It's not always easy to determine if you need to replace your car tyres. Here are three signs that might mean that it's time to invest in a new set.

Their tread depth indicators have reached the legal limit

All tyres have tread depth indicators; these are small bars on the rubber. When these bars wear down to the point where they sit at the same level as the tread blocks, it means that the tread depth is too low.

Tyres with a low tread depth can be extremely dangerous to drive on. They can significantly increase your stopping distances, particularly during periods of heavy rain or snow when the roads are wet. There is also a much higher risk of your vehicle losing its grip on the road and aquaplaning.

As such, if you notice that your tyres' tread depths have gotten quite low, you should have them replaced as soon as possible.

The sidewalls have started to deteriorate

A tyre's sidewalls can develop cracks for any number of reasons. Oftentimes, this damage is the result of the sidewalls scraping against the kerb whilst the vehicle is being parked. However, UV rays and high temperatures can also result in this form of deterioration, as can the passage of time (over the course of a year or so, the rubber on a tyre slowly becomes more brittle and prone to cracking).

Regardless of the cause, sidewall cracks should not be ignored. This damage can weaken the tyre structure and increase its susceptibility to blowouts. If this should happen when you're driving on the road, you could end up losing control of your car and hitting another road user or pedestrian.

You're inflating them more frequently

If you've recently started carrying around heavy items, such as luggage or sports equipment, in your car, then you will probably find yourself having to inflate your tyres more frequently. This is perfectly normal and does not mean that you need new tyres.

However, if there have been no changes to your driving habits but you still have to top up the tyres pressure levels more often than you used to, this could be cause for concern. This usually indicates that one or more of the tyres has developed tiny lacerations that are allowing air to seep slowly out of the tyre.

Unlike a standard puncture, these lacerations are not always immediately visible. The most obvious sign is having to continually top up the tyre's air pressure. In this situation, if you're unsure as to whether your tyre has sustained this type of damage, you should take your vehicle to a tyre specialist to have them assess them and, if necessary, replace the affected tyres.