Calibration Advice (issues with drafting numbers)
Calibration Advice (issues with drafting numbers)
Hello,
Just got my iBike Pro Gen3 (bar mounted, wireless, v400 firmware) on Monday and have gone through all of the steps for configuration. I've been actively reading up on all the threads to make sure I have the calibration decent. I have a PowerTap as well, so I'm comparing the two (manually) to get some confidence in the configuration of the iBike. I've done 3 solo rides (all mostly easy) and they look spot on and now two group rides where the data was very noticeably low. I've done 4 calibration rides and about 6 coast downs. I was hoping that the most recent configurations would solve my group ride issue, but yesterday continues to appear way off when in pacelines. When reviewing the attached files, I see a very noticeable difference between the iBike and PT only when in the group. The second half of my ride was solo and was very accurate with the iBike and PT only being 5 watts off in average and normalized power. A scenario that's been very consistent for me when riding alone. Attached are the files in question, but I was wondering if anyone might give me some thoughts on how to tackle this issue as the problem only seems to crop up in pacelines or on someone's wheel.
So for more details, in the ride files, at 28min in, I start a 50min tempo ride with 8 other riders. This is a very steady 24-25mph ride with everyone taking pulls. When I look at the data on my iBike, this segment is where all of the difference is exposed between that and the PT. The remainder of the file was a solo ride and seems to track well (the reason why I don't know how to fix this issue).
During the ride, while looking at both, it was VERY common for the iBike to be easily 100w lower than the PT. Even pulling through and taking a 30sec or 1min pull, still about 100 watts low and never really raised much when my nose touched the wind as I'd expect it to. As noted above, while riding solo at 18-22mph (on the hoods, bars and drops) the PT and iBike were VERY consistent with each other.
So for that 50min I have this data from the iBike:
Dist: 20.24m
Energy: 469.8
Avg Watts: 155.9
NP: 205w
The PowerTap on the other hand had:
Energy: 660
Avg Watts: 224
NP: 246
This data discrepancy changed my overall TSS for the day from 148 (on the PT data) down to 109. That much of a difference, compounded over days would be a lot for me to not account for... Today I did another group ride and had the same experience with avg and np watts both being easily 30-40 watts off from my PT putting my TSS off by 40+ points.
Just as a side note, going on perceived effort, the 224/246w data (solid tempo for me) is exactly what that ride felt like.
So with the fact that solo riding is spot on, I'm not inclined to do more calibration rides or coast downs. I'm thinking something needs to be tweaked in this configuration. Does anyone have any insight or advice on how to fix this? I've attached both the PowerTap and iBike files to the post and listed below are my current configurations for the iBike in a screen shot.
Some additional rider / setting info if it matters:
Rider: 178lb / 5'10"
Racer Settings on iBike:
EST Fric: Yes
Fric: 45
Coast-Down & o/b Ride Data: (from Edit Profile screen)
Aero: 0.657
Wind Scaling: 2.330
CdA: 0.282
Fric: 4.171
Weight: 206lb
Riding Tilt: 0.0
Crr: 0.0046
Any help would be greatly appreciated.
Thanks,
Todd
Just got my iBike Pro Gen3 (bar mounted, wireless, v400 firmware) on Monday and have gone through all of the steps for configuration. I've been actively reading up on all the threads to make sure I have the calibration decent. I have a PowerTap as well, so I'm comparing the two (manually) to get some confidence in the configuration of the iBike. I've done 3 solo rides (all mostly easy) and they look spot on and now two group rides where the data was very noticeably low. I've done 4 calibration rides and about 6 coast downs. I was hoping that the most recent configurations would solve my group ride issue, but yesterday continues to appear way off when in pacelines. When reviewing the attached files, I see a very noticeable difference between the iBike and PT only when in the group. The second half of my ride was solo and was very accurate with the iBike and PT only being 5 watts off in average and normalized power. A scenario that's been very consistent for me when riding alone. Attached are the files in question, but I was wondering if anyone might give me some thoughts on how to tackle this issue as the problem only seems to crop up in pacelines or on someone's wheel.
