Hi there subaru585,
As you no doubt know, the bearing on a drawing die is there to preserve the die size in light of wear on the front face and to allow a worn die to be re-polished without always changing the die size. The bearing also validates the wire diameter.
The length of the bearing however significantly adds to the mechanical stress in the wire by friction or drag and this is especially true of polycrystalline dies. Thus the length of the bearing is always kept at a reasonable minimum.
As I recall, historically in the late 1970's, Philips polycrystalline dies (PCD) recommended the bearing of their dies should vary between 0.2 and 0.4 times the die diameter for soft materials such as copper and aluminum and 0.3 and 0.5 times the die diameter for hard materials such as steel.
On the other hand, the WAI Nonferrous Wire Handbook (1981) suggests a die can have a bearing length of close to 0.5 times the wire diameter for soft materials and up to 1 times the wire diameter for hard materials. (We assume this applies to standard drawing dies made from carbide and solid diamond.) Further it suggests that the bearing should be between 0.15 times and 0.25 times the die diameter for polycrystalline dies and that is much less than the older Philips recommendation above.
I am personally not aware however of any algorithm for calculating bearing for carbide, polycrystalline or solid diamond dies and wire die companies may consider this as confidential or proprietary information or “know how”.
You might wish to check with your new die supplier and with the company that made your die polishing machinery to see what they say.
Hopefully others will have more to add to this thread.
Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com 
