Mike Causer writes:

On Fri, 17 Feb 2006 09:19:21 +0000, Tony Raven wrote:

Given how often lawyer lips have come up in this and the previous
threads on the topic, there is no chance that anyone has forgotten
the lawyer lips. The intent of laywer lips is not to provide axle
retention for disk brakes, it is to prevent people who don't know
how to use QRs from losing their front wheels.

Correct but by default it should prevent a QR from exiting the fork
for forces many times the highest calculated here for an ejection
force.

Sadly not. British Standard 6102-1:1999 (which is based on ISO
4210:1996 but has advanced in some respects) requires wheel
retention by the QR mechanism of 2300N (517lbf) for 30 seconds, but
with open QR the lips have to withstand a load of just 100N
(22.5lbf). [Section 9.4.4]

Wow. Of course, those are the legal standards and not actual
measurements. Laywer lips do vary in design from just a couple of
small bumps at the tips of the dropouts to flanges that are almost
half the height of the QR nuts.

But do the math. Since the ejection force is applied to only one
dropout, the British Standard requirements are effectively that the QR
has to withstand a pullout force of 108.5 lbf and the lawyer lips only
11.25 lbf! I can't help but think that decent quality skewers and
forks would exceed this handily, hopefully anyway since even moderate
braking with a current design disk brake would create a force that
would exceed those numbers.