So for more details, in the ride files, at 28min in, I start a 50min tempo ride with 8 other riders. This is a very steady 24-25mph ride with everyone taking pulls. When I look at the data on my iBike, this segment is where all of the difference is exposed between that and the PT. The remainder of the file was a solo ride and seems to track well (the reason why I don't know how to fix this issue).
During the ride, while looking at both, it was VERY common for the iBike to be easily 100w lower than the PT. Even pulling through and taking a 30sec or 1min pull, still about 100 watts low and never really raised much when my nose touched the wind as I'd expect it to. As noted above, while riding solo at 18-22mph (on the hoods, bars and drops) the PT and iBike were VERY consistent with each other.
So for that 50min I have this data from the iBike:
Dist: 20.24m
Energy: 469.8
Avg Watts: 155.9
NP: 205w
The PowerTap on the other hand had:
Energy: 660
Avg Watts: 224
NP: 246
This data discrepancy changed my overall TSS for the day from 148 (on the PT data) down to 109. That much of a difference, compounded over days would be a lot for me to not account for... Today I did another group ride and had the same experience with avg and np watts both being easily 30-40 watts off from my PT putting my TSS off by 40+ points.
Just as a side note, going on perceived effort, the 224/246w data (solid tempo for me) is exactly what that ride felt like.
So with the fact that solo riding is spot on, I'm not inclined to do more calibration rides or coast downs. I'm thinking something needs to be tweaked in this configuration. Does anyone have any insight or advice on how to fix this? I've attached both the PowerTap and iBike files to the post and listed below are my current configurations for the iBike in a screen shot.
Some additional rider / setting info if it matters:
Rider: 178lb / 5'10"
Racer Settings on iBike:
EST Fric: Yes
Fric: 45
Coast-Down & o/b Ride Data: (from Edit Profile screen)
Aero: 0.657
Wind Scaling: 2.330
CdA: 0.282
Fric: 4.171
Weight: 206lb
Riding Tilt: 0.0
Crr: 0.0046
Any help would be greatly appreciated.
Thanks,
Todd
- Attachments
-
- 090805_cal_data.ibcd4m
- LastCalibrationRideData
- (334.07 KiB) Downloaded 309 times
-
- iBike_08_07_2009.csv
- iBikeRideFile
- (2.14 MiB) Downloaded 346 times
-
- PT_8_7_2009.csv
- PowerTapRideFile
- (649.37 KiB) Downloaded 370 times
Re: Calibration Advice (issues with drafting numbers)
I predict that when Boyd and the others check this out, they will say that the wind scaling is your culprit. That 2.x number is at the super-high end of workable, and it would cause your drafting numbers to skew weird.
The solution would be to make sure you're getting good airflow around your Ibike unit, then re-do the calibration ride. Maybe do a 2 mile out and 2 mile back. But I've had good results with just the 1 mile out and back. Absolutely still or light winds don't seem to be completely necessary (which is good, since I almost never get 'em. Riding directly into and back with the wind, though, DOES seem to be important. Steady wind is key, as gusts will cause problems, as will being passed by lots of cars. Since that w.s. # seems so off, it might also be worth re-doing the coast-downs too.
The solution would be to make sure you're getting good airflow around your Ibike unit, then re-do the calibration ride. Maybe do a 2 mile out and 2 mile back. But I've had good results with just the 1 mile out and back. Absolutely still or light winds don't seem to be completely necessary (which is good, since I almost never get 'em. Riding directly into and back with the wind, though, DOES seem to be important. Steady wind is key, as gusts will cause problems, as will being passed by lots of cars. Since that w.s. # seems so off, it might also be worth re-doing the coast-downs too.
