هيئة التقييس لدول مجلس التعاون لدول الخليج العربية  
GCC STANDARDIZATION ORGANIZATION (GSO)  
 
 
مشروع مواصفة نهائي 
Final Draft of  Standard FDS  
  
 
 
 
إعداد اللجنةالفنية الفرعية  الخليجية رقم TC 02/SC 01 
 
Prepared by GSO Technical Sub -Committee No. TC 02/SC 01  
 
  
 
GSO 02  /01/FDS/  645:2017  
 
 
 
 
إطارات المركبات التجارية  الجزء الأول: المسميات والتمييز والبيانات الايضاحية 
والابعاد والاحمال وضغوط النفخ 
Tyres  for Commercial Vehicles Part 1: Nomenclature, Designation, 
Marking, Dimensions, Load Capacities and Inflation Pressures  
 
 
 
 
   ICS:  43.020  
هذه الوثيقة مشروعلمواصفة قياسية  خليجية تم توزيعها 
لإبداء الرأي والملحوظات بشأنها ، لذلك فإنها عرضة 
للتغيير والتبديل ، ولا يجوز الرجوع إليها  كمواصفة 
قياسية  خليجية إلا بعد اعتمادها من الهيئة. This document is  a draft Gulf Standard  
circulated for comments. It is, therefore, 
subject to alteration and modification 
and may not be referred to as a Gulf 
Standard  until approved by GSO.  GSO 645:2017            GSO STANDARD 
 
 
2 
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  deleted paragraphs  تقديم 
 
هيئةةة التقيةةي  لةةدو  مجلةة  التعةةاو   لةةدو  الخلةةي  العربيةةة هيئةةة إقليميةةة تضةةم فةة  عضةةويتها أجهةة   التقيةةي  
الوطنيةةة فةة  الةةدو  الأعضةةاء ، ومةةن مهةةا  الهيئةةة إعةةداد المواصةةفات القياسةةية واللةةوا ا الفنيةةة الخليجيةةة 
بواسطة لجا  فنية متخصصة . 
قةةةةر  المجلةةةة  الفنةةةة  لهيئةةةةة التقيةةةةي  لةةةةدو  مجلةةةة  التعةةةةاو  لةةةةدو  الخلةةةةي  العربيةةةةة فةةةة  اجتماعةةةة   قةةةةةةم ( ) 
الةةةةةةةةةةذي عقةةةةةةةةةةد بتةةةةةةةةةةا ي ......./......./....... هةةةةةةةةةةة ،الموافةةةةةةةةةة. ......./...../.......   اعتمةةةةةةةةةةاد تحةةةةةةةةةةدي  
المواصةةةةفة القياسةةةةية الخليجيةةةةة  قةةةةم  GSO 645:2017  "إطةةةةا ات المركبةةةةات التجا يةةةةة الجةةةة ء الأو   
المسةةةةةةميات والتمييةةةةةة  والبيانةةةةةةات الايضةةةةةةاطية والابعةةةةةةاد والاطمةةةةةةا  وضةةةةةةغو  الةةةةةةنف  " التةةةةةة  تةةةةةةم د اسةةةةةةتها و 
إعةةةدادها ضةةةمن برنةةةام  عمةةةل اللجنةةةة الفنيةةةة الفرعيةةةة الخليجيةةةة  قةةةم TC 02/SC01   " اللجنةةةة الفنيةةةة
الفرعية الخليجية لمواصفات المركبات والإطا ات " المد جة ف  خطة دولة الكويت . 
على أ  تلغ  المواصفة القياسية الخليجية  قم GSO 645:2005  و تحل محلها 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs  Tyres for Commercial Vehicles  Tyres Part 1: Nomenclature, 
Designation, Marking, Dimensions, Load Capacities and Inflation 
Pressures  
 
 
1- SCOPE AND FIELD OF APPLICATION  
 
 This standard is concerned with new tyres for commercial vehicles ( Light 
Trucks, Heavy Trucks, Buses and trailers ). This standard is not applicable for 
tyre types identified by speed category less than 80  km/h. It is also not 
applicable to motor cycle, road equipment or agricultural equipment tyres.  
 
2- COMPLEMENTARY REFERENCES  
 
2.1 GSO 51/2017  “Passenger Car Tyres - Part 1: Nomen clature, Designation, 
Marking, Dimensions, Load Capacity and Inflation Pressure ”.  
 
