Group ride

[jkallo]

I intended to almost call a conclusion to my PT/iBike comparison last night. After a couple hundred miles of ride in which they lined up very well, last night I finally got the first stereotypical Chicago lakefront ride. A storm was rolling in so the barometric pressure was haywire, the wind was heavy, gusting and switched directions repeatedly (and included lots of crosswind). I made a point of making hard accelerations when the wind was gusting. If there was a ride it was going to have trouble with, this was it. I got home, downloaded and found one watt difference in average over the hour. NP and TSS were well within a couple of percent. Perfect.

This morning was my team's practice crit. I rode down with the group then raced, came home, downloaded and was dismayed to find pretty much unsuable data from the ibike. Wattage average was 20 watts off and you can see the discrepancies in the graphs. Oddly, even taking a few minutes sample from a time I was riding alone (yeah, I got dropped) shows skewed watt average. Maybe the result of the software analysis?

So my questions are:
1. Is this a predictable result of using a first gen unit in a pack/paceline situation?
2. Is there something I can look for in this file to determine that the problem was indeed the pack riding?
3. Is this something that is fixed in the gen iii unit?

[jkallo]

And if anyone would like to see the file in question, I can post it.

[coachboyd]

It didn't rain on you last night did it?
Can you post the file from this morning, I'll take a look at it but more than likely it's an issue with the wind reading. I recently got caught in a storm and found that my wind scaling has changed since then (but the unit still works perfect), I think another person found this out as well. It's VERY easy to check wind scaling with the new 3.09 firmware, you can put the unit on absolute speed, ride one direction for a bit and look at the wind speed, then flip the bike around ride the other way, and you should expect to see the inverse number for wind speed.

[jkallo]

Thanks Boyd.

No, no rain actually on me last night, but it was sure wet this morning. I just checked to make sure I didn't have mud in the air intakes (nobody had fenders this morning). I did the exact pre-ride protcol that I'd been doing for the last few rides with the exception of doing a second tilt correction (while waiting for people to show up). The race started at 35:00 with me chasing an off the line attack and I stopped to watch at 51:00. I was dropped from at least 46:00 on.

I appreciate anything you might be able to contribute.

[coachboyd]

I am seeing 57 degrees for this ride. Were you wearing a vest or anything else clothing wise that would cause your cda to be higher than normal?

Also, your riding tilt is listed at +.2, and this is what's causing the difference in watts pre and post ride. If you go to your profile and change the riding tilt to -.3, and then adjust your friction number to keep crr the same as it was before, you'll see much better numbers on the bike.

Gen 3 fixes that problem of seeing different numbers pre and post ride.

[jkallo]

Getting ready to play with the tilt changing, but you know I did change something this morning: I went from wearing my club kit (bib shorts, lycra jersey etc) to wearing my team kit (knickers and wool jersey) for the first time since using the ibike. Do you think that could have accounted for a 20 watt average variance?

[jkallo]

Oh I see -- you mean on-bike numbers (as opposed to corrected in iBike3). Well I made the corrections, so we'll see next time.

In the meantime, I've tried bumping the aero number up a bit under the assumption that my kit change might have made the difference. While I can bump it up enough to match the average wattage from the PT, then the NP etc are all way high. I'm going to try doing coastdowns in my other kit, make a profile and apply it to the ride to see what happens.

But this is not a normal result for riding in race situations (i.e. occasionally in the pack, near the pack, off the front, following an attack etc etc)?

Er, forget that question -- I've just found Coach Boyd's previous posting with the file from the crit.

[Velocomp]

I opened your ride file and checked your serial number. You used a Gen I iBike in this comparison.

As reported previously, Gen I and Gen II iBikes can read low in drafting situations. This is a characteristic of the firmware algorithms used in these older iBikes.

This issue was corrected in the Gen III model.

[jkallo]

Excellent -- I was wondering if that was one of the Gen III upgrades.

As it turns out, I just went out and did coast downs wearing my other kit and made a profile. When applied to the ride this morning, the overall wattage variation drops to 8 watts. Low, but once again pretty amazing.

[coachboyd]

Thats really good then, especially considering that you were likely standind at some points, which can lead to the iBike reading lower watts due to you having a higher cda.

This is one of the reasons the group ride setting in the Gen3 gets the watts so close in a pack.