tireless

Having or showing a capacity for persistent effort; not tiring or relenting.

Without a tire: as, a tireless wheel.

Not tiring or becoming tired; not yielding to fatigue; untiring; unwearying.

Untiring.

Indefatigable, untiring and not yielding to fatigue

Without a tire (wheel covering); tyreless.

characterized by hard work and perseverance

showing sustained enthusiastic action with unflagging vitality