Tire performance categories
Once upon a time, there were “regular” passenger tires, “performance” tires and racing tires. This was pretty much the case, back in the “simpler” days before personal computers, I-pods and cell phones, and when music that was called rock ‘n roll was actually rock ‘n roll music. Things change.
Technology has rushed forward over the last couple of decades with a speed-of-light vengeance, and this certainly includes the tire market. Today, there is a dizzying array of performance tires.
Today’s market — at least, at this moment in time — offers five somewhat distinct categories of street-legal performance tires. Here, we’ll try to make sense of it all for you.
As the name implies, a cosmetic performance tire is usually an all-season passenger tire that has the looks of a performance (or racing) tire, with regard to whatever the individual customer perceives as a visual performance statement. It generally has an “S” or “T” rating.
In the “old days,” this commonly involved tires that featured a wider section width and tread for that “beefy” look; raised white letters or a red stripe on the sidewall; perhaps an aggressive tread pattern; and so on.
This genre was initially very popular with owners of older muscle cars and pony cars like the GTO, Mustang, Camaro, etc., as well as pickups and vans. This specific sect is declining in popularity in favor of the lower profile “tuner” sizes. Granted, older/vintage muscle cars remain extremely popular among collectors, but collectors and restorers prefer tires that emulate the original tires without going “overboard” in terms of tire style.
Kumho Tire U.S.A. Inc. Vice President of Marketing Rick Brennan notes that in today’s market, the “cosmetic” performance category has widened dramatically. No longer referencing only raised white letter models to suit older muscle car enthusiasts, today’s cosmetic category now includes import tuners and even SUV and light truck applications, where the consumer wants the “look” of performance (low profile, wide section width), and doesn’t necessarily care about the performance level or speed rating.
The speed ratings within this category can range widely simply based on the specific brand and model line of the tire being selected. As a result, speed ratings can range from “S” all the way to “W.” Basically, the speed rating is a default of the selection process, since this type of customer is focused on tire appearance.
High performance (HP)
A high performance tire is traditionally an M+S touring tire that is rated “H” or “V.” It is designed to deliver a smooth, quiet ride, all-season performance and a high speed capability along with acceptable handling and tread life. Most H-, T- and V-rated original equipment tires would fall into this category.
The “high performance” category has become fairly difficult to define, as it encompasses an extremely broad range of applications.
Ultra-high performance (UHP)
As noted by Cooper Tire & Rubber Co.’s John Pecoraro, manager of product marketing, UHP tires tend to have lower profiles and more advanced tread compounds and constructions than HP tires in order to deliver enhanced handling and high speed capability. These attributes are usually at the expense of tread life and sometimes ride comfort and noise.
According to The Tire Rack, UHP summer tires offer a good blend of dry and wet performance and are not intended for snow or ice conditions. UHP all-season tires offer more versatility to include snow traction, with a slight trade-off in terms of dry and wet traction and handling.
All-season M+S UHP ultra-low profile tires are designed to offer year-round traction with tread designs and compounds that remain more flexible in cold weather to help blend all-season traction with good handling and high speed capabilities. UHP tires generally fall into the V-rated or higher speed rating range.
Max performance (MP)
Max performance tires are, generally speaking, what were once referred to as ultra-high performance tires. As the term Max implies, these tires are designed to deliver the ultimate in wet and dry performance, but are definitely not suitable for winter conditions. They tend to be ultra-low profile sizes that represent the state-of-the-art in tire design and technology, from component construction to tread compounding. Per The Tire Rack, Max performance summer tires offer an “unsurpassed blend of dry and wet street traction and handling.” These technologically advanced tires feature ultra-low profiles and high speed ratings, combined with unique materials to target dry and wet handling and traction.
Max performance tires generally include “W” and “Y” speed ratings.
Extreme performance (EP)
These tires are at the top of the road-legal food chain. They are primarily Y-rated (186 mph and higher). Kumho’s Brennan says an EP tire is as close to a race tire as it gets while still being street-legal and DOT-approved.
Extreme performance tires focus strictly on dry handling and traction. Features include stiffer sidewalls, jointless construction and soft tread compounds. The tread design generally features less void area. They are purposely engineered to offer maximum dry road performance at the expense of ride comfort.
