BRITISH STANDARD AUTOMOBILE SERIES BS AU 50 1 1 1c 2001 ISO 4000 1 2001 Passenger car tyres and rims — Part 1 Tyres (metric series) ICS 83 160 10 NO COPYING WITHOUT BS I PERMISSION EXCEPT AS PERMITTED[.]
Size and construction
The tyre characteristics shall be designated as follows:
Nominal section width / Nominal aspect ratio Tyre construction code Nominal rim-diameter code
The nominal section width of a tyre must be specified in millimetres, concluding with either a zero or five This ensures that within a single series of tyres sharing the same nominal aspect ratio, all values consistently end in either 0 or 5.
For sizes mounted on 5° tapered (code-designated) rims, the nominal section width designation shall end in 5. 4.1 3 Nominal aspect ratio
The nominal aspect ratio (H/S) shall be expressed as a percentage and shall be a multiple of 5.
The tyre construction code shall be as follows: ắ B for bias-belted construction; ắ D for diagonal construction; ắ R for radial ply construction.
Radial tyres designed for some existing vehicles with a maximum speed capability exceeding 240 km/h may be designated and marked differently (see annex D).
Tyres intended for vehicles with a maximum speed capability over 240 km/h may feature the code-letters ZR, which denote their dimensional and constructional characteristics for radial ply tyres, instead of the standard tyre construction code R.
For speeds exceeding 300 km/h, see annex D.
Use of any other code letter (for example, in the case of a new construction type) should first be submitted to ISO for acceptance.
For tyres mounted on 5° tapered (code-designated) rims, the code shall be as given in Table 1
Table 1 — Nominal rim diameter code
Nominal rim diameter code Nominal rim diameter, D r mm
For safety reasons, particularly regarding mounting, tyres that require new-concept rims must have a code number that matches the nominal rim diameter (D r), expressed as a whole number in millimetres.
Service description
The service description shall be as follows:
Tyres designed for vehicles with a maximum speed capability over 300 km/h do not require a service description It is essential to consult the tyre manufacturer regarding the maximum speed capability and load capacity of these tyres.
The load index, as specified in Table 2, indicates the maximum tyre-load-carrying capacity for each tyre under the service conditions set by the manufacturer for a single mounting.
Tyres are classified into speed categories based on their maximum rated speed, with each category represented by a specific letter-symbol as outlined in Table 3.
Other service characteristics
4.3.1 The word “TUBELESS” shall appear on tyres without tubes.
4.3.2 The words “REINFORCED” or “EXTRA LOAD” shall appear on tyres designed for loads and inflation pressures higher than the standard version.
4.3.3 The letters “LL”, close to the tyre size designation, or the word “LIGHT LOAD” shall appear on the sidewalls of tyres designed for loads lower than the standard version.
4.3.4 The letter “T”, immediately preceding the tyre size designation, shall be used to characterize high-pressure, special, temporary-use spare tyres.
Specific indications may be included to denote the intended vehicle type using the symbol “P,” indicate temporary use of certain spare tyres with the phrase “TEMPORARY USE ONLY,” specify bias-belted construction with the term “BIAS-BELTED,” and identify radial ply construction with the word “RADIAL.” Additionally, these indications may cover the direction of mounting, rotation, tread pattern type, and other relevant characteristics.
The optional "P" marking can be utilized to clarify any potential ambiguity concerning the tyre type It must be placed in a manner that prevents confusion with other service condition markings.
Table 2 — Correlation between load index (LI) and tyre-load-carrying capacity (TLCC)
The maximum tyre load capacity corresponding to the load index shall apply for speeds up to and including 21 0 km/h.
For tyres in the speed category V (between 21 0 km/h and 240 km/h), the maximum load capacity per tyre shall be reduced to
1 00 % at 21 0 km/h, 97 % at 220 km/h, 94 % at 230 km/h and 91 % at 240 km/h, and linear interpolation is permitted.
For speed categories W and Y, the maximum load capacity per tire, as indicated by the load index, is applicable for speeds of up to 240 km/h for W and 270 km/h for Y.
For tyres in the speed category W (between 240 km/h and 270 km/h), the maximum load capacity per tyre shall be reduced to
1 00 % at 240 km/h, 95 % at 250 km/h, 90 % at 260 km/h and 85 % at 270 km/h, and linear interpolation is permitted.
