Probably the worst tyres I ever had were a set of well-aged, worn Semperit Speed-Life that I got with a set of spare wheels for the 900 turbo. I thought it a good idea to wear them down to legal minimum over the summer before putting fresh winter tyres on in autumn. To accelerate this process, I threw in a few laps on our local race-track, err, privately operated toll road. Unfortunately, even though the day was sunny and warm, there were still some damp patches of asphalt where the shadow of trees reached the track. Almost lost it at Flugplatz, sliding over all 4 wheels to the outside. Luckily, there was just enough asphalt left...
Half a lap later at Wippermann my rear axle got impatient and tried to overtake. Two near losses during the first lap... during a guided lap at that!
After that day I had enough and got the summer wheels with the Michelin Energy Saver back on (which also were not very good in the wet, to say the least. But even they gave more confidence.)
Second worst would probably be some 11 year old Toyo summer tyres on my 9000 Griffin. They were taken off nearly new and kept in cool, dark storage for a decade. No cracks, rubber very soft and pliable. My mechanic gave them to me for free - and made it clear to look out for accelerated aging. First two months were great - whithin their abilities. They were a bit worse in the wet, but not terrible, and within what you would expect after reading 11 year old tyre tests. What they lacked in performance was probably due to being an old design, not the age per se. Then suddenly they hardened completely, developed fine cracks, and lost all wet grip. I replaced them immediately. Still not to bad, as I got 9000km out of them over these two months.
Lesson learnt: even an old tyre can work it it was stored correctly, but you have to keep an eye on it. If you have a feel for your car, you will notice (and hopefully change them) before they become dangerous. Not something to put on your mom's car*.
The biggest disappointment I have had with Continental. One set of winter tyres (TS790 or TS810, can't really remember) on a Saab 900 turbo, and three Sets of EcoContact on two different w123 (200d manual, 300d automatic). All of these were great when new. But the winter tyre lost all grip in it's second year with plenty of tread; the summer tyres would suddenly use all wet grip over a weekend after within their first season.
When 88 asthmatic horses working through a soft slushbox overwhelm the rear tyres and you intitiate a drift/powerslide when slowly taking off from a red traffic light while turning right, then something is awfully off.
So I replaced all sets at >5mm tread... The first I thought was a fluke, the second confirmed the pattern and the 3rd finally ended the learning experience. I may be slow, but eventuell even I do learn.
Interestingly, it seems Continentals second- and third-tier brands like Uniroyal and Semperit are much more consistent. These are, however, not so well-rounded. They have clear strengths and equally clear weaknesses: Semperit always were good in the dry und handled surprisingly well, even their winter tyres (Speed Grip 2), but were terrible in the wet (summer) or in the snow (winter). Uniroyals are good in the wet and immune to aquaplaning, but have very indifferent, mushy handling, not so great dry braking and ridiculous wear in the summer heat.
Guess you can't have all... I see why Conti is winning tyre tests - they are great when new. But they can't keep that up. If you want the absolute best, buy Conti and replace every three to for months. If money matters, get something else. If you drive a lot, Michelin will be much cheaper on a per-km-basis. It might start a bit below the Conti performance-wise, but it will keep this perfomance level consistently until you reach the wear marks.**
*Unless you have a badass mom, of course. Mine learned to drive in a VW beetle and knows how to drift a rear-engined car... but she also totalled two fwd cars. Are these facts linked?
**with the exception of aquaplaning, of course. Only tread depths and negative profile area protect you there.
