– What it means and why it is important

This past week I found myself in the market for a new set of tyres. I phoned all the usual fitment centres, asked for prices and compared specs. Besides for a tyre’s physical dimensions, which we are all familiar with, there is also a load index and speed rating. Most of the salesmen I spoke to paid no heed to this, while one salesman in particular tried upselling me  “V” rated tyres, for my SUV which I never push beyond 130 Km/h, saying that the “S” rated ones are wholly insufficient.

In this article, sourced from Tirebuyer.com  we will explain tyre speed rating and load index, seeing that these two specifications are not well understood.

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Tyre speed ratings are set by the tyre manufacturers and are an indication of the tyre’s maximum speed capability in ideal conditions. The tyre load index rating communicates how many pounds a tyre can safely carry. Put together, they make up the service description.

Knowing this service description information is highly recommended whenever you’re replacing Original Equipment (OE or factory) tyres. Even if you don’t plan on pushing limits in speed or load categories, matching or improving the speed rating and load index of your factory tyres will help keep your vehicle’s performance characteristics consistent.

How to find tyre speed rating

Most tyres are constructed to reflect the more common, practical speeds of everyday commuters with a quite significant safety buffer on the top end. Tyre speed rating is communicated with the final letter in the tyre service description, and each letter translates to a specific top speed in miles per hour.

Both speed rating and load index are part of a group of (three) digits at the tail end of the tyre size information. Together these figures make up the tyre’s service description.

If your vehicle is still equipped with its factory tyres, you can refer to the driver’s side doorjamb placard, which includes tyre information.

Service description on doorjamb

In the doorjamb image above (belonging to an Audi A3), the car’s tyre information is: 225/45R17 94H. In this example, 94H is the service description, with the 94 indicating load index, and the H indicating speed rating.

You can also find this information printed on the sidewall of all tyres.

Service description on tyre sidewall

How is tyre speed rating established?

Speed rating is established under controlled testing where – once again, under optimal conditions – the tyre is verified as capable of safely running at (up to) the indicated miles per hour. Heavily worn, damaged, punctured, or repaired tyres would all be considered sub-optimal, and no longer capable of safely accomplishing their max speed rating.

Speed Rating

Going back to our Audi, the H speed rating is equal to 130 miles per hour (210 Km/h), meaning that under optimal conditions, the tyre can perform at speeds up to 130 mph (210Km/h. The speed rating doesn’t imply the vehicle can drive that speed, but the tyres are capable of supporting the car at that speed.

What are the different speed ratings?

L

Most boat and utility trailer tyres have this speed rating which is a maximum of 75mph

M & N

An M indicates the tyre has been approved for speeds up to 87 mph (140 km/h) and an N is approved for speeds up to 81 mph (130 km/h) under optimal conditions. You’ll find M and N ratings on tyres for temporary use like spare tyres.

P

A P indicates the tyre has been approved for speeds up to 93 mph (150 km/h) under optimal conditions.

P tyres are uncommon these days. Even tyres with specialty function and performance such as winter tyres and off-road tyres typically achieve at least a Q speed rating.

Q

Q tyres are approved for speeds up to 99 mph (160 km/h) under optimal conditions. Tyres toward the low end of the speed rating range often prioritize a particular function or unique performance over maximum speed rating. Some studdable and studless winter tyres, for example, are Q speed rated.

R

Speed rating R allows for speeds up to 106 mph (170 km/h) under optimal conditions. Like Q, R tyres generally prioritize a particular function or unique performance over maximum speed capability. R speed tyres are rare but can be found on some heavy-duty light truck (LT) tyres, as well as studdable and studless winter tyres.

S

An S speed rating indicates the tyre has been approved for speeds up to 112 mph (180 km/h) under optimal conditions. Everyday passenger vehicle tyres can be S speed rated, but S tyres often prioritize specific performance or function. Many all-terrain LT tyres are becoming available in an S rating as that’s the OE spec for many of these vehicles like the Ford Raptor.

T

A T rating indicates the tyre is approved for speeds up to 118 mph (190 km/h) under optimal conditions. T ratings are most associated with standard touring tyres, and everyday passenger vehicles like family sedans and minivans.

H

An H speed rating indicates the tyre is approved for speeds up to 130 mph (210 km/h) under optimal conditions. An H speed rating is at the low end, or at the start of the performance tyre speed ratings. H speed rated tyres are ideal for sport and luxury coupes and sedans, but not typically considered full-fledged performance vehicles. H speed ratings are common in the grand touring all-season tyre category.