For tyres in the speed category Y (between 270 km/h and 300 km/h), the maximum load capacity per tyre shall be reduced to
1 00 % at 270 km/h, 95 % at 280 km/h, 90 % at 290 km/h and 85 % at 300 km/h, and linear interpolation is permitted.
See 4.2.3 and Table 3 list speed categories and their symbols.
For speeds exceeding 300 km/h or when using ZR-marked tyres, it is essential to consult the tyre manufacturer regarding the maximum load capacity allowed in relation to the tyre's maximum speed.
For vehicles designed to reach a maximum speed of 60 km/h, it is permissible to exceed the maximum load capacity indicated by the load index, provided that the reference inflation pressure is increased in consultation with the tyre manufacturer If no agreement is reached, the following pressure increases are recommended: for 60 km/h, a 10% load increase requires a 10 kPa inflation pressure increase; for 50 km/h, a 15% load increase necessitates a 20 kPa increase; for 40 km/h, a 25% load increase calls for a 30 kPa increase; for 30 km/h, a 35% load increase demands a 40 kPa increase; and for 25 km/h, a 42% load increase requires a 50 kPa inflation pressure increase.
This list is not comprehensive, and additional categories and symbols may be included in the future Radial ply tyres intended for speeds over 300 km/h are marked with "ZR," along with their dimensional and constructional specifications instead of the standard tyre construction code For the maximum speed capability, it is advisable to consult the tyre manufacturer.
The marking shall include designations of: a) size and construction; b) service condition characteristics (see 4.1 4 and 4.2 for special cases); c) any other service characteristics.
The location of the marking of the load and speed characteristics shall be distinct, but near the marking of the size and construction.
No location is specified for the markings related to other service characteristics (see 4.3).
A tubeless tyre with a nominal section width of 165 mm, an aspect ratio of 80, and radial ply construction features a rim diameter code of 15 It has a load index of 87, indicating a load-carrying capacity of 545 kg, and is classified in the speed category H, allowing for speeds up to 210 km/h.
1 65/80 R 1 5 87 H TUBELESS NOTE See annex E for other existing size markings.
A tyre with a nominal section width of 225 mm, an aspect ratio of 45, and radial ply construction is designed for high-speed operations exceeding 240 km/h (code ZR) It features a nominal rim diameter corresponding to 406 mm (code 16).
225/45 ZR 1 6NOTE See annex D for special cases of radial tyres designed for speeds exceeding 21 0 km/h.
Rounding values
Except in the cases given in 6.2.1 and 6.2.2, round the formula-derived values for tyre dimensions to the nearest millimetre (see ISO 31 -0).
Calculation of design tyre dimensions
6.2.1 Theoretical rim width,R th th 1 N
R = K × S whereS Nis the nominal section width andK 1 is the rim/section width ratio.
For tyres mounted on 5° rims (code-designated) with nominal rim diameter expressed by a two-figure code:
K 1 = 0,7 where the tyres have a nominal aspect ratio of 50 to 95;K 1 = 0,85 where this ratio is 20 to 45.
NOTE K 1 values for other tyre and rim types are to be defined in a future revision.
R = K × S rounded to the nearest standardized rim, where K 2 is the rim/section width ratio coefficient.
For tyres mounted on 5° drop-centre rims, the nominal diameter is indicated by a two-figure code, with specific values for the aspect ratios: 0.7 for nominal aspect ratios of 95 to 75, 0.75 for 70 to 60, 0.8 for 55 and 50, 0.85 for 45, 0.9 for 40 to 30, and 0.92 for 20 and 25.
NOTE Other values of K 2 for other tyre and rim types are to be defined in a future revision.
The design tyre section width, S , is the nominal section width, S N, transferred from the theoretical rim, R th, to the measuring rim, R m, so that:
S = S + R - R withR mandR thexpressed in millimetres.
For those tyres having a nominal rim diameter code, use the corresponding value of D rgiven in Table 1
See annex A for general guidelines to the tyre design dimensions for the metric series of passenger-car tyres mounted on 5° rims (code-designated).
Calculation of maximum overall (grown) tyre dimensions in service tyres mounted on their
The calculation of maximum overall (grown) tyre dimensions in service for types mounted on their measuring rims is for use by vehicle manufacturers in designing for tyre clearance.
Calculate these dimensions with the coefficient appropriate to the design tyre section width and design tyre section height (see Table 4).
