How to calculate wheel load rating

By Julia Freeman

Every tyre has a tyre load rating, or load index, printed on its sidewall. This is a code that specifies the maximum weight a tyre can safely carry under a range of standard conditions. These conditions include its inflation pressure and the speed at which the vehicle might travel.

Wheel Load Rating

Because it is affected by a wide variety of factors, the precise weight a tyre will support before failing is not an easy thing to calculate and it is not something you usually want to work out for yourself. In most cases, stick with the tyre specifications and inflation pressures advised in your owner's manual.

Tyre load rating

Although a tyre load rating can be translated into an actual weight-bearing capacity, the maximum dynamic load it experiences depends on its location on the vehicle, manoeuvring forces, inflation and even weather conditions. As a guide, however, a Load Index of 100 means the tyre is rated for 800kg, which is equivalent to more than 17 hundredweight sacks (if you can remember what they look like!). This figure includes the weight of the vehicle, passengers, fuel and cargo.
 
Even if you know the exact weight of your vehicle (the GVWR plus load) you can’t just divide by four to work out the load on each wheel. The weight is distributed differently between the axles. It is not unusual for the rear load to be double the front. Most manufacturers publish the weight distribution, somewhere – but probably not in your manual.

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Finding the tyre load rating

For example, if the code on your sidewall is 215/65R16 98T, the load index is 98 and the speed rating is T. The T means the tyre is safe on a vehicle capable of travelling up to 118mph and the 98 suggests it can carry 750kg. However, as explained above, the real calculation is complex and so manufacturers assign the ratings to keep you safe under a variety of road conditions. Those calculations also assume you drive sensibly, follow the inflation guidelines, and don’t try towing a concrete mixer with your Vauxhall Astra.
 
The Load Index only translates into a specific weight tolerance for typical passenger vehicles. The same tyre fitted to a sports vehicle of the same weight would experience more strain when manoeuvring at speed, and on a van would experience additional forces because of the higher centre of gravity. For that reason, higher-rated tyres are recommended for sports and commercial vehicles. In our experience, they assume about 10% more load.

How do XL tyres carry more weight?

Load capacity is related to inflation pressure, so if you can inflate a tyre higher without it exploding you can safely increase the load. Extra-load tyres can be inflated to a higher pressure – typically 41psi instead of 35psi.
 
XL tyres are ideal if you only carry a heavy load occasionally, but a lot of motorists like the way they handle even for everyday driving.
 
The majority of premium tyre ranges now offer XL versions of their normal tyres, so there is a Pireli Cinturato P7 in an XL version and a Bridgestone Turanza T005 in XL. You can also fit an XL runflat like the Bridgestone Turanza T005 Runflat, or XL rated winter or all-seasons, like the Falken Euroall Season AS210 or Falken Eurowinter HS01.

Book with Protyre

If you are unsure about your load rating or which tyres to get, click the ‘Find My Protyre’ button below and speak with the team at your local Protyre centre. With their wealth of knowledge and years of experience, you can be certain you will receive high-quality advice from our friendly team. Or you can book a free tyre check at a time and date to suit you, where our tyre technicians will be able to carry out a range of safety checks on your tyres to help keep you safe on the road.

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About the author

Article Author Photo
By Julia Freeman
Julia is Head of Retail Marketing for Protyre and loves engaging with customers and the business as a whole to make sure Protyre is more than just a local garage.
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