1 - Understanding tyre markings
The markings on the sidewall of a tyre give the necessary information on it’s characteristics and intended use.
As a worldwide standard, the basic information is always presented in the same format.
Among this information can be found the commercial brand of the manufacturer and the model, followed by a group of figures and letters : e.g. 205/65/R15 91V.
- The first three figures (ex. 205) indicate the width, in mm, of the tread, or sculpture, which is the part of the tyre that is in contact with the road. For certain types of vehicle, particularly 4 x 4’s, the width may be given in inches.
- The next number (in this case 65) indicates as a % the ratio between the height of the sidewall and the width of the tyre. One exception, this ratio is not shown when it’s equal to 80%.
- The letter (R) indicates the type of structure of the tyre : Nearly all modern tyres (with the exception of some tyres for classic and vintage vehicles) have a Radial structure, expressed by the letter R. The letter D can also sometimes be seen, nearly always in the case of motorcycle tyres of a Diagonal belted structure.
- The two-digit number (e.g 15) indicates the internal diameter in inches, which corresponds to the diameter of the wheel on which the tyre is to be fitted. For certain types of vehicles (4 x 4’s, commercial vehicles, and HGV’s, this dimension may be expressed in a half unit, e.g. 22,5 inches.
- The following number (91) gives the load index : A rating of 91 indicates a maximum load per tyre of 450 kg. (see the table of load index equivalence).
- Lastly, the letter (V) indicates the speed index, V corresponding to a maximum speed of 240 km/hour see the table of speed rating equivalence).
On some models of tyres you may see an arrow which indicates the direction in which the tyre should be fitted. If there is no arrow the tyre can be fitted either way around.
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2 - Special markings
M+S Mud & Snow : Snow Tyres
XL, EL, RF (extra load - reinforced) : Reinforced tyres that have a load index superior to equivalent tyres without this marking.
MFS, FR, ML, G1 : Protective reinforcement for rim edges (recommended in particular for alloy wheels)
A : Asymmetric profile.
RunFL, , Pax, RFT : Run Flat tyres designed for use when deflated.
BSW : Black Side Wall
OWL or ORWL : Off White Letter Indicates the presence of white sidewall lettering (4x4’s)
Demo, Demont : A new tyre under warranty that has already been fitted to, and removed from, a vehicle.
DA : Second choice tyres showing an aspect defect but sold with the manufacturer’s original warranty.
B or AU : Tyre homologated by Audi
A* or * : Tyre homologated by BMW
J : Tyre homologated by Jaguar
MO, MB or A-MO : Tyre homologated by Mercedes
N2, N3 or N4 : Tyre homologated by Porsche
PE : Tyre homologated by Peugeot
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3 - Load and speed index tables
|
Speed Index
| Code Letter |
Max. Speed in km/h |
| J |
100 |
| K |
110 |
| L |
120 |
| M |
130 |
| N |
140 |
| P |
150 |
| Q |
160 |
| R |
170 |
| S |
180 |
| T |
190 |
| U |
200 |
| H |
210 |
| V |
240 |
| W |
270 |
| Y |
300 |
| ZR |
> 240 |
|
Load index
| Index |
Load in kg |
Index |
Load in kg |
| 80 |
450 |
103 |
875 |
| 81 |
462 |
104 |
900 |
| 82 |
475 |
105 |
925 |
| 83 |
487 |
106 |
950 |
| 84 |
500 |
107 |
975 |
| 85 |
515 |
108 |
1000 |
| 86 |
530 |
109 |
1030 |
| 87 |
545 |
110 |
1060 |
| 88 |
560 |
111 |
1090 |
| 89 |
580 |
112 |
1120 |
| 90 |
600 |
113 |
1150 |
| 91 |
615 |
114 |
1180 |
| 92 |
630 |
115 |
1215 |
| 93 |
650 |
116 |
1250 |
| 94 |
670 |
117 |
1285 |
| 95 |
690 |
118 |
1320 |
| 96 |
710 |
119 |
1360 |
| 97 |
730 |
120 |
1400 |
| 98 |
750 |
121 |
1450 |
| 99 |
775 |
122 |
1500 |
| 100 |
800 |
123 |
1550 |
| 101 |
825 |
124 |
1600 |
| 102 |
850 |
125 |
1650 |
|
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4 - Tyre maintenance
Tyres are designed to run safely, giving the best driving conditions day after day. Regular maintenance is essential however in order to keep tyres in good condition.
Proper inflation is essential and responsible for good handling and maximum safety.
Correct inflation pressure also contributes to fuel saving, longer tyre life and reduced wear of vehicle components. In some cases accidents can be avoided by correct tyre maintenance.
Tyres are the only point of contact between a vehicle and the road surface. In spite of this, they are still too often neglected. Tyre condition should be checked regularly and inflation pressures verified monthly at least.
Certain safety devices such as ABS braking and traction control systems and may also malfunction in the case of under inflated tyres.
Tyres under inflated by only 10% compared to the recommended pressure can cause hazardous driving conditions. Low pressure can actually cause tyres to burst : the sidewalls crease and deform, the associated friction generates excessive heat build up damaging the tyres and reducing stability.
Use a hand held pressure gauge in preference to the ones fitted to hoses in service stations which are often imprecise.
- Always check tyre pressures cold, i.e. before having covered more than 5 km.
- Check tyre condition regularly and particularly after having encountered potholes, hitting the kerb or driven over rough terrain for which the tyres are not intended. Swelling, cuts, cracks and other defects can cause tyres to burst.
