On 3/5/2019 3:20 PM, John B. Slocomb wrote:
On Wed, 6 Mar 2019 09:41:29 +1100, James
wrote:

On 6/3/19 2:48 am, wrote:
On Tuesday, March 5, 2019 at 7:45:36 AM UTC-8, wrote:


The carbon clinchers: Front; 1.13 Kg Rear with 11-29 cassette; 1.58 Kg.

That is with tires and tubes. And the speedo magnet.


If you changed to a Garmin or other GPS based speedometer, you could
save valuable grams from the front wheel because there's no need for a
magnet.

I've always been a little skeptical about GPS calculated measurements.
I remember back when we lived on the boat the GPS would sometimes
measure the altitude at 10 feet which was about twice the height above
sea level that the receiving antenna was mounted at.

As you should be; GPS has a notoriously large margin of error for
measuring altitude.

I think it's the trigonometry of the computation; the GPS (as I
understand it) measures distance to a collection of satellites whose
positions are well known, then computes location from triangulating the
results. I'm guessing that since most of the satellites are usually not
directly overhead, but rather the line of sight to the satellite is
usually be much closer to tangential to the earth, then very small
errors in the distance-to-satellite computation turn into much larger
errors in the altitude computation.

I think this is why higher-end bike GPS's have a pressure-based
altimeter as well, to correct the fluctuations in the GPS-computed
altitude. I know my Garmin Edge's regularly solicit known altitude
input at the start of a course.

Mark J.