Re: Calibration Advice (issues with drafting numbers)
I thought there was quite a bit of variability. My wind scaling with a Gen3 is >3 while my Gen2 reads 1.3 with the same mount.R Mc wrote:That 2.x number is at the super-high end of workable, and it would cause your drafting numbers to skew weird.
Re: Calibration Advice (issues with drafting numbers)
I thought that was a high number too, but assumed that it was related to the fact that I have it bar mounted and sticking out pretty far compared to all the stem mount's I see. I'll run another o&b ride and some coast downs this morning before my ride and see if that helps at all. But I'm not optimistic as I've done three sets of these already...
Re: Calibration Advice (issues with drafting numbers)
So I have new ride data with a fresh calibration ride this morning (4miles instead of 2m) and 6 coast downs. The data is actually worse now than it was with my previous settings because even solo riding is off now (reporting lower than PT). The conditions this morning were very calm. The road was straight and only barely changing in gradient. But not having much luck here.
With today's group ride, I saw this difference between PT and iBike.
iBike:
Avg Watts: 133
NP: 226w
Energy: 1195
TSS: 152
PowerTap:
Avg Watts: 181
NP: 264
Energy: 1618
TSS: 207
As a reference here are the two screen shots from the two full attempts to calibrate using the cal ride and coast downs. The first one was done several days ago and reads great when solo. The second one was done today and is worse.
Done on 8/5/09 Done on 8/9/09 Please note, at least one or two of the middle coast downs was bad data. I reached a point in the road where it dipped down slightly so the coast down went on MUCH longer than others. The first two and last two were probably the best ones I did where the ones in the middle hit that part of the road where the coasting was accelerated by the slight gradient change.. So that's probably why they look so odd. What I do find interesting is that one coast down value from my first set and one from my second set match. Does that mean anything? Oh and why are Friction values the same for all of them?
So I'm at a loss at what to do at this point.
With today's group ride, I saw this difference between PT and iBike.
iBike:
Avg Watts: 133
NP: 226w
Energy: 1195
TSS: 152
PowerTap:
Avg Watts: 181
NP: 264
Energy: 1618
TSS: 207
As a reference here are the two screen shots from the two full attempts to calibrate using the cal ride and coast downs. The first one was done several days ago and reads great when solo. The second one was done today and is worse.
Done on 8/5/09 Done on 8/9/09 Please note, at least one or two of the middle coast downs was bad data. I reached a point in the road where it dipped down slightly so the coast down went on MUCH longer than others. The first two and last two were probably the best ones I did where the ones in the middle hit that part of the road where the coasting was accelerated by the slight gradient change.. So that's probably why they look so odd. What I do find interesting is that one coast down value from my first set and one from my second set match. Does that mean anything? Oh and why are Friction values the same for all of them?
So I'm at a loss at what to do at this point.
Last edited by tbarczak on Sun Aug 09, 2009 4:18 pm, edited 2 times in total.
Re: Calibration Advice (issues with drafting numbers)
I don't know why, but something is wrong with the wind sensor. The mount is super-solid on your bars right?
Those 6 coast-downs today are really all over the place.
I did a profile for my time-trial bike a while ago with bad wind (too much cross-wind and gusty), and it came back with a 1.7 or so wind-scaling. What I noticed was really pronounced under-reporting with tail-winds--which is comparable to the problem you're having in groups with the first profile. With the new profile look at what happens to your cda with that high w.s. number: @ 211 the ibike thinks that you are more aero than most pros on their time trial bikes.
Given the aero values (which look suspect to me, because most of mine tend to cluster like, say 245, 255, 234, 252, i.e. the variation shows up in the tens digit not the hundreds.) that show up in today's coast-downs--that under-reporting between the ibike and the p-tap is happening because that wind-scaling is essentially causing the ibike to halve your actual cda as it calculates power.
That's what it looks like to me--but helping you get better results is beyond what I know--partly because there's a lot that could be off.
Those 6 coast-downs today are really all over the place.