Extreme performance tires are not intended for snow or ice conditions, or for high speeds through standing water. These specially tuned tires combine big block tread designs (again, less void area) with very aggressive tread compounds and internal construction to specifically target dry road steering response, traction, handling and high speed capabilities for “serious” driving enthusiasts.
Speed ratings denote the maximum documented speed capability, which many consumers misunderstand. For example, a “W” rating indicates that the tire is capable of 168 mph, but that’s in a straightaway. And for obvious reasons, no consumer should ever attempt to operate any vehicle at this rate of speed on a public roadway anyway.
Speed ratings are based on laboratory tests where the mounted and inflated tire is run at ever-increasing speeds while pressed against a large-diameter metal drum, or road wheel, with speeds increasing in 6.2 mph steps in 10 minute increments until the required speed has been achieved without tire failure.
Aside from the “speed” inference, we can confidently assume additional information in terms of a tire’s speed rating. A higher speed rating infers that the tire has been designed and constructed to provide higher levels of steering response, sidewall rigidity and tread grip.
In basic terms, a lower speed-rated tire may feature a softer and more flexible sidewall, while a higher speed-rated tire may feature a stiffer sidewall. This is a very broad over-simplification, but the point is that the higher the speed rating, the better the tire will likely “handle” in terms of steering response, handling stability, braking performance and dry traction. However, a higher speed rating also makes it more likely that a degree of ride comfort has been traded off in favor of handling and traction performance.
The speed rating is displayed on the tire sidewall and is integral to the tire size and/or load index designation markings. For example, an S-rated tire may feature the “S” speed rating immediately following the aspect ratio number, or immediately following the load index number, or both. Here are three examples of an S-rated tire:
2. 225/50R16 89S.
3. 225/50SR16 89S.
When “Z” speed-rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required: in excess of 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified.
That ultimately caused the automotive industry to add “W” and “Y” speed ratings, to identify tires that meet the needs of new vehicles that feature extremely high top-speed capabilities.
While a “Z” speed rating still often appears on some tire size designations, the “Z” still signifies a maximum speed capability in excess of 149 mph, but this may be followed by an additional rating of “W” (168 mph) or “Y” (186 mph) to more clearly define a particular tire’s maximum speed capability.Here are three examples of the use of the Z rating:
1. 225/50ZR16 (in excess of 149 mph).
2. 205/45ZR17 88W (168 mph).
3. 285/35ZR19 99Y (186 mph).
When the “Y” speed rating is enclosed in parentheses, this indicates that the top speed of the tire has been tested in excess of 186 mph. An example: 285/35ZR19 (99Y).
The banding on the sidewall of a tire is required to list the materials and number of layers of each material used to reinforce the rubber. A typical tire’s basic construction materials, as listed on its sidewall, are as follows:
TREAD: 2 POLYESTER + 2 STEEL + 1 NYLON. SIDEWALL: 2 POLYESTER.
The branding in this example identifies that molded into the rubber under the centerline of the tread lies two radial body plies of polyester cord, two belts of angled steel cord and one circumferential cap ply of nylon cord. It also identifies that in each sidewall at the widest points between the tire’s inner and outer sidewalls (at the section width) lies two radial body plies of polyester cord (a continuation of the same two body plies that were listed under the centerline of the tread).
Many high-speed tires use circumferential reinforcements above the steel belts. These are either in the form of belt edge strips (approximately one-inch wide bands covering only the inner and outer edges of the steel belts), full cap plies (covering the entire width of the steel belts) or a combination of both.
However, because belt edge strips are not present under the centerline of the tread, they are never reflected in the basic construction material’s branding for the tread area.
Many UHP tires also use fabric or steel cord reinforced sidewalls to increase steering response and cornering stability. However, because sidewall-reinforcing material is not present at the widest points of the tire’s sidewalls, they, too, are never reflected in the basic construction material’s branding for the sidewall area.
Tire and wheel terminology
Here are commonly used terms that your technicians need to understand when working with tire and wheel packages.
Overall diameter: the outside diameter of the tire when mounted and inflated, but with no vehicle load.
