Frequently Asked Questions About Tires

What do the numbers on my tire mean (e.g., 225/45R18)?

Each part of the tire size has a specific meaning:

• 225 = Width of the tire in millimeters (sidewall to sidewall)
• 45 = Aspect ratio - the sidewall height as a percentage of the width (45% of 225mm = 101.25mm)
• R = Radial construction (standard for modern tires)
• 18 = Diameter of the wheel in inches that the tire fits

What is aspect ratio and why does it matter?

The aspect ratio is the height of the tire's sidewall expressed as a percentage of its width. A lower aspect ratio (like 35 or 40) means a shorter, stiffer sidewall that provides better handling but a firmer ride. A higher aspect ratio (like 65 or 70) means more sidewall cushioning for a smoother ride but less precise handling. Most passenger cars have aspect ratios between 45 and 65.

What do the load index and speed rating mean (e.g., 95W)?

These numbers appear after the tire size and indicate:

• Load Index (95) = Maximum weight the tire can support. 95 = 690 kg per tire. Never go below your vehicle's required load index.
• Speed Rating (W) = Maximum safe speed. W = 270 km/h. Common ratings: T (190 km/h), H (210 km/h), V (240 km/h), W (270 km/h), Y (300 km/h).

Always match or exceed your vehicle manufacturer's specifications for both load index and speed rating.

How do I find my tire size?

You can find your tire size in several places:

• Tire sidewall - Look for numbers like "225/45R18" printed on the side of your current tires
• Door jamb sticker - Usually on the driver's door frame, shows original equipment sizes
• Owner's manual - Lists all approved tire sizes for your vehicle
• Fuel filler door - Some vehicles display tire information here

How do larger tires affect my speedometer?

Larger diameter tires travel further per revolution, so your speedometer will read lower than your actual speed. For example, with tires 3% larger in diameter, when your speedometer shows 100 km/h, you're actually traveling at approximately 103 km/h. This means:

• You may unknowingly exceed speed limits
• Your odometer will record fewer kilometers than actually driven
• Service intervals based on mileage will be inaccurate

Use our tire calculator to see the exact speedometer error for any tire combination.

How do smaller tires affect my speedometer?

Smaller diameter tires travel less distance per revolution, so your speedometer will read higher than your actual speed. For example, with tires 3% smaller in diameter, when your speedometer shows 100 km/h, you're actually only traveling at approximately 97 km/h. This is generally safer for speed limits but means:

• Your odometer will record more kilometers than actually driven
• Service intervals will come sooner than necessary
• Fuel economy readings will appear worse than reality

Can I correct my speedometer after changing tire sizes?

Yes, there are several ways to correct speedometer error:

• Dealer recalibration - Some vehicles can be reprogrammed through the OBD port
• Speedometer calibrator - Electronic devices that correct the signal before it reaches the speedometer
• Different gear ratio - Changing differential gears can compensate (usually only practical for off-road vehicles)
• GPS speedometer app - Use a phone GPS app to see actual speed (for reference only)

How much speedometer error is acceptable?

Most automotive experts recommend keeping overall tire diameter within 3% of the original to minimize speedometer error and avoid drivability issues. A 3% difference means:

• At 100 km/h indicated, actual speed would be 97-103 km/h
• Over 100,000 km, odometer would be off by 3,000 km

Larger differences may also affect ABS, traction control, and other vehicle systems that rely on wheel speed sensors.

What is plus-sizing?

Plus-sizing is the practice of installing larger diameter wheels with lower profile tires while maintaining approximately the same overall tire diameter. For example, going from 205/55R16 (stock) to 225/45R17 (Plus 1) or 235/40R18 (Plus 2). The goal is to improve handling and aesthetics while keeping the speedometer accurate.

What are the benefits of plus-sizing?

• Better handling - Lower profile tires have stiffer sidewalls, providing more precise steering response
• Improved braking - Wider contact patch can improve braking on dry surfaces
• Better aesthetics - Larger wheels fill the wheel wells better for a sportier look
• High-speed stability - Less tire flex means more stable handling at speed

What are the downsides of plus-sizing?

• Harsher ride - Less sidewall means less cushioning from road imperfections
• Higher cost - Larger wheels and low-profile tires are more expensive
• Increased damage risk - Less rubber protecting the wheel from potholes and curbs
• Reduced fuel economy - Wider tires generally have more rolling resistance
• More road noise - Wider tires can be noisier on certain road surfaces

How many sizes can I plus-size?

