The Load index is also determind at the maximum speed and with full inflation. It can therefore be theoretically possible to load the car beyond the stated amount, albeit being highly unrecommended. Bias-Ply tires either have a Ply Rating (specifying the amount of plies) and/or Load Range from A (two plies) to E (10 plies).
0 — 450 Kilograms
81 — 462
82 — 475
83 — 487
84 — 500
85 — 515
86 — 530
87 — 545
88 — 560
89 — 580
90 — 600
91 — 615
92 — 630
93 — 650
94 — 670
95 — 690
96 — 710
97 — 730
98 — 750
99 — 775
100 — 800
101 — 825
102 — 850
103 — 875
104 — 900
105 — 925
106 — 950
107 — 975
108 — 1000
109 — 1030
110 — 1060
111 — 1090
112 — 1120
113 — 1150
114 — 1180
115 — 1215
The “E” Approval is the European standard of all tires after 1997. It includes the “E” stamp (which can also be printed as a small “e” for tires in line only with directive 99/33/EEC), and a circulated (or rectangulated) number which is a code for the tire’s place of origin: A country code, followed by the numerical approval for the given brand. For instance, a tire with the first two figures of “E10″ stands for a tire from Yugoslavia; where a tire with the last two last figures, “0U” stands for Ling-Long Tires from Shandong, China (Tires that were found to be highly inefficient in a certain test in Britian).
The American DOT approval has taken it a step further to specify in twelve letters to describe the exact origin of the tire, plus the date of production, which is the date I described above.
Other tire markings include: An D or DA stamp (for “Defected” Tires), a Yellow dot which is a bit more dense and heavy than the rest of the tire. This is aligned with the heavy point of the rim, where the air nuzzle is placed. A red dot for a “protruding” spot on the tire, and lines and figures that are used in the manufacturing process to categorise the different layers, before they are extruded or mounted toghether. This process also creates the little “studs” of rubber than seem to cover the face of a new tire, formed by the escape of air bubbles from inside the layers when they are vulcanized.
The “dense” and “high” spots of the tire are discovered through the carefull inspection of the tire after it’s assembled in the factory. After being extruded, wrapped and vulcanized, the tire is checked with X-ray, weight and Uniformity. New tires are also wrapped in an external sylicon layer than wears off after 5000km or so.
The tire also includes a specification for it’s plies and, in radials, for the plies of the sidewall and the plies of the tread. The plies include: External rubber layer for grip around the tread. Internal rubber layers for structural rigidity of the tread and sidewall. Belts of dual steel nets that reinforce the tire’s carcass, and than synthetic fabrics of one of these kinds:
1. Nylon: The first fabric applied into tires, nowadays replaced due to it’s “morning sickness” which made it deform until heated by driving. Older tires also used Cotton.
2. Polyester: The most popular replacement of nylon. Less rigid than nylon fabric, but does not distort. The Polyester can be produced in different densities for different qualities.
3. Rion: Good for ride comfort and grip (better hysteresis), but is vulnerable for moist, should it protrude through even shallow cuts of the tire. Replacing it with polyester and improving the steel cords reduced the amount of carcass distortions in modern tires.
4. Kevlar: A replacment for the steel nets because it provides better rigidity for the same weight (about four times as much!), although being more expensive and less resistant to punctures.
5. Inner-liner: The internal layer supposed to hold the air inside the tire. It is made of special synthetic rubber (usually Bromo Isobutylene) and an internal fabric layer.
The tread depends on the tire’s type. Normal road tires have a soft tread of about 8.5mm, while M&S tires will have a greater “void ratio” (i.e. more lugs). The tread ratio increases for mud tires, snow tires and special ice tires, and the rubber compound become more stiff. On the road, the greater “void ratio” means that a greater part of the rubber is not gripping the ground. However, it is required for dispersing heat and channeling water on wet roads.
