A German Continental Tire engineer once went thru my shop in 1972. I asked him lots of questions while we serviced his Beemer, which had his Continentals aboard (he was one of the designers on the Continental Twins team). One of the most important answers he gave me was as follows, which I've used for 40+ years since on cars, bikes, and my motorhome with excellent results:
To find the correct tire pressure for your bike (or car or motorhome), measure the pressure of cold tires, then ride 10 miles at least. Stop and measure the pressure again. If it rose 2 PSI, you have the correct pressure. If it rose MORE than 2 PSI, add 2 PSI, let them cool off to cold again, and repeat the test. If it rise LESS than 2 PSI, decrease by 2 PSI and repeat the test from cold.
Using this, I ran the Continentals I [briefly] had at 34 PSI front, 36 PSI rear 1-up, 38 PSI rear 2-up. Sidewall rating was 40 PSI max. cold.
When I switched to Dunlop's K81 (true trigonometrics, not the current versions) It came to 38 PSI front, 38 PSI rear 1-up, and 40 PSI 2-up (these had a narrow footprint when riding straight up). Sidewall rating was 44 PSI max. cold.
When I went to the Avons, it has not mattered which tire I use, it has so far always been the same: 36 PSI front, 38 PSI rear 1-up, 38 PSI 2-up, 40 PSI 2-up with all her stuff on a long trip. Sidewall rating is 42 PSI max. cold.
Keep in mind: the label on the bike's fender was made for bias-ply tires of inch profiles (in :70 and :80 ratios) of the 1970s technology. Today, ALL bike tires are made on metric round profiles, usually :90 or sometimes :80 profiles (ie. they are taller, even those labelled in inch sizes), so they need more PSI to keep their shape and not roll under with loads and corners, as shown in TT's wise pictures above.
