Demystifying Your Tyre Sidewall – Decoding the Markings

Ever wonder what all those numbers, letters and symbols moulded into your tyres actually mean? Tyre sidewalls contain a wealth of coded information once you know how to decipher it. Learn to read key data like size, load index, speed rating and date of manufacture.

Locating the Tyre Size Markings

The tyre size tells width, height, rim diameter and often the overall diameter. It is generally the first number-letter sequence stamped on the sidewall.

For example, a P215/65R15 97V tyre breaks down as:

  • P - Passenger vehicle tyre (not all tyres specify)
  • 215 - Section width in millimeters
  • 65 - Aspect ratio - section height as percentage of width
  • R - Radial construction
  • 15 - Rim diameter in inches
  • 97V - Load index 97 and speed rating V (covered next)

So in plain English, it's a 215mm wide tyre with a sidewall height 65% of the width, made for a 15 inch wheel.

Knowing the full size helps select the right replacement tyres for your vehicle.

Decoding the Load Index Ratings

Load index indicates maximum weight carrying capacity at the specified inflation pressure. Higher numbers denote heavier load ability.

Common passenger tyre load indexes:

  • 95 = 690 kg
  • 98 = 730 kg
  • 99 = 775 kg
  • 100 = 800 kg
  • 101 = 825 kg

Compare to your vehicle's weight and intended use to pick tyres with adequate load ratings. This ensures durability and proper load handling.

Understanding Tyre Speed Ratings

The speed rating designates the maximum safe speed that the tyre can handle under load. Speed ratings go up to Y which allows speeds over 300km/h!

Most common speed ratings:

  • Q = 160 km/h
  • R = 170 km/h
  • S = 180 km/h
  • T = 190 km/h
  • U = 200 km/h
  • H = 210 km/h

Choose tyres with speed ratings that match or exceed your vehicle's capabilities for safety, especially at highway speeds.

Locating the Tyre Date Code

Check the DOT date code on the sidewall, which identifies the tyre's age. It will be a 4 digit number representing the week and year of manufacture.

For example, a date code of 2218 means the tyre was produced in the 22nd week of 2018.

Tracking date codes allows replacing tyres before they exceed safe age limits - generally around 5-10 years.

Other Key Sidewall Markings

Here are some other useful identifiers on tyre sidewalls:

  • Brand, model and size details
  • Country of manufacture
  • Treadwear, traction and temperature grades
  • Safety certifications like DOT
  • Tire identification number (TIN)
  • Recommended rim widths
  • Maximum cold inflation pressures

Learning to interpret the wealth of data molded into tyre sidewalls empowers drivers to understand sizing, capabilities, age and more at a glance. Become a sidewall code cracker and make informed decisions about your tyres.

About the Author

Brett is Darra Founder Kevin's son. He grew up over the past 30 years of owning Darra and before that his whole life of Kevin being around trucks, transport and everything mechanical. So whilst he is not one to pick up the tools, its certainly been a big part of his life since Kevin's 'right-of-passage' was to get him to strip an old Holden straight-six 202 engine and put it back together. These days his time is spent with his 4 kids between UK, Singapore and Australia where he has a variety of businesses.