Understanding Tyre Sizes: Complete Guide to Reading Tyre Numbers
When shopping for new tyres, one of the most important things to understand is tyre sizing. Those numbers on your tyre sidewall aren't random – they contain crucial information about your tyre's dimensions, capabilities, and compatibility with your vehicle.
What Do Tyre Size Numbers Mean?
Let's break down a common tyre size: 225/60R16 98H
Width: 225
- This is the tyre's width in millimetres from sidewall to sidewall
- 225mm equals approximately 8.9 inches
- Wider tyres generally provide better grip but may increase fuel consumption
Aspect Ratio: 60
- This represents the tyre's sidewall height as a percentage of the width
- 60 means the sidewall height is 60% of 225mm = 135mm
- Lower numbers mean shorter sidewalls (sportier, better handling)
- Higher numbers mean taller sidewalls (more comfortable ride)
Construction: R
- R stands for "Radial" construction
- Nearly all modern tyres are radial
- You might occasionally see "D" for diagonal or "B" for bias-belted (rare today)
Rim Diameter: 16
- This is the wheel diameter in inches that the tyre fits
- Must match your wheel/rim size exactly
- Common sizes: 15", 16", 17", 18", 19", 20"+
Load Index: 98
- Number indicating maximum weight capacity
- 98 = 750 kg (1,653 lbs) per tyre
- Higher numbers mean greater weight capacity
- Critical for safety – never use tyres with lower load index than specified
Speed Rating: H
- Letter indicating maximum safe speed
- H = 210 km/h (130 mph)
- Common ratings: T(190km/h), H(210km/h), V(240km/h), W(270km/h), Y(300km/h)
Additional Markings You Might See
DOT Code
Example: DOT XXXXXX3218
- Last four digits show production date
- 3218 = 32nd week of 2018
- Tyres older than 6 years should be inspected regularly
EU Tyre Label Information
Modern tyres include efficiency ratings:
- Fuel Efficiency: A (best) to G (worst)
- Wet Grip: A (best) to G (worst)
- Noise Level: In decibels with 1-3 sound wave symbols
Norwegian Winter Requirements
Look for these markings for winter driving in Norway:
- M+S (Mud and Snow)
- 3PMSF symbol (Three Peak Mountain Snow Flake)
- Studded tyre approval markings if using studded tyres
How to Find Your Correct Tyre Size
1. Check Your Current Tyres
Look at the sidewall of your existing tyres for the size marking.
2. Vehicle Owner's Manual
Your manual lists approved tyre sizes for your specific vehicle.
3. Driver's Side Door Jamb
Many vehicles have a sticker with tyre pressure and size information.
4. Vehicle Registration Documents
Norwegian vehicle registration often includes approved tyre sizes.
Can You Change Tyre Sizes?
Plus Sizing (Larger Wheels)
You can often use larger wheels with lower-profile tyres:
- 205/60R16 → 205/50R17 (maintains similar overall diameter)
- Benefits: Better handling, sportier appearance
- Drawbacks: Less comfort, higher cost, more road noise
Downsizing
Sometimes you can use smaller wheels:
- Common when switching to dedicated winter wheels
- Must maintain load and speed requirements
- Check with tyre professionals for compatibility
Common Tyre Size Mistakes to Avoid
1. Wrong Load Index
- Using tyres with insufficient load capacity is dangerous
- Can lead to tyre failure and accidents
2. Mismatched Sizes
- All four tyres should be the same size (unless specifically designed otherwise)
- Different sizes can damage drivetrain components
3. Ignoring Speed Rating
- Don't use tyres with lower speed rating than original equipment
- Higher speed ratings are usually acceptable
4. Mixing Tyre Types
- Don't mix summer and winter tyres
- Stick to same brand/model when possible for best performance
Norwegian-Specific Considerations
Winter Tyre Requirements
From November 1st to March 31st, Norwegian law requires:
- Winter tyres (M+S marking minimum)
- Studded tyres allowed October 15th - April 30th
- Minimum 3mm tread depth (5mm recommended)
Studded vs. Non-Studded
Studded Tyres:
- Better on ice
- Road fees in major cities
- More road noise
Friction Tyres (Non-studded):
- Better on wet/dry roads
- No road fees
- Quieter operation
When to Replace Tyres
Tread Depth
- Legal minimum: 1.6mm
- Replace summer tyres at 3mm
- Replace winter tyres at 4mm
Age
- Replace tyres older than 10 years regardless of appearance
- Consider replacement after 6 years for safety
Visible Damage
- Cracks in sidewall
- Bulges or bubbles
- Uneven wear patterns
Conclusion
Understanding tyre sizes is essential for safe driving and optimal vehicle performance. When in doubt, consult with our tyre experts at Kisolve – we're here to help you choose the perfect tyres for your Norwegian driving conditions.
Remember: proper tyre sizing isn't just about performance – it's about safety for you and your family on Norwegian roads.