I've been curious about the IBike since it's a lot cheaper than the other powermeters around and it claims to be as accurate (the basic unit is 430 bucks brand new). I emailed tech support a few questions and this is what they came back with.
I've been eying powertaps lately, but I think I might try this one out instead if/when I get a PM. The concept seems pretty cool and someone who I was riding with seemed to really like it and they had the 2nd generation.
Here goes...
Question 1) I had heard that earlier models had a problem with giving whacky
readings on bumpy roads, is this still the case?
Answer 1:
1)No. The new models are 5 times more vibration resistant than the GEN I
iBike. In fact, as the person who handles all the technical support, this
problem was all but eliminated with the GEN II models. GEN III will be ever
better. Just make sure you mount the unit correctly.
Question 2) How do you do the coast down if there are no flat roads that are 4
miles long?
Answer 2: I think you're referring to the 4 mile out and back. The coast downs only
require about 50 yards or so to do. You just pedal up to 20mph and then
coast down to 8mph and the iBike measures you're frictional and aero losses.
The 4 mile out and back can be shortened some if you can get a relatively
flat course, but it must be an out and back (it's measuring your riding
tilt). The course doesn't need to be perfectly flat either, just don't pull
or tug on the bars. The new unit will also have a input profile based on
height, weight, etc. that the guys over at DLP racing (they do a lot of
testing for us) say comes extremely close to the actual profile builds.
Question 3) The ibike works by making calculations based on the airflow coming
into the unit, how does drafting affect this? Does the Ibike drop
readings or give funky readings during pack riding?
Answer 3: In pack riding the iBike performs quite well. This is because both you and
the iBike will receive the benefit of the draft regardless of the height
difference. Your whole body receives the draft in the pack. The iBike will
over compensate one you're riding behind just one other rider (not in the
pack) because it's likely that your head will not receive the draft but your
body will (where the iBike is mounted). It will be less than a 5% difference
from my experience.
Question 4) Is the instantaneous power (i.e. 5 second power) accurate on the
ibike? I'm asking since the power being applied is higher than the
windspeed would lead a unit to believe during the start of a sprint,
unless the rate of change of windspeed is also going into the calculation.
Answer 4: Wind speed is always a part of the iBike power calculation. I think the
iBike has very accurate instant power readings. The only problem I've seen
in very violent sprints is that the rocking of the bike can cause the slope
to go down and reduce the power numbers slightly. I've never heard anybody
really having a problem with this as the loss is minimal.