2.2        GSO 646/2017  “Tyres for Commercial Vehicles , Part 2: Testing Methods”  
 
2.3        GSO 647/2017  “Tyres for Commercial Vehicles  Tyres, Part 3: General 
Requirements ”.  
 
3- DEFINITIONS    
 
3.1        Pneumatic tyre  
Circular shaped tyre made of an elastic material and enforced with steel 
strand  and/or fabric and reinforced with suitable fibers  or cords and 
designed to be  mounted on the rim.  
 
3.2       Type of pneumatic tyre  
A category of pneumatic tyres which do not differ in such essential respe cts 
as: 
(a) The manufacturer’s nam e; 
(b) Tyre-size designation;  
(c)  Category of use (normal tyre, snow tyre, special use tyre);  
(d) Structure (diagonal (bias -ply, radial);  
(e) Speed category symbol;  
(f) Load -capacity indexes;  
(g) Tyre cross -section.  
 
3.3  Manufacturer   
It refers to the person or body who is responsible to the Type Approval 
Authority (TAA) for all aspects of the type -approval and for ensuring t he 
conformity of production.   
3.4  Brand name/trademark  GSO 645:2017            GSO STANDARD 
 
 
4 
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  modified paragraphs  
  deleted paragraphs  It is the identification of the brand or trademark as defined by the tyre 
manufacturer and marked on the sidewall(s) of the tyre. The brand 
name/trademark may be the same as that of the manufacturer".  
 
3.5  Trade description/commercial name  
It is an identification of a range of tyres as given by the tyre manufacturer. It 
may coincide  with the brand name/trademark.  
 
3.6  Category of use as:   
 
3.6.1   Normal tyre   
It is type of a tyre i ntended for normal, on -road use.  
 
3.6.2  Snow tyre  
It is a type of tyre whose tread pattern, tread compound or structure are primarily 
intended to achieve better performance in snow conditions than that of a normal 
tyre with regard to its ability to initiate or maintain vehicle motion.  
 
3.6.3  Special use tyre  
It is a type of tyre designed for mixed using both on - and off -road or for other special 
duty. It is primarily intended to initiate and maintain the vehicle in motion in off -road 
conditions.  
 
3.6.3.1        Professional off -road tyre  
It is a special use tyre primarily used  for service in severe off -road       
conditions.  
 
3.2.3.4 Use at restricted speed.  
 
3.7  Structure  of a tyre  
It refers to the technical characte ristics of the tyre's carcass. A distinction is 
made between the following structures in particular:   
  
3.7.1  Diagonal or "bias -ply"  
It is a pneumatic -tyre structure that has ply cords extend to the beads and 
are laid at alternate angles substantially less than 90° to the centreline of the 
tread . 
 
3.7.2  Radial  
It is a pneumatic -tyre structure that has ply cords extend to the beads and are laid 
substantially at 90° to the centerline of the tread, the carcass being stabilized by an 
essentially inextensible circumferential belt.  
 
3.8 Bead  
It is the part of a pneumatic tyre which is of such shape and structure as to 
fit the rim and to hold the tyre on it.   
 
3.9 Cord  
It means the strands forming the fabric of the plies in the pneumatic tyre.  
 
3.10        Cord separation  GSO 645:2017            GSO STANDARD 
 
 
5 
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  deleted paragraphs         It is the separation of the cords from their coating.   
 
3.11  Ply 
A layer of rubber - coated parallel cords . 
 
3.12        Ply separation  
It is the parting o f adjacent plies.  
  
3.13 Carcass  
It is the part of a pneumatic tyre other than the tread and the rubber 
sidewalls which, when inflated, bears the load.  
  
3.14  Tread  
It is that part of a pneumatic tyre which comes  into contact with the ground, 
protects the carcass against mechanical damage and contributes to 
ground adhesion . 
 
3.15       Tread separation  
It is the pulling away of the tread from the carcass.   
 
3.16 Tread groove  
It refers to the space between two adjacent ribs and/or blocks in the tread 
pattern.  
 
3.2.7  Cross section  
 
3.17 Chunking  
The breaking away of pieces of rubber from tread.  
 
3.18  Sidewall  
It is the part of a pneumatic tyre between the tread and the area designed 
to be covered by the rim flange .  
 
