I have Marathon Plus tires:
- 5 years old
- 15000 km
- bike stored indoors
I'm getting more punctures than I used to, but maybe that's caused by my riding now on worse road surfaces than I used to. The punctures tend to be slow leaks from sharp grit (crushed stone which surfaces an unpaved path) embedding in the rear wheel.
Total weight (me and the bike and stuff) is about 200 lb, and the tires are always properly inflated.
Is it plausible that the tires are less puncture-resistant than they used to be, i.e. is it worth replacing them now if I want to avoid punctures? How can I tell? Is the fact that they still have tread (aren't worn smooth) proof that they're not worn significantly?
Against 'time bombs' such as shards, flints and glass, only a thick rubber belt like Smart Guard will work.
Is it possible that the inner belt isn't working as well as it used to?
The tires are still very rideable but is it likely that they're now significantly less reliable than when new?
It's not nearly as visibly worn as shown on Schwalbe's 'Tyre Wear' page, which shows tyres that are "worn out" and "need replacing urgently", and which says,
The tires of the Marathon family usually last between 6000 and 12000 km. ... The Marathon Plus is outstanding with its extremely high mileage of often much more than 10000 km.