I did a profile for my time-trial bike a while ago with bad wind (too much cross-wind and gusty), and it came back with a 1.7 or so wind-scaling. What I noticed was really pronounced under-reporting with tail-winds--which is comparable to the problem you're having in groups with the first profile. With the new profile look at what happens to your cda with that high w.s. number: @ 211 the ibike thinks that you are more aero than most pros on their time trial bikes.
Given the aero values (which look suspect to me, because most of mine tend to cluster like, say 245, 255, 234, 252, i.e. the variation shows up in the tens digit not the hundreds.) that show up in today's coast-downs--that under-reporting between the ibike and the p-tap is happening because that wind-scaling is essentially causing the ibike to halve your actual cda as it calculates power.
That's what it looks like to me--but helping you get better results is beyond what I know--partly because there's a lot that could be off.
- lorduintah
- Posts: 657
- Joined: Fri Jan 11, 2008 9:37 am
- Location: Plymouth, MN
Re: Calibration Advice (issues with drafting numbers)
What does your profile look like when you allow Crr to vary? It is still likely that the wind scaling factor has an issue (air port partially or inconsistently blocked; RWS, if in use, is not sealed to the iBike or is mounted in a bad place.) Did you zero the wind and redo the tilt calibration right before starting your coast downs and cal ride - just asking. Are you braking during the CDs or is a brake pad rubbing because you have a warped wheel? Unlikely if the Crr you have is not a high value, but again just looking for things to check.
Check your tilt and then push down fairly firmly on the red button a couple times - then reread your tilt again (this is NOT a tilt cal) - you just use the tilt display and turn 180 and see if the negative of the first reading within a tenth or two shows up. If that changes between the before and after button pushing by any appreciable amount, your mount might be loose.
The other thing I noticed - the time between coast downs is only a minute or two? That is not right - coasting from 20 to 8 and riding back to your starting point should take a lot longer - you should be coasting for 1/4 mile or more and then riding back, accelerating up to 20, etc.
John or Coach will be asking for the files, too.
Tom
Check your tilt and then push down fairly firmly on the red button a couple times - then reread your tilt again (this is NOT a tilt cal) - you just use the tilt display and turn 180 and see if the negative of the first reading within a tenth or two shows up. If that changes between the before and after button pushing by any appreciable amount, your mount might be loose.
The other thing I noticed - the time between coast downs is only a minute or two? That is not right - coasting from 20 to 8 and riding back to your starting point should take a lot longer - you should be coasting for 1/4 mile or more and then riding back, accelerating up to 20, etc.
John or Coach will be asking for the files, too.
Tom
Re: Calibration Advice (issues with drafting numbers)
Thanks. That point about the coast downs is something I think I really messed up on. I didn't think about re-using the exact same stretch of road to repeat each. In stead I just kept riding, doing some along the way back to back.
This morning I went out and did a fresh wind and tilt cal and then 4 more coast downs on a very flat stretch of road. Wind / weather conditions were the same as yesterday and the road surface was also very similar. I didn't want to redo the cal ride as I felt like I did a great one yesterday (which is still represented in the screen below). Here is the screen shot of all of that data with the cal ride from 8/9 as well as the last four coast downs from 8/10 being what I think are the first best set of them I've done to date. But now I have so much data from so many coast downs and such, I'm not sure how to lock in the right values. I assume from all of this it's probably going to be a deal where I manually enter the best values and go from there. Another thought I had was to simply exclude all of the 8/9 coast downs using that "Remove Selected" button and then save the remaining values to the profile and send to iBike. But just not sure if that's the right way to go..
This morning I went out and did a fresh wind and tilt cal and then 4 more coast downs on a very flat stretch of road. Wind / weather conditions were the same as yesterday and the road surface was also very similar. I didn't want to redo the cal ride as I felt like I did a great one yesterday (which is still represented in the screen below). Here is the screen shot of all of that data with the cal ride from 8/9 as well as the last four coast downs from 8/10 being what I think are the first best set of them I've done to date. But now I have so much data from so many coast downs and such, I'm not sure how to lock in the right values. I assume from all of this it's probably going to be a deal where I manually enter the best values and go from there. Another thought I had was to simply exclude all of the 8/9 coast downs using that "Remove Selected" button and then save the remaining values to the profile and send to iBike. But just not sure if that's the right way to go..