3.19 Lower sidewall   
It refers to the area between the line of maximum section width of the tyre 
and the area designed  to be covered by the rim flange.   
 
3.20 Section width (S)   
It is the  linear distance between the outsides of the sidewalls of an inflated 
pneumatic tyre, excluding elevations due to marking, decoration or 
protective bands or ribs.  
 
3.21  Over all width  
It is the linear distance between the outsides of the sidewalls of an inflated 
pneumatic tyre, including marking, decorat ion and protective bands or ribs.   
 
3.22 Section height (H)  
It is a distance that equal s to half the difference between the outer diameter 
of the ty re and the nominal rim diameter.   
3.23 Nominal aspect ratio (Ra)  GSO 645:2017            GSO STANDARD 
 
 
6 
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  deleted paragraphs  It is one hundred times the number calculated  by dividing the section height (H) by 
the nominal section width (S 1). Both dimensions shall be expressed in the same units.  
 
3.24 Outer diameter (D)  
It refers to  the overall diameter of an inflated new pneumatic tyre . 
 
3.25 Rim 
A metallic support for a tyre, or a tyre and t ube assembly upon which the 
tyre bead is seated.  
 
3.26 Theoretical rim  
It means a rim with width equal s to (x) times the nominal section width of a 
tyre; the value of (x) shall be specified by the manufacturer of the type .  
 
3.27 Measuring rim  
The rim on which a tyre shall be fitted for dimensional measurements  
 
3.28 Test rim  
The rim on which a tyre shall be fitted for strength, speed and endurance 
tests  
 
3.29  Ply rating (PR)  
Index of tyre strength, does not necessarily represent the actual number of 
plies in the tyre.  It is used to relate a given size tyre with its load and inflation 
pressure.  
 
3.30  Maximum load for a tyre  
Load for each individual tyre from maximum load applied to the tyres 
installed on  a vehicle loaded with the maximum load specified by the 
manufacturer.  
 
3.31 Load capacity index  
It is one or two numbers which indicate the load the tyre can carry in single 
or in single and dual operation at the speed corresponding to the 
associated speed category and when operated in conformity with the 
requirements governing utilization specified by the manufacturer.  
 
3.32 Speed symbol  
A symbol indicating the speed at which the tyre can carry a load 
corresponding to  its load index under the service conditions specified by the 
tyre manufacturer.  
 
3.33 Void to fill ratio  
It is the ratio between the area of voids in a reference surface and the area 
of this reference surface calculated from the mould drawing .  
 
3.34 Tyre c lass  
It means one of the following groupings:   
 GSO 645:2017            GSO STANDARD 
 
 
7 
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  deleted paragraphs  3.34.1 Class C2 tyres: Tyres identified by a load capacity index in single formation 
lower or equal to 121 and a speed category symbol higher or equal to "N" .  
 
3.34.2       Class C3 tyres: Tyres identified by:  
(a) A load capacity index in single formation higher or equal to 
122; or  
b) A load capacity index in single formation lower or equal to 
121 and a speed  category symbol lower or equal to "M".    
 
3.35          Model rim assembly  
It means a test device that:  
(a) includes a rim which conforms to the published dimensions of a   
commercia lly available rim .  
(b) includes an air valve assembly for testing tubeless t yres.    
(c) an innertube and flap (as required) for testing tube  type tyres .  
(d) undergoes no permanent rim deformation . 
(e) allows no loss of air through the portion that it comprises of the tyre-
rim pressure chamber when a ty re is properly mo unted on the assembly 
and subjected to the requirements of this standard . 
 
4- DIMENSIONS MEASUREMENT  
 It should be as specified in the Gulf standard GSO 51/2017 mentioned in Item 
2.1, or in the publications of at least one of the organizations specified in  6.4 
in addition to the following items:  
 
4.1 Speed c ategory  
 Tyres shall be designated according to the maximum speed using the letters 
mentioned in Table 1   
 
                                                  TABLE  1  
                      Maximum Speed and C orresponding Symbol for Tyre D esignation  
 
Speed -category symbol  Corresponding speed (km/h)  
F 
G 
J 
K 
L 
M 
N 
P 
Q 
R 
S 
T 
U 
H 80 
90 
100 
110 
120 
130 
140 
150 
160 
170 
180 
190 
200 
210 
 
4.2 Nominal rim diameter  GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs  In addition to the nominal rim dimeters mentioned in the gulf standard GSO  
51/2017, the following values shall be added to this standard.   
 
