A tandem will fit in an Element but it is tight. The front wheel is off. The rear wheel is on "platform" and rests between the driver and passenger seats. If you had a manual transmission it might make shifting difficult. For a longer trip I made a boom tube support so I could remove the rear wheel and have a be able to hold my wife's hand while driving. Gas mileage for an Element is nearly the same in town or on the highway. We love our Element and live with the 20-21 mpg on the highway.