Most vehicles can safely accommodate Plus 1 or Plus 2 sizing without modifications. Going beyond Plus 2 often requires modifications like fender rolling, suspension changes, or different offset wheels. Always check:

• Your vehicle manufacturer's approved tire sizes
• That there's adequate clearance for the wider tires
• That the load index remains adequate
• That the overall diameter stays within 3% of original

When should I replace my tires?

Replace your tires when:

• Tread depth reaches 3mm for summer tires or 4mm for winter tires (legal minimum is 1.6mm in most countries)
• Age - Inspect carefully after 6 years, replace after 10 years regardless of appearance
• Visible damage - Bulges, cracks, cuts, or exposed cords
• Performance issues - Vibrations, pulling, excessive noise, or reduced grip

Can I replace just one or two tires?

While replacing all four tires at once is ideal, you can replace two tires if necessary. However:

• Always replace in pairs - Never replace just one tire (except for a spare)
• Put new tires on the rear - This provides better stability, especially in wet conditions
• Match specifications - New tires should match the existing ones in size, type, and speed rating
• All-wheel drive caution - AWD vehicles often require all four tires to be the same diameter to avoid drivetrain damage

How do I check my tire's age?

Look for the DOT code on the tire sidewall. The last four digits indicate the week and year of manufacture:

• Example: DOT ... 2319 = manufactured in week 23 of 2019
• The DOT code may be on the inside of the tire - you might need to look on both sides
• Tires made before 2000 have a 3-digit code (no longer commonly found)

Can I use any size tire on my car?

No. You should only use tire sizes approved by your vehicle manufacturer. Using incorrect sizes can:

• Cause rubbing on suspension, fenders, or wheel wells
• Affect handling, braking, and stability
• Damage ABS, traction control, and other safety systems
• Void your vehicle warranty
• Create legal issues in some jurisdictions

Check your owner's manual or door jamb sticker for approved sizes, or use our calculator to compare options.

When should I switch to winter tires?

Switch to winter tires when temperatures consistently drop below 7°C (45°F), even if there's no snow. Below this temperature, summer tire rubber hardens and loses grip. Most experts recommend installing winter tires in late October or November (depending on your location) and switching back to summer tires in April or May.

Are all-season tires good enough for winter?

All-season tires are a compromise. They work adequately in mild winter conditions (light snow, temperatures just below freezing) but are not suitable for harsh winters. If you regularly experience:

• Heavy snowfall
• Ice on roads
• Temperatures below -7°C (20°F)

...you should use dedicated winter tires. They can stop up to 50% shorter on snow compared to all-season tires.

Can I use winter tires year-round?

Technically yes, but it's not recommended. Using winter tires in warm weather causes:

• Rapid tread wear - the soft compound wears much faster
• Longer braking distances on dry, warm pavement
• Reduced handling precision
• Higher fuel consumption due to increased rolling resistance

You'll end up spending more on tires and fuel while getting worse performance.

What do the snowflake and mountain symbols mean?

3PMSF (Three Peak Mountain Snowflake) - This symbol (❄️ inside a mountain outline) indicates the tire meets specific snow traction performance standards. Tires with this symbol have been tested and proven to provide traction in severe snow conditions. All dedicated winter tires have this symbol, and some all-season tires do too.

M+S (Mud and Snow) - This older marking indicates the tire has some capability in mud and snow, but it's a less rigorous standard than 3PMSF. Many all-season tires are M+S rated.

How often should I check tire pressure?

Check tire pressure at least once a month and before long trips. Tires naturally lose about 1 psi (0.07 bar) per month, and more during temperature changes. Check pressure when tires are "cold" - driven less than 1 mile or after sitting for 3+ hours. Use the pressure recommended on your door jamb sticker, not the maximum pressure printed on the tire.

How often should I rotate my tires?

Rotate tires every 10,000-12,000 km (6,000-7,500 miles), or as recommended in your owner's manual. Regular rotation ensures even wear across all tires and extends their life. A good time to rotate is during oil changes. Follow the rotation pattern appropriate for your vehicle type (front-wheel drive, rear-wheel drive, or all-wheel drive).

How do I know if my tires need alignment?

Signs your vehicle needs a wheel alignment:

• Vehicle pulls to one side
• Steering wheel is off-center when driving straight
• Uneven or rapid tire wear
• Steering wheel vibrates
• After hitting a large pothole or curb

Have your alignment checked annually or after any suspension work.

What causes uneven tire wear?

Common causes include:

• Center wear - Over-inflation
• Edge wear (both sides) - Under-inflation
• One-sided wear - Alignment issues (camber or toe)
• Cupping/scalloping - Worn suspension components or unbalanced tires
• Diagonal wear - Lack of rotation