Car Tyre limitations

We pay quite a lot of attention attention to the maintenance of our car, like washing, servicing, repair and daily check and cleaning .But we pay very little attention to our tyres fitted on the car. Very few of us know that each tyre comes with a load as well as speed limitation. Fully loaded car being driven at higher speed than recommended may lead to tyre burst and serious injuries to occupants and damage to the car. It is quite possible that you may not be able to drive the car in future.

If you look at the side wall of the tyre you will find makings like10/55 R 16 87 M besides the manufacturers name,  other details and also the week and year of manufacture. These markings describe the tyres capability fully. These alphabets and number represent different things.

170- This refers to the section width of the tyre or the cross section of the tyre in mm. The bigger this figure the more wider will be your tyre.

55- This refers to the aspect ratio of the tyre and refers to the height of the side wall of tyre as a percentage of the nominal section width. Here it means that the height of the side wall is 55% of the width of the tyre or slightly more than half.

R - This refers to the radial construction of the tyre. Radial construction means that the tyre’s body piles out from the imaginary center of the wheel.  

16- This refers to the diameter of the tyre from the center to the inner rim in inches. Why it is still in inches and not in metric system still eludes me.

87- This is the load index and refers to the load capacity of the tyre and is an important factor to be taken into account while loading the car. This indicates the maximum load that can be carried by the tyre .Please pay attention to it. Here in this example it means that the maximum load carrying capacity is 355 kg. This number starts with 60 which means 250 kg and goes beyond hundred for transport vehicles. The details of the load index to the total load carrying capacity (TLCC) of the tyre can be found out from the manufacturer’s manual.  As a rough guide load index 60 means that the TLCC is 250 Kg, for 70 it is 355 Kg, for 90 it is 600 Kg. Approximate values can be interpolated by taking these figures as a guide. Besides these the tyre of transport carriers or high performance cars may also carry markings like RF which means reinforced and XL which means extra load.

M- The last alphabet is equally important as it refers to the speed limitation of the tyre. Please pay attention to it while driving on the highway. This letter refers to the maximum speed at which tyre can be driven. Please remember that this speed limit has to do with a reasonably new tyre in good condition with respect to the threads and the sidewall. For older tyres or worn out tyres, please keep a lower limit. Here in this example M refers to the maximum speed the tyre can sustain and here in this example it means that the maximum safe limit is 130 km/hr.  E refers to a speed limit of 60 Km/hr and with increasing alphabet the speed limit rises by 10 Km/hr, except for H where it means 210 Km/hr. Q refers to 160 and V to 240 and Y the maximum to 300 Km/hr.

Please read these markings on your car carefully and for old tyres please reduce both these factors considerably in order to avoid serious damage to the car and self. A large number of accidents due to tyre blow out or puncture or loss of control can be easily attributed to non- adherence or not paying attention to these limitations. In my experience I have found that a vast majority of persons using car are not even aware of these limitations and take the maximum speed as mentioned on the speedometer as a guide and feel that the car can be pushed up to that maximum speed. But the speedometer refers to the performance of the engine and has no relation to the limitations of the tyres.

If you are driving on a concrete surface highway or expressway then please lower these limits as concrete surface generates more friction as well as more heat than tar surface.

Take care and safe driving.