Robert
Go to
www.gearchart.com.
Select "gearchart creator"
Select "Schumacher 1.8:1 option"
enter spur "86" pinion "36"
enter tyre size 63mm
select rollout
The chart you get can then be printed and kept
you will get rollouts for every spur from 81 to 91 and every pinion from 29 to 44.
check across to find out your rollout
86/36 = 46.03
83/32 = 42.39