Tire ratings are downright weird and you may not have known that. Notably, tires are rated for maximum speed with those ratings listed in the form of a variety of letters and numbers on a tire’s sidewall.
This “nomenclature” outlines nearly everything about them. Including tire size, construction, and the speed rating, among other important specifics.
Tire Ratings and the Federal Government
Tire speed ratings are assigned by the federal government, a one-letter label found along with a two-digit load rating and listed ahead of the manufacturer’s brand name. This rating only declares a tire’s ability to withstand high speeds.
Further, a side advantage is that the higher ratings usually confirm that the tire offers exceptional ride and handling. In other words, the higher the rating, the better control offered.
Tire ratings are rather odd too. You would guess that “Z” would be the maximum rating, but it is not — it is now reserved solely for sports cars. To understand everything, we will need to analyze the history of these ratings and tell you what to consider when you go shopping for tires. Only then will you be capable of understanding the all-too-apparent strangeness.
It Started in Europe
Tire speed ratings started in Europe in the 1960s, according to the NHTSA’s TireWise. Initially, only foreign-made tires offered ratings, but the United States finally established ratings per the Federal Motor Vehicle Safety Standard (FMVSS) 109.
European officials automatically assigned a “Z” rating to tires operating at speeds of 149 mph and above. The last letter of the alphabet was selected because at the time there was not a car made that would travel much beyond the bottom number. Moreover, with no speed limits on the German autobahn, the “Z” designation was deemed adequate. Soon, however, that postulation was proven wrong.
As passenger vehicles have progressed and are achieving ever higher speed thresholds as consumers now choose such high-performance models. These include the Nissan Greddy GR43 GT-R, Dodge Challenger SRT Hellcat, and the Mercedes-AMG E 63 S, thus the “Z” rating was not quite sufficient.
The US Steps Up
So, the federal government entered the fray, developing a modified speed rating standards starting with “B” and ending with “Y”. However, you will not find “B” tires on passenger vehicles, as they are rated to just 31 mph.
Although you may well find “M” or “N” tires, rated to 81 and 87 mph, individually. Those ratings are usually given to temporary spare tires — for instance, the donut tires found in many late-model trunks and cargo compartments.
After “N” you will find Q-rated tires as both “O” and “P” are not used. Inexplicably, the “H” rating was not initially used (along with “A” and “I”). But the “H” ranking was later added, filling a gap between the 124 mph speed rating for the “U” and the 149 maximum rating for the “V” to deliver a 130 mph limit.
It is worth noting that “H” tires once formerly set aside for performance cars are now equipped in certain family vehicles. As such, these tires help manufacturers meet the most recent safety standards as well as deliver enhanced acceleration, braking, and handling. On the other hand, “H” tires have a propensity to wear out quicker.
Your Next Set of Tires
If you are shopping for new tires, what’s the best tactic? That is easy — pick the same tires that came with your vehicle. That said, if you want to make adjustments, going up on the speed rating can enhance cornering.
On the other hand, if you lower your speed rating the outcome may be inferior handling and unstable steering. Both may result in a safety issue with unintended consequences.