iBike needs wind cal during ride?

Sarg
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Joined: Sat Jun 07, 2008 5:57 pm

Re: iBike needs wind cal during ride?

Post by Sarg »

I couldn't do more than three attachments so here is my profile. :D
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Avanti
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Re: iBike needs wind cal during ride?

Post by Avanti »

rruff wrote:
Avanti wrote:So every profile I've done my Numbers slowly get less and less I'm expecting that in 12 mths I'll be talking about a windscaling factor of 0.400 or something along those lines.
Since your wind scaling is dropping, that means it is getting more sensitive... which doesn't seem like a bad thing to me. I'd guess it won't drop much further, but who knows.

I check and adjust my WS pretty often since it does wander. If you understand what it is, it's easy to adjust based on the data in the " analyze wind" screen in the software, after doing a few out-back laps. An indicator that something is wrong is if you get a net wind on your rides that doesn't make sense, and your wind offset is ~0.

Once you get your CdA and Crr values nailed, there is no reason to redo the cals for those... just adjust the wind scaling factor when necessary.
Thanks rruff, could you expand further on this..I understand tweaking the Wind Scaling factors this I have been doing when my profile drifts slightly. However what I really have no idea about are how the values like Friction, Aero and CDA do to a profile.
For instance with friction on my latest profile I went for the safer option and allowed the unit to calculate the 'estimated value', this value came to 7.965 wheres my previous profiles were around the 5.335. This to me sounds like a large jump ? I've done my best to do alot of research on the units via forums etc and for the best part I've done an ok job profiles do bewilder me though. Being a competitve cyclist and really using my power meter to improve my condition I just never know if my unit is dialled in and giving me accurate results ie Is my traning improving my condition. Any help would be appreciated.
rruff
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Re: iBike needs wind cal during ride?

Post by rruff »

Worry about getting your CdA and Crr values right... these are the characteristics of you and your bike that determine your power requirements. CdA is aero drag and Crr is rolling resistance. Weight also matters, but that is easy. Forget about Fric and Aero for now, as they combine other variables related to the iBike sensors. Fric combines the riding tilt, so if that changes it can have a big effect on this variable. In reality, a riding tilt error isn't important though, since the iBike now corrects for tilt automatically.

Since it is difficult to separate CdA and Crr accurately via the coastdowns, it's usually better to select an appropriate estimated value for Crr, and let the CdA be the only variable determined. Once you get a good CdA value, you can keep it unless your position or bike changes significantly. You only need to watch your Wind Offset and tweak your Wind Scaling when necessary.
Avanti
Posts: 33
Joined: Tue Mar 30, 2010 10:59 pm

Re: iBike needs wind cal during ride?

Post by Avanti »

rruff wrote:Worry about getting your CdA and Crr values right... these are the characteristics of you and your bike that determine your power requirements. CdA is aero drag and Crr is rolling resistance. Weight also matters, but that is easy. Forget about Fric and Aero for now, as they combine other variables related to the iBike sensors. Fric combines the riding tilt, so if that changes it can have a big effect on this variable. In reality, a riding tilt error isn't important though, since the iBike now corrects for tilt automatically.

Since it is difficult to separate CdA and Crr accurately via the coastdowns, it's usually better to select an appropriate estimated value for Crr, and let the CdA be the only variable determined. Once you get a good CdA value, you can keep it unless your position or bike changes significantly. You only need to watch your Wind Offset and tweak your Wind Scaling when necessary.
Ok that all makes sense, so what procedure do you normally follow when you believe your scaling is out ? Ie I'm guessing you analyse the Wind?
rruff
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Re: iBike needs wind cal during ride?

