Swapped bars & stem

[Pete]

Hi
I recently swapped out the bars & stem on our track bike.
I also changed the mounting from bar to stem.
Due to being rushed that day and the difficulty of doing a cal ride for track bikes, I just did a tilt cal with the new setup and left the profile otherwise the same.
After the loading the ride I did a correction for altitude to ensure it started & ended the same.
Power seems OK but perhaps a bit high with several PB's set so I'd like to verify how reliable they might be.

What I'd like to know is what values in the profile would be different from a cal ride and can they be manually applied to this ride done with just the Tilt?
Eg I'm wondering about "riding tilt" and whether that is compensated for anyway by the post-ride altitude corrections?

On the other hand, once we perform a proper cal ride, can we apply the new profile to the ride referred to above?
Or does this method only apply CdA & Crr, which I expect to be not materially changed?

Whilst this is just for one ride, I am concerned we might have an ongoing issue as some clubs/Commissaires will not allow bike computers on track bikes and certainly for championship events it would need to be removed. Ideally the mount can stay in position but that may not always be the case either.
The stem mount should allow for consistent forward tilt however there is risk of side-to-side variation.

Ride file attached. (NB young rider, 38kg, 650c wheels FTP ~100w)

iBike_12_31_2014_1649_11_km_HiDef.ibr

(387.29 KiB) Downloaded 250 times

Cheers
Pete

[Russ]

Hello Pete,
I have taken a quick look and two things jump out right off, wind looks unbalanced on the high side and your cda looks really quite a bit below average. So I tried 'return to original download' followed by a check calibration, this is the significant part:
Aero 0.292 -> 0.231
Wind Scaling 1.244 -> 0.986
CdA 0.235 -> 0.235 m^2
Fric 3.928 -> 2.201
Riding Tilt -0.5 -> -0.1 %
From this (assuming you did an out an back or a loop) I would change wind scaling and tilt and try again. You might review your cds and crr for being reasonable. You could play around with Isaac suggestion of a profile but just use it to get the values (for your weight and height, etc) unless you are fairly sure they are reasonable. CRR of .0041 is right fantastic and probably requires (in my opinion) a very smooth surface to be realistic as roughness in the roads raises CRR.

Regards,
Russ

[Pete]

Thanks Russ
Just to clarify:
This was for my 10yo son on his track bike.
He is 150cm & 37kg so the low CdA is expected and the result of proper cal ride prior to these changes.
Riding circles at the velodrome. "Plexi-pave" surface, so smoother than asphalt but not quite wooden boards.
We use the same Crr for concrete tracks too.

Where does 'riding tilt' come from and can it be user set?
Same question from 'wind scaling'
(I assume these are not actually from 'tilt cal' & 'wind cal' as I would need to manually set them wouldn't I?)

Tried 'check calibration' for myself but we had some drafting as I did a few lead-outs etc
Also because I set start & end elevation (to same value) the ride is not considered out-and-back or a loop

[Velocomp]

Where does 'riding tilt' come from and can it be user set?
Same question from 'wind scaling'
(I assume these are not actually from 'tilt cal' & 'wind cal' as I would need to manually set them wouldn't I?)

Tried 'check calibration' for myself but we had some drafting as I did a few lead-outs etc
Also because I set start & end elevation (to same value) the ride is not considered out-and-back or a loop

Riding Tilt is measured during the Cal Ride, and cannot be user set.

Wind Scaling is also measured during the Cal Ride. It can be manually overridden in the profile menus, but that is a tricky thing to do...

Don't do a Check Calibration if you've done drafting; this procedure assumes you have done a solo ride.

If your ride file truly is an out-and-back ride, then Check Calibration should work.

[Steve_Davidson]

Hi
I recently swapped out the bars & stem on our track bike.
I also changed the mounting from bar to stem.
Due to being rushed that day and the difficulty of doing a cal ride for track bikes, I just did a tilt cal with the new setup and left the profile otherwise the same.
After the loading the ride I did a correction for altitude to ensure it started & ended the same.
Power seems OK but perhaps a bit high with several PB's set so I'd like to verify how reliable they might be.