                                               TABLE 2  
                                      Nominal Rim D iameter  
Nominal rim diameter code  
("d" symbol)  Value of the "d" symbol  
expressed in mm  
8 
9 203 
229 
14.5 
16.5 
17.5 
19.5 
20.5 
22.5 
24.5 368 
419 
445 
495 
521 
572 
622 
 
4.3  Load capacity i ndex  
The list of these indices and their corresponding loads is given in Table 3 . 
 
 
TABLE  3  
Load Capacity I ndices  Load -capacity index  
Corresponding 
maximum mass  
to be carried (kg)  
Load -capacity index  
Corresponding 
maximum mass  
to be carried (kg)  
Load -capacity index  
Corresponding 
maximum mass  
to be carried (kg)  
Load -capacity index  
Corresponding 
maximum mass  
to be carried (kg)  
Load -capacity index  
Corresponding 
maximum mass  
to be carried (kg)  
60 
61 
62 
63 
64 
65 
66 
67 
68 
69 
 
70 
71 
72 
73 
74 
75 
76 250 
257 
265 
272 
280 
290 
300 
307 
315 
325 
 
335 
345 
355 
365 
375 
387 
400 90 
91 
92 
93 
94 
95 
96 
97 
98 
99 
 
100 
101 
102 
103 
104 
105 
106 600 
615 
630 
650 
670 
690 
710 
730 
750 
775 
 
800 
825 
850 
875 
900 
925 
950 120 
121 
122 
123 
124 
125 
126 
127 
128 
129 
 
130 
131 
132 
133 
134 
135 
136 1 400  
1 450  
1 500  
1 550  
1 600  
1 650  
1 700  
1 750  
1 800  
1 850  
 
1 900  
1 950  
2 000  
2 060  
2 120  
2 180  
2 240  150 
151 
152 
153 
154 
155 
156 
157 
158 
159 
 
160 
161 
162 
163 
164 
165 
166 3 350  
3 450  
3 550  
3 650  
3 750  
3 875  
4 000  
4 125  
4 250  
4 375 
 
4 500  
4 625  
4 750  
4 875  
5 000  
5 150  
5 300  180 
181 
182 
183 
184 
185 
186 
187 
188 
189 
 
190 
191 
192 
193 
194 
195 
196 8 000  
8 250  
8 500  
8 750  
9 000  
9 250  
9 500  
9 750  
10 000  
10 300  
 
10 600  
10 900  
11 200  
11 500  
11 800  
12 150  
12 500  GSO 645:2017            GSO STANDARD 
 
 
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4.4 Load-capacity variation with speed   
Table 4 shows  a function of the load -capacity indices and nominal  speed  
category symbols the load variations which a pneumatic tyre can withstand 
when used at speeds different from that conformin g to its nominal speed 
category symbol.   
 
TABLE 4  
Load C apacity Variation with S peed  of Commercial Vehicles Tyres (Radial and 
Diagonal)  
Variation of load capacity ( %) 
Speed  
(km/h)  All load indices  Load indices  
≥ 122 * Load indices ≤ 121 * 
 Speed category symbol  Speed category 
symbol  Speed category symbol  
 F G J K L M L M N P** 
0 +150  +150  +150  +150  +150  +150  +110  +110  +110  +110  
5 +110  +110  +110  +110  +110  +110  +90 +90 +90 +90 
10 +80 +80 +80 +80 +80 +80 +75 +75 +75 +75 
15 +65 +65 +65 +65 +65 +65 +60 +60 +60 +60 
20 +50 +50 +50 +50 +50 +50 +50 +50 +50 +50 
25 +35 +35 +35 +35 +35 +35 +42 +42 +42 +42 
30 +25 +25 +25 +25 +25 +25 +35 +35 +35 +35 
35 +19 +19 +19 +19 +19 +19 +29 +29 +29 +29 
40 +15 +15 +15 +15 +15 +15 +25 +25 +25 +25 
45 +13 +13 +13 +13 +13 +13 +22 +22 +22 +22 
50 +12 +12 +12 +12 +12 +12 +20 +20 +20 +20 
55 +11 +11 +11 +11 +11 +11 +17.5  +17.5  +17.5  +17.5  
60 +10 +10 +10 +10 +10 +10 +15.0  +15.0  +15.0  +15.0  77 
78 
79 
 
