I have two computers on my bike - one wireless Flight Deck and one wired
VDO, the former with a virtual cadence, the latter with heart rate
indication. They are operated by the same magnet on the front wheel.
They are fairly accurate, and the wireless doesn't give me any problems.
But there are inaccuracies at times. F.ex. when I accellerate (or the
opposite)they disaggree on the current speed.
I have calibrateded the two computers accurately by riding 10 km between
km-stones (milestones). Yet at times the one is a little ahead of the
other. In the long run - which means over 200 km - the relative
difference between them is about 1 - 2 pct., which I find satisfying and
better than the measurement I get from my car.
But when it comes to max speed there are huge differences - and I find max
speeds way above what I had read when I was going the fastest. I think I
have figured out why.
Inside the sensor is a little metal piece rattling around, as you may be
able to hear, activated by the rotating magnet and turning a contact off
and on.
Sometimes it will skip a turning on, somtimes it will be delayed a
fraction of a second.
If the frequency of the skipping is fairly constant, you will be able to
work the inaccuracy into the calibration, so the measurement in the long
run will be fairly acurate anyway.
But the max speed is probably a calculation made from only one turn of the
magnet. If the metal piece inside the sensor is delaied for a split
second, the next measured period will be too short - just as the former
was too long. But multiplying this inaccuracy will display the
unrealistic high speed. There is nothing to do about it - other than
disregarding max speeds you didn't see when it was going on for some
time. (Which is difficult. If I go 60 km/h I don't like to move my eyes
from the road to the computer for long.)
Once in a while one of the sensors get out of place - sometimes so much
that the measurement stops. At other times so little that the reception of
the magnetism only skips once in a while, giving a low measure.
Sometimes I try to tell myself not to look at the computers - so I can
understand why it can be a good idea to place your computer under the seat.
But if you want it to be reliable, you have to keen an eye on it.
Ivar
Den 12.12.2006 kl. 00:10 skrev David L. Johnson <[email hidden]>:
Quoted message said:Ken C. M. said:I rode for a couple of hours this afternoon on the road bike, I have the
cycle computer reading off the rear wheel and the head unit mounted on
the seat post. It's an Ascent wireless model. This isn't the first time
I have notice it, but thought it might make for an interesting tech sort
of thread here, now this was a two and a half hour ride. When I got home
I checked the readings, and clearly it's not getting info from the
pick-up all the time. It said my average speed was about 7.5 miles per
hour, and total distance was 15.5 miles. Now I KNOW that I am slow, but
not even close to being THAT slow. Now the cycle computer in question is
not a very expensive model. and not a GREAT brand, but really now? I
mean enough already. So whats some advice about computers, go with a
wired design like my Cateye Enduro 8 on my other bike, or just get a
better wireless model?
Quoted message said:The last computer(s) I got were also these wireless Ascent. POS. Mine
would get interference from everything; many rides would indicate a max
speed of 76 mph. Now, I like to downhill fast, but not that fast. They
also are hard to read in the sun, rattle, and finally they broke. What
did I expect for $20, I guess.
I do like the wirelessness. It is just one less thing to fuss about.
Also, many wired computers have cheesy wiring and/or connections, so they
don't last all that long for me, anyway.
I got a Planet Bike Aero to replace these (going to switch from bike to
bike as soon as I get a second holder/sender). Much nicer screen, good
information, and, so far, no interference.
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