Load index and speed code: the answers | Pneumatici SuperStore

Question 1

What is the load index and where do you find it?

Accepted Answer

The load index is the two- or three-digit number that follows the size: it indicates the maximum load a single tyre can carry at the specified pressure. It is found just before the speed letter, for example 91 in 205/55 R16 91V. It is not the weight in kg but a code standardised by ETRTO: for example 91 corresponds to 615 kg, 95 to 690 kg and 100 to 800 kg per tyre.

Question 2

How do I calculate the vehicle's maximum load from the load index?

Accepted Answer

Multiplying a single tyre's load by four gives only a theoretical reference: with index 91 (615 kg) that is 2,460 kg. The value to respect is the vehicle's maximum permitted mass given by the manufacturer, and the fitted index must not be lower than the specified one. The manufacturer also takes into account the weight distribution on each axle, not just the simple total.

Question 3

What is the conversion table between load index and kilograms?

Accepted Answer

For the most common values on cars, per single tyre: 80 = 450 kg, 85 = 515 kg, 88 = 560 kg, 91 = 615 kg, 94 = 670 kg, 95 = 690 kg, 98 = 750 kg, 100 = 800 kg, 105 = 925 kg, 110 = 1,060 kg. Each index point adds about 2.5-3% of load. The full table is internationally standardised and published in manufacturers' documentation.

Question 4

Can I fit a lower load index than the one on the registration document?

Accepted Answer

No: the load index must not be lower than the one specified by the vehicle manufacturer. A tyre with too low an index risks overheating, deformation and failure when the car is loaded. A higher index is instead possible, as Michelin confirms, sometimes with slightly firmer ride and a higher cost. Before buying, compare the manufacturer's indications with the tyre sidewall.

Question 5

What does the dual load index mean, such as 107/105T?

Accepted Answer

The dual index is typical of tyres for vans and light commercial vehicles (C): the first number (107) applies to single fitting, that is one wheel per side, the second (105) to twin fitting, that is two wheels side by side on the same side. On vans with single wheels the first value counts. The load to respect depends on how the vehicle is used.

Question 6

What are LT tyres and how are they read?

Accepted Answer

LT stands for Light Truck: it is a North American category for pick-ups and heavy SUVs, with a multi-ply casing. The marking may appear as a prefix (LT265/70 R17) and carries a load range (C, D, E) indicating strength. In Europe C tyres for vans are more common. To replace them you must respect the size, load and speed specified on the registration document.

Question 7

How do you read the load index on motorcycle tyres?

Accepted Answer

On motorcycles the number (for example 58 in 120/70 ZR17 58W) is the same load index as on cars, and it may differ between front and rear. The same table applies: 58 = 236 kg per tyre. The load must be enough for the motorcycle, rider, passenger and luggage and the size must be the one specified for the motorcycle. If the tyre is bias-ply, the size often shows a dash instead of R.

Question 8

What is a tyre's speed code?

Accepted Answer

It is the letter that follows the load index and indicates the maximum speed at which the tyre can carry its load, under standard test conditions. For example in the code 205/55 R16 91V the letter V corresponds to 240 km/h. It does not indicate the speed you are advised to keep nor does it replace speed limits: it is a construction characteristic.

Question 9

What are all the speed codes, from J to Y?

Accepted Answer

J = 100 km/h, K = 110, L = 120, M = 130, N = 140, P = 150, Q = 160, R = 170, S = 180, T = 190, U = 200, H = 210, V = 240, W = 270, Y = 300 km/h. The letter indicates the maximum speed at which the tyre can carry its maximum load. The Z in the size (ZR) is an old notation for speeds over 240 km/h; today what counts is the speed code in the service description.

Question 10

Can I fit tyres with a higher speed code than the one on the registration document?

Accepted Answer

Yes, Michelin confirms that tyres with a higher speed code than the one indicated can be fitted. The practical consequences may be a higher cost and, sometimes, slightly firmer behaviour. A higher code does not increase the car's maximum speed or the permitted one. A lower code, however, must be avoided, except for the exceptions provided for winter tyres.

Question 11

What happens if I exceed the tyre's maximum speed?

Accepted Answer

The speed code indicates the maximum speed at which the tyre can carry its maximum load. Beyond that value stress and heat in the structure increase, with a risk of damage, especially with low pressure or a high load. With under-inflated, overloaded or damaged tyres the real margin is smaller. The value is not a target to reach: speed limits always apply.