80 
81 
82 
83 
84 
85 
86 
87 
88 
89 412 
425 
437 
 
450 
462 
475 
487 
500 
515 
530 
545 
560 
580 107 
108 
109 
 
110 
111 
112 
113 
114 
115 
116 
117 
118 
119 
 975 
1 000  
1 030  
 
1 060  
1 090  
1 120  
1 150  
1 180  
1 215 
1 250  
1 285  
1 320  
1 360  137 
138 
139 
 
140 
141 
142 
143 
144 
145 
146 
147 
148 
149 2 300 
2 360  
2 430  
 
2 500  
2 575  
2 650  
2 725  
2 800  
2 900  
3 000  
3 075  
3 150  
3 250  167 
168 
169 
 
170 
171 
172 
173 
174 
175 
176 
177 
178 
179 
 5 450  
5 600  
5 800  
 
6 000  
6 150  
6 300  
6 500  
6 700  
6 900  
7 100  
7 300  
7 500  
7 750  
  197 
198 
199 
 
200 
 12 850  
13 200  
13 600  
 
14 000  GSO 645:2017            GSO STANDARD 
 
 
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Speed  
(km/h)  All load indices  Load indices  
≥ 122 * Load indices ≤ 121 * 
 Speed category symbol  Speed category 
symbol  Speed category symbol  
65 +7.5 +8.5 +8.5 +8.5 +8.5 +8.5 +13.5  +13.5  +13.5  +13.5  
70    +5.0 +7.0 +7.0 +7.0 +7.0 +7.0 +12.5  +12.5  +12.5  +12.5  
75    +2.5 +5.5 +5.5 +5.5 +5.5 +5.5 +11.0  +11.0  +11.0  +11.0  
80 0 +4.0 +4.0 +4.0 +4.0 +4.0 +10.0  +10.0  +10.0  +10.0  
85 -3 +2.0 +3.0 +3.0 +3.0 +3.0 +8.5 +8.5 +8.5 +8.5 
90 -6 0 +2.0 +2.0 +2.0 +2.0 +7.5 +7.5 +7.5 +7.5 
95 -10 -2.5 +1.0 +1.0 +1.0 +1.0 +6.5 +6.5 +6.5 +6.5 
100 -15 -5 0 0 0 0 +5.0 +5.0 +5.0 +5.0 
105  -8 -2 0 0 0 +3.75  +3.75  +3.75  +3.75  
110  -13 -4 0 0 0 +2.5 +2.5 +2.5 +2.5 
115   -7 -3 0 0 +1.25  +1.25  +1.25  +1.25  
120   -12 -7 0 0 0 0 0 0 
125      0 -2.5 0 0 0 
130      0 -5.0 0 0 0 
135       -7.5 -2.5 0 0 
140       -10 -5 0 0 
145        -7.5 -2.5 0 
150        -10.0 -5.0 0 
155         -7.5 -2.5 
160         -10.0 -5.0 
     * The load capacity indices refer to a single operation.  
     ** Load variations are not allowed for speeds above 160 km/h.  For  speed category symbols "Q" and  
         above the speed category corresponding to the speed category symbol (see paragrap h 4.1 Table  
         1) specifies the maximum speed permitted for the tyre.  
 
5-          MARKING   
Pneumatic tyres subm itted for approval shall bear  on both sidewalls in the case 
of symmetrical tyres and at least on the outer sidewall in the case of 
asymmetrical tyres the following information in either Arabic and/or English : 
 
5.1 The manufacturer's name or  the brand name/ trademark . 
 
5.2 The trade des cription/commercial name. The trade description is not required 
when it coincides with the Brand name/trademark . 
 
5.3 The tyre -size designation  
 
5.4 An indication of the structure as follows:  
 
5.4.1 The letter "D" or “ no indication ” on diagonal (bias -ply) tyres.  
 
5.4.2 The letter "R" placed in front of the rim -diameter marking and , optionally, the 
word "RADIAL" on radial -ply tyres.  GSO 645:2017            GSO STANDARD 
 
 
11 
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  deleted paragraphs  5.5 The speed -category symbol  
 
5.5.1  An indication of the tyre's nominal speed category in the form of the symbol 
prescribed in paragraph 4.1. 
 
5.5.2  The inscription M+S or M.S or M&S if th e tyre is classified in the category of use 
"snow tyre" . 
 
5.6  The load -capacity indices as defined in parag raph 4.3 , Table 3.  
 
5.7  The word "TUBELESS" if the tyre is designed for use without an inner tube . 
 
5.8 The date of manufacture in the form of a group of four digits, the first two 
showing the week and the last two the year of manufacture.  This marking may 
be restricted to one sidewall only.  
 
