Speed Ratings Update
Thirty years ago the tire industry thought it had created the pinnacle of speed ratings. It jumped to the end of the alphabet scale, and there was a presumption no tire would ever eclipse the Z speed rating, and its sustained speeds above 149 miles per hour.
The evolution of tire technology proved otherwise.
“The trend in speed ratings across the board is higher,” says Woody Rogers, product information specialist at Tire Rack Inc. “If you look at cars sold new in the last 10-plus years, the fitments that they’re coming with are moving up consistently, as are rim diameters. Those two are going hand-in-hand.”
Radial passenger tires typically carry speed ratings in the Q to Y range, and with maximum speeds of 99 mph and 186 mph, respectively, those ratings exceed every posted speed limit in the United States. Even winter tires’ speed ratings are higher than the nation’s speed limits.
But in the 707-page report, “The Pneumatic Tire,” the National Highway Traffic Safety Administration points out, “The government high speed performance test is meant to assess the capability of the tire in an intermediate speed range from 85 to 100 mph.
“The speed rating of a tire indicates the maximum speed at which it can safely carry a given load at a specified inflation pressure.”
There’s one thing a higher speed rating doesn’t do, says Rogers. It doesn’t automatically qualify a tire as a performance tire.
“Speed ratings are not necessarily a performance rating,” he says. “Just because it has a higher speed rating doesn’t mean it’s going to be the best handling or highest-traction tire in a given size.”
He points to touring tires as a broad example. Overall, consumers expect touring tires to offer reasonable handling, good tread life and a smooth, quiet ride. “It’s not for the hard-core, performance-focused, handling-focused customer. But there are many of these tires that have V or higher speed ratings,” Rogers says.
And if he took a touring tire to the test track to measure its handling and traction, it wouldn’t perform as well as a tire specifically designed as a performance, or ultra-high performance tire. “They may not be able to go as quickly as an H-rated, but truly performance-focused product that has a lower speed rating. But it has more grip and handling, shorter tread ware and a less comfortable, louder ride than that touring tire with the V speed rating.”
Still, higher speed ratings do bring other benefits. Tires that run at higher speeds have to be more robust to handle and disperse the heat they generate, and that ultimately makes the tire more durable.
“It may affect the responsiveness of the tire. How does it handle and drive? A speed rating can definitely have an effect in how it feels just driving in traffic,” Rogers says. “I can’t call that performance, because I’m not at the limit on the test track, and I’m not measuring the stopping distance in a panic stop with anti-lock brakes. But just to drive it, everyday drivability can very much be affected by the speed rating.”
And that then gives a glimpse into what automobile manufacturers are thinking when they choose higher speed-rated tires for their latest models. For example, the Toyota Prius comes with V-rated tires. As quickly as Rogers asks himself why, he answers the question – the tire either offers the fashion the automaker wants, or it delivers other qualities. The speed rating is just a bonus.
The next performance category
Tire Rack is known for its tire tests, as well as its tire categories. And the online tire dealer says performance tires demand four categories: high performance, ultra-high performance, max performance, and extreme performance.
Tires in the max and extreme performance categories are summer-only products. Max performance tires offer both dry and wet traction, while extreme performance tires are focused exclusively on dry handling at the limit. Ride, comfort and noise aren’t the priorities.
So how far away are today’s performance tires from needing another new category?
“I can’t envision anything fitting in above extreme without jumping into what we already have, streetable track tires,” Rogers says. “There’s a small group, a pretty specialized product, that are capable of driving on the road but their primary reason for being is to use on the track.” The P Zero Trofeo R from Pirelli & Cie SpA is designed for the Chevy Camaro Z28. (Translated from Italian, Trofeo means trophy.) The next step up in category is for dedicated track and competition tires which are still street legal, like those from Hoosier Racing Tire Corp. Yes it’s legal to drive them on the street, but even the tire manufacturer advises against it.
Rogers says the window between extreme performance tires and track tires is “narrowing for sure.” ?
Speed rating Maximum speed
L 75 mph 120 km/h
M 81 mph 130 km/h
N 87 mph 140 km/h
P 93 mph 150 km/h
Q 99 mph 160 km/h
R 106 mph 170 km/h
S 112 mph 180 km/h
T 118 mph 190 km/h
U 124 mph 200 km/h
H 130 mph 210 km/h
V 149 mph 240 km/h
Z 149+ mph 240+ km/h
W 168 mph 270 km/h
Y 186 mph 300 km/h
(Y) 186+ mph 300+ km/h
Speed ratings are a guide, but they’re not the rule in defining a performance tire. Still, the highest-rated tires typically are built with leading edge technology.
The origin of speed ratings
The speed rating system was born in Europe, and evolved alongside the development of radial tires in the 1950s. The system originally consisted of three symbols and classes:
S – classification for a standard tire,
H – classification for a high speed tire, and
V – classification for a very high speed tire.
Eventually as cars became more complex, tire manufacturers worked to upgrade to more advanced tires to match, and the speed rating system became more elaborate. The categories were expanded to span the alphabet, with earthmover and farm tires at the lower end and tires for high performance sports cars at the upper end.
In the 1990s U.S. tire manufacturers voluntarily adopted the load index and speed rating symbols.
Source: The Pneumatic Tire, U.S. Department of Transportation, National Highway Traffic Safety Administration
Tire Rack: by the numbers
4: Number of tires listed on an average sales ticket
7: Warehouses in the U.S. (Nevada, Colorado, Louisiana, Indiana, Connecticut, Delaware and Georgia)
35: Average number of seconds it takes to drive the Tire Rack test track
50: Percentage split of the company’s wholesale and consumer business
100: Number of people working the phones and answering consumer calls at Tire Rack
1,600: Winter tires and wheels assembled per day in November in each of the Indiana and Delaware warehouses
2000: The last year Tire Rack exhibited at the Specialty Equipment Market Association (SEMA) Show
600,000: Square footage of Tire Rack’s largest warehouse, at the South Bend, Ind. Headquarters
6-8 million: Unique visitors to tirerack.com each month
The controversy surrounding truck tire speed ratings
This spring the speed ratings on commercial truck tires became a hot issue following an Associated Press (AP) investigation. The news agency focused on the common 75 mph speed rating, and how highway speed limits in at least 14 states are 75 or 80 mph. Parts of Texas have limits that are posted at 85 mph.
Jim Park, equipment editor for Heavy Duty Trucking, a sister publication of Modern Tire Dealer, says the AP didn’t mention what he calls a “rule of thumb” for truckers: “Add 5 psi to their normal inflation pressure for every 5 mph over the rated speed they plan to travel.”
Truckers and fleet managers are much more likely to continue to manage tire pressures rather than the remedy the AP offered – have tire manufacturers make tires with higher speed ratings.
“It won’t happen. It’s all about fuel economy today so that’s where the R&D dollars are going.”