Re: Calibration Advice (issues with drafting numbers)
Yes, you could remove the coast-downs you don't want, then let the software average the remaining 4.
My guess--and . . . it's only a guess . . . is that that with an aero number around 753, the 1.9 wind scaling will deliver usable results.
My guess--and . . . it's only a guess . . . is that that with an aero number around 753, the 1.9 wind scaling will deliver usable results.
Re: Calibration Advice (issues with drafting numbers)
I can't think of any reason why it would be necessary of even desirable to always be on the same stretch of road.tbarczak wrote:I didn't think about re-using the exact same stretch of road to repeat each. In stead I just kept riding, doing some along the way back to back.
- lorduintah
- Posts: 657
- Joined: Fri Jan 11, 2008 9:37 am
- Location: Plymouth, MN
Re: Calibration Advice (issues with drafting numbers)
Because you are doing a calibration and you are establishing a set of parameters controlled by the coast down - this is the only way to get a set of parameters and the quantity of data for that which yield reproducible information. If you keep doing CDs on different places along a road, the road conditions change - affecting the analysis of the coefficients that you want. So the variations in road conditions are going to be an unknown confounding factor adding to error.
Tom
Tom
Re: Calibration Advice (issues with drafting numbers)
Actually, the coefficients should be about the same wherever you do your coastdowns... provided that conditions are reasonable. Rather than introducing "confounding factors" a variety of conditions should produce values that are more representative of what you will see while riding. If you do coastdowns only on one piece of road with wind blowing from one direction, then you will only get data that represents those conditions. The data may be more consistent, but that doesn't make it more accurate.
IMO is always a good idea to check your calibration regularly to make sure that it is good. It is easy to do... especially since the Abs Wind and auto tilt adjustments... and it has been mentioned in these forums many times.
IMO is always a good idea to check your calibration regularly to make sure that it is good. It is easy to do... especially since the Abs Wind and auto tilt adjustments... and it has been mentioned in these forums many times.
- lorduintah
- Posts: 657
- Joined: Fri Jan 11, 2008 9:37 am
- Location: Plymouth, MN
Re: Calibration Advice (issues with drafting numbers)
That's where the out and back ride come in to play. Here you get the wind scaling and tilt. THE CDs work on the Crr and Aero. The Crr is supposed to be a constant factor and removing other variables should lead to a more accurate and precise estimate - same for Aero.
Tom
Tom
Re: Calibration Advice (issues with drafting numbers)
Limiting the test conditions to only one specific case may make your results more consistent, but will not make your results more accurate for all conditions.
Have you done CDs on a flatish road where you had a slight headwind in one direction and tailwind in the other? If the results are different with the headwind and tailwind, then which values would be the more accurate to use?
Have you done CDs on a flatish road where you had a slight headwind in one direction and tailwind in the other? If the results are different with the headwind and tailwind, then which values would be the more accurate to use?
- lorduintah
- Posts: 657
- Joined: Fri Jan 11, 2008 9:37 am
- Location: Plymouth, MN
Re: Calibration Advice (issues with drafting numbers)
There is obviously a difference of opinion.
Tom
Tom
Re: Calibration Advice (issues with drafting numbers)
Would be interested in seeing some thoughts on these two concepts from the developers. I wonder what they might think is the better testing approach because I didn't even give a thought to this topic when doing my setup from what I read in the manuals.
Re: Calibration Advice (issues with drafting numbers)
Gosh, the issue of CD's with a slight headwind/tailwind has been discussed at least several times somewhere on this forum.
