On the RD-7402 the upper pulley wheel has it's teeth made out of metal, whereas the lower pulley wheel is full plastic. Why is this, greater forces on the upper?
Yes, specifically sideways force when shifting. Plastic uppers work fine, but DuraAce has always been about making stuff better regardless of value for money. Metal teeth should last longer, even though not by enough to justify the expense
On the RD-7402 the upper pulley wheel has it's teeth made out of metal, whereas the lower pulley wheel is full plastic. Why is this, greater forces on the upper?