Throughout the years bicycle designers have produced belt-driven bicycles. While these belts cannot be shifted between gears like a chain, they offer singlespeed or hub geared drivetrains with improved increased wear resistance, quieter operation, and lubrication-free cleanliness. Belts also do not change length during their lifespan in the same way that chains "stretch" or increase in pitch as their link pivots wear. This keeps the pitch of the belt's teeth constant and dramatically decreases wear on gear teeth. Belts have failed to overtake chains in popularity for bicycles because they have historically been less efficient. Also replacement of the one-piece belt requires traditional diamond bicycle frames to have a split chainstay or seatstay.