AeroPod, PowerPod and Newton

Ok I just did another cal ride w/coastdowns. I did this after changing my stem and the location of the IBike on the stem. I know I could have just re-did the wind scaling and stuff but a wanted a fresh profile. I let the unit get acclimated to the temp., then did the tilt cal., and wind cal. Did my 4 mile ride on an almost completely level road..out and back. Afterwards I did the coast downs which it then made me do another wind cal first. After analyzing the data in the IBike software my crr was only like .0014 or .0019. Changed the setting to crr adjusted and sent into IBike unit anyways. Then I went in and edited my profile and adjusted my crr to .0056. I attached my cal ride. Coachboyd or anyone else want to look at it and make some adjustments I would greatly appreciate it. Thanks

Clint

This is a really good chance to demonstrate just how good the "Est CdA" feature is.

I emailed Clint and asked him his height and body weight.

Based on his answers, the Est CdA feature in the Fast Start menus would have returned a value of CdA on the hoods of 0.352.

As you can see from his coast down information, Clint did 13 coast downs. The overall value of CdA returned from his coast downs? 0.352...

Now, the Crr is too low, about 0.002. Normal would be about 0.005

Why is the Crr low? Clint reports that he had a slight tailwind while doing his coast downs.

While it is fine to do a Cal Ride in windy conditions, we recommend that coast downs be done in quiet wind.

Why? Since Crr is determined at the low speed portion of a coast down, the iBike will return a low value of Crr in a tail wind, because the tail wind makes it appear that frictional drag is low. Since the iBike can't measure ambient wind speeds below zero, it interprets the long coast down distance caused by the tail wind as very low friction.

In Clint's case, using the Est CdA feature would have given him a great setup, with about 30 seconds of button pushing, and a 2 mile cal ride. No coast downs needed!

But, all those coast downs probably qualified as an interval workout!

Ok, that sounds really great and thank you for helping me out. I have been doing a lot of road rides and practice races with some groups to help me out for my mtn bike racing. The thing is now I am getting more into analyzing data which is why I wanted my IBike to be more accurate. So this being said...........what should I have in my profile then for crr?? I know you said around .005. Should I just stay with the .0056 I am using right now? I did a ride the other day with the new profile using the crr value of .0056 in my new profile and it actually felt right, but then again just because it felt right does not mean the power numbers are right.

And if all of the above is correct, is there a procedure to double check a profile (crr,aero,wind scaling etc.)so I/we do not have to have you guys do these tweaks for us. I don't want to have to use a DFPM just to make sure my IBike is correct. Thanks again Velocomp for all of your help.

Oh, and yes I did get a short interval workout doing the coast downs.

Clint

0.0056 is fine. This is a good number for average road conditions and tires.

One of the things I'm trying to express in this thread is that getting accurate readings from the iBike is much easier now because of firmware changes, better microprocessor and electronics in the Gen III, and improved user set up procedures.

The original iBike required a coast down in order to achieve accurate readings. With the Gen III iBike, you'll obtain extremely good results with the Fast Start screens and a Cal Ride.

Remember, to get good coast down results you need to do the following:

1) Read and follow the instructions

2) Make sure the iBike is mounted firmly (no movement due to flexible aero bars or lousy mounting)

3) Calibrate the iBike properly (tilt, wind) prior to the coast downs

4) Maintain the same ride position for all coast downs

5) Perform coast downs in non-windy conditions, with little traffic, on a flat-to-uphill road

6) Repeat the coast downs on the same stretch of road

7) Perform 4 or more coast downs

8) Analyze coast downs properly in the iBike software

In your case there was a problem in 5); the coast downs were performed in a tailwind.

If all eight of these conditions are met you will get excellent results and obtain measurement-based validation of the CdA and Crr of your iBike. But the results you get from all this extra work will be only marginally better--if at all better--than the results you achieve from the simple Fast Start and Cal Ride procedure.

This is why we recommend the Fast Start and Cal Ride procedure for 98% of all riders...

Good job, and now I see where you were going. I met all of the conditions except the wind, although the wind was blowing, it was hardly noticeable. Thanks again.

Clint