I have an 09 Rocker C 1584cc, 96cu, fuel injected, with a stage I kit. Someone just recently mentioned I should use 92 octane! Is that true? What are the pros and cons if Harley suggests 87 octane?

 

Don't know about your specific bike but the owners manual for my 07 EG says minimum of 91 octane. I think you have the same basic engine but I could be wrong.

 

91-93 any higher is a total waste and may not run right.
Your ride is designed to run on 91 that is governed mostly by compression.
The higher the compression the higher the octane needed. Higher octane burns slower .
If you put to high and octane in, fuel does not ignite when it should to low it can ignite under compress before it should.