Width
Tire section width is the distance between the sidewalls of an inflated but not loaded tire. As a rule, this parameter is indicated in millimeters, but there are also inch designations for the profile width.
Width is one of the characteristics that determines the compatibility of a tire with a specific wheel (the second characteristic is the mounting size). It is worth noting that the width of the tire does not have to strictly correspond to the width of the rim; certain deviations are allowed. There are special tables that allow you to determine the permissible width values for a particular wheel; in addition, such recommendations may be indicated in the documentation for a specific car.
The following tire width options are available on the modern market:
135 mm,
145 mm,
155 mm,
165 mm,
175 mm,
185 mm,
195 mm,
205 mm,
215 mm(in inches this is
8.5”),
225 mm,
235 mm,
240 mm(in inches this is
9.5”),
245 mm,
255 mm,
265 mm(in inches this is
10.5”),
275 mm,
285 mm,
290 mm(in inches this is
11.5”),
295 mm,
305 mm,
315 mm,
320 mm(in inches this is
12.5”),
325 mm,
335 mm,
345 mm(in inches this is
13.5”) and
over 345 mm(
over 13.5”).
Aspect ratio
Tyre aspect ratio. This parameter is usually expressed as a percentage of the width, since it is not the height itself that is of practical importance, but its ratio with the nominal section width.
In general, the lower the ratio, the more stable the tyre, the better it is suitable for high-speed driving on flat roads. Higher ratio, in turn, work better on rough surfaces and over obstacles, making them good for bad roads and
off-road. If we talk about specific numbers, nowadays, the following options are spread on the market:
— Low profile tyres:
25%,
30%,
35%,
40% ;
— Medium profile :
45%,
50%,
55%,
60% ;
— High profile :
65%,
70%,
75%,
80%,
82%,
85%, and
90% or more.
Tyre inner diameter
Tyre inner diameter in inches. The key parameter that determines the possibility of installing a tyre on a car: the tyre diameter must match the diameter of the rim. It is worth noting that some vehicles have +/- 1 inch diameter tolerance; this point should be clarified separately in each case.
In modern passenger vehicle tyres, the following rim diameters are most widely used:
12",
13",
14",
15",
16",
17",
18",
19",
20",
21",
22",
23",
24".
Speed rating
The speed rating that the tyre corresponds to.
This indicator determines the maximum speed that tyre is allowed to operate. It is designated by the letters of the Latin alphabet, each of which corresponds to a certain speed limit:
F — 80 km/h; G — 90 km/h; J — 100 km/h; K — 110 km/h; L — 120 km/h; M — 130 km/h; N — 140 km/h; P —
150 km/h ; Q —
160 km/h ; R —
170 km/h ; S —
180 km/h ; T —
190 km/h ; U —
200 km/h ; H —
210 km/h ; V —
240 km/h ; W —
270 km/h ; Y —
300 km/h ;
The maximum permitted speed must not be exceeded — this creates the risk of an accident. However, there are other rules associated with choosing a tyre by this factor. So, ideally, the actual driving speed should be at least 10 – 15% lower than the speed rating of the installed tyres — this will give an additional guarantee in case of emergency situations. In addition, in some tyre models, as the speed approaches the maximum, the upper limit of allowable load is reduced; see “Load Index” for details.
Fuel efficiency
The rolling resistance rating that the tyre corresponds to. The higher this figure, the lower the resistance, the less fuel is spent to overcome it and the more economical the tyre is. Efficiency indices are denoted by letters of the Latin alphabet in descending order of efficiency:
A(highest efficiency),
B,
C,
D,
E,
F,
G(lowest efficiency).
With other things being equal, more economical tyres tend to cost more, but the difference is offset by fuel economy.
Wet Grip
An index that determines the overall performance of a tyre on wet pavement. Lettered from
A(highest) to
G(lowest); intermediate options, respectively —
B,
C,
D,
E and
F.
The higher this indicator, the stronger the tyre grips to the wet road, the more efficient and safer it will be in difficult weather conditions. At the same time, it is worth noting that a low grip index does not mean unsuitability for driving in rain or snow — you just need to be more careful using such tyres. Conversely, a high index does not relieve the driver of the need to be careful in difficult weather conditions.
Wear resistance (Treadwear)
Tyre wear resistance rate according to the Treadwear standard issued by the US National Highway Traffic Safety Administration.
This rate indicates how far the tyre is able to travel until the tread reaches a critical level of wear. Treadwear is indicated in conditional points; formally, every 100 points correspond to 48,000 km (30,000 miles). However, it should be noted that testing according to this standard is carried out under perfect conditions — on flat roads, without numerous sharp accelerations and brakings, at a stable temperature, etc. Therefore, real wear resistance, usually, is lower by at least 20 – 30 %; and for a full guarantee, the claimed indicator is generally recommended to be divided by two. For example, formally the value of Treadwear 240 corresponds to a mileage of 48 × 2.4=115.2K km — however, in fact it is hardly worth counting on more than 90K km, and it is best to keep on the value of 55 – 58K km.
Generally, Treadwear ratings up to 250 are considered fairly low, 251 – 300 are considered average, 301 – 350 are above average, and over 350 is typical for
the most durable tyre models. Note that this characteristic is given mainly for summer, less often — all-weather tyres; winter tyres should be quite soft, which makes it difficult to achieve more or less worthy wear resistance rating.
