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An upright bike more closely simulates riding a bicycle, while a recumbent bike lets you lean back and pedal with your legs in front of you. You can buy equipment that will raise the wheels off the floor or rollers that will turn under your wheels so you can ride in place. Get on it in the shoes you will wear during the workouts and see if it can be adjusted so you can ride it comfortably.
Try both an upright bike and a recumbent bike. Convert your regular bicycle to an exercise bike. Ensure that the bike is the right size.