From the Yamaha Workshop Manual:
Spring rate (K1) 8.1 N/mm (0.83 kg/mm)
Spring rate (K2) 11.8 N/mm (1.2 kg/mm)
Spring stroke (K1) 0 to 55 mm
Spring stroke (K2) 55 to140 mm
Total fork travel is 140mm.
Essentially, stock dual-rate springs are too soft in the first part of their travel but too stiff in the latter part.