When should I replace my tyres?

I bought a used car recently and I will be using it frequently on the highway. I am wondering whether I should replace the tyres. How can I know whether the tyres are due for replacement?
Byamugisha Derrick.

Hello Derrick, besides helping your car to drive, tyres play a crucial role by contributing to your road safety while braking and provide useful traction to allow better car handling and control. Good tyre treads also contribute to good fuel economy while loss of traction makes the car engine work harder or run at higher engine revolutions. Tyres are built with treads which are designed to suit different terrain and purpose. These treads are designed differently to suit high speed driving on a hard concrete or tarmac road, wet or slippery soft terrain and uneven rocky off-road terrain. When tyre treads wear down the crucial roles mentioned cannot be fulfilled. You can know when the tyre treads are worn out by visual inspection. Extremely worn out tyre treads will be evident. Where you are in doubt you can use the tyre tread wear bars designed and fitted between treads on all major commercial and private tyres. When the tyre tread reaches or exceeds the tread wear bar it should be replaced. A coin test can also help using a Bank of Uganda 100 shillings coin. If your tyre tread is below the 100 mark, consider it unsafe.