On the subject of tyre enlargement,Do not put a 18 "wide tyre of over 110/18 on the back end of a commando the handling is not any better if anything it is worse, trust me the commando was designed with 19"tyres back and front.
There was a slight change to the commando handling when a 360x19 was put on the front,it quickened the steering .
On G15 cs/N15cs,there is a definite improvement to the handling and steering when modern tyres are used,especially the semitrail type tyre.
On the subject of tyres on the Norton p11,there is a very marked improvement to the steering and handling if again using modern semi trail tyres .
I wished people who own or have ridden these beauties,to stop using K70 Dunlop tyres,and please change your tyres and fit grippy Avon distanzia.
Another problem that I have found that people under inflate their tyres ,on some service sheets I have seen tyre pressures as low as 20lbs,please pump them up on modern tyres, on my G15cs and the P11 i pump them up to 28 front,and 32 back,and on the Commando 30 front 34 back.
My bikes are
Matchless G15 cs
Norton P11
Norton commando combat fastback LR
BSA Devimead gemello(egli type A65)750