Continental's website recommends after 10 years -
https://www.continental-tires.com/products/b2c/tire-knowledge/replacing-tires/#:~:text=All%20tires%20(including%20spare%20tires,following%20the%20%E2%80%9CDOT%E2%80%9D%20symbol.
"Continental is not aware of any technical data to support the removal of service for tires past a specific age. But the same principle applies to the tires of your vehicle as it does for any other part of your car – age matters.
Together with other members of the tire and automotive industries, Continental advises that all tires (including spare tires) made more than ten years ago should be removed from service and replaced with new tires."
It's interesting that they say there is no data to support it, but still recc to buy new @ 10 years? I'm not disagreeing, just curious as to their basis for that.
A few years ago I replaced the 7 year old expensive (Michelin, $600 each) tires on my motor home. They looked great, lots of tread and no sign of any cracking. Once they were removed I was surprised to see severe cracking and "zippering" on the inside of all the tires. That experience is why I don't go longer than six years.
Don't get me wrong, I am on the side of "safety first", "better safe than sorry", etc. And the thought of my safety relying on those 4 patches of rubber is concerning. And while I won't argue the 6 year number, and wouldn't try to convince anyone else otherwise, I do think there are considerations. I'll assume the 6 year number is conservative enough to consider most use cases (90%?), so much of the 'bad case' conditions are covered. This isn't a brick-wall, binary decision, it's a curve. And if 6 years covers most everything, than clearly those under better conditions would be in much better shape for longer (how much is tough to say w/o data).
In my case, low miles, mostly (~100% for DW) trips on local roads with 45 mph limits. I might be on the expressway at 70~75 for 10 minutes and 60~65 another 10 minutes once or twice a month, maybe. And few of those times would be in any extreme hot weather. And we rarely load our cars up, it's mostly just one or two of us. And with tire pressure monitors, we aren't running low (leads to over-heating and sidewall damage), and I make sure they aren't over-inflated. And as I mentioned, garage kept most of the day as well, so little UV exposure. I have to believe that is a far different scenario from a motor home tire used in Texas heat and probably long, loaded hot, highway miles.
But I still question if I'm skimping? Just replace them at 6 years regardless, sure, not cheap, but still 'affordable'. Better safe than sorry?
I guess what keeps me wanting to stretch a bit, based on the above, is it might be safer in my case - I tend to keep my cars a long time, last one was 16 years. Say I keep this one that long (I'll be 85, so who knows about driving?). Well, if I replace at 6 years (with good tread), then what happens at 12 years? Will I convince myself I'm only going to keep the car a few more years, no need to replace them now, I can get by? And I go on to 16 years, now the tires are 10 years old, and tread is less than it would have been. So for me, replacing at a little beyond the expected max 'half-life' of the car might actually give me the best 'average' tire quality, at 2/3rds the cost (and environmental impact).
I suspect the degradation between years 8-10 is far greater than the degradation between 6-8, so in my case, stretching to 8 years seems justified. But that is specific to me, I'm not arguing with anyone over their personal decision.
-ERD50