Basically, as I understand it, a slight headwind is more desirable than a slight tailwind because of two reasons. As you slow down from 20 to 8 mph, the low speed end of the coast is much less accurate because that is where you are trying to get the CRR to separate out of the data. The tailwind confounds that and the wind sensor is probably less accurate with a slight tailwind at slow speed. In addition at the high speed end where you are trying to get the CdA from the data, the tailwind dilutes the aero data by lowering the relative air speed undesirably. While I may not have the exact t's and c's I think the gist of this is accurate. Of course zero wind is the most desirable.
Further, for what I suppose are heuristically derived reasons (found to work best by experience) Coach Boyd has been recommending either a slight bowl shape CD path or slight up hill, at the terminal end, such that the coastdown is in the 20-25 or so seconds of length range.
Regards,
Russ
Basically, as I understand it, a slight headwind is more desirable than a slight tailwind because of two reasons. As you slow down from 20 to 8 mph, the low speed end of the coast is much less accurate because that is where you are trying to get the CRR to separate out of the data. The tailwind confounds that and the wind sensor is probably less accurate with a slight tailwind at slow speed. In addition at the high speed end where you are trying to get the CdA from the data, the tailwind dilutes the aero data by lowering the relative air speed undesirably. While I may not have the exact t's and c's I think the gist of this is accurate. Of course zero wind is the most desirable.
Further, for what I suppose are heuristically derived reasons (found to work best by experience) Coach Boyd has been recommending either a slight bowl shape CD path or slight up hill, at the terminal end, such that the coastdown is in the 20-25 or so seconds of length range.
Regards,
Russ
- lorduintah
- Posts: 657
- Joined: Fri Jan 11, 2008 9:37 am
- Location: Plymouth, MN
Re: Calibration Advice (issues with drafting numbers)
Russ -
You have made some good points - that tie in well to my comments - needless I did not explicitly comment on headwind/tailwind, But the "bowl" shape almost completely dictates one location and not a series of locations. Thus my point of repeating the CDs at the same location in the same direction over more than just a few traverses.
Now - if you happen to have miles of path/road that say are in a slight incline all the way and you have no wind or a small headwind along that entire section of test area, I am sure you could employ the series of sequential CDs. I sure don't have that around, but I do have a 3/4 mile stretch that works great - when the wind is calm or low velocity.
Experimentally, I prefer separation of variables. I'll make another profile, if I am going to change gear or where I ride. It just so happens that is not currently the case.
Tom
You have made some good points - that tie in well to my comments - needless I did not explicitly comment on headwind/tailwind, But the "bowl" shape almost completely dictates one location and not a series of locations. Thus my point of repeating the CDs at the same location in the same direction over more than just a few traverses.
Now - if you happen to have miles of path/road that say are in a slight incline all the way and you have no wind or a small headwind along that entire section of test area, I am sure you could employ the series of sequential CDs. I sure don't have that around, but I do have a 3/4 mile stretch that works great - when the wind is calm or low velocity.
Experimentally, I prefer separation of variables. I'll make another profile, if I am going to change gear or where I ride. It just so happens that is not currently the case.
Tom
Re: Calibration Advice (issues with drafting numbers)
So with some help from CoachBoyd, I've gotten a lot closer with my data. With a stem mount instead of my previous bar mount and doing better coast downs, I'm now within 20 watts consistently of good data. For some reason the latest data seems to just be consistently 20 watts on average lower than my PT.
Here's the new profile data. I'm curious, does anyone have any advice on a way to tweak the settings to compensate for an average of 20 watts?
Here's the new profile data. I'm curious, does anyone have any advice on a way to tweak the settings to compensate for an average of 20 watts?
Re: Calibration Advice (issues with drafting numbers)
Your Crr is low. Try setting that to .0055, and check your wind scaling a few times. When you get that properly adjusted, you should see ~0 watts while coasting (+- fluctuating depending on your speed). Adjust CdA while keeping WS constant so that your coasting watts are ~0. When you get that right it will be accurate... if it doesn't match your Powertap, then the Powertap is probably wrong.
