Decoding Tyre Size

So you've made it to here... we're guessing you need a little help decoding your tyre size. Never fear we're here to help, the below information will shed some light and get you on your way!
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The tyre width is measured from end to end of the tyre including the sidewall but excluding and raised lettering or rim protectors. In this visual 255 indicates that the tyre's width is 255 millimetres.

Safety Tip: Tyre width is important as it can affect both your car's performance and how economical it is with fuel.

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35% is described as the aspect ration, this mark represents the height od the tyres sidewall as a percentage of the nominal section width.

Safety Tip: Check tyre pressures regularly. Tyres with a low profile can sometimes look normal even with dangerously low pressure.

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The letter R stands for Radial, the type of tyre fitting to your car. The number is the diameter of the tyre's inner rim, or the size of your wheel rim. This is measured in inches e.g. R19.

Safety Tip: It's vital to fit the correct size wheel to tyre combination in order to obtain optimum performance from the tyre.

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Using the "tyre load index table" which can be found below, you're tyre's load index indicates the maximum weight in kg that your tyre can safely support.

Safety Tip: Avoid exceeding this weight as it can result in steering instability and even rupture.

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Speed index is a letter which relates to the "tyre speed index table" below. The last letter indicates the maximum speed for the tyre at full load (in this case Y = 300 kph).

Safety Tip: It's really important to check your speed index as choosing a tyre with a rating too low for your vehicle can invalidate your insurance.

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The manufacturing week and year allow you to understand when the tyre was manufactured and is indicated by 5118 (51 being the week of manufacture and 18 being the year of manufacture).

Safety Tip: Make sure your getting rubber that is not aged and has been exposed to the elements as this reduces the tyres life.

Tyre load index table

Load Index Pounds Kilograms
Load Index Pounds Kilograms
Load Index Pounds Kilograms
70 739 335 89 1,279 580 108 2,205 1,000
71 761 345 90 1,323 600 109 2,271 1,030
72 783 355 91 1,356 615 110 2,337 1,060
73 805 365 92 1,389 630 111 2,403 1,090
74 827 375 93 1,433 650 112 2,469 1,120
75 853 387 94 1,477 670 113 2,535 1,150
76 882 400 95 1,521 690 114 2,601 1,180
77 908 412 96 1,565 710 115 2,679 1,215
78 937 425 97 1,609 730 116 2,756 1,250
79 963 437 98 1,653 750 117 2,833 1,285
80 992 450 99 1,709 775 118 2,910 1,320
81 1,019 462 100 1,764 800 119 2,998 1,360
82 1,047 475 101 1,819 825 120 3,086 1,400
83 1,074 487 102 1,874 850 121 3,197 1,450
84 1,102 500 103 1,929 875 122 3,307 1,500
85 1,135 515 104 1,984 900 123 3,417 1,550
86 1,168 530 105 2,039 925 124 3,527 1,600
87 1,201 545 106 2,094 950 125 3,638 1,650
88 1,235 560 107 2,149 975 126 3,748 1,700

Tyre speed index table

Speed Code Speed (mph) Speed (k/ph) Category
L 75 mph 120 km/h Off-Road & Light Truck Tires
M 81 mph 130 km/h Temporary Spare Tires
N 87 mph 140km/h
P 93 mph 150 km/h
Q 99 mph 160 km/h Studless & Studdable Winter Tires
R 106 mph 170 km/h H.D. Light Truck Tires
S 112 mph 180 km/h Family Sedans & Vans
T 118 mph 190 km/h Family Sedans & Vans
U 124 mph 200 km/h
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars
W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars
ZR 149 mph 240 km/h Exotic Sports Cars