Isaac software will not alter tyre circumference - why?

[Dr Matt]

I am trying to alter the tire circumference in Isaac following these instructions in order to calibrate the powerpod to read realistic power numbers.

I have followed the youtube video word for word https://www.youtube.com/watch?v=Z70DBxEto48

1. Edit > Edit Profiles > Tire Sidewall Markings > Manual > Tire Circumference > 2xxx > Accept
2. Tools > Switch Profile After Ride > profile that should have been in ibike > pick above profile......

.....and the ride distance does not change. What??? If I can't change this distance by altering the tire circumference then I can't get a proper calibration of the scaling factors etc as the Isaac file says it is 39.2km when I know the course distance is 42.9km.

Any ideas?

[Dr Matt]

Okay, so I found where to alter distance

Analyze > Analyze device settings

Problem is to get the distance in the powerpod file to match the known course length the wheel circumference needs to be 2310mm, its measured at 2140 (23mm GP4000 tubular).

There is a DFPM recording in the powerpod file, they are not even close to matching either Average Power of Normalsied Power. My CdA in the powerpod is also off the mark, it should be around 0.225 based on all my Golden Cheetah aerolab measurements.

Anyone know what is going on? I have also attached mounting to the TT bike.

[Velocomp]

1) You can adjust CdA manually in the Edit/Edit profiles command

2) Your speed sensor is not working properly. This is causing your distance problems. If it is a magnet less speed sensor, move it to your front wheel hub.

[Dr Matt]

Its a wahoo front wheel magnet less sensor mounted to front hub. Bought it brand new when I got the power pod. Will check it on ride tomorrow using two garmins (one GPS, other wheel sensor). Thanks

[Velocomp]

We have found that the Wahoo sensors are noisy. We've seen this in ride files from many devices. The Garmin magnet less sensor works much better.

[Dr Matt]

Just wanted to close this out. John was correct and the speed sensor was not working properly. Thanks

[Dr Matt]

Not been riding the TT much. Had the Wahoo speed sensor warranty replaced, mounted on the front wheel. Took it racing today and still having the same issue. The power numbers coming from the powerpod are all over the place and the distance measured by the powerpod is a couple of km less than it should be. The raw data file attached. Tweaking the cda/scaling etc doesn't help as the distance is almost 10% out.

Maybe it is the wheel sensor fault again, or maybe it is too noisy as you say. I don't really want to spend more $ on another wireless wheel sensor for the problem to persist.

How can I verify its the wheel sensor and not the powerpod? If the wahoo sensor was dropping the occasional pulse then you should see speed halve every now and then. When I zoom in on the speed it does look a bit noisy, but I dont see the speed going from 40km/hr to 20km/hr then back to 40km/hr. Shouldn't the powerpod smooth this speed measurement out anyway?

[Velocomp]

Sorry to say, the speed sensor is showing lots of dropouts. When the signal drops out, PP thinks you're not moving, so the distance does not increase. This is why your total distance is a bit short.

Do you have this sensor mounted on your front hub?

I would try the Garmin speed sensor. I know it is an expense, but in our experience these sensors work properly.

[Dr Matt]

Yes, mounted to the front hub. If I had known i would have bought the Garmin instead of the Wahoo, maybe need to update the incompatible sensor list....... https://velocomp-llc.myshopify.com/prod ... ower-meter

**edit** This is going on a TT bike with a disc rear wheel so the rpm sensor needs to be front fork/wheel mounted. Can I clarify. If the Wahoo magnetless is not recommended, and the Velocomp magnetless is not recommended either, are you sure the Garmin magnetless will 100% absolutely work? Or is it better to get the type of speed sensor tripped by a spoke magnet? Are there any cadence sensors that are not recommended?