- Tyres should not show signs of excessive or uneven wear. Premature or uneven wear is generally caused by defective suspension geometry and requires specialist attention.
- Each tyre valve should be fitted with a dust cap, screwed finger-tight.
- The spare wheel should also be checked regularly and particularly before a long trip.
Out of season tyres, when fitted to rims, can best be stored flat and piled on top of one another.
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5 – Tyre Replacement
First of all, it’s essential to choose tyres of the same category as those already fitted to the vehicle or recommended by the vehicle manufacturer.
You can choose all-season tyres, summer or snow tyres, high-mileage, comfortable or those giving the best handling qualities according to your preferences or driving style but it is important to use the type of tyre that is best adapted to your vehicle and it’s use and conforming to the recommendations and homologations of the vehicle manufacturer.
It is often advisable to fit new tyres to the rear of the vehicle, in this way, if only two tyres are replaced, they can later be moved to the front.
New tyres should be run-in : Drive at moderate speeds for the first 300 km, specially on wet roads. Check also that wheel nuts are tight after 150 km.
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6 – Tyres and the Law*
Tyres on the same axle (front or rear) must be identical both in their commercial and technical aspects :
Since October 2000, car tyres are inspected as to their dimensions, speed and load index. Since January 1st 2003, tyres on the same axle must have the same symmetrical characteristics : brand, design and degree of wear.
Moreover, the technical characteristics of all four tyres must be equal or superior to those defined by the vehicle manufacturer – if this is not the case you may be liable to a fine, the vehicle may fail it’s MOT test or equivalent of, and your insurance company may refuse to cover you in the case of an accident.
The law* defines tyre wear as follows :
"The difference in depth between the main grooves on tyres on the same axles must not exceed 5 mm ".
" The 1,6 mm high wear indicator displays the minimum legal rubber thickness allowed ".
*The following information is taken from ‘Le code de la route’ as exists in French law. National legislation in other countries may differ and should be consulted.
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7- Tyre Vocabulary
- Alphanumeric : Adjective describing the system used to designate the dimensions of tyres based on load and including load capacity, structure type, the height / width ratio and the wheel diameter expressed in inches.
- Aquaplaning : The loss of adhesion at high speed caused by a film of water between the tyre and the road surface.
- Aspect Ratio : The ratio of the sidewall to the width of the tyre tread expressed as a percentage So a tyre of 220mm width with a sidewall height of 110mm would be a 50Aspect Ratio, or 50 profile tyre.
- Balance : The state in which a tire and wheel assembly spins with all its weight distributed equally.
- Bead seat : Point of contact between the bead and the rim ensuring an airtight seal.
- Carcass or Covering : The tyre body beneath the tread and sidewalls.
- Cold inflation pressure : Inflation pressure of a tyre having run less than a mile or having cooled for at least three hours.
- DOT : Abbreviation of the U.S. Dept. of Transportation. This marking on a tyre confirms that it conforms to the standards of the aforementioned authority.
- Load capacity : The load that a tyre can withstand at a given inflation pressure in conformity with the standards of the Tire and Rim Association.
- Load Index : An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of the tire.
- Metric LT: Tyre designation system comprising width in mm, aspect ratio, speed index, structure type and the rim diameter in inches (e.g. LT205/65HR15).
- Metric LTP: Tyre designation system for light commercial vehicles introduced in 1992 comprising width in mm, aspect ratio, speed index, structure type and the rim diameter in inches (for example, LTP235/75R15).
- Metric Tyre Designation : Tyre designation system comprising width in mm, aspect ratio, speed index, structure type and the rim diameter in inches (e.g. 205/65HR15).
M+S, M/S or M & S : Markings on the sidewall confirming that a tyre conforms to the RMA definition of a mud and snow tyre.
- Numeric System : Dimensional designation system comprising the tube diameter and the rim diameter in inches. (e.g. 7,35-14).
- P Metric System : Tyre designation system comprising width in mm, aspect ratio, speed index, structure type and the rim diameter in inches (e.g. P225/70R15).
- Ply : A rubber-coated layer of fabric containing cords that run parallel to each other; extends from bead to bead and goes between the inner liner and belts of tread.
- Radial Tyre : Tyre construction where the cords in the body run at 90 degrees to the centreline of the tread.
- Regrooving : The process of cutting new grooves into worn tread to extend the life of truck tyres . An illegal operation on car, 4x4 and light commercial tyres.
- Retreading : The process of replacing the tread layer on a tyre. Generally reserved for commercial, agricultural and industrial tyres.
Ribs : The circumferential part of the tread between two adjacent grooves.
- Series : See Aspect Ratio.
- Shoulder : The part of a tire where the sidewall and tread meet.
- Sidewall : The part of the tire between the tread and the bead.
- Speed Index : Alphabetic system indicating a tyre’s capacity to run at a given speed.
- Tread : That part of a tyre that is in contact with the road.
- TWI : Tread Wear Indicator, rubber element in the tread indicating the point at which a tyre should be replaced, standard height 1,6mm.
- UTQG : Uniform Tire Quality Grade. A system of measurement of tyre performance based on test results relative to three criteria : tread wear, traction and resistance to heating.
- Wheel alignment : The mechanical condition of adjustable components within the vehicle’s suspension. When a vehicle is in alignment, the caster, camber, toe-in and thrust settings are set to specification.
Source : http://www.TireSafety.com (by Bridgestone®/Firestone®)
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