Triumph themselves tell you to use 15/50 in temperatures above 10deg C. Somewhere in the mighty document that is the workshop manual there is a lubrication chart with this info. I use it in every Triumph triple and twin except the little triples and in every instance the owner has reported better gear selection and clutch operation and a quieter engine. In one or two far north Western Australian bikes, I know guys use a 60 wt top number due to very hot conditions and long high speed rides with higher powered bikes. On pg 136 of the manual it says either 10/40 or 15/50 oil, but does not say why. I have seen the chart/table however, and obviously used the 50 oil and found it better.
The point TRIUMPH was making to me was all the bike makes have gearbox failures that are more frequent than TRIUMPH I was complaining to them that the ROCKET forum had several owners complaining about the trans problems so what could they do to give more support to the loyal owners that love the bikes
