Humour me for a sec -- can you please double-check that when you hover over the Altitude column in the Edit tab... that when you right-click it gives you "Remove column" option? Right-click is also CTRL-click (not flower-click) on a Mac.

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AndyF
bike geek

You mean, the little spike in the blue line about 500m into the test? That's due either to a momentary blip in either speed or power.

Where are you getting speed from? Which power meter do you have?

Hi Andy,
In the edit tab, it has options to fix elevations errors and fix gps, but I don't see anything about turning off altitude.
Under the Eoffset, I can check the "constant" altitude / velodrome box.

Hi RChung,
I see the little blue spike too, I was curious about the spikes that look like vampire fangs in the green elevation bar, and was wondering if that would throw off my data.

Also, what is the Eoffset do, and should I leave the eoffset auto box checked?

I really appreciate you guys helping me go through this.

I have been racing on a 2013 CBoardman TT Bike and recently got a SWorks Shiv through my team shop. I am trying to figure out which bike is faster through the Aerolab Chung Analysis heading into our State Championships. Once I get that resolved, I plan on testing my wheels, suits and helmets to find the fastest combo.

Why don't you post the file link here? And don't forget to tell us all the external parameters: total mass rider + bike, air density, Crr, and what kind of power meter.

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AndyF
bike geek

I am going to try to upload the file.
The above picture is a run on my new Shiv.
Garmin 500 with GPS Turned off, all smart recording turned off and have a garmin speed sensor on my wheel
Shiv has a Elsa Powermeter (spider)
Total mass bike plus rider is 90 kg
Crrr set at .005
Eoffset Auto is checked on
Air Density Rho:1.2268 ( Temp 58 F, Pressure 30.03, Dew Point 47 degrees)

even with GPS turned off, I am getting the blips on the Elevation

Here is the file from the above run on the Shiv

Ah, I understand now. The green line just shows what your device reports as the elevation, and it seems your device jumps around a bit. However, the green line is just used as a reference and comparison -- the blue line is calculated independently so an error in the green line doesn't affect the blue line.

Awesome, that makes me feel better about my tests.

What is the Eoffset, and should I leave the auto checked?

I sincerely appreciate your willingness to help.

Eoffset is the elevation offset. If you don't check it, at the start of your ride the blue line will begin at zero and it will show the elevation profile relative to your start point (for me, my house). I live near sea level so for me it hardly ever matters. If you have an altimeter and you live in Denver at 1600m elevation that's a big difference -- so eoffset moves the start point of the blue line up to 1600m.

[Edited to add] BTW, speaking of sea level, the air density calculator in Golden Cheetah is based on the barometric pressure at your location (aka "station pressure") not the official barometric pressure you get from the national weather service or official weather stations. The difference is that "official" barometric pressure is always standardized to sea level. So if you really live at an altitude like Denver, you have to make an adjustment for being a mile high (or 1600 meters). Since I live near sea level, station baro pressure and official baro pressure are essentially the same. This is only something to worry about if you're at altitude and you care about the exact CdA that Golden Cheetah gives you. If you're comparing two bikes, it won't matter since (presumably) you'll be using the same source for your baro pressure. The one time it might matter is if you test one bike at sea level and the other in Denver.

Thank you very much for the information.

Yesterday I had perfect conditions for testing. I have a local business park that was completely deserted and there was zero wind. I was testing my two TT bikes, trying to determine which one I am going to race for my upcoming District TT (40K race). I have been racing on a 2013 Chris Boardman 9.8, and this year due to team sponsorship, I was able to get a 2016 Specialized Shiv for a great deal. Over two separate days of testing, I have found the Shiv CdA ranges from .226 to .236 CdA for an average of .230 (7 runs). The Boardman from .246 to .256 with an average of .252 CdA (5 runs). I am pretty confident now the Shiv is faster by avg of .022 CdA. From looking at if .003 saves 3 watts or .13 mph, I would think I am gaining approx .9 mph in speed?

I am now planning on testing skin suits, helmets, wheels and shoe covers. I really appreciate the info you share and willingness to answer questions.

Thank you,
Robb

Always nice when you get the right conditions. Did you test both bikes on both days? Did you have the same wheels, or tyres, or at least tyre pressures?

Also those numbers are a little high perhaps. What value were you using for Crr?

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Developing aero, fit and other fun stuff at Red is Faster

Hi Skippy,

I was using .005 for Crr for all tests and keeping it constant for both days, I wore the same skin suit, helmet and shoes.
I used the same front and rear wheel with 100 psi in both.
So the only thing I was really looking at was the two frames and my position on each, to see which would be the fastest.

My next step now, will be determine which skin suit, helmet and wheel set is the fastest combo. Once I have those, I plan to make some final runs with lower tire pressure, shaved legs and shoe covers to see what my final CdA will be.

*** I did test both bikes on both days. I also switched the order of bikes, on the first day, I tested the boardman first, shiv second. On the second day (one with perfect conditions) I did the Shiv first, boardman second and then made a few more runs on the shiv.

Was your position the same on each (i.e. pad x/pad y/saddle height and setback/crank length)?

Good stuff here all around. Multiple runs of each bike, tight distribution of estimates within each bike, and the distribution of CdA estimates between either bikes don't overlap at all.

While it's clear that you have a lower CdA on the Shiv, can you say with confidence that the difference is due to the bike? ...that is, do you have the same coordinates ('fit') on both bikes? (Genuine question...)

I've been keen on doing this and have found my 'half-pipe' to do my testing on. I think your post has just given me the final push that I need to get out there and do (...I was also waiting on the weather, which is here!).

We did our best to "mirror" the two bikes, i.e. saddle fore and aft, saddle height, drop from saddle to pads, crank length are the same. The only differences are the pads on the Shiv are a little closer together and the front end on the shiv is way cleaner (less cables) as we were able to do more internal routing.

Lots of goodness in what you're doing.

In the UK, Crr of 0.005 on the road is optimistic.

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Developing aero, fit and other fun stuff at Red is Faster

What is the crr that you usually use?

On a typical UK road with good tyres: .006 upwards.

Lately I've been able to solve for CdA and Crr in most cases, but that's another story. :)

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Developing aero, fit and other fun stuff at Red is Faster

With everyone's help and guidance, I am excited about my upcoming District Championships 40 K TT.
I feeling very confident that I will be using my fastest combo set up. Now it just comes down to power.

A couple of questions about testing...

1) I thought i read somewhere that a savings of .003 