Section width (also called overall width): the maximum width of the tire’s cross section of an unloaded, mounted and inflated tire (the widest point of the tire when mounted and inflated, but with no vehicle weight).
Free radius: the radius of the tire/wheel assembly that isn’t affected by load. This is the distance from the wheel axle centerline to the top of the tire tread face.
Loaded radius: the distance from the wheel axle centerline to the ground, drawn vertically. This is the distance from the vehicle hub centerline to the ground when the tire is inflated and when the tire supports vehicle weight.
Nominal wheel diameter: This refers to the size of the wheel applicable for mounting the tire (diameter of the rim seat that will support the tire bead). The bead-to-bead diameter is measured at the inside diameter of the tire, once mounted.
Section height: the distance from the bead to the tread face.
Loaded section height: the loaded radius, minus half of the nominal rim diameter.
Aspect ratio: This refers to the tire’s section height in relation to its section width, as a percentage. For example, a 60-series tire features a sidewall that is 60% as tall as the tire’s section width. A 50-series tire will feature a shorter sidewall, approximately 50% of the section width.
As a formula, aspect ratio can be determined by taking the nominal section height, dividing it by the nominal section width, and multiplying the result by 100. For example, if the section height is three inches and the section width is 10 inches, divide three by 10 and multiply that by 100. The tire in our example is a 30-series tire.
Tread width: This is the distance measured from the inner tread shoulder to the outer tread shoulder.
Tread width is not to be confused with section width, as section width is always greater.
HANDBOOK Q&A: What is the load index? Where is it located on the tire?
A tire’s load index refers to its load carrying capacity, or how much weight the tire can safely support. The load index is a two-digit number which appears at the end of the tire’s size designation.
The higher the load index number, the more weight the tire can safely support. Always help your customer select a tire that features the same or higher load index rating as compared to that vehicle’s original equipment (OE) tire.
Typically, the load indexes that apply to passenger cars and light trucks range from 70 to 110.
LT TIRE DIMENSIONS
They are similar yet different than passenger tire sizing
The sidewall of a non-P-metric light truck tire offers an abundance of information relative to size, maximum inflation, serial number, manufacturing location, tread wear rating, traction rating, rotational direction (if applicable), speed rating (if applicable), and more.
In essence, this information serves as a very complete identification and, if you will, owner’s manual for that specific tire.
Since much of this sidewall information can be confusing, we’ll walk you through the scenario to help you understand the data provided that applies to a tire’s dimensions.
Light truck tire sizing (designated LT) can involve one of three sizing systems: LT metric, LT high flotation and LT numeric.
1. LT metric is very similar to the P-metric passenger tire system, with two simple additions. At the beginning, the letters “LT” indicate a light truck application. This is followed by the conventional P-metric designations including section width (mm), aspect ratio, construction type and rim diameter, followed by an alpha character which denotes load range. For example: LT235/75R15C.
Note that any tire that features an “LT” designation is designed for use on vehicles that may carry heavy loads and/or tow large trailers. This includes medium and heavy-duty pickup trucks, usually in the three-quarter-ton and one-ton truck range, full-size vans and some SUVs. LT tires provide increased reserve capacity to handle heavier cargo loads.
2. LT high flotation tires, which are designed with lower aspect ratios and are intended to provide increased traction in “loose” conditions (sand, soft dirt, watery off-road), are sized to clearly indicate tire diameter in inches, cross section in inches, construction type, rim diameter and load range. They also carry an LT identifier as well.
An example is a 31x10.50R15 LT/C. In this case, the 31 indicates a 31-inch overall tire diameter, a cross section (section width) of 10.5 inches, radial construction, 15-inch wheel rim diameter, light truck designation, and a load range of C.
3. LT numeric is an older system, primarily involving commercial vehicle applications. This sizing system identifies cross section in inches, construction type, rim diameter in inches, and denotes a light truck application and load range. For example: 7.50R16LT/D. This refers to a cross section width of 7.5 inches, radial construction, light truck application, with a load range D.
Tires identified as “ST” are “special trailer” tires, designed only to be used on boat, car and utility trailers. They should never be used on passenger cars, vans, light trucks or SUVs.