MOI is the very reason that Steinway developed the patented Accelerated action where all the lead weights are placed near the balance rail, but first of all, I do not understand why piano manufacturers started to add lead weights. The Renner grand action model doesn't come with the lead weights and DW is more than 100g. If you add some leads to achieve 50g DW, it makes it feel even heavier ( I placed the mass about 100mm from the balane pin). As someone mentioned, there is MOI from the hammer side. In a piano, the bass hammers are bigger thus heavier. This means that bass keys already feel heavier than the treble side. If you add leads to achieve lower DW, it makes it even heavier in the bass section. Is this what pianists want? As far as I know, piano is the only keyboard instrument that is equipped with the leads in the keys. On a harpsichord, or on a pipe organ, the touch weight is virtually the same in bass and in treble. So, it doesn't seem there is a good reason that bass side "has to be" heavier than the treble side. My guess is that the piano manufacturers first tried to achieve the same touch weight in bass and in treble like these keyboard instruments, and added leads considering the balance weight (static balance) only. It didn't work out that way, but people are just used to it. Does anybody know the history of the lead weights - when, who, why they started to use?