Although E15 is not yet mandated for motorcycles, it becomes a problem when dispensed in a hose through which both E10 and E15 run.
If E15 remains in the hose from the previous customer, it mixes with the E10 causing a higher than E10 concentration for a motorcycle. The EPA wants to require that a minimum purchase of 4 gallons be made. This immediately becomes a big problem for motorcyclists.
Read the complete article by Matthew L. Wald.