Horseshoes of Speed appear in both the core rule book and Ultimate Equipment. If the Ultimate Equipment source is loaded it takes precedence over the version in the core rule book. The lines in the data for Horseshoes of Speed from the two sources are different.
Using the Core version, a horse goes from speed 50 to 80, which is correct.
Using the UE version, a horse goes from a speed of 50 to 110, double the increase.