My understanding is that part of what keeps the recap in place is the tire pressure of the old carcass. It is glued on, but it's a press fit too, so if the carcass loses pressure and the rubber heats up, the glue fails, and kaboom, tread on the road. The circumference of the carcass increases as the pressure increases, so in a perfect world that pressure would keep the tread in place if the glue failed.

I used retreaded tires on an old VW Type 1 I drove when I was a teenager, snow tires no less, and they worked just fine. It did bug me that the carcasses were different brands, and one had been a white wall, which the retreader just painted over with some black goop.

Of course retreads are a big thing on heavy trucks, most drive wheels and trailers have recaps on them, just not steer axles as a rule. When a new tire costs $500 and a retread is $175, makes a lot of sense. I just don't see where there's enough money savings with passenger car tires to have an economic advantage to retreads.

__________________
2002 Ford ZX2
2 x 2013 Honda Civics