As budgets get pinched, lots of people are considering part-worn tyres. After all, a part-worn good-brand tyre may be cheaper than a brand new budget tyre. Which might be rubbish. But are part worn tyres safe? Will buying them actually save you money?

Let’s start with safety. It’s certainly true that worn tyres affect stopping distances far more than you might expect. The British Rubber Manufacturers Association (BRMA) commissioned MIRA to study the effects of tread depth on stopping distances. This study found that on smooth asphalt, the difference between tyres with 6.7mm of tread and the legal minimum of 1.6mm was marked. In short, there was a 36.8% increase in stopping distance in wet weather conditions. That’s pretty huge and could be the difference between a near-miss and a dangerous accident. You can find more details on the RoSPA website.

Less tread = less grip

That study led RoSPA to recommend that tyres be changed at 3mm – well before the legal limit of 1.6mm over 75% of the tyre’s width. In Germany, the limit is already 3mm – this is one source of cheap part-worns. That said, it’s not unusual to see part-worn tyres with 5mm or even 6mm of tread remaining. Presumably this is where a set of tyres has been replaced and not all were entirely worn to the limit in that country. Or they’re considered not worth re-fitting if removed to allow winter tyres to be used.

I personally don’t go in for the scaremongering that surrounds part-worn tyres. Some go on about how you have no idea of the history of the tyre, but that’s true every time you buy a car that isn’t brand spanking new. Do you fit a full set of brand new tyres every time you buy a car? No, I thought not.

But it is tricky to know what’s best sometimes. I’ve opted to buy brand new tyres for my 2CV recently. I couldn’t afford a full set of range-topping Michelins, so had to opt for the Toyo budget tyre. In my experience, it’s a really good tyre, but on the new European tyre ratings, it scores a lowly E for wet weather grip. I must concede, the car does understeer a fair bit in the wet when really pushing on. Might I have been better off seeking a part-worn set of Michelins instead? Possibly – though that leads to other issues. Michelins typically have a low wear rate, so a tyre with lots of grip could be ancient. Has the sidewall started cracking? Has the compound gone all hard? It might still be a liability in an emergency situation. But even by fitting brand new tyres, I’ve boosted the stopping power of the car. Poor tyres with lots of tread are still better than the same poor tyres with very little tread!

And that’s the biggest problem with tyres. Even rubbish ones can be ok for 99% of the time. It’s when you really need them – an emergency stop in wet weather, or an emergency swerve – that you can all too swiftly discover their limitations. I still recall binning a set of Goodyear tyres on a Peugeot 306 after an old lady stepped out in front of me. As I hit the middle pedal, the car locked up far too easily! Fortunately, I think the resulting skid actually helped me miss her. Despite that, I bought a brand new set of Avon tyres and both stopping and acceleration were immediately boosted in the wet. No more wheelspin. Far harder to force a lock-up.

So, this piece has no conclusion to offer I’m afraid. I can’t demand you always buy the best tyres out there, because I’ve just failed to do that with my 2CV. The Rover on the other hand wears really good rain tyres – it has much more performance and more weight to control in an emergency. I certainly wouldn’t rule out part-worn tyres, but I would aim for a really good brand. The near-limit Bridgestone tyres the Rover was wearing when I bought it were actually still very grippy. The cheap, Chinese tyres with lots of tread were not as stable during harsh, damp cornering. All I would say is think long and hard and consider the stopping distance rule. Whatever the tyre, less than 3mm of grip can have a very detrimental effect.