Some modern tandems use a 160-mm-wide axle that allows a wheel that is completely "dishless" (i.e. symmetric). The disadvantage is this may increase the Q-factor of the stoker's cranks and may also cause "heel-strike" of the stoker's shoes on the chain stays. Others use shorter axles (often 145mm wide) thereby trading a little decrease in the strength of the wheel for the advantage of a similar decrease in the bending moment of the axle spindle.