5.9  In the case of tyres which can be regrooved, the symbol "      " at least 
20 mm in diameter, or the word "REGROOVABLE", moulded into or on to each 
sidewall.  
 
5.10  An indication, by the "PSI" index, of the inflation pressure to be adopted for the 
load/speed endurance tests, as explained in Table 5 , Appendix A.   
 
5.11  The inscription "MPT" (or alternatively "ML"  or “ET” ) and /or "POR" if the tyre is 
classified in the category of use "special" . In addition, they may also bear the 
inscription M+S or M.S or M&S.  
 
ET means Extra Tread, ML stands for Mining and Logging, MPT means Multi -  
Purpose Truck and POR means Professional Off Road.  
 
5.12 The prefix “LT”  before the tyre size designation, or t he suffix "C" or "LT" after the 
rim diameter and, if applicable, after the ty re to rim fitment configuration  
(Metric A Tyre) .  
 
5.12.1  This marking is optional in the case of tyres fitted on 5° drop centre rims, suitable 
for single and dual fitment, having a load capacity index in single lower or 
equal to  121 and destined for the equipment of motor vehicles . 
 
5.12.2  This marking is mandatory in the case of tyres fitted on 5° drop centre rims, 
suitable for single fitment only, having a load capacity index higher or equal to 
122 and destined for the equipment of motor vehicles . 
 
5.13 The suffix "CP" after the rim diameter and, if applicable, after the tyre to rim 
fitment configuration.  This marking is mandatory in the case of tyres fitted on 
5° drop centre rims, having a load capacity index in single lower or equal to 
121 and specifically designed for the equipment of motor caravans . 
 GSO 645:2017            GSO STANDARD 
 
 
12 
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  deleted paragraphs  5.14 The inscription "FRT" (Free Rolling Tyre) in case of tyres designed for the 
equipment of trailer axles and axles of moto r vehicles other than front steering 
and drive axles.  
 
5.15 Country of production  
 
5.16 Tread wear indicator  
 
5.17 Appendix B give an example of an arrangement of the tyre marking.  
  
6- DIMENSIONS,  LOAD  CAPACITIES  AND  INFLATION  PRESSURES  
 
6.1 Section  width  
 
6.1.1  The section  width  shall be obtained  by means  of the following  formula,  
(which  applies  to tyres  with a metric  size designation.  For tyres  with a code  
size designation,  item  6.3 applies).  
 
S = S1 + K (A – A1) 
 Where:  
S  = is the section  width  rounded to the nearest millimeter  
         and measured  on the measuring  rim. 
S1  =  is the nominal  section  width  in millimetres,  as shown  on the  
         sidewall  of the tyre in the tyre designation  as prescribed.  
A  =  is  the width  of the measuring  rim in millimetres,  as s h own    
         by the manufacturer in the descriptive note, and  
  A1    =   is the width  of the theoretical  rim in millimetres.  
A1 shall be taken  equal  to S1 multiplied  by the factor  x as prescribed  by 
the tyre manufacturer  and K shall be taken  equal  to 0.4. 
 
6.1.2      For tyres identified by the "tyre to rim fitment configuration" symbol "A",   
               K shall be taken to equal 0.6.   
 
6.1.3       Tyre section width specifications   
 
6.1.3.1   The overall width of a tyre may be less than the section width determined in     
              accordance with item 6.1.1.  
 
6.1.3.2  The overall  width  of a tyre may  exceed  that value by 4%  in case  of radial  ply 
tyres  and by 8% in case  of diagonal  (bias -ply) tyres.  However,  for tyres  of a 
section  width  exceeding  305 mm intended  for dual  mounting  (twinning),  the 
nominal  value  shall not be exceeded  by more  than  2% for radial  ply tyres  
with nominal aspect ratio higher than 60, or 4% for diagonal  (bias -ply) 
tyres.  The res pective limits shall be rounded to the nearest millimetre (mm).  
 
