I live in England, and the choices of oils here seem to differ from most of the ones mentioned in other threads. I just bought a Sportster Iron, and I've done a few miles so want to do the 5k service. I got the engine oil and filter but I'm not sure what grade to put in the transmision. Surely a gear oil EP75/90 will do? Or something similar? Why is there such mystique surrounding Harleys' choice of oil? I've always serviced my own bikes, German, British, Italian and Jap and have never come across this problem before.

 

Welcome from sunny Southern California. Post your question on the sportster section and more people answer from there.

 

Welcome!

 

A big welcome to you from sunny Southern California. Glad to have you on board.

 

Hello. Yes the oil crap I read in this forum just perpetuates the absurdity even further.
As far as your engine goes any 20w-50 will do just fine. You don't need an over-priced v-twin oil. Only a fool will spend their money on such an obvious marketing ploy. A shared sump bike MAY benefit from that over priced v-twin JASO approved oil however our bikes aren't shared sump. Yours shares tranny/primary fluid.
Now in my shared sump bikes I use rotella t conventional diesel oil,and I still use it in my primary. My bike has 106hp/115tq and my clutch doesn't slip whatsoever.
None of my shared sump bikes have ever had an issue using rotella however you mentioned gear oil.
As far as gear oils go some contain friction modifiers which will ruin your clutch. Red line shockproof does contain friction modifiers so stay away from it. Amsoil severe gear will work in your application if it's available,and a 70w-90 is fine. I use the shockproof heavy in the 70w-140 flavour and change it every 20000kms.
I really like how my clutch feels with rotella on all my bikes. I noticed clutch function was I bit more grabby with thicker fluid until the bike was up to temp but with rotella I never had a change in operation with rotella.
I think you need a gl-5 gear oil in your bike however I'm not 100% sure on that. I'm sure someone will pop in here for you and clarify. Do not use transmission fluid. They all contain friction modifiers to some degree

 

Welcome

 

Welcome from South Florida.

 

+1, welcome to the forums, you'll have much better luck in the specific sections for your bike or question. Good luck.

 

Welcome from the Sunshine State.