Problems with calibration rides and coastdowns....

[JR_70]

Just wondering why I might be having so many issues with my calibration rides and coastdowns.

I follow the procedure outlined - do the wind offset, ride the 2 mile calibration ride and then immediately do 6-8 coastdowns on a pretty quiet street.

Every time I have done the procedure I get very low CdA numbers - ranging from 0.135 to 0.270 - one time I got a 0.370 - but I don't know what happened there. The latest cal ride gave me a CdA of 0.233 - which I am currently using - however, I am a "big" guy - at 196lbs and 6'3 on a Cervelo P3C - but every time I do the calibration ride - my CdA comes up quite low - usually hovering around 0.200 +/- a few.

I have set the Crr to 0.0055 - even though on my coastdowns - again that number would almost never come close to that figure - usually 0.0022 to 0.0045 was the highest value it ever calculated. But for the sake of making it consistent - I am inputting 0.0055 before doing the cal ride or coastdowns.

On my coastdowns - my Fric is almost always 9.4xx give or take and my Aero is usually 0.130-0.210 ish...mostly between 0.170-0.200.

A couple of questions ....

1. What am I doing wrong that I am getting such low CdA numbers?
2. Why am I having such a tough time to get consistent repeatable numbers? It seems to me that if I am following the same procedure - using the same bike/wheels/tires/pressure/etc and riding the same course - that the numbers should be much closer on repeatable sessions...
3. Ultimately, how am I supposed to know what is a good profile and what is a bad profile....other than having to send them to Aaron or Boyd after each ride????

Any comments, suggestions, or advice - would be greatly appreciated.

Cheers!

[rruff]

I'm assuming that you are in the aero position... where is your iBike mounted? Are riding tilt and wind scaling consistent whenever you do the cal ride?

[JR_70]

Hey there..yep, I do the coastdowns and cal ride in the aero position. iBike is stem mounted. Riding tilt is either -0.4% or -0.5% every time I get my results. Wind scaling is usually very close if not exactly the same.

Thanks.

[coachboyd]

What type of road surface are you using for the coastdowns? If you are on a very smooth road, then .0055 might be a high estimate of crr (especially with good tires).

If you are in a fairly good aero position and have good tires on a good road I wouldn't be surprised to see a crr of .004 and a cda of .240 (even though you are a "big guy").

If you do coastdowns on a very good road surface, untypical of what you normally ride, then you may want to set the crr to .004 to .0045 and afterwards in the profile adjust the friction number a little bit higher to reflect the change in road conditions. This will keep riding tilt the same but will increase the crr to reflect the change in road conditions.

[JR_70]

Hey Boyd...JR here...thanks for your help...

I know I have asked you the same questions - just wondering if anyone else is having the same experience.

As I noted to you - the road surface is "pretty good" - it is definitely not new pavement - and it is somewhat chippy...but it is not terribly rough either. I am running Conti GP 4000S tires (and they are relatively brand new).

The pavement is very typical of what I would normally ride - it is similar to the road that is on the shoulder of most highways around here...

So do you think I need to lower the Crr? Or keep it at the norm for road surfaces at 0.0055?

[bex]

Hi JR.
I am no expert and yes I have had significant problems establishing a profile. I have had big differences in the numbers each time I have used the same piece of road. I have no problem about consistency, what my concern is, is the accuracy (for me) of an incorrect profile. I do not want to do a fitness test and put my self in a tier 3 when I should only be a tier 1 or 2. How do I know, other than to do some intervals based on the numbers and find I have over/under trained. I dont know enough (yet) about the units or training with power to know if this is a valid concern or not, I would think it is.
One thing is for sure, the folks on this forum and all at Velocomp are incredibly helpful, going to all lengths to solve problems. To that end its possible I have a defective wind port and we are looking into that.
As for the rr of the roads, analytic cycling put asphalt road at 0.004 and rough asphalt at 0.008, so I guess somewhere between the two is good.
Are you doing IM Canada?

Bex

[JR_70]

Hey Bex...you echo my concerns exactly - I know that I could use "whatever" numbers come up for my profile - but likewise - I am trying to do the fitness tests and use that data to do intervals - judge watts output on hill climbs etc. So I want to make sure it is as accurate as possible.

I believe I may have a defective windport as well as it seems that I am getting some funky data on various rides as well...

I am guessing then that 0.0055 is a good number (perhaps 0.0050 might even be closer) to use.

I am doing IMC - how about yourself?

[bex]

My wife does the endurance stuff. I just want to use a power meter and cycling to get fit.
She did IMC last year (12:56) Just did Sylvan Lake 1/2, not sure of her time yet but she did the bike in 2:57. She has an Iaero on her bike and its fine (we believe) she just never did the fit test yet. Too busy with training. So the NP IF TSS are out the window. We will get this done now though.
We will be in Penticton for IMC and will be lining up for next year for her. The goal is to qualify for Hawaii in the 50/55 AG.
As for the Ibike, most of what I have read suggests that a wind scaling between .7 and 1.something is acceptable. My Ipro is always above 2.47 (that was the lowest I ever got)
I recently noticed that I had what I thought was a good profile using just the "basic" set up, no coast downs, ans as per suggestion for the tech Guys.
My first part of a ride gave me almost zero watts down hill, so I stopped, did another wind calib then went again, OK for 20 minutes or so then back to zero watts.
I have communicated this to Velocomp and we are getting it resolved.
You need to give me your race number, we will look out for you! Maybe swap stories before the event.

Bex