Rolling cone bit with elements fanned along the gage curve

The invention relates generally to earth-boring bits used to drill a borehole for the ultimate recovery of oil, gas or minerals. More particularly, the invention relates to rolling cone bits and to an enhanced cutting structure for such bits. Still more particularly, the invention relates to the placement of gage cutter elements on the rolling cone cutters at locations that increase bit durability and rate of penetration. An earth-boring bit for drilling a borehole comprises a bit body having a bit axis, at least two rolling cone cutters rotatably mounted on the bit body, a plurality of inner row cutter elements positioned on at least one cone cutter in a first inner row, a plurality of gage-cutting cutter elements positioned in a first fanned-gage row on a first one of the one cutters, and a plurality of gage-cutting cutter elements positioned in a second fanned-gage row on a second one of the one cutters, wherein the gage-cutting cutter elements on the bit define a gage curve and cutter elements in the first fanned-gage row and the second fanned-gage row contact the gage curve at different points. In one embodiment, each cutter element has an extension, and the extensions of the uppermost fanned-gage row cutter element and the first inner row cutter element define a step distance such that the ratio of the step distance to the extension of the first inner row cutter element is greater than 0.5. Alternatively, the first and second fanned-gage rows are positioned to have different oversize angles, positioned such that the ratio of the diameter of the largest fanned-gage row cutter element to the diameter of the first inner row cutter elements is not greater than 0.75, or positioned such that the lowermost fanned-gage row contains more cutter elements than any other fanned-gage row.