Low Power on MTB Ride - Calibration Suspect?

Post Reply
jfeat
Posts: 7
Joined: Sat Apr 21, 2018 4:27 am

Low Power on MTB Ride - Calibration Suspect?

Post by jfeat »

I have a road bike and mtb. I have set up the road bike in profile 1 and the mtb in profile 2. Both calibrated using the one way method. I have just completed a 15 mile out & back offroad ride on the MTB with no hills, just 100 feet of elevation difference between highest and lowest point.

I am surprised by the low power figure, and wonder if it is because the cda, cm, and crr figures in my profiles are virtually identical for each bike? The power figure matters to me because I am following a power-based training plan. I moved PP from the road bike just prior to this ride, which is presumably why there is a few minutes of 0 power as PP readjusted to the MTB.

MTB tyres are 27.5 x 2.25 with average 24.5 psi, whereas the road bike has 700c x 25 tyres at 90 psi.

Should I copy the road bike profile into profile 2, and then use profile 1 to recalibrate the mtb, so ending up with road bike as profile 2 and mtb as profile 1?

The wind speed surprises me too, it is always an "icicle" even though it was a out & back ride with a 8mph wind from the southwest, which did not change in direction.

I am happy with the road bike calibration - the power figures I get from PP look realistic.

Ride file attached for review.

Many thanks
jfeat
Attachments
iBike_05_17_2018_1451_16_Miles.ibr
(192.87 KiB) Downloaded 175 times
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by Velocomp »

Your MTB would benefit from an out-and-back setup. Wind scaling is too low.

Your CdA is set for a TT bike, and your Crr is low.

I've attached corrected ride file and profile.
Attachments
jfeat.ibp
(548 Bytes) Downloaded 162 times
jfeat_JRH_05_17_2018_1451_16_Miles.ibr
(300.51 KiB) Downloaded 182 times
John Hamann
jfeat
Posts: 7
Joined: Sat Apr 21, 2018 4:27 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by jfeat »

Wow! What a difference! The numbers are now far closer to what my perceived effort was!posting.php?f=93&mode=reply&t=4606&sid= ... 299215f53d#

Will do an O&B calibration ride on the MTB soon.

Many thanks John

jfeat
jfeat
Posts: 7
Joined: Sat Apr 21, 2018 4:27 am

Re: Low Power on MTB Ride - Calibration Suspect? New Issues

Post by jfeat »

Friday
Out & back MTB calibration, followed by road bike O&B calibration, all seemed well. Downloaded to Isaac. No .cal files appeared until the following day in the Isaac folder. But MTB Crr & Cda seemed quite different to JH corrections. Similar to original TT aero position Cda?

Saturday
53 mile road ride (4h 12m) & power figures seemed good, albeit head unit gave some absurdly high power figures at one point. CdA .338, Crr .0060, Avg 146w, NP 187w, IF 0.93, TSS 337 (all from Isaac). I think the power blip was the result of my number plate getting dislodged for a few minutes and funelling the wind into the PP port.

Sunday
47 mile MTB ride (4h 53m) did not go well. I calibrated on Friday with the mtb-specific sensors, except for a heart rate monitor which I wore on Saturday. When I started riding the device decided to do another O&B calibration ride! I can't remember the exact sequence of events. I was on the start line with probably 100 other riders so I couldn't do much other than get going. Anyway I did try rebooting, turning off and restarting, re-detectong all the sensors so I could convert the O&B calibration into a one way calibration. Pesky unit insisted on completing the O&B calibration so I let it think that that is what it was doing. I stopped at 50% and then kept going. When it finished I clicked the button and thankfully it started to produce what looked like meaningful numbers and I rode to them.

Again I got some absurdly high numbers from time to time, but this time I couldn't see any reason for it. My normalised power from the head unit ended at 430w (impossible!), with an IF of 2.14 and TSS of 2238.6. I would tell you what Isaac concluded but there is no ride file for 95% of the ride, just a couple of very short files from the strart when I was trying to stop the re-calibration.

As I write this the device is plugged to the PC and showing a green light. It is next to my road bike which has not moved for several hours. I have also just noticed that I have two ride files for Saturday's road ride. One has recorded 54 miles in the filename, the other 56, but the data looks the same.

Please advise.

jfeat
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by Velocomp »

Please post your .ibr ride files.
John Hamann
jfeat
Posts: 7
Joined: Sat Apr 21, 2018 4:27 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by jfeat »

MTB cal ride attached from Friday May 18.
Road cal ride attached from Friday May 18.
Saturday May 19 Road ride attached
Sunday May 20 MTB ride file not created as an ibr file so I tried to attach 2 screenshots from Bryton app. You can see the calibration pattern at the start of the ride. However the portal apparently does not allow upload of png files.

I cant help feeling the device is defective?

jfeat
Attachments
iBike_05_18_2018_1536_3_Miles_CalRide.ibr
(48.14 KiB) Downloaded 147 times
iBike_05_18_2018_1336_2_Miles_CalRide.ibr
(39.3 KiB) Downloaded 172 times
iBike_05_19_2018_0816_54_Miles.ibr
(767.19 KiB) Downloaded 161 times
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by Velocomp »

On your 54 mile ride, something bumped your PP out of position at the 20 mile mark. After it recalibrated itself it was fine.

Your road calibration looks fine.

Your MTB calibration requires changes to your CdA and Crr (they have road bike values). Set your CdA to 0.45 and Crr to 0.008 in your MTB profile.

I don't think anything is wrong with your PP.
John Hamann
jfeat
Posts: 7
Joined: Sat Apr 21, 2018 4:27 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by jfeat »

I will be delighted if it is working as designed. But it begs the already asked questions:

1) Why is there no file for Sunday's 47 MTB ride? Why would I get power data to the haed unit but no data record from the device? And I can provide confirmation of this.
2) Why would it start recalibrating immediately after an apparently good O&B calibration?
3) Why is the device creating duplicate ride files in one case? And why does Isaac try and pull down repeat files it already holds in my data folder?
4) Why is the light green on when connected to the pc - this status is not recorded on PP status light cribsheet?
5) Why would an MTB calibration come back with road figures for CdA & Crr? In an earlier post you edited my MTB profile and suggested I do an O&B calibration - I have done that (&some!) but the calibration seems to have returned the device to similar road figures?

Please restore my confidence in this product - I want it to work!

jfeat
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Low Power on MTB Ride - Calibration Suspect?

Post by Velocomp »

1) It's possible your unit needs a hard reset--press hold button for 10 seconds, until light goes out and then comes back on. Connect your device to Isaac to reset date and time. It's also possible your ride memory is full; use Device/Erase All Rides to clear out memory

2) If your device goes into an immediate recalibration, the likely cause is that it is pointed too high. Make the word PowerPod approximately level to ground and do a new cal ride

3) I don't understand this question.

4) It sounds like your unit needs a hard reset; see 1) above

5) You need to use Device/Device Setup for your MTB, and select MTB parameters (wheel diameter and road type). Make sure your sensors are different for your road and MTB bikes. If not, PP won't switch to the correct profile.
John Hamann
Post Reply