What I'd like to know is what values in the profile would be different from a cal ride and can they be manually applied to this ride done with just the Tilt?
Eg I'm wondering about "riding tilt" and whether that is compensated for anyway by the post-ride altitude corrections?

On the other hand, once we perform a proper cal ride, can we apply the new profile to the ride referred to above?
Or does this method only apply CdA & Crr, which I expect to be not materially changed?

Whilst this is just for one ride, I am concerned we might have an ongoing issue as some clubs/Commissaires will not allow bike computers on track bikes and certainly for championship events it would need to be removed. Ideally the mount can stay in position but that may not always be the case either.
The stem mount should allow for consistent forward tilt however there is risk of side-to-side variation.

Ride file attached. (NB young rider, 38kg, 650c wheels FTP ~100w)

The attachment iBike_12_31_2014_1649_11_km_HiDef.ibr is no longer available

Cheers
Pete

Pete,

The Newton can be used on the track but to comply with the rules it has to be fitted securely and the screen not visible by the rider to avoid distraction. Also it has to be fitted such that it does not protrude from the front of the stem.

I fitted mine under the stem with the screen facing the ground and the front intake just behind the front of the stem (see pictures). I managed to modify a low cost garmin mount with the metal fitting from the ibike mount for the Newton to slot into. The unit is very secure, unobtrusive and track legal for racing .

A calibration ride has to be performed as the wind scaling will be different to normal mount locations being underneath and close to the stem front plus the tilt cal will be off.

As it is not permitted to ride on the track in the opposite direction for the out and back cal ride you have fool the unit and have both sectors equal in terms of slope. This is very difficult on an indoor velodrome especially if it is busy as you are meant to ride above the blue line and may have to move to avoid other riders etc.

I rode on the velodrome a few times using estimated values and the results were not great so had to resort to some novel thinking to be able to get a good cal ride.

Basically I started at a set point (in line with the start/finish line) and rode around the track apron which is pan flat and consistent. I didn’t know what stage of the cal process the Newton was at so just road round for 6 minutes and then stopped at my start point, got off the bike, tilted it over and walked it in a tight circle to mimic the turn in an out and back, checked the screen said ‘go back’ and then rode round again for the same set time to finish at the start point and voila the unit had a good cal ride.

I then done a few rides round the track for the remainder of the session and when I checked back home the calibration was excellent using the check cal feature.

You've got to be careful riding round the apron that you don't go too fast but other than that it's an easy way to get a good calibration.

One thing you'll notice from the track is changes in apparent wind speed when drafting etc due the changes in dynamic pressure at the intake.

Cheers

Steve

Newton Track bike mount

Newton track mount.png (864.77 KiB) Viewed 7857 times

Mount with Newton in place

Newton track mount with Newton.png (837.88 KiB) Viewed 7857 times

[Velocomp]

I think the Cal Ride complexity here is that, when the Newton is mounted upside down, the accelerometer thinks that down is up and up is down. This would tend to confuse the Newton during cornering, but not while the slope is unchanged.

I'd love to see one of Steve's ride files.

[Steve_Davidson]

I think the Cal Ride complexity here is that, when the Newton is mounted upside down, the accelerometer thinks that down is up and up is down. This would tend to confuse the Newton during cornering, but not while the slope is unchanged.

I'd love to see one of Steve's ride files.

John,

Attached is the cal ride and following session.

iBike_12_12_2014_0841_3_Miles_CalRide.ibr

(55.29 KiB) Downloaded 233 times

iBike_12_12_2014_0855_19_Miles.ibr

(181.87 KiB) Downloaded 231 times

[Pete]

Thanks guys.
I had wondered about the viability of the upside-down option.
Or just right way up and duct tape the screen for races.
We're at the track again this weekend so will decide & action by then.

