In a message dated 1/2/03 5:14:31 PM Pacific Standard Time, mdsimont@snet.net writes:
<< Interestingly, Josh Putnam's page says 90 degrees from the steering
axis and Tom Kellogg (or whoever at Spectrum) says in the verbal
definition "leads the steering axis", which I would interpret as
horizontal. (I personally have always assumed it was at 90-degrees - or
did those master fork builders always know the head-tube angle of the
particular fork they were building at the moment.) >>
The only way you can measure the trail distance on the wheelbase datum line,
is if you have a drawing (or a computer drawing) of the entire frame. Once a
fork is built and out of a bike, the only meaningful measurement is at 90
degrees, because that's the only one you can physically determine with tools.
If the theoretical head angle is known, you could mathematically get the
other measurement, but why? Every frame I drew and built, I measured the fork
offset at 90 degrees, because that's how I was going to check it for accuracy
when it was finished.
Stevan Thomas
Alameda, CA