AeroPod, PowerPod and Newton

Okay, I tried a calibration ride with my new Aero today, and it failed. Twice.

However, I think I may know what the problem is/was, but I'd like confirmation from the experts here. I took the time to actually run a string around the circumference of my 700c rear tire, and came up with 84.5 inches, or 2146mm. Now, the "default" is 2096mm, and apparently for a 700c tire also. I wonder why the difference, but nevertheless, I discovered when I tried to upload the data from the iBike Aero, that the setting in Isaac was set at the 2096 measurement. I am thinking this difference in numbers is what caused the calibration ride to fail. I "THOUGHT" I had actually sent the setting to the Aero when I changed it in Isaac, but apparently, it didn't make it all the way to the unit, or something. So....

Here's the question, should I use the "default", or (for accuracy's sake) should I use my actual measurement of the circumference of my rear wheel? I'm using a Garmin GSC-10 speed/cadence sensor, along with a Garmin 910XT unit. I checked, and the measurement in the Garmin is set something way different, but that was "automatically" calculated, but I think that's the circumference at the magnet that activates the sensor, and thinking about it, the GSC-10 only sends impulses when the magnet passes by the receiving part, so that information (the circumference) should only be valid for the 910XT, right?

I'm confused on this, but I'd really like to get a valid calibration ride, so I can actually start using the data that the Aero provides. Any help/insight/suggestions would be greatly appreciated.

Thanks
Steve

We'll need to get your issue settled before June 1, when we discontinue support for Gen III and older products!

In Isaac, use the Device/Device Setup... command to set the parameters of your iAero, including wheel circumference. You'll be able to manually enter 2146. Click the Send to iBike command to transfer the data to your iAero.

Then, in your iAero setup, go through the Fast Start sequence to verify that everything was done according to plan.

Before doing your Cal Ride, make sure you do Tilt and Wind calibrations.

So, the wheel circumference is the actual measurement around the outside of the rim/tire combination? I wonder why my measurement is so far off from what the standard one is for 700c?
Thanks for the input, off I go to give it another go!
Steve

Here's the proper procedure for determining tire circumference:

Air up to normal riding pressure.

Get a tape measure at least 16 feet long and lay it out on a flat surface, ideally against a solid wall. I put it about 18" away from the wall.

Now with someone to help you stay balanced, put the bike so the valve stem is at the bottom at zero inches.

Keeping the bike as upright as possible push yourself forward for two revolutions. Your friend can help balance you from falling away from the wall. Try to do this as close as possible to your normal riding position which of course isn't easy. But you'll laugh and have fun.

At two revolutions (one will do if you have a short wall) with the valve stem straight down read the distance it traveled. It should be in the 82.5 inch range per revolution.

I did this roll out three times and was very careful to note the number, then took the average of the three. We're talking differences of a 1/32" so be careful.

Take your "inch" measurement and multiply by 25.4 to get mm. Mine comes out to 2092mm.

Sorry for the wordy explanation

Umm DUH! Figured out what the discrepancy was.. (insert head slap* here) I have 700x35C tires, not the smaller ones. The reason the cal ride was failing is because I thought I had to acknowledge the unit when I did the "turn around, go back" movement. Today, I rode, (twice, and failed) and the third time, I re-READ the instructions, and no where did it say I had to touch ANYTHING, so I tried it, without touching anything when I made the return trip. Guess what.. GOOD CAL! Finally. Yes, I really like the unit, for sure, and will probably keep it for a long time, although I wouldn't mine the "newest" Newton, I cant afford that one..
Thanks again
Steve

Congratulations! But I would still do a proper tire roll out. The wider the tire the better the chance for variations.

I probably will, some time in the near future, I really want to get to know this little device first. I still am not sure what the numbers mean, and Isaac confuses me, but with the help of a couple of books I've bought, and a few rides, I think I'll start to understand the relationships that are going on.. I'm REALLY new at this, just got in shape enough to be able to even ride the bike, and am trying to increase my fitness to the level that I can go for a while without having to stop. Power seemed the way to go as an actual measurement of energy, and therefore calorie, and training effect, and progress over time. Heart rate is fine for weights, and perhaps indoor rowing, but I really enjoy getting out and riding.. Hopefully, I'll get better..
thanks for the input, I appreciate it!
Steve