6.2        Outer D iameter  of a T yre   
 
6.2.1     The outer diameter of a tyre shall be obtained by means of the following  GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs               formula:  
  
D = d + 2H  
where:  
D is the outer diameter expressed in millimetres;  
d is the conventional number de noting the nominal rim diameter 
expressed in millimetres;  
H is the nominal section height rounded to the nearest millimetre 
and is equal to  
H = S1 • 0.01 Ra, where  
S1 is the nominal section width in millimetres;  
Ra is the nominal aspect ratio;  
All as shown on the sidewall of the  tyre-size designation in 
confor mity with the requirements of paragraph  5 above.  
 
6.2.2 For tyres identified by the "tyre to rim fitment configuration" symbol "A", the 
outer  diameter shall be that specified  in the tyre -size designation as shown on 
the sidewall of the tyre.  
                
6.2.3        Tyre outer diameter s pecifications    
 
6.2.3.1     The outer diameter of a tyre must not be outside the values D min and D max   
                obtained from the following formulae:  
 
        Dmin = d + (2 * H min)  
 
        Dmax = d + (2 * H max) 
 
      where:  
 
                   Hmin = (H * a) rounded to the nearest mm  
 
       Hmax = (H * b) rounded to the nearest mm  
 
6.2.3.2   For tyres identified by the "tyre to rim fitment configuration" symbol "A" , the 
nominal section height H is equal to: H = 0.5 (D -d), rounded to the nearest 
mm. (For references see paragraph 6.2.1  above).  
 
6.2.3.3          Coefficients "a" and "b" are respectively:    
6.2.3.3.1       Coefficient "a" = 0.97    
 6.2.3.3. 2     Coefficient "b"    
Coefficient "b"  Radial  Diagonal   
for normal use tyres  1.04 1.07 
for special use tyres  1.06 1.09 GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs  6.2.3.3.3   For snow tyres the  outer diameter shall not exceed the following value : 
 
       Dmax,  snow = 1.01 • D max  rounded to the nearest mm  
                     
Where :  
        
Dmax is the maximum outer diameter established in conformity with the above.  
                 
 For tyres of the category of use "snow tyre" the outer diameter (D max) established in    
 conformity with the above may be exceeded by 1%"  
 
6.2.4 The outer  diameter  of a tyre shall not differ  from  the value  “D" by more  than  
± 1.5%  in the case  of tyres  used  on the road,  nor by more  than  +5% and not 
less than  -2% in the case  of tyres  for special  use such  as off-road  use. 
 
6.3 For the existing  types  of tyres  whose  designation  is given  in publications  
mentioned  in 6.4, the section  width  and the outer  diameter  shall be as 
mentioned  in those  publications.  
 
6.4 Dimensions  load,  capacities  and inflation  pressures  shall be in accordance  
with what  is mentioned  in current  publications,  at the date  of manufacture  of 
the tyre or any later  date,  of at least  one of the following  organizations:  
 
6.4.1  "The Tyre and Rim Association  TRA in USA".  
 
6.4.2  "The European  Tyre and Rim Technical  Organization  ETRTO".  
 
6.4.3  "Japan  Automobile  Tyre Manufacturers  Association  JATMA".  
 
6.4.4 "Deutsches  Institut  Für Normung  (DIN)".  
 
6.4.5  "British  Standards  Institution".  
 
6.4.6 "Scandinavian  Tyre and Rim Organization  STRO".  
 
6.4.7  "The Tyre and Rim Organization  of Australia".  
 
6.4.8  "Association  Francaise  de Normalisation  AFNOR"  
 
  GSO 645:2017            GSO STANDARD 
 
 
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  modified paragraphs  
  deleted paragraphs  REFERENCES : 
 
1. ECE No. 54 “ Uniform provisions concerning the approval of pneumatic tyres for   
             commercial vehicles and their trailers, Revision 3; 26th March 2013 .  
 
2. ECE No. 54 “Uniform provisions concerning the approval of pneumatic tyres for  
commercial vehicles and t heir trailers, Revision 3/ Amendment 1: 3rd February 
2015 .  
 
3. ECE No. 54 “Uniform provisions concerning the approval of pneumatic tyres for  
commercial vehicles and their trailers, Revision 3/ Amendment 2; 5th February 
2016 .  
 
