I had a seasoned Harley independent mechanic say this 40 psi was preferred over the Harley owner's manual recommendation of 30 psi front tire for OEM Dunlops.
Reason... longer tire life, not necessarily handling.
But...with 30psi I've experienced near 10,000 miles.
XL1200N Nightster.
Yes No?

 

As time goes by so Harley change the spec. In 2017 All 1200 Sportsters had the recommended front pressure set at 36psi.

 

Be sure you have all the facts when you consider what others use on other bikes or years. Consider suspension rates, tire size, type of tire, construction, ECT..

Start if nothing has been changed with what your owners manual says. Then if you like, you can go up but never more then what it says on sidewall of tire. (Cold setting)

Going up would tend to more then likely just tend to make ride fill rougher. Not sure about others but I have never seen a motorcycle tire wore out first on the side wall. (AKA chicken strip)

May tend to give you a tad better fuel mileage at 40. Tire obviously would tend to stay rounder at speed. Seen a video of a tire at high speed and it had all kinds of out of shape places from road imperfections.

Now at 30, that does tend to make a tire stick to the road as it rolls along and in turns. You don't tend to want a motorcycle sliding side ways.

 

Why not ask him for his source? Once you know it, you can check it and verify it for yourself