Shimano RS700 wheels with Continental 5000 TL 700X25.
Wheetset and tires were new.
I mounted one tire on the rear wheel with a struggle, but in one effort.
I tried mounting the other tire on the front wheel, but after struggling hard, wearing light work gloves to increase the grip, I gave up after struggling for 15 min and with bruises on my palms.
Tire lip in the rim well, and pulling all the slack as much as possible.
I decided to leave the half mounted tire in the sun for about 3 hrs (26 Deg C).
Then I tried to remount the tire which I did successfully with a struggle, but one hard try. There was definitely a difference.
I suspect there was a slight difference in tire diameter, and rims have a different profile.
However, heat made quite a difference.