78 Gl1000. Both tires say max 41psi. What should it be at? The bike is naked, no luggage/fairing. Mostly riding solo. The front was at 36 and the back was at 28psi! Maybe this is why mileage suffered? Both are at 36-37 now.
Mag, you really need to find your tire size & manufacturer (it's on the tire sidewall), then go to the web site of that tire manufacturer. On most tire companies web site there will be a tire fitment guide. Those fitment guides will usually furnish recommended tire pressures & other need to know facts for specific motorcycles. (The newer tire constructions of today VS. 27 years ago sometimes demands different tire pressures).
I used your GL 1000 as a guide & went to the Dunlop site using a standard replacement tire. Unfortunately the GL 1000 wasn't listed but the GL1100 was. The fitment site recommended slightly higher air pressures than the owners manual showsfor their replacement tires.
On my 1200 it showed my replacement front tire recommended at 36 psi & my owners manual recommends 32 psi. Through trial & error I have been running 36 psi cold as that seems to give me the best handling & braking,so it looks like their recommendations are spot on (at least for me).
When I bought my last tires (for a different make bike than we are talking about here) the tire dealer (a very large motorcycle tire retailer) said they usually recommend splitting the difference between an older bikes owners manual tire pressures & the max pressure printed on the tire sidewall. That would also work out pretty close in my case also.
Sorry, no actual tire pressures for you but something to guide you, maybe.