W

A W means the tyre is approved for speeds up to 168 mph (270 km/h) under optimal conditions. W speed rated tyres land firmly at the performance end of the speed rating spectrum. Ws are suitable for performance coupes and sedans, and even street driven exotic sports cars.

W speed rated tyres generally offer plenty of performance for the street, including “spirited” (but responsible) drivers. At the same time, W tyres don’t necessarily sacrifice everyday driving factors like comfort (ride quality, road noise), and treadlife warranty.

V

A V rating indicates the tyre is approved for speeds up to 149 mph (240 km/h) under optimal conditions.

H and V tyres often go hand in hand. While the V rating technically allows for a higher maximum speed, practically speaking, this a distinction without much of a difference (in light of U.S. speed limits). Like H tyres, Vs can deliver a taste of the performance attributes associated with high speed rated and high-performance tyres (W, Y, and Z).

Y

Y rated tyres have been tested at speeds up to, and in excess of, 186 mph (300 km/h) under optimal conditions. If Y speed rating is indicated without parentheses (as normal), this means the tyre is rated up to 186 mph. If the Y speed rating is indicated inside of parentheses, this means that particular tyre size and specification has been tested at speeds in excess of 186 mph. A Y speed rating denotes maximum tyre performance.

Z

A Z rating indicates the tyre has been approved for speeds of 149+ mph (240+ km/h) under optimal conditions. This rating is associated with maximum tyre performance and is a match for performance coupes and sedans, sports cars, and supercars. While speed rating is typically adjacent to the load index, and outside of (after) the tyre size expression, the Z speed rating can be found within the structure of the tyre size:

235/40ZR18

To understand the speed restriction of a Z speed rated tyre, refer to the additional speed rating adjacent to the load index. In the case of a Z tyre, the speed rating will either be W, Y, or (Y).

The one outlier here is the Z rating, which pertains to only high-performance tyres. You won’t find Z indicated within the service description as usual. Instead, the Z is integrated as part of the tyre size information on high-performance tyres.

Decades ago, the Z speed rating was established as a catchall for any high-performance tyres built to exceed speeds of 149 mph. Greater specificity was not considered necessary.

But with the introduction of an increasing number of performance vehicles capable of approaching and even exceeding the 200 mph mark, speed ratings were expanded to give greater specificity to the actual top speed limitation.

Now that we’ve covered top speed limitation, let’s dive into how much weight your tyres can carry by reading the tyre’s load index.

What is tyre load index?

The tyre load index rating communicates how many pounds a tyre can safely carry.

Going back to the Audi example, the car’s service information is: 225/45R17 94H. 94 indicates the load index. Referring to the tyre load rating index chart below, the number 94 translates to a load-carrying capacity of 1477 pounds (per tyre).

How to find tyre load index

While you’re probably unlikely to approach the top speed rating of your tyres, pushing load index ratings is more common, especially when it comes to hauling and towing with trucks and SUVs. Use the chart below to understand the weight limitations of your vehicle’s tyres. Additional attention should be paid to the vehicle’s hauling and towing limits, which are set by the manufacturer and involve tyre capacity, as well as drivetrain and other considerations. Check your vehicle owner’s manual for details.

Tyre load rating index

Note: You should never replace your tyres with a lesser speed and load rating than the original equipment tyres. 

You can replace a tyre/your tyres with a high-speed rating and load rating.

Simply put, the load index is the weight that particular tyre can safely carry. A load rating of 87, equates to 545kg on each wheel. If we were to multiply this by the four wheels, the weight of the vehicle should not exceed 2180Kg.

To take this further, one would have to establish the weight balance of the vehicle, and how that is split between the front and rear axle. If you accustomed to heavy towing for example, where much of the weight is on the rear axle, you may see find that, eventhough the overall weight of the vehicle is correct, there is too much weight on the rear tyres, and they should be uprated.

In summary, when in the market to purchase new tyres, remember to ensure you are choosing the correct load index and speed rating to suit your vehicle and driving habits. 

Your tyres must be able to support the load of the vehicle; this capacity is called the load index. Look up the index to determine the weight, then multiply it by the number of tyres to get the total load supported. The speed rating, denoted as a letter on the sidewall (5), is the maximum speed the tyre is capable of. Be aware that tyres with a higher maximum speed tend to have faster tread wear. The speed rating must be at least as high as the vehicle’s top speed.