Table 4 — Coefficients for calculation of tyre dimensions
Structure Construction code Nominal aspect ratio, H/S a a b c d
1 ,04 0,96 0,97 a The maximum overall section width may be exceeded by the thickness of a special protective rib on one sidewall. b As of 1 992-01 -01 c As of 1 995-01 -01
6.3.1 Maximum overall (grown) width in service, W max
The maximum overall width in service, denoted as \$W_{max}\$, is determined by taking the greater value between the product of the design tyre section width, \$S\$, and the relevant coefficient, \$a\$, as outlined in Table 4.
W max = Sa ắ the addition of 8 mm to the design tyre section width, S: max 8
6.3.2 Maximum overall (grown) diameter in service, D o max o max r 2
See Table 4 for the value of coefficientb.
Calculation of minimum tyre dimensions for radial ply tyres mounted on their measuring rims
See Table 4 for the value of coefficientc.
6.4.2 Minimum tyre overall diameter, D o min o min r 2
See Table 4 for the value of coefficientd.
Range of approved rims
The approved rim widths are determined by multiplying the nominal section width, \( S_N \), by the coefficients listed in Table 5 These calculated values should then be rounded to the nearest standardized rim width according to ISO 4000-2.
The maximum overall (grown) width in service, W max, and the minimum tyre section width, S min, will change by
40 % of the change in rim width, expressed in millimetres.
Table 5 — Approved rim widths for passenger car tyres as a function of nominal aspect ratio
Dimensions in millimetres Coefficients for calculation of approved rim width
Tyre dimensions are presented in tables, like Table 6, which illustrates tyres fitted on 5° rims, identified by a specific code, with the nominal rim diameter represented by a two-figure code (refer to section 4.1.5).
Table 6 — Example of tyre dimension table
Tyre size designation a Measuring rim code b Design dimensions Maximum dimensions in service
……… ……… ……… ……… ……… ……… a See 4.1 b The measuring rim width, R m , is expressed by a code See 6.2.2 for calculation of R m and ISO 4000-2 for standardized rims. c For special service tyres, the values given may be exceeded by 1 %.
To accurately measure tyre dimensions, first mount the tyre on an approved rim and inflate it to the recommended pressure for at least 24 hours at room temperature After this period, readjust the inflation pressure to the original value Next, measure the section width and overall width of the tyre at six evenly spaced points around its circumference, and calculate the average of these measurements Finally, determine the overall diameter of the tyre by measuring its maximum circumference and dividing this value by π (approximately 3.1416).
Table 7 — Recommended pressures for measurement of tyre dimensions
Tyre Pressure kPa Standard load and P-type LIGHT LOAD version 1 80
T-type temporary-use spare tyre 420
Cold inflation pressures for tyres should be established in collaboration with both tyre and vehicle manufacturers This agreement must consider the tyre's load-carrying capacity, maximum speed, camber angle, tyre positioning on the vehicle, service conditions, and the vehicle's construction and characteristics.
For standard load radial ply tyres, the recommended cold inflation pressure should not exceed 350 kPa when used on code designated rims, regardless of the speed category, unless the tyre manufacturer specifies otherwise.
For normal road applications, the specified inflation pressure may not be less than 1 40 kPa For special applications, consult the tyre manufacturer.
NOTE Cold inflation pressure is the pressure of the tyre at ambient temperature, and does not include pressure build-up due to tyre usage.
Load capacities for passenger car tyres are given in annex B.
NOTE For sizes not included in annex B, consult the national standardization organization.
See annex C for tyre load-carrying capacity at various inflation pressures.
When choosing tyres for a vehicle, it is crucial to ensure that the vehicle's maximum load on each tyre does not exceed the tyre's maximum load carrying capacity This maximum load on a tyre is calculated by distributing the total weight of the fully loaded vehicle across the axles and then dividing that figure by two.
The normal load on a vehicle's tyre must not exceed 88% of its maximum load-carrying capacity This load is calculated by distributing the curb weight, accessory weight, and normal occupant weight to each axle, as outlined in Table 8, and then dividing by two Definitions of these weights and other relevant factors are provided below.
The vehicle manufacturer may specify an inflation pressure less than that corresponding to the maximum tyre load.
In this case, the load on the tyre (at the corresponding vehicle loading condition) shall not exceed the tyre load capacity at the specified inflation pressure.
Maximum loaded vehicle weight is the sum of a) curb weight, b) accessory weight, c) vehicle capacity weight, and d) production option weight.
