Simple Question: iBike Dash + Power + DFPM

[Norm]

I have my iBike Dash + Power paired with a PT wheel. Speed, cadence, HR, and DFPM all seem to be paired correctly and the DFPM is zeroed. The unit is not in trainer mode and my speed sensor on my front wheel.

Here's the problem: When I spin my front wheel I get a reasonable speed readout plus huge power numbers, but the PT wheel is sitting still. What's going on here? Shouldn't the power number be zero until the DFPM starts delivering data?

I noticed the problem on my virgin ride with the Dash, which happened to be on rollers. I run on e-motion rollers, but with my Gen III I always relied on the PT power data instead of the estimated power curve for the e-motion rollers in trainer mode. I think I should be able to do the same with the Dash, correct?

[Norm]

Ah ha! I think I see now. In the 'Configure User Screens' section there's a field for DFPM power, so I'm guessing I can build a screen with that instead of Power if I want (which I do). So now this begs the question: Does DFPM contribute to any of the aggregate power fields (i.e. Normalized Power, FTP, Avg Power, etc.)?

Is there a reference available for all the custom fields and their meanings?

[rcmaps]

....and my speed sensor on my front wheel.

Here's the problem: When I spin my front wheel I get a reasonable speed readout plus huge power numbers, but the PT wheel is sitting still. What's going on here? Shouldn't the power number be zero until the DFPM starts delivering data?

There's the problem... when you spin the front wheel, you must have lifted the front of your bike up - the iDash thinks you are climbing up an incline at a certain speed hence the huge power spike!

I often get 1000W easily this way as I have to lift the front of my bike up 90 degrees to get out of my tight garage while wheeling it using the back wheel (my bike sensor is on the back wheel). It's a real pain as I then need to "fix" this later to get a proper correct max power wattage reading while on an actual ride later on.

Now, I just turn on the ibike after getting out of the garage to overcome this problem.

[Norm]

There's the problem... when you spin the front wheel, you must have lifted the front of your bike up - the iDash thinks you are climbing up an incline at a certain speed hence the huge power spike!

Yeah, that's right. I was assuming that the Dash's power values would be replaced by those of the DFPM if one was present, which was the case with the gen III iAero. Instead, if I'm reading things correctly, the power values displayed on the Dash are always iBike power and if you want to see DFPM power you need to configure a screen to display DFPM power as a separate value.

That should work fine for me in most cases except sprint intervals, where jumping out of the saddle and hammering hard puts the iBike at a disadvantage.

[Velocomp]

That should work fine for me in most cases except sprint intervals, where jumping out of the saddle and hammering hard puts the iBike at a disadvantage.

Try as we might, we haven't been successful in determining whether or not hard sprinting can be issue for the iBike, or if instead this is an urban myth. Some ride files with sprints would be great to look at...

[Norm]

Try as we might, we haven't been successful in determining whether or not hard sprinting can be issue for the iBike, or if instead this is an urban myth. Some ride files with sprints would be great to look at...

Thanks John, I'll give sprints a try with the Dash once I'm back on the road again. Right now we have 6" of snow on the ground, so I'm stuck on the rollers for a while.

[Norm]

OK, I was back on the rollers this morning with fresh insights and a new user screen with fields for both Power and DFPM. I knew that the lack of wind would seriously throw off the Power number, so I put the Dash in trainer mode thinking that I would base my workout on the DFPM numbers but that I could also compare DFPM data with the power curve for the e-motion rollers to see how close the curve was to actual power. I was defeated on both counts.

In trainer mode, DFPM is always 0. So it seems that I have to rely on the power curve model for my trainer. That's not the worst of situations, but I would like the DFPM data since I do have access to it.

It looks like the way DFPM data is handled on the Dash is different from the gen III units. Under gen III, power would be reported from the DFPM if it was present, so when I jumped on my rollers I didn't bother with trainer mode. On the Dash it seems that DFPM data is only used for continuous CdA calculations and for reporting in the DFPM text field. Is this correct?

Maybe it's time for me to just ditch the PT wheelset -- I never really liked it anyway.

BTW I'm now on my 4th generation of iBike products and I can say that John and the rest of the Velocomp crew have a solid product and great customer service. I can't wait to try my Dash out on the open road.

[racerfern]

@ Norm

Define sprints. Group ride or solo? Intervals? of what length? I have yet to see where the iBike "fails" in any sprinting situation. Even jumping out of the saddle I'm not sure how I could even begin to know if the iBike didn't report correctly. I don't have a DFPM to compare to but my jumps see to be in line with perceived exertions. Of course I might sprint just a wee bit slower than others.

[Norm]

@ Fernando

Yeah, you're not selling that slow sprint talk here -- I've lined up beside people like you before.

When I say sprints I mean max solo efforts, out of the saddle and rocking the bike hard for 10 to 60 seconds. When spring comes around, my coach's idea of fun is working in 2 or 3 days of 21s each week: 3 sets of 7 sprints of different lengths depending on how sadistic he feels that morning.

Back in the old days iBike had a difficult time accurately capturing those efforts, so I got into the habit of using a PT wheel when doing sprint intervals. It's been a couple of years since I last paid any attention to the issue, but I'm looking forward to checking out the Dash when sprint training starts again this spring.

[racerfern]

I do some real hard 30s-60s sprints at varying times. Usually seated but sometimes standing. Again, without a DFPM to compare to I'm not sure I could tell if there were a problem. For me a lot has to do with the beginning gear. If I'm in a tall gear starting at 35RPM and winding up to 90rpm I'm pretty sure wattage output doesn't equal the perceived effort because of the low cadence. Those can be real killers until you wind up a bit. However, starting in the small chainring and switching up to the big ring makes it more tolerable and the power output seems to be better.

I guess we'll have to start thinking about those exercises in the coming months. I also do some of my sprints up short hills. I still shoot for the same power band but don't have to worry about covering larger distances that can have interruptions.

[bjrmd]

Here is a 1 min interval, powertap elite as reference. using ibike 3 aero
Very close.
Have other days as well that are about the same.
Very important to have the wind cal done.

[Velocomp]

Thanks!

For accurate results the PT needs to be calibrated properly too...

This is what we see all the time. The results are extremely close and any differences are only for the first few seconds. For transient impulses (5 seconds or less) the filtering characteristics of the electronics are more important than the sensor readings themselves. We chose a smoother filter so that watts readings don't jump around too much.

[Norm]

@bjrmd

That's a really pretty graph. It's encouraging to see these two PMs tracking so closely on an effort.

I noticed that your speed didn't increase despite the power you generated, so I assume this is a climb and you were probably out of the saddle. Do you have a similar effort in the flats at almost double the speed? This is the most important scenario for me, where correct aero measurement is huge and gravity is next to nothing.

If not, it's no big deal: I'll generate my own in a couple of months.

[racerfern]

Great graph and confirmation that the iBike performs just fine on its own. Agreed, it appears a hill was being climbed. However, Off topic, I also see where the rider overcooked on initial push and had a significant power drop for the rest of the interval which appears to be about 60s long. Nice effort nonetheless, these aren't easy.

[bjrmd]

Did some more comparisons and did a high speed interval, enclosed. Still very close. I am getting good correlation as long as the wind cal is near zero. Problem is it frequently changes even with minimal temp change. If my riding cda display is off what it should be, it generally means I need to stop and zero out the wind port.