This is a tourist trap of some German rental car agencies! Only AFTER you've agreed on a price and made a conctract they demand substantial extra payment (in this case about 1/3 of the rental price) and threaten to give you an ill-equipped car with summer tires in winter time.

I've just made this experience with Hertz. For a rental in February you really need winter tires or all season tires. But they'll give you summer tires anyway and tell you that this voids your insurance coverage, for which you have already paid.

It's a shame!