Mobil1 20/50, in bike for 18 months, about 1100 miles on that oil (Yes I know, not that much!)
This is what Blackstone Labs said when I had the oil analysis done...
ROBERT: You had this oil in your bike for 18 months, but it was still in great shape when you changed it so we think
you can go two years (at least) next time. Universal averages show typical wear levels for this type of engine after about 1,050 miles on the oil. You ran just a few miles less than that, and your wear metals are all at or better than average. A trace of fuel was present, though we don't consider this a problem. Typically fuel comes from idling or low-rpm operation. No water found, and solids are low (see silicon and insolubles). The TBN of 8.3 is strong. Nice.
I ran my truck (5.3l V8) for the exact amount of time, 18 months on Mobil 1 5/30, about 4000 miles. Mostly short trips...
They pretty much said don't do that... and change the oil every 12 months.
My wife's car had about 6000 miles in 5 months on Mobil1 5/30, they said try 8000 next time, all was good.
We did just buy a new car and the dealer said we don't have to change the oil until 5000 miles with no break-in oil change or anything. Bought the car with 5 miles, they said change it at 5000. I couldn't believe that! On a motor that's breaking in?? So at 501 miles I changed it to Mobil1. The factory oil looked like chocolate milk and smelled like motorcycle oil (For those who change their car and bike oil, you know the difference..) very odd.
So In 10 years when we buy another car, I'll be changing the oil at about 100 miles instead
One of the big factors in how long you wait to change it is how long the motor is on at a time.
If you do short trips all the time (I'm talking about start the engine let it idle for a few minutes then drive 2 miles and shut it off, you need to change the oil more frequently. If you do nothing but long highway, you can go longer on oil changes. Your oil lasts longer if your engine can get to full operating temp (Oil.. not coolant) so it can burn the condensation and fuel particulates out of your oil (as best as possible). On short trips this will not happen. And it take a lot longer for your oil to get as hot as your coolant. If you've ever had a car that has both oil and coolant temps, you've seen this in action.
But the old rule of every 3k miles.... that's out the window on any synthetic oil today (Unless you do nothing but very short trips)