Originally Posted by RIPbiker13

The compression ratio is low enough that running the lower octane won't harm anything.

In high compression engines the lower octane fuel can prematurely detonate (before TDC) and over time wear the rod bearings.

As it stands, the only benefits I can see by running the higher octane fuel is better fuel economy and a cleaner burning fuel that won't cause carbon to build on the injectors, decreasing their lifespan. If 87 was all you had in the middle of nowhere, run it until you find better fuel. Otherwise I would stick to the dealer's recommendation of 91+ octane.

Originally Posted by handyhoward

I might as well add my two cents... I have run 87 octane regular unleaded with or without ethanol for the past 8 years in my carbureted 03 Fatty. Never a hiccup... HD's recommended octane has everything to do with pre-ignition (ping or knock). If your engine runs without pre-ignition on 87 octane, you will not gain a thing by running on a higher octane. It is a good rule of thumb to run on the lowest octane that you can without pre-ignition because the fewer additives in your gasoline the cleaner and crisper (power) your engine will run.

Originally Posted by lh4x4

HD recommends 91 octane but the fuel injected ones will run fine on 87 and even 85 if you are at 6,000 feet.

Just don't lug the motor. The ECM will retard the ignition a little with the lower octane gas to prevent pining.

I run five fuel injected HD's for years and all over this country without a single issue with the 89 octane that I use.

But, it is your bike put whatever you want in it.