EDIT: First step is to set your Crr to .0055 in the calibration file and let the program figure out a CdA.
EDIT: First step is to set your Crr to .0055 in the calibration file and let the program figure out a CdA.
-
- Posts: 84
- Joined: Sun Aug 31, 2008 7:54 pm
- Location: 'twixt Sylvan Lake and Eckville in Alberta, born in Manchester England. Always an Englishman
Re: Calibration Advice (issues with drafting numbers)
I would be interested to know where the 0.0026 came from as the "setting in Ibike"
I tried another profile a few days ago.
Did a reset
entered my data
Checked my crr was at 0.055
did the calib ride and cd's
did the download and there was 0.0017 as the "setting in ibike.
Weird.
So doing the coast whilst in the coast screen is a way of checking if your wind scaling is correct? Coasting watts should be around zero? At what speed?
Bex
EDIT: I redid my profile, ensured my crr was 0.0055 (again) and this time I got a really good set of numbers, and I say that based on the crr figure I ended up with which was 0.0059
Now I am happy with my profiles.
I tried another profile a few days ago.
Did a reset
entered my data
Checked my crr was at 0.055
did the calib ride and cd's
did the download and there was 0.0017 as the "setting in ibike.
Weird.
So doing the coast whilst in the coast screen is a way of checking if your wind scaling is correct? Coasting watts should be around zero? At what speed?
Bex
EDIT: I redid my profile, ensured my crr was 0.0055 (again) and this time I got a really good set of numbers, and I say that based on the crr figure I ended up with which was 0.0059
Now I am happy with my profiles.
Re: Calibration Advice (issues with drafting numbers)
So if I go into the Process Calibration Ride screen (the one I posted the screen shot of) and change the CRR value to a Fixed CRR value of 0.0055, it changes many of the numbers including Friction, Cda and Aero. I then want to upload that data as Profile 1 to my iBike and then go for a ride using the watts data on the Coast Down screen (before actually doing a coast down) and then see if that is showing zero watts during a coast? If it doesn't show zero watts and instead shows positive watts, do I then increase my Crr or reduce it to bring it down to zero?
Just wanted to make sure I have it straight.
Thanks.
Just wanted to make sure I have it straight.
Thanks.
Re: Calibration Advice (issues with drafting numbers)
I would leave the Crr alone until you have a good reason to believe it should be different than .0055. At high speeds the drag is dominated by aerodynamics, so coast in a variety of conditions at fairly high speeds (>20mph at least) and see if the values tend towards positive or negative. If they are nearly always positive, then this means that CdA is too high and should be adjusted down while keeping the same wind scaling factor.
Of course this assumes that you keep the right position, have been riding long enough for the tilt to auto-adjust, your wind scaling is spot on, and the wind offset is zeroed.
Of course this assumes that you keep the right position, have been riding long enough for the tilt to auto-adjust, your wind scaling is spot on, and the wind offset is zeroed.
Re: Calibration Advice (issues with drafting numbers)
I did as advised, setting the CRR to 0.0055 and going out and coasting through some 20+ MPH speeds watching the watts zero out.
Very interesting observation. Within the 20-25mph range of coasting, I observed the watts on the 'coast' screen drop negative between 10 and 25 a lot. That matches up very well with the inconsistency of data between this device and the PT.
So, my next question is, based on your advice I'm not going to touch Crr, rather I'm going to adjust the CdA. It sounds like my CdA is too low and that I want to increase the number to bring the coast watts up towards zero. Today the value is set at: 0.256
How much of a change do you recommend I attempt manually with that value?
Very interesting observation. Within the 20-25mph range of coasting, I observed the watts on the 'coast' screen drop negative between 10 and 25 a lot. That matches up very well with the inconsistency of data between this device and the PT.
