To get back to the cupping.
This is usually due to suspension faults, as someone has already said. The cause depends on the type eg. how far between peaks. The cause, shocks, loose suspension, alignment.
I don't have cold weather down here, so I use the one set of tyres all year, I suppose that the winter tyres that you use, would be a much softer compound than a summer tyre and would not stand up to the heat as well.
As for Jasion's "go fast handling tip" of running the tyre at max pressure.
The Tyre Co. put a fair bit of work into designing a tyre. The contact patch, as all bike riders know, is all important. The shape, length, cooling, water dispercial and life are the design criteria. These can only be meet if the load @ pressure specifications are complied with. As the load is increased the pressure has to be increased to produce the same patch profile. The rating on the tyre has the sign @ inserted between the load and the pressure. They go together, each is not an option. The pressure on the car sticker is the recommonded pressure for normal use, for more load or sustained high speed the pressure can be increased a few psi. I run 35 front 33 rear on Bridgstone SO-2.
Increasing the pressure to the max will stiffen the side walls, to give faster steering but with the loss of tyre contact patch and designed profile. This sort of pressure is ok for an auto X but it is definitly not to be used on the hi-way for general use.
IT IS DANGEROUS.
With out the necessary load to match the pressure the tyre contact patch will distort to a shallow dome shape. This is diabolical in the wet as it destroys the water handling qualities of the tyre, to produce a condition of aquaplaning. The steering may be quicker but losing it in wet weather, will also be quicker.
Be aware of the reasions and results of doing this and be safe.
Harvey.