[Steve_Davidson]

I think the Cal Ride complexity here is that, when the Newton is mounted upside down, the accelerometer thinks that down is up and up is down. This would tend to confuse the Newton during cornering, but not while the slope is unchanged.

I'd love to see one of Steve's ride files.

John,

Attached is the cal ride and following session.

iBike_12_12_2014_0841_3_Miles_CalRide.ibr

iBike_12_12_2014_0855_19_Miles.ibr

John,

I thought the files look sensible (although I need better tubs and to tweak the position a bit but at the moment its just training ).

My thinking about the unit being inverted was that its a dual axis accelerometer therefore it shouldn't matter what orientation its in as long as it's calibrated for that position. I certainly noticed when I had the bike on the parking bar hanging from the saddle and therefore tilting down, it showed negative slope on the screen whilst I was doing some adjustments and checks and this can be seen in the ride file at 2 points.

cheers

Steve

[Steve_Davidson]

Thanks guys.
I had wondered about the viability of the upside-down option.
Or just right way up and duct tape the screen for races.
We're at the track again this weekend so will decide & action by then.

Pete,

Best to ask the commissaires if your allowed to have a computer with duct tape over the screen to save any protest or disqualifications later. We are not allowed them over here in the UK on the velodromes and a few people have been pulled from training sessions due to having Garmin units on the stems even with tape on the screen. All the folks I've seen with SRM's have the computer fixed under the saddle and some have been covered in tape as well to avoid others seeing the numbers.

cheers

Steve

[Russ]

zoom in on highest power lap

Davidson_ibike.jpg (233.19 KiB) Viewed 7720 times

I find this an interesting view. I don't know track details but is the up and down slope properly unequal for the track?
If not, then bike tilt correction may be off, of course dynamics of high and lower power may skew the tilt too.

Other wise It looks reasonable to me (maybe I should say, for you)

I assume that the sine wave cycle of slope matches on lap? I notice the range of times vary from this 11 second to about 14.
I guess you did some passing with this power burst??

Have you analyzed the distribution of power output vs tactics during the race and vs if a less variable power lap might allow a higher average power lap with greater energy reserve later in the race...? Just some thoughts, I don't really need answers as I am thinking rhetorically. I am not a racer, so if I am asking dumb questions, please excuse me!

Russ

[Russ]

Wow, I just went back and scrolled along through the ride, zoomed in.
It becomes apparent that your positive and negative slopes are power related in appearance!
Maybe you knew this already.

0-200 w Negative slope
200-400watts balances positive/negative
300-500 aprox 2/3 positive
300-up all positive.

Interesting, I did not expect that!

Oh, I only looked over this aspect, not your cal ride, etc.
I think Fernando and others at Velocomp may be better equiped to
fully evaluate...

Russ

[Steve_Davidson]

Davidson_ibike.jpg

I find this an interesting view. I don't know track details but is the up and down slope properly unequal for the track?
If not, then bike tilt correction may be off, of course dynamics of high and lower power may skew the tilt too.

Other wise It looks reasonable to me (maybe I should say, for you)

I assume that the sine wave cycle of slope matches on lap? I notice the range of times vary from this 11 second to about 14.
I guess you did some passing with this power burst??

Have you analyzed the distribution of power output vs tactics during the race and vs if a less variable power lap might allow a higher average power lap with greater energy reserve later in the race...? Just some thoughts, I don't really need answers as I am thinking rhetorically. I am not a racer, so if I am asking dumb questions, please excuse me!

Russ

Russ,

I wan't racing, it was a drop in practice session so groups of people were doing different things so I was solo riding and then joining and leaving groups at times.

The jump was me dropping from the blue line (halfway up the track) down to the black pursuit line and just riding quickly to avoid a group. The blue line or above is where your meant to ride for most riding so there is a upward and downward slope at each bend and is quite a change in effort to hold speed going round the bends.

For info it was the Sir Chris Hoy velodrome in Glasgow which is a 250m track and a world class venue.

Cheers

Steve