So, my next question is, based on your advice I'm not going to touch Crr, rather I'm going to adjust the CdA. It sounds like my CdA is too low and that I want to increase the number to bring the coast watts up towards zero. Today the value is set at: 0.256
How much of a change do you recommend I attempt manually with that value?
-
- Posts: 84
- Joined: Sun Aug 31, 2008 7:54 pm
- Location: 'twixt Sylvan Lake and Eckville in Alberta, born in Manchester England. Always an Englishman
Re: Calibration Advice (issues with drafting numbers)
Is it possible perhaps to now change that Cda number in profiles, save (the original profile info) the profile and apply it to a ride file made with the original profile (the one that has a value of 0.256 Cda) keep making changes (and apply to the ride file) until you remove the discrepancy (or get close enough to be acceptable) then send it to the unit and go try the coasting test again?
Just a thought
Bex
Just a thought
Bex
Re: Calibration Advice (issues with drafting numbers)
In IB3 go to "Tools/ Tweak CdA" and there you can adjust it until you like what you see. You can also use "Tools/Switch Profile After the Ride", but you need to have another profile already made. Your CdA is low compared to what most most people have on a normal road bike. Something in the .30-.40 range is typical.
I should emphasize that getting your Wind Scaling as accurate as possible is important to. This is easy to check by doing a series of out-back rides any time and checking that the avg wind comes out to zero (or close to it).
I should emphasize that getting your Wind Scaling as accurate as possible is important to. This is easy to check by doing a series of out-back rides any time and checking that the avg wind comes out to zero (or close to it).
Re: Calibration Advice (issues with drafting numbers)
OK, novice question here but I go into Profiles > Edit Profile and then click Advanced Profile Settings in order to change my CdA. I then do so, hit the accept button (at which point it tells me I'm switching to a User Edited profile) but then the screen where I can send the profile to the iBike doesn't show my new profile values. So am I going about editing CdA wrong or is there another way to do this?
EDIT: Wow, I've taken a CdA of 0.349 and Crr of 0.0055 and did a "Tweak Cda" on multiple files I have and that fixes all of them. Almost perfectly. Now I'm just frustrated because I don't know how to set that CdA in the profile.... argh..
EDIT: Wow, I've taken a CdA of 0.349 and Crr of 0.0055 and did a "Tweak Cda" on multiple files I have and that fixes all of them. Almost perfectly. Now I'm just frustrated because I don't know how to set that CdA in the profile.... argh..
- Morocco Mole
- Posts: 170
- Joined: Thu Mar 19, 2009 6:58 am
- Location: Brisbane, Australia
Re: Calibration Advice (issues with drafting numbers)
ok, you are so close. Follow the steps
- edit profile
- advanced Profile Settings
- Make changes to your CdA, be careful not to change your wind scaling, you actually need to modify the Aero number to get the CdA you are after without affecting WS
- Click the Accept button
- You should be back at the Edit Profiles Screen, make sure you profile is selected, you can confirm the new CdA value over on the right
- Click Send to ibike
- Click Accept to Save and Close
I have attached 3 .jpgs that go through an example of changing a CdA from .256 to .349
Cheers
- edit profile
- advanced Profile Settings
- Make changes to your CdA, be careful not to change your wind scaling, you actually need to modify the Aero number to get the CdA you are after without affecting WS
- Click the Accept button
- You should be back at the Edit Profiles Screen, make sure you profile is selected, you can confirm the new CdA value over on the right
- Click Send to ibike
- Click Accept to Save and Close
I have attached 3 .jpgs that go through an example of changing a CdA from .256 to .349
Cheers
Re: Calibration Advice (issues with drafting numbers)
Awesome, thank you. The edits saved. Now I just need to go out and test the new values.
Re: Calibration Advice (issues with drafting numbers)
The manual edits really made a difference. Today's ride was the closet I've seen yet with a group ride scenario. I'm still tweaking the CdA up a touch for tomorrow, but now there's real progress. Thanks for all the help with this.