Max Landotter writes: http://pardo.net/bike/pic/fail-001/FAIL-001.html
>> If you look at the failure pictures at:
> One of the pictures mentions "vanity grooves" in tandem with strap
> wear as a cause of failure. Nothing to do with the OP, of course,
> but care to enlighten us to what a "vanity groove" is? I'm assuming
> it's not a dance track released by a celebrity, but I've been known
> to be pretty slow...
The groove in the middle of the face of the crank reduces the
torsional strength by about 50%. You'll note that Shimano and
Campagnolo ceased machining these groves on their cranks a few years
ago. Other manufacturers didn't catch on and make U-channel shape
cranks that are even weaker in torsion and lateral bending.
The groove has no positive function but people liked its looks.
Therefore "vanity groove".