When I bought my 91 Miyata 1400A, it had the original Miyata branded 700x20 tan walls on it. They looked pretty darn fresh and I rode them for a few months, fast and hard with no problems. But I thought I might be pushing my luck so I went ahead and changed them - twice! - with good quality 700x23s, and the bike just felt dead! Neither of the new set of tires performed nearly as well as those old Miyata tires did. Its almost as if the bike was built around those original tires.
I still have those tires hanging up in the garage, and I have been tempted more than once to put them back on!
If the original were radials, found on some Miyata bicycles, like the
1000 I had. I did ride the 1000 with the original tires but chose to install new ones. They did feel like a lesser set of hoop protectors. Sadly, I do not have any pictures of those tires.