My bike is tuned for premium, but if I ran into that situation and really needed gas I would put enough regular in the tank to get me back to civilization. It won't hurt anything in the short term, as the knock sensor in the ECM will prevent any serious detonation from occurring--but since it retards ignition advance on the fly to accomplish this your performance won't be up to snuff until you refill. You also may hear some early detonation before the knock sensing function kicks in, and if so I would try to minimize this for the duration.

 

You could always use the lower octane gas and add a supplement octane boost if you were all torn up about it.

I am pretty sure that I have mistakenly gotten a little too much lower grade from a multi-grade pump. The bike drove a little different but we are still on the road together.

 

If I was almost out of gas, I would get the regular, but ride it EZ.