Around here, it's the higher octanes (which means 91, and sometimes 90 and 89) which are usually E10. E15 is relatively rare, but one chain has E15 as standard for 91, and that is also the only consumer fuel chain right here (Topeka, Kansas, USA) which is carrying E85. I've run lots of vehicles on E10/91 and E10/90, never had a problem with them. E85 definitely reduces power in OEM flex-fuel circumstances, but there is at least one way to do better (
@obi_waynne, I hope this is OK, you know where I'm going):
I have also wondered about engine tuning/remapping and flex fuels. Given how much potential energy is not being used productively in any engine, it seems to me that there should be ECU remapping out there to recover all of that power and then some. But I have not found such a thing in general aftermarket search, at least yet. I do wonder what would happen if one took a flex-fuel vehicle, filled it with E85 only, set up a good remapper, and let it go.
There is another aspect of stock flex-fuel setups which may be relevant as well. The ones I have thus far heard of, require that one use E15 or lesser numbers one full tank in three (3) or so. Don't know why. Perhaps there are sensors that have to be recoated or something. I'd love to know a lot more about this, I'd love to replace those sensors if the appropriate replacements exist. In my non-flex Tahoe testbed for the above link, I do have to use non-E85 one tank in three or four, or the computer really does seem to lose understanding of something, a stutter comes in.