What’s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer. Neither is a huge surprise, but we measured a 10-percent drop in fuel economy and a four-percent degradation in 0-to-60-mph acceleration from the 15s to the 19s, which is worth considering should you be thinking about “going big.” Increasing wheel diameter and width, in turn, requires wider tires with shorter and stiffer sidewalls, which we found will increase skidpad grip, but as our test shows, there is a limit to this assertion. The 19-inch package came with the widest tires (235/35R-19) mounted to the widest wheels (8.5 inches), but this setup had less grip around the skidpad than the narrower 225/40R-18s on 8.0-inch-wide wheels. We asked the folks at Goodyear why that might be, and they postulated that the added width may have given the outside tire more grip, which would increase body roll and could therefore decrease the load on the inside tire enough to lose 0.01 g on the skidpad.
Surprisingly, the 225/40R-18s showed a big skidpad advantage compared with the 225/45R-17s (0.89 g versus 0.85 g). We *suspect the difference is due to the grippier compound (lower wear rating) of the W-rated 18s. Goodyear does offer a W-rated GT in the 225/45R-17 size, which is what we intended to use, but Goodyear sent us the V-rated version for our test.
