PLT Tire Basics, Part I - Tire Review Magazine

PLT Tire Basics, Part I

In the first part of this two-part Tire Review exclusive series, we talk about the information on the sidewall, tire pressure, vehicle load carrying capacity, speed ratings and more.

We all like to think tires are one of the most technologically advanced parts on a vehicle. Unfortunately, many of our end-user customers don’t see it that way. To the vast majority of the tire-buying public, tires are round and black, and that’s about it. 

Picture-1-Tire-Sizing
Picture 1: The information molded on the tire sidewall includes: (1) the type of vehicle and/or service for which the tire was designed; (2) width in millimeters; (3) aspect ratio; (4) construction; (5) rim diameter; (6 & 7) service descriptions and load capacity; and (8) load rating.

To put it simply, we need to be better educated so we can educate them. 

So, we are going to focus on the many elements of tire technology and drill down to the basics. In this two-part Tire Review exclusive series, we are going to talk about the information on the sidewall, tire pressure and load, UTQG, DOT, vehicle load carrying capacity, tire rotation, the effect of time and temperature on tire pressure and much more. You may know some of this, but it’s always good to brush up and/or learn something new. The idea here is the more you know about the inner workings and technology of tires, the better you’ll be able to sell them. Let’s start with some basics.

Tire Sidewall

The information molded on the tire sidewall helps us better understand the tire’s intended purpose as well as dimensions, load capacity, high temperature/high-speed durability, year and week of production and more. Better understanding this information will help us explain to customers how they can choose the right set when it’s time to replace their tires. Picture 1 shows a typical tire sidewall and the information on it.

Service Type or Size Designation

Some tire size designations start with a letter(s) that identifies the type of vehicle and/or type of service for which they were designed. Passenger tires that are designed based on the Tire and Rim Association’s (TRA) standards start with the letter “P” and are known as P-metric size tires. Passenger tires designed based on the European Tyre and Rim Technical Organization’s (ETRTO) standard start without any letters and are known as hard-metric or Euro-metric sizes. Euro-metric sizes are dimensionally equivalent to P-metric sizes but typically differ subtly in load carrying capabilities. 

Light truck tires designed based on TRA standards often start with “LT” and are designed for vehicles capable of carrying heavy cargo or towing large trailers, such as pickup trucks. In older size conventions, the LT designation may be at the end of the tire size, which designates flotation light-truck sizes. A Euro-metric size designed for carrying cargo and/or towing often ends with the letter “C” which signifies the tire is a “commercial” tread intended for vans or delivery trucks. A tire size that begins with a letter “T” signifies the tire is a temporary spare or mini-spare. 

One of the most often asked questions is, “what are the differences between P-metric, Euro-metric and LT-metric tires, and which one should we recommend to customers?” There is also a debate as to whether you can substitute one type of tire with another. 

When it comes to replacing tires for a passenger car, SUV or pickup trucks, the most important consideration is to maintain sufficient load carrying capacity. Same size LT-metric tires, in comparison to the same size P-metric or Euro-metric, may have similar dimensions, but they usually have a higher load capacity, and as a result, operate at higher inflation pressures. LT-metric tires are designed to carry a higher load, and therefore, have very different construction and contour. So, replacing LT-metric tires with a P-metric or Euro-metric, and vice versa, is never recommended. 

TRA and ETRTO sizing are very similar. The two standards use different calculations to determine a tire’s maximum load carrying capacity. Oftentimes, Euro-metric tires have a higher load carrying capacity than same size P-metric tires. There are several tire companies that allow replacing P-metric tires with Euro-metric tires when the maximum load carrying capacity is equal or higher. But they caution replacing Euro-metric to P-metric same size tires and require checking the maximum load carrying capacity of both before the tire change is recommended. The majority of tire companies develop P-metric and Euro-metric tires the same way; however, it’s always wise to stay with the same tire designation that came OE on the vehicle when possible.

PLT-Tires-Basics-1-Table-1
Table 1: Tire Load Index, Passenger Car Tires

To illustrate this topic, let’s take a P215/60R16 and 215/60R16 tire. They are both popular sizes and fit on several sedans in the market. They both have similar dimensions, but the P215/60R16 has a load index of 94 with maximum load carrying capacity of 1,477 pounds at 35 psi, while the 215/60R16 has a load index of 95 for a maximum of 1,521 pounds at 36 psi. While changing a P-Metric tire with a Euro-Metric provides sufficient load capacity, swapping Euro-metric to P-metric should be checked with tire manufacturers.

