Yes, that's what Avon recommend (max for 21" 90/90). My "B" 18" 410 / 80 and on WM5 (3"wide). When teenagers Harvey and I had unpaid jobs in the paddocks of the IOM TT 1966 it looked as if all bikes ran on Dunlop Triangular tyres and they looked triangular except Honda as they had much wider rims, more support also more rubber on the road. When the "A" gets home again and thinking of removing 19" S/S rim and lacing on a 21" WM 4 as the 410 x 19 I had to cut tread off the chain side to clear, I will also increase gearing which it can take as seldum change from top.