Retreads are pretty much used by all London Taxi drivers and those people drive! I wouldn't do more the 70mph on them but they should be fine otherwise. In my 26 years of living in the UK, I have never seen a belt come off a tire. But then again, you can get 3 points per tire if it's below the legal limit (12 points to lose your license) so people don't wear tires to the extent that they do here.

I think as long as you understand that you're wearing retreads, and drive that way, you should be good.

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With best regards

Al