4. ECE No. 54 “Uniform provisions concerning the approval of pneumatic tyres for  
commercial vehicles and their trailers, Revision 3/ Amendment 3; 26th March 
2013 . 
  
5. ECE No. 54 “Uniform provisions concerning the approval of pneumatic tyres for  
commercial veh icles and their trailers, Revision 3/ Corrigendum 1; 18th December 
2014 .  
 
6. ECE No. 54 “Uniform provisions concerning the approval of pneumatic tyres for  
commercial vehicles and their trailers, Revision 3/ Corrigendum 2; 25th August 
2014 .  
 
7.       FMVSS No. 119 “New pneumatic tires for motor ve hicles with a GVWR of more  
      than 4,536 kilograms (10,000 pounds) and motorcycle”; 2008  
 
8. GS 645 “ Multi -Purpose Vehicles, Trucks, Buses and Trailers Ty res Part 1 ”; 2005 &  
            2009  
 
9. GS 646 “ Multi -Purpose Vehicles, Trucks, Buses and Trailers Ty res Part 2 ”; 1996 &  
            2009  
 
10. GS 647 “ Multi -Purpose Vehicles, Trucks, Buses and Trailers Ty res Part 3 ”; 1996 &  
            2009  
 
 
 
 
 
 
 
 
 
 
 
 
 
 GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs  APPENDIX  A: Table 5 Relation between the pressure index and the units of pressure  
 
Pressure  Index ("PSI")  Bar kPa 
20 1.4 140 
25 1.7 170 
30 2.1 210 
35 2.4 240 
40 2.8 280 
45 3.1 310 
50 3.4 340 
55 3.8 380 
60 4.1 410 
65 4.5 450 
70 4.8 480 
75 5.2 520 
80 5.5 550 
85 5.9 590 
90 6.2 620 
95 6.6 660 
100 6.9 690 
105 7.2 720 
110 7.6 760 
115 7.9 790 
120 8.3 830 
125 8.6 860 
130 9.0 900 
135 9.3 930 
140 9.7 970 
145 10.0 1 000  
150 10.3 1 030  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs  APPENDIX  B: ARRANGEMENT OF TYRE MARKINGS  
 
 
 
 Minimum Heights Markings, (mm)  
Tyres of nominal rim diameter  508 
mm (Code 20) or of nominal section 
width  235 mm (Code 9)  Tyres of nominal rim diameter  508 
mm (Code 20) or of nominal 
section width  235 mm (Code 9)  
b 6 9 
c 4 
d 6 
(*) PSI marking instead of kPa is allowed for tyres first type approved before 1 January 
2018.  
1. These markings, given as an example, define a pneumatic tyre:  
 
▪ Having a nominal section width of 255;  
▪ Having a nominal aspect ratio of 70;  
▪ Of radial -ply str ucture (R);  
▪ Having a nominal rim diameter of 572 mm, for which the symbol is  22.5;  
▪ Having load capacities of 3,150 kg when single and 2,900 kg when twinned 
(dual), corresponding respectively to the load indices 148 and 145 shown in 
Table3 paragraph 4.3.  
▪ Having a reference speed of 100 km/h corresponding to speed category 
symbol: J  
▪ Classified in the category of use Snow: M+S  
▪ Able to be used additionally at 120 km/h (speed category symbol L) with a load 
capacity of 3,000 kg when single and 2,725 kg when twi nned (dual), 
corresponding respectively to the load indices 145 and 143 shown in Table3 
paragraph 4.3.  
▪ Capable of being fitted without inner tube: "TUBELESS"  
▪ Manufactured during the twenty -fifth week of the year 2003, and  
▪ Requiring to be inflated to 620 kP a for load/speed endurance tests, for which 
the PSI symbol is 90.  
 
2.  In the particular case of tyres having a tyre to rim fitment configuration "A", the marking 
shall be in the form of the following example:  
 
235-700 R 450A  
  Where:  
 235  is the nominal section width in mm  
 700  is the outer diameter expressed in mm  
 R  is an indication of the structure of the tyre  
 450  is the nominal diameter of the rim expressed in mm  
 A  is the tyre to rim fitment configuration  
GSO 645:2017            GSO STANDARD 
 
 
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  deleted paragraphs  The marking of the load index, speed category symbol, date of  manufacture and 
other markings shall be as given in the example above.