Curb weight refers to the total weight of a motor vehicle when it is equipped with standard features, including the maximum allowable amounts of fuel, oil, and coolant This weight may also include additional components such as air conditioning and optional engine upgrades.
Accessory weight refers to the total weight of optional features beyond standard items that can be replaced, including automatic transmission, power steering, power brakes, power windows, power seats, radio, and heater, as long as these features are offered as factory-installed equipment, regardless of whether they are actually installed.
The standard occupant weight is calculated as 68 kg multiplied by the number of occupants, as outlined in Table 8 If local regulations account for luggage, an additional weight of 7 kg per occupant should be considered, placed in the luggage compartment Occupant distribution refers to how occupants are arranged within the vehicle, as detailed in Table 8.
Table 8 — Occupant loading and distribution for vehicle normal load for various designated seating capacities
Designated seating capacity, number of occupants Vehicle normal load, number of occupants Occupant distribution in a normally loaded vehicle
5 and above 3 2 in front, 1 in second seat
Vehicle capacity weight is the rated cargo and luggage load plus 68 kg multiplied by the vehicle designated seating capacity.
Production option weight refers to the total weight of installed regular production options that exceed 2.3 kg beyond the standard items they replace This weight is not included in the curb weight or accessory weight and encompasses features such as heavy-duty brakes, ride levellers, roof racks, heavy-duty batteries, and special trim.
Vehicle camber angles significantly affect tyre performance, particularly in extreme driving conditions It is crucial that the static camber angle of a passenger car remains within the specified limits for various tyre sizes, as outlined in Table 9.
Table 9 — Maximum camber angle for different aspect ratio
Aspect ratio Maximum camber angle
Annex A (normative) Guideline values for metric-series tyres
The design dimensions for metric-series tyres fitted on 5° rims are specified in Tables A.1 to A.9, categorized by a two-figure code representing the nominal rim diameter and based on the nominal aspect ratio.
Table A.1 — Nominal aspect ratio ( H/S ) of 95 to 75 ( K 1 = 0,7; K 2= 0,7)
Section height, H , at H/S (%) of mm code mm
Rims outside the approved range in use from previous designs are not approved for new designs.
Table A.2 — Nominal aspect ratio (H/S) of 70 (K 1 = 0,7;K 2= 0,75)
Rims outside the approved range which are in use from previous designs are not approved for new designs.
Table A.3 — Nominal aspect ratio (H/S) of 65 and 60 (K 1 = 0,7;K 2= 0,75)
H, at H/S (%) of mm code mm
Rims outside the approved range in use from previous designs are not approved for new designs.
Table A.4 — Nominal aspect ratio of (H/S) 55 and 50 (K 1 = 0,7;K 2= 0,8)
Design tyre dimensions mm Approved rim width codes
Section height, H , at H/S (%) of mm code mm
Rims outside the approved range in use from previous designs are not approved for new designs.
Table A.5 — Nominal aspect ratio (H/S) of 45 (K 1 = 0,85;K 2= 0,85)
Design tyre dimensions mm Approved rim width codes
Rims outside the approved range in use from previous designs are not approved for new designs.
Table A.6 — Nominal aspect ratio (H/S) of 40 and 35 (K 1 = 0,85; K 2= 0,9)
Section height, H , atH/S(%) of mm code mm
Rims outside the approved range in use from previous design are not approved for new designs.
Table A.7 — Nominal aspect ratio (H/S) of 30 (K 1 = 0,85 ;K 2= 0,9)
Rims outside the approved range in use from previous designs are not approved for new designs.
Table A.8 — Nominal aspect ratio (H/S) of 25 (K 1 = 0,85 ;K 2= 0,92)
Rims outside the approved range in use from previous designs are not approved for new designs.
Table A.9 — Nominal aspect ratio (H/S) of 20 (K 1 = 0,85 ;K 2= 0,92)
Rims outside the approved range in use from previous designs are not approved for new designs.
Annex B (normative) Load capacity indices for passenger car tyres
Table B.1 presents equivalences for standard load version tyres based on overall diameter, with load-carrying capacity indices corresponding to a basic inflation pressure of 240 kPa The load indices listed are recommended values for international application, while the sizes in parentheses indicate tyres that are equivalent in overall diameter but possess higher load capacity indices.
Table B.2 presents the tyre load capacity indices categorized by nominal rim diameter and aspect ratio, based on a standard pressure of 240 kPa for regular load tyres and 280 kPa for reinforced or extra load tyres.