I think some of you guys are confusing Directional Tread tires and Asymmetric Tread tires.

Directional Treads (Yokohama AVS dB and chevron pattern tractor tires) are mounted so that they rotate in the correct direction when the vehicle is moving forward. That means that all four tires can be the same but the left and right tires are mounted differently and should not be interchanged side to side. A Directional Tread tire rotating backwards would tend to hydroplane much much better than other tires. Try swapping a tractor's chevron pattern tires side to side and see what happens in a wet field.

Asymmetric tread tires have a tread that is different from the inside to the outside of the tread. This could be a different groove/sipe pattern ( the old Michelin XAS and XVS are very good examples) or it could be different rubber compounds on the inside and outside of the tread. The Dunlop SP Sport A2 has both tread pattern differences (minor) and tread compound differences. All four tires are the same and should be mounted with the sidewall marked "outside" on the hubcap side of the wheel. (For those of you with alloys, that would be the lugnut/valve stem side). This would be very difficult have mislabeled since the tread and sidewall markings are determined by the tire mold. The tires can be interchanged side to side. To get the maximum benefit of the design (better response, less noise) they should be mounted properly.

Take a look at the Yokohama AVS dB and Dunlop SP Sport A2 at www.tirerack.com