Finally, don’t mix P-metric and Euro-metric tires on a car since it could compromise ride, handling, braking and cornering performance.

PLT-Tires-Basics-1-Table-2
Table 2: Tire Load Range, Light Truck Tires

Tire Dimensions

The three-digit numeric code (No. 2 on Picture 1) on the sidewall identifies the tire’s section width in millimeters, which is 265mm in this example. The actual tire may not match perfectly to this, but it is close. The two-digit number following the section width (No. 3 on Picture 1) identifies the tire’s aspect ratio, identified as a percentage of the section height divided by the section width. In Picture 1, the aspect ratio of the tire is 70%, so the section height of tire will be 185.5mm. The higher the aspect ratio, the taller the tire sidewall is (same width tire). 

The letter “R” following the tire aspect ratio identifies the tire’s construction as a radial tire. Rarely will you see a tire with the designation of “D,” which identifies that the tire has a bias ply construction meaning the body plies crisscross on a diagonal. The last two digits on tire size (No. 5 on Picture 1) refer to the rim diameter of a tire. The two digits identify the size of the wheel that the tire is intended to fit. 

Service Descriptions

The two- or three-digits after the rim diameter (No. 6 on Picture 1), along with the letter next to it (No. 7 on Picture 1) are known as service descriptions. Service descriptions show the maximum loading capacity of a tire along with the maximum speed and condition that the tire can be run.

Table 1 shows the typical passenger tire load index along with the maximum loading capacity. The maximum loading capacity at maximum pressure is also available on the tire sidewall. In Picture 1, a load index of 116 on a P265/70R17 will be a maximum of 2,756 pounds of load per tire. In addition, passenger tires are also identified as light load (LL), standard load (SL) or extra load (XL) on the sidewall. This is the same in both P-metric and Euro-metric sizes, however, the inflation pressure at maximum load slightly varies between the two.

Light-truck tires are identified by load range, which varies from load range B to load range F. The majority of tires in the market are load range C, D and E. Table 2 shows the load index in the tire. Each load index in light truck sizes are also identified by two numbers (No. 6 on Picture 1). The first number is the maximum load in single wheel (2 tires on rear). The second number is the maximum load in dual-vehicle applications (4 tires on rear). In Picture 1, 121/118 represents the maximum load of 3,197 pounds in single and 2,910 pounds on a dual application.

Table 3 illustrates the speed capability of tires. Speed ratings were established to match the speed capability of tires with the top speed of the vehicles to which they are applied. Speed rating does not suggest the speed of the vehicle and only shows the tire’s maximum capability. A tire’s maximum load (Table 2) is the most weight the tire is designed to carry. Since a tire’s load carrying capacity is related to the tire’s size and how much inflation pressure is actually used, maximum loads are rated with the tire inflated to an industry-assigned inflation pressure. 

PLT-Tires-Basics-1-Table-3
Table 3: Tire Speed Ratings

Inflation Pressure

The main job of a tire is carrying a vehicle load, but that won’t happen if the tire is not inflated. OEMs assign a tire size with a specific pressure when they release a vehicle in order to carry the load of the vehicle, its passengers and provide the best balance of handling, traction, fuel efficiency and durability. The inflation pressure that can run the vehicle is almost always different than what’s on the sidewall, which indicates the maximum pressure and corresponding load for the tire. That’s often not the pressure at which the vehicle operates. The pressure which a vehicle needs to run on can be found in the placard in the driver’s door panel. In case of a tire size change, the proper inflation pressure will be recommended to maintain the same amount of load.

Higher inflation pressure provides higher load capacity, and that’s why light load passenger tires have maximum load pressure of 35/36 psi, while extra load passenger tires have a maximum load pressure of 41/42 psi.

Inflation pressure also has a direct effect on fuel efficiency, traction and wear. As inflation pressure reduces, fuel efficiency of the tire will be reduced. Lower inflation pressure can also produce more friction on the shoulder area and cause early shoulder wear. At the same time, higher inflation pressure can cause more friction on the center area and result in early center wear.

