratio (as a decimal).
   
2. Wheel diameter (mm) = rim diameter in inches × 25.4 (mm per inch).
   
3. Overall diameter (mm) = 2 × sidewall height + wheel diameter.
   
4. Percent change = (new_diameter − old_diameter) / old_diameter × 100%.

Example (compare 225/65R17 → 235/65R17):

• For 225/65R17:
  
  • Width = 225 mm.
    
  • Sidewall = 225 × 0.65 = 146.25 mm.
    
  • Wheel = 17 in × 25.4 = 431.8 mm.
    
  • Overall diameter = 2 × 146.25 + 431.8 = 292.5 + 431.8 = 724.3 mm.
    
• For 235/65R17:
  
  • Width = 235 mm.
    
  • Sidewall = 235 × 0.65 = 152.75 mm.
    
  • Wheel = 431.8 mm (same rim).
    
  • Overall diameter = 2 × 152.75 + 431.8 = 305.5 + 431.8 = 737.3 mm.
    
• Difference = 737.3 − 724.3 = 13.0 mm.
  
• Percent change = (13.0 / 724.3) × 100% ≈ 1.8%.

Takeaway: A 1.8% increase is small and usually acceptable (within common tolerance rules). Always confirm with manufacturer or fitment tools before changing sizes.

The “3% rule” and safe limits

A common industry rule-of-thumb: keep the overall tire diameter within ±3% of the original equipment diameter to avoid problems with speedometer accuracy, clearance and vehicle electronics (ABS/traction control). 

Most tire sellers and fitment tools use that guideline when suggesting alternate sizes. If you exceed the 3% threshold you should get professional approval and possibly a re-calibration for the speedometer or further vehicle modifications.

Note: Manufacturers like Michelin recommend sticking to OEM or manufacturer-approved alternatives for maximum safety.

OEM vs alternate sizes — How to choose

When to stay OEM

• You carry heavy loads or tow frequently.
  
• Your vehicle has advanced driver assistance systems (ADAS) or AWD—mixing sizes can cause damage or incorrect system behavior.
  
• You want the vehicle to behave exactly as designed.

When an alternate size is acceptable

• If the alternate size keeps overall diameter within ±3% and maintains or exceeds the load index & speed rating.
  
• When all four tires are changed to the same alternate size (do not mix sizes on AWD unless the manufacturer permits).

Checklist before switching:

• Match or exceed load index.
  
• Don’t go below speed rating required by the manufacturer.
  
• Stay within ±3% diameter (rule-of-thumb).
  
• Check physical clearance (suspension, fenders, wheel wells).
  
• Confirm brakes and ABS compatibility (some systems are sensitive).

Common Tire Size Mistakes to Avoid

When choosing tires, it’s easy to make mistakes that can affect safety, handling, and performance. Here are the most common ones and how to avoid them:

1. Choosing width without checking load rating

• A wider tire might look better or give more grip, but it could carry less weight than your vehicle needs.
  
• Tip: Always check that the load index meets or exceeds your vehicle’s requirements.

2. Ignoring speed rating

• The speed rating shows the maximum safe speed for the tire.
  
• Using a tire with a lower rating than recommended can be unsafe, especially at highway speeds.
  
• Tip: Match or exceed the OEM speed rating.

3. Assuming “bigger is better”

• Bigger tires can look impressive, but they may rub fenders, throw off your speedometer, reduce fuel efficiency, or affect handling.
  
• Tip: Keep diameter changes within about 3% of the original size.

4. Mixing tire sizes on AWD vehicles

• All-wheel-drive (AWD) cars rely on tires of the same size to work properly.
  
• Different sizes can damage the drivetrain or cause handling issues.
  
• Tip: Always use the same tire size on all four wheels for AWD vehicles.

5. Trusting visual fit alone

• Just because a tire looks like it fits doesn’t mean it’s safe. It could rub suspension parts, reduce clearance, or overload the tire.
  
• Tip: Always check tire size numbers, load index, and speed rating, not just appearance.

How to Use a Tire Size Chart When Buying Tires Online

Buying tires online can be simple and safe if you follow these steps:

1. Confirm your OEM size

• Check your current tire sidewall, owner’s manual, or driver-side door sticker to find the factory-recommended size.
  
• This is your starting point — always know the exact numbers before searching online.

2. Match wheel diameter

• Make sure the tires you choose fit your wheel (rim) size exactly.
  
• Example: If your OEM tire is 225/65R17, the replacement must be for 17-inch wheels.

3. Check load & speed rating

• Load index = maximum weight each tire can safely carry.
  
• Speed rating = maximum safe speed.
  
• Always pick tires that meet or exceed the OEM ratings.

4. Compare approved alternate sizes

• Some slightly bigger or smaller sizes can work, but keep the overall diameter within ±3% of the original.
  
• Check the tire chart to see safe alternate options.

5. Tips to avoid fitment errors

• Double-check width, diameter, and ratings before adding to cart.
  
• Look at product photos and descriptions carefully.
  
• Avoid “just looks like it fits” — numbers matter more than appearance.

6. When to consult a tire professional

• If you want to significantly change tire size (bigger wheels or lower-profile tires).
  
• If your vehicle is AWD (all four tires must match).
  
• If you’re unsure about load index, speed rating, or clearance.

FAQs About Tire Size Charts

Can I put larger tires on my car?

Sometimes — if overall diameter stays within ~±3% and load/speed ratings meet or exceed OEM. Confirm clearance and ABS/ECU compatibility.

What does LT mean vs P?

LT = Light Truck (designed for heavier loads and tougher construction). P = Passenger metric (cars, SUVs). Don’t swap LT for P without checking load/inflation tables.

How do I convert metric to imperial?

1 inch = 25.4 mm. To get rim diameter in mm: multiply the rim inches by 25.4 (e.g., 17 × 25.4 = 431.8 mm). See the diameter formula above.

Does tire size affect gas mileage?

Yes — wider/heavier tires can increase rolling resistance and lower mpg; larger overall diameter can change gearing slightly, affecting fuel economy.

How often should I replace tires?

Replace when tread wear indicators are reached, when uneven wear or structural damage appears, or as recommended by manufacturer guidelines (inspect monthly).

Conclusion

A tire size chart is one of the most powerful tools for any vehicle owner. Understanding tire size numbers helps you avoid costly mistakes, improve safety, and make smarter buying decisions.

Always prioritize correct fitment, load rating, and manufacturer guidelines over appearance alone. When used properly, a tire size chart gives you complete confidence when replacing or upgrading your tires.