Recently I noticed that when the inertia value of a balance wheel is high (i.e. >10 mg/cm^2), it is often used as a marketing tool. Not all marketing tools are a scam, of course, an I'm just wondering how much value this has.
I know all other things being equal, a larger diameter and heavier balance wheel (hence more inertial since the moment of inertia of a circle is mr^2) will be more shock stable. Other than that I *believe* that it may use more energy since each oscillation will require more energy to change direction or stop and turn around.
Anyone more technical want to help me with this?
Here are a few values of some movements for which the moment of inertia is known (all units in mg/cm^2) in descending order:
Omega 8500 (in-house co-axial hour vision) - 21
IWC 80110 - 18
Rolex 3135 - 16
JLC 975 "autotractor" - 14.95
Valjoux 7750 - 12
JLC MC Lab 2 (first watch with no lubrication)- 11.5
ETA 2892 (and thus 2893 and 2894 + other derivatives) - 10.1
Omega 2500 (Co-axial 2892)- 9.4
JLC 899 (and derivatives such as VC 1124 and many others)- 3.8
Eta 2004 - 2.7