Tyres have come a long way since the beginning of motoring – and we’re not talking miles or kilometres. Today’s tyres are very complex components that are multi-layered and in some cases have different rubber compounds across their carcass. Believe it or not, tyres are one of the most important features for car safety and fuel economy, so understanding them will help you save money and be safer when travelling.
With that in mind, I thought it would be good to explain the markings and what the ratings are for a particular tyre because you don’t want to mix tyre ratings on a vehicle and you certainly don’t want the wrong capacity as you could have a very severe accident.
You will see a code system moulded into the sidewall that tells you their technical capabilities. This code provides information on the tyre’s construction (e.g. radial), its size, its load-carrying capacity and its speed rating.
For example, the code on mid sized cars could be 205/65R16 95V. The 205 indicates the width in mm and the 65 is the aspect ratio (the comparison of the height to the width). R stands for Radial – there used to be cross-ply tyres but they are not common anymore. The 16 in our example is the size of the wheel in inches and finally the 95V is the load weighting and speed rating, which we’ll talk about later. Note that this size code mixes mm with inches – odd, but could be a by-product of several committees designing the codes!
Load Ratings
Now for the load rating. The load rating number for a passenger car is typically between 81 and 96. At the low end, 81 means that the tyre can withstand 462kg per tyre and up at 96 the tyre is rated to withstand 710kg per tyre. It is important that you don’t have a low weight rated tyre on a heavy car. For most cars there will be recommended tyres and often you will only see the load rating on special tyres such as the skinny emergency use wheels now common in cars.
Speed Ratings
Finally we have the speed rating. This is also confusing as it uses the alphabet and starts at “N” and finishes at “Z”. But Z is not the fastest rating – “Y” is!
N equals 140km/h (87.5 mph) and this continues logically with each sequential letter representing another 10km/h increase until U, which equals 200km/h (125mph). Then come “H” at 210km/h followed by V and Z both at 240km/h.
As tyre technology developed and manufacturers started supplying road tyres for ever faster cars, they needed some new ratings but they had already got to Z, so W was used to represent 270km/h and Y to represent 300km/h (187 mph).
It is doubtful that you will see any new ratings developed as Governments and Police Forces are desperate to make everyone drive at the speed of walking – although if this trend continues we could see ratings of G and less as manufacturers won’t need so much technology to develop a tyre rated up to 40km/h – that’s just 25 mph!
Reblogged this on AutoKnol.