Ergomo or Wireless Powertap?

On Feb 27, 8:04 am, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

Which is better?
(approx same price)

powertap is more reliable from our experience with both.

On Feb 27, 4:04 pm, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

Which is better?
(approx same price)

It seems like the Ergomo measures only the left side and extrapolates
the right. That seems unfortunate to me.

Joseph

Quoted message said:

On Feb 27, 4:04 pm, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

Which is better?
(approx same price)

It seems like the Ergomo measures only the left side and extrapolates
the right. That seems unfortunate to me.

Joseph

I agree. Some data posted to the wattage lists on google groups... pedaling
left leg only results in more than double the reading from PowerTap. Since
left-right balance can vary for a variety of reasons, this is a real weakness of
the Ergomo:
-------------------------

PT Ergomo diff diff DE* %error Ergomo v PT
1* 145 58 87 29 150.00%
2* 186 81 105 24 129.63%
3* 192 91 101 10 110.99%
4* 239 97 142 45 146.39%
5* 288 124 164 40 132.26%

6 96 109 -13 -11.93%
7 118 133 -15 -11.28%
8 141 143 -2 -1.40%
9 165 160 5 3.13%
10 180 182 -2 -1.10%
11 216 211 5 2.37%
11 236 228 8 3.51%
12 256 245 11 4.49%

* = pedaling left leg only
DE* = difference of power for single leg reading on Ergomo doubled
compared to PT

On Feb 27, 7:06 pm, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

Quoted message said:

On Feb 27, 4:04 pm, Dan Connelly <d_j_c_o_n_n_e_l@y_a_h_o_o_._c_o_m>

Quoted message said:

Which is better?
(approx same price)

Quoted message said:

It seems like the Ergomo measures only the left side and extrapolates
the right. That seems unfortunate to me.

Quoted message said:

Joseph

I agree. Some data posted to the wattage lists on google groups... pedaling
left leg only results in more than double the reading from PowerTap. Since
left-right balance can vary for a variety of reasons, this is a real weakness of
the Ergomo:
-------------------------

PT Ergomo diff diff DE* %error Ergomo v PT
1* 145 58 87 29 150.00%
2* 186 81 105 24 129.63%
3* 192 91 101 10 110.99%
4* 239 97 142 45 146.39%
5* 288 124 164 40 132.26%

6 96 109 -13 -11.93%
7 118 133 -15 -11.28%
8 141 143 -2 -1.40%
9 165 160 5 3.13%
10 180 182 -2 -1.10%
11 216 211 5 2.37%
11 236 228 8 3.51%
12 256 245 11 4.49%

* = pedaling left leg only
DE* = difference of power for single leg reading on Ergomo doubled
compared to PT

It is unfortunate that all of these systems have either one glaring
flaw, or tie you in to a single specific (expensive) component.

If I knew more about embeded programming I'd think about trying to
roll my own. I'd like to use force sensors in my shoes, and then based
on wheel speed, cadence, and calibrated crank length I could figure
out the power. If I did something like that I'd be limited by having
to use a full fledged system like Linux, while somebody who knew what
they were doing could program a chip to do it. This way the system
would be accurate (ideally at least) and would not be dependant upon
any one component, so it could be used on multiple bikes with multiple
wheels, cranks, etc.

I wonder if you could get reasonable readings with sensors like these
sadwiched between the shoe and cleat:

http://www.tekscan.com/flexiforce/specs_flexiforce.html

Joseph

Dan Connelly said:

Which is better?
(approx same price)

I think wired PT SL is preferable to either.

Robert Chung said:

Dan Connelly said:

Which is better?
(approx same price)

I think wired PT SL is preferable to either.

Reliability with the wireless connection? Or $400 cheaper with no non-cosmetic
disadvantage?

Wires break, especially long ones, which is the main reason I was biased to the
wireless version. But then $400 will buy a lot of spare wires.

Dan

Dan Connelly said:

Quoted message said:

I think wired PT SL is preferable to either.

Reliability with the wireless connection? Or $400 cheaper with no
non-cosmetic disadvantage?

Both. At the moment, all SL 2.4's are low serial number.

Quoted message said:

Wires break, especially long ones, which is the main reason I was
biased to the wireless version. But then $400 will buy a lot of
spare wires.

The harness is pretty sturdy. Don't try anything cute and just mount it in
the recommended way, up the seat stay and across the top tube. In any event,
a spare harness (which you can mount on another bike) is only $50.

And, as I said on Wattage, being able to check the accuracy trumps having an
altimeter.