Driving my car back to the dealer for a return with £20 part-worn Linglong's was an eye-opening experience. I don't think I crossed 55mph the entire time, and driving through the soaking wet countryside (thanks M25 closure) was actually quite unpleasant. Without wishing to come across poorly - if you can't afford new tyres, I don't think you can afford to run a/the car. They are a safety critical item and if a part-worn tyre fails, it is not just your own life that you are putting at risk. I look at it this way - you don't buy part-worn clutches, wipers or brakes, do you? Part-worn tyres often have "lots of life left in them", but so do part-worn brake discs, pads and every other consumable on a car. Ultimately, you might find some part-worn tyres that are in great condition! I have personally sold a couple surplus tyres that had nothing wrong with them - but, you might not be so lucky. Those four tyres are the one thing between you and the road. You don't see part-used parachutes, lifeboats or helmets! Do you really want to gamble your life by saving £40 per corner? I know I don't.