2012 FLHX i think... I have used Amsoils 20w50, Mobil 1 20w50 and finally just went back to HD Formula plus...really not much difference to me, all about the same....Main thing is actually changing it.

 

I think I've tried everything except used motor oil and I have found HD Formula plus to be as good as anything.

 

I run Amsoil 20/50 in the Motor, Amsoil 75/140 in the Tranny and Harley Formula Plus in the Tranny! Bike is nice and quiet and runs perfectly with this combo.

 

Amsoil 20-50 in the motor - Spectro heavy duty 6 speed in the tranny - and formula + in the promary. Works for me.

 

Mobil 1 20w50 V-Twin in the engine, Bel-Ray Primary oil in the primary and Redline Shockproof in the tranny.

I was using Mobil 1 Racing 4T 10w40 in the primary but swapped it back out for the Bel-Ray. The Bel-Ray just has a great feel to it, very smooth engagement and a positive lock-up.

Plus the Bel-Ray is red, if you get a leak it easier to tell what is leaking.

 

Engine: Mobil 1 V-Twin 20w50
Primary: Mobil 1 Racing 4T 10w40
Tranny: Mobil 1 Gear Lube 75W-140

 

Engine: Mobil 1 V-Twin 20w50
Primary: Mobil 1 Racing 4T 10w40
Tranny: Mobil 1 Gear Lube 75W-140 +1

 

viscosity is measured differently on gear oil, vs engine oil. a 75/90 wt gear oil has almost the same viscosity as 20/50 enigne oil.

now having said that, i wouldn't use it in the primary....... ymmv

 

I use Red Line Synthetic Primary 75W80.

 

Idiots are born every day so there's always a fresh batch.
Motor oil, HD Primary oil and ATF are great choices for the primary.
Gear Lube....not so much.