Understanding the Writing on Your Car Tyres
You have probably noticed some writing on the sidewall of your car tyres – a series of embossed numbers and letters that follow a strict pattern. But what do they mean?
Let’s take an example from a tyre:
175/80 R14 88H
It may look cryptic, and short, but that string of numbers and letters tells you what you need to know about the tyre.
- 175: This denotes the tyre width, specifically measured on the inflated tyre and excluding any raised areas on the sidewall. It’s easier to visualise once you know it’s measured in millimetres.
- 80: Okay, this one is a little more mathematical. This is the aspect ratio which is calculated as the height of the sidewall expressed as a percentage of the tyre width. Confused? Think of it this way – on our example tyre, the sidewall height is 80% of 175.
- R: This tells us the tyre has a radial construction. You can safely ignore this one, as almost all tyres are now radials.
- 14: We switch from metric to imperial now, as this measures the wheel rim diameter in inches. The wheel rim diameter simply tells you what size wheels your car tyres were made to fit.
- 88: This is the load index – a numerical code telling you the maximum load the tyre can carry at up to the maximum speed it can travel at. You would need to check a load index table to see that our example can carry 560 kg (yes, back to metric!)
- H: This final code letter tells us the speed rating – the maximum allowed speed the tyre is capable of enduring for ten minutes without running the risk of sustaining damage. This needs to at least match the maximum speed of your car.