Post by rruff »

Wind Scaling:

If you are getting net wind that doesn't make sense (via the "Analyze Wind" tab in the software), and you've made sure that your Wind Offset is ok, then your wind scaling is probably off. You can check this at any time by doing some out-back "laps". The best venue would be a quiet residential area with little traffic. Even better would be a spot where you can ride in the same part of the road for both directions... this will ensure that obstructions are not causing the wind to look different on one side of the street vs the other. Light winds will give the best results... at any rate you will want to avoid spending a significant amount of time *ever* going slower than a tailwind. If you have a tailwind, slow down quickly at the turnaround to minimize this.

This actually works the best if the out-back course is fairly short and you do several laps... this will help account for any shift in the wind that may occur.

a) Make sure your Wind Offset is zeroed.
b) Do a Trip Reset.
c) Ride back and forth over the course at a normal riding speed... the more laps the better.
d) End at your starting point and do another Trip Reset.

You can create as many of these files as you like to check repeatability.

When you get home, go into iBike software and check "Analyze Wind" for this file. Ideally you want to see zero, but a few 1/10ths of a mph plus or minus isn't bad either. The adjustment to wind scaling that would be applicable is (Vb/Vw)^2. For instance if your avg bike speed is 19.0 and your avg wind speed is 20.0, the correction to your wind scaling would be (19/20)^2= .90. Multiply this by your old wind scaling to get the new value.
coachboyd
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Re: iBike needs wind cal during ride?

Post by coachboyd »

A quick question.

With the wind scaling that has changed with temperature, was the unit mounted on the handlebars (if so I am assuming off to one side or the other)?
In the summer I am guessing you had either no gloves or short finger gloves on, now that it's getting colder you are probably going to bigger gloves. If you are on the hoods, these can definitely give off a different wind shear and affect the wind scaling.

I have a couple different profiles for summer and winter clothes (to accommodate for the different cda). It might be a good idea for you to have a couple different profiles with different wind scaling numbers.
Although this Gen 3 rechargeable steer tube mount system may be the perfect answer for you for both cold weather battery performance AND better wind scaling handling, since it will be farther away from your hands.
Boyd Johnson
http://www.boydcycling.com - high performance carbon wheels and accessories
Avanti
Posts: 33
Joined: Tue Mar 30, 2010 10:59 pm

Re: iBike needs wind cal during ride?

Post by Avanti »

Ok so one final question I promise !

I'll swing out and do that tonight, was I right in changing the friction number to estimated ? I think not by what you have stated, as ideally that number once is calibrated correct and your mount is steady and not moved should not change correct? So should I change my Friction numbers back to my old value and focus on windscaling?
rruff
Posts: 445
Joined: Wed Apr 23, 2008 10:48 am

Re: iBike needs wind cal during ride?

Post by rruff »

What are your values for Crr and CdA?
Avanti
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Re: iBike needs wind cal during ride?

Post by Avanti »

CRR = 0.0059
CDA = 0.379
rruff
Posts: 445
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Re: iBike needs wind cal during ride?

Post by rruff »

Avanti wrote:CRR = 0.0059
CDA = 0.379
Those numbers seem reasonable, but if you are in doubt, then go through the full calibration procedure. When you have good Crr and CdA numbers, then you can keep them. Focus on keeping your Wind Scaling accurate if it drifts.
Mark_H
Posts: 28
Joined: Mon Aug 09, 2010 11:50 am

Re: iBike needs wind cal during ride?

Post by Mark_H »

Temperature picked up here again recently and I got a ride in with good wind data. Today, wind data borked again, yet temp is mildish. I *DID* change the battery prior to the ride. I updated the date and time and downloaded the profile before setting off. Could this be related to the problem??? With the cold weather I've replaced the battery a few times over the past weeks and this is also when the wind problem has started... coincidence??
Zoltan
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Location: HUNGARY

Re: iBike needs wind cal during ride?

Post by Zoltan »

ScottChapman wrote:Do you always show a tailwind?

What was the temperature during your rides?

How long have you experienced this?
for me it occured only in my last ride, but during the whole ride. Could you figure out what to be blamed?
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