Nice,
So as a ‘for instance’
Try getting the rear wheel back in once you’ve fitted the recommended size AVON.
The 4.00x18 continental or metzler will still be a bit of a battle but will go,,,,,,just
Continental Classic Attack get a vote (I'm guessing in 90/90 and 110/90 sizes), as do Continental RB2/K112 though these don't get a mention on the Conti web site and where dealers claim to have them, the front doesn't appear to be available in 18", only 19". I wonder if there are any Conti Go! kicking about as I like those on my R80.
The Metzelers (ME11/ME77) are good and the ME33 is a marked improvement over the Michelins but don't use it as there are safety issues.
The Avon Roadriders are good but they might be too tight a squeeze.
Yes, Continental Classic Attack 90/90 R18 front and 110/90 R18 is what I have fitted to my 1982 R65. These modern technology radial tyres give excellent feedback, ride quality and grip for classic bikes.
I also used a pair of these on my Manx Norton which were a big improvement over the Avon tyres.