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!

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.

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.

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..

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.

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

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 IndexPoundsKilogramsLoad IndexPoundsKilogramsLoad IndexPoundsKilograms
70739335891,2795801082,2051,000
71761345901,3236001092,2711,030
72783355911,3566151102,3371,060
73805365921,3896301112,4031,090
74827375931,4336501122,4691,120
75853387941,4776701132,5351,150
76882400951,5216901142,6011,180
77908412961,5657101152,6791,215
78937425971,6097301162,7561,250
79963437981,6537501172,8331,285
80992450991,7097751182,9101,320
811,0194621001,7648001192,9981,360
821,0474751011,8198251203,0861,400
831,0744871021,8748501213,1971,450
841,1025001031,9298751223,3071,500
851,1355151041,9849001233,4171,550
861,1685301052,0399251243,5271,600
871,2015451062,0949501253,6381,650
881,2355601072,1499751263,7481,700

Tyre speed index table

Speed CodeSpeed(mph)Speed(k/ph)Category
L75 mph120 km/hOff-Road & Light Truck Tires
M81 mph130 km/hTemporary Spare Tires
N87 mph140km/h
P93 mph150 km/h
Q99 mph160 km/hStudless & Studdable Winter Tires
R106 mph170 km/hH.D. Light Truck Tires
S112 mph180 km/hFamily Sedans & Vans
T118 mph190 km/hFamily Sedans & Vans
U124 mph200 km/h
H130 mph210 km/hSport Sedans & Coupes
V149 mph240 km/hSport Sedans, Coupes & Sports Cars
W168 mph270 km/hExotic Sports Cars
Y186 mph300 km/hExotic Sports Cars
ZR149 mph240 km/hExotic Sports Cars