It is a tolerance stack-up issue, especially bad with Conti and some rims, despite the erroneous information from mongrels.

If you heat the tire even on the hot sun, it is almost manageable with a Kool Stop and I do not care how strong someone is or how smart they think their technique is, some brands of rims and Conti do not play well. Period. I know how to put a tire on.

https://www.sigmetrix.com/tolerance-stack-up/

(I also know something about design. Tires and rim Mfgs are out of control,)