A wheelchair comprising: a frame; one or more front wheels proximate to a front end of the frame; one or more rear wheels proximate to a rear end of the frame; one or more middle wheels between the front end of the frame and the rear end of the frame; a drive system for driving at least one of the one or more front wheels, the one or more rear wheels, and the one or more middle wheels; and a wheel-positioning system adapted to adjust a height of the one or more front wheels relative to a height of at least one of the one or more rear wheels and the one or more middle wheels, the wheel-positioning system comprising: one or more arms pivotally coupled to the frame at a pivot point, wherein the pivot point is between the one or more front wheels and the one or more middle wheels; and an adjustment mechanism operatively coupled at or proximate to a rear end of the one or more arms, wherein the one or more front wheels are operatively coupled to a front end of the one or more arms and the one or more middle wheels are operatively coupled to the one or more arms at a position between the front end and the rear end of the one or more arms, and wherein the adjustment mechanism is adapted to move the one or more arms between a first position and a second position separately from the operation of the drive system so that the one or more front wheels are in a first position when the one or more arms are in the first position and a second position when the one or more arms are in the second position. a frame; one or more front wheels proximate to a front end of the frame; one or more rear wheels proximate to a rear end of the frame; one or more middle wheels between the front end of the frame and the rear end of the frame; a drive system for driving at least one of the one or more front wheels, the one or more rear wheels, and the one or more middle wheels; and a wheel-positioning system adapted to adjust a height of the one or more front wheels relative to a height of at least one of the one or more rear wheels and the one or more middle wheels, the wheel-positioning system comprising: one or more arms pivotally coupled to the frame at a pivot point, wherein the pivot point is between the one or more front wheels and the one or more middle wheels; and an adjustment mechanism operatively coupled at or proximate to a rear end of the one or more arms, one or more arms pivotally coupled to the frame at a pivot point, wherein the pivot point is between the one or more front wheels and the one or more middle wheels; and an adjustment mechanism operatively coupled at or proximate to a rear end of the one or more arms, wherein the one or more front wheels are operatively coupled to a front end of the one or more arms and the one or more middle wheels are operatively coupled to the one or more arms at a position between the front end and the rear end of the one or more arms, and wherein the adjustment mechanism is adapted to move the one or more arms between a first position and a second position separately from the operation of the drive system so that the one or more front wheels are in a first position when the one or more arms are in the first position and a second position when the one or more arms are in the second position.