However, on mud, snow and ice, the tread generates grip by biting into the road surface. Mud tires usually also “ridges” inside the tread that help push the chunks of mud (or snow) that get trapped in it, while a road tire will get “plugged.” Likewise, the edges of the tread are placed in a sharper angle relative to the road, which helps disperse the chuncks. The tread is even present on the shoulders, to provide grip by biting into the sides of wheel ruts in the mud or snow. These tires don’t have sips in the shoulders or on the tread. Those little “sips” are intended to give the tread some flexibility and to open up and sip water when it contacts the road, and than squirt them out as the tire continues to rotate. The sips are removed to improve the rigidity of the lugs in mud or snow tires.
These tread patterns are bad on dry tarmac roads as they will suffer from acute wear, produce a lot of vacuum and turbulances to create noise, and provide reduced grip. The more agressive or effective a mud tire is on mud, or a snow tire on the snow, the worst it is on the road. It’s bigger “chunks” of tread will produce a louder noise and it will be highly effected load. On such tires, even one passenger will increase stopping distances in sudden braking. Ice tires with nails will also damage the road surface.
One interesting tire is a tire for dune-driving. These tires are round-shaped in all directions, including the section of the tread. It has no tread depth, and only little “flippers”, all designed for the tire to drive over the sand and not “bite” into it and create steps that will make it sink.
The tread on most tires is also devised in such a shape so that the tread is not the same on any “cube.” Each one is slightly different in shape and/or size. Even the most slim differences change the direction of air turbulence and make the different sounds that cancel each other out, to produce a noise below 75db (85 in DOT standards).
To a certain extent, the shape of the tread can be indicate it’s design: You can see trucks with front tires that are shaped with longitudinal “ribs.” The ribs offer a low rolling resistance (less wear and gas consumption), good steering control and good ventilation against heat build-up. The problem of this design is with longitudinal forces of strong braking and acceleration, especially on the wet.
The rear tires of the same trucks, as well as many SUV vehicles are formed as “lugs” that have grooves that open to the sides. These offer better grip, but still far from ideal on public roads, added to an increased rolling resistance and more noise. These wheels are good for the back of trucks or for light off-road use.
The classic road tire is formed in a way that divides it into “blocks.” This formation offers a good compromise between wet and dry performance, as well as between longitudinal and lateral wear. The downside is that the tire is heavier, more suspect to wear, sliding and noise than more complex designs. Most road tires combine at least two of the three above “types” together: The tire will have one or two central “ribs” for directional control, milleage and reduced noise, while the blocks besides it provide increased logitudinal grip and the lugs on the shoulder provide good lateral grip.
Some tires are assymetic. These tires have a tread where on shoulder is designated to serve as the “inside” shoulder, which is cruical for steering feel and stability, while the outside shoulder provides lateral grip. The idea behind most assyemtric tires is to give the best void ratio and water drainage capability to the inside the shoulder, while making the center the tread have better dry grip, and the outside shoulder have better still dry grip. The result is a tire that functions neatly when driving straight over wet surfaces, but also offers increased lateral grip in the dry. This is often a performance tire. The shortcoming of this kind of tire is that it cannot be rotated like a normal tire, and you can only swap them front to rear.
Other tires are directional, set to roll in a certain direction. This is achieved by setting the layers and especially the steel nets in an angle, and positioning the tread blocks in an angle that helps disperse water (and occasional sand or mud), typically these are performance tires.
Truck tires are built to withstand increased loads. Their tread is built with ribs that are turned in a “serpentine” formation to reduce the wear on their edges and change the angle of water drainage. The tread is supported by wires inside the tire. This can be seen when a tire’s tread gets worn and the shaved face of the tire appears wavey. In order to avoid wear in the center of the tread, the tire is intentionally built in a concave shape and with a “step” on the shoulder (a “decoupling rib”), to reduce the wear on the shoulder.
Got a puncture on the highway? Don’t be so quick to pull over. Statistics show that vehicles standing alongside the highway, attract attention and get hit at speed, causing deadly collision. If there is no good stopping place, it might even be desirable to keep driving on the punctured tire at a crawling pace (About 10km/h) over