75 norton 850 tire sizes

I was just looking for my MK1 and found this site

http://www.nocnsw.org.au/technical/tyres-norton-commando

Looks good info? the tyre choice may be out of date though

"For 1971-75 Commandos:

Concours display:Front and Rear: Dunlop 4.10H19 K81 (New old stock if possible- Made in England is best!)

All around riding:Front and Rear: Avon 100/90H19 Roadrunner Universal

Very fast riding:Front: Avon 90/90H19 Roadrunner AM20Rear: Avon 100/90H19 Super Venom AM18"

I always liked a smaller section (3.25 or 90/90) on the front as I felt it sharpened up the steering a bit.

That list was written before Avon introduced the Roadrider, so all round is Roadriders 100/90 19 front, 100/90 19 rear, fast is Roadrider 90/90 19 front 100/90 19 rear. 90/90 on front gives faster steering.