What does the speed rating on tires mean?

The letter you see on the side of the tire indicates the maximum speed at which that rubber is designed to operate safely. It's not that your car will go faster if you put tires with a higher letter, but rather that if you use one lower than what's recommended for your vehicle, you're compromising safety because the material doesn't hold up well at those speeds and can fail.

That's why it's important that when you change your tires you look for at least the same index as the originals had. If your car is approved for tires with code H, you shouldn't drop to G. That said, you can go up without any problem (for example, using V instead of H), although it's usually more expensive and in practice most people drive well below those limits.

The letter is there because each vehicle has its own needs depending on weight, power, and driving characteristics. Although it might seem like all the codes are the same, they range from A to Y, and the difference between one and the other is quite a bit of speed. If you're unsure, check your car's manual or the driver's door, where the technical sheet with the specifications you need is stuck.

The key thing is that speed rating has to match or exceed what your car came with from the factory - it's not a case of "higher is always better" without limits. The letter (A through Y) indicates the maximum safe speed in km/h: an H rating handles 210 km/h, a V handles 240, a W handles 270, and so on. The most common mistake is thinking you can go down a rating to save money, but if you put tires with a lower code than what's specified, you lose safety and your car also handles poorly when braking or taking curves. Check your manual or look at what's written on the side of your current tires, and keep that same rating or step up to a higher one if you want, but never go down.

The speed rating code tells you what the maximum sustained speed is that the tire is designed for, and it appears as a letter on the tire's sidewall. When I changed my car's tires a while back, I almost made a mistake choosing cheaper ones with a lower rating than the factory original, but then someone explained to me that it can affect safety and handling, especially on the highway or if you need to brake in an emergency. The important thing is that the code you put on is equal to or higher than the original - not so you can go faster, but because the tire needs to be built to handle those demands. If your car came with a V rating, you shouldn't drop down to T or S; you can keep it or go up, but don't go lower.

It's not actually that complicated once you get it, but people explain it in a way that makes it sound way more confusing than it is. That speed rating is just a letter that shows up on the tire's sidewall along with other numbers, and it basically tells you what the maximum speed that tire can safely handle while rolling without degrading or failing. That's it.

The important thing is that when you change your tires, that code has to be the same or higher than what your car came with from the factory. If your vehicle originally had a T (190 km/h), you can't put on an S (180 km/h) even if it's cheaper. That said, you don't gain anything by putting on tires with a higher code if you don't need it, besides spending more money.

There's a detail some people miss: that code also affects how the tire performs in other things. Tires with higher speed ratings usually have different compounds, normally stiffer ones, which can mean they roll a bit differently when it comes to comfort or grip in wet conditions compared to cheaper, lower-speed options. Nothing dramatic, but it's something people don't always take into account when they're heading to the shop looking for a deal.