This means that your tyres have perished between the treads or around the sidewall. Changing weather conditions is usually the cause, as tyres will expand and contract when exposed to heat and cold. Over time, this can weaken the tyres, and breaks in the fabric of the tyre will occur. These splits or cracks in tyres will usually be picked up during your vehicle's MOT. Once a tyre has split, it needs replacing, as its condition will only worsen over time and can become potentially dangerous. This may result in a price reduction to replace the tyres.