Tire pressure does not stay constant during vehicle operation, and that’s why it’s recommended to be checked regularly. According to a study conducted by the National Highway Traffic Safety Administration, 27% of passenger cars have at least one tire that’s underinflated by 8 psi or more. Higher temperatures increase the tire pressure, and that’s why the tire pressure should always be measured cold. For every 10-degree drop of temperature, tires roughly lose 1 psi. 

Also, tire pressure will reduce over time. Tires can lose one psi per month under normal conditions, so it’s always recommended to check the pressure regularly. 

In part 2 of this series, we’ll further discuss tire basics, including DOT information, UTQG warning and much more.

Check out the rest of the January digital edition of Tire Review here.

You May Also Like

Training and Technology Will Lead the Way in OTR Tires

When we look at how OTR tires keep up with innovations in equipment, it’s all about maximizing productivity.

Yokohama-construction-tires-OTR

After two years of probably the strangest logistics we've lived through—and a roller coaster ride of an economy—the OTR tire market is surprisingly robust. The construction industry has slowed down slightly, and there's a lot of talk about a recession, but so far, we haven't seen a lot of publicly or privately funded projects pull back, and quarries and mines are running hard. All that activity is good for the tire industry.

Maxam Tire Completes Core Size Range for Agrixtra H Series

Maxam Tire completed the core size range for four-wheel drive self-propelled nutrient applicators. The company says these sizes to the Agrixtra H will further allow farmers’ and growers’ access to its product line. Related Articles – Yokohama OHT Releases New Size for Alliance Agri Star II – Winter Tire Market Flat, But EV-Specific Products Bring

Maxam_Tire-Agrixtra-H-more-sizes
Yokohama OHT Releases New Size for Alliance Agri Star II

Yokohama Off-Highway Tires America (YOHTA) has released the new 800/70R38 size of its popular Alliance Agri Star II farm radial tire. The new, larger size features a 173D high-load rating and is rated for speeds of up to 40 mph. Related Articles – Last-Mile Delivery Tires Set to Outpace Long-Haul Tire Volumes – Yokohama Releases

Alliance-agri Star II
Winter Tire Market Flat, But EV-Specific Products Bring Opportunity

Affected by pandemic supply chain disruptions and the uptick in sales of all-weather tires, the winter tire market in the U.S. has been largely flat in recent years. Despite the expectation that this will continue, tire dealers in snowy regions like the northern U.S. and Canada still should plan ahead to meet consumer demand in

Nokian+Tyres+Hakkapeliitta+R5
Hankook Tire Launches iON Evo EV Tires in the US

Hankook Tire America launched the company’s first tires specifically designed for electric vehicles (EVs) in the US. The iON evo AS and iON evo AS SUV are built with Hankook’s “EVolution” technology, which focuses on tread wear, noise reduction and unique grip performance for EVs, said the company. Related Articles – Vredestein Launches New Pinza

Other Posts

Goodyear and Gatik Demonstrate Goodyear SightLine Technology

Goodyear and Gatik demonstrated, in a proof of concept, intelligent tires powered by Goodyear SightLine technology.

Continental Debuts Enthusiast-Driven ExtremeContact Sport 02

From timed autocross laps to drifting on a skid pad and mastering knee-jerk braking and turns on a raceway, dealers, influencers and members of the media were treated to a crash course in performance racing while testing out Continental’s newest UHP summer tire, the ExtremeContact Sport 02. Related Articles – BKT Tires Launches Agrimaxfactor Tire

Conti-extremecontact-02-closeup
BKT Tires Launches Agrimaxfactor Tire For Tractors

BKT has launched the Agrimaxfactor, a new tire series for tractors for transport and soil tillage operations. Related Articles – Continental Tire Launches ExtremeContact Sport02 – BKT Launches EM 933 Super Excavating Tire – Kenda Unveils Vezda Touring 4S, its First ‘Four-Season’ Offering The company says it developed the series in response to the request

BKT_AGRIMAXFACTOR_Field
Michelin’s Enviro System Unveils Tire with 58% Sustainable Materials

Michelin says its subsidiary Scandinavian Enviro Systems is the first tire manufacturer in the world to unveil tires with a high proportion of environmentally sustainable materials that have been approved for use on ordinary road vehicles. These include tires for buses and cars containing recovered carbon black from Enviro, among other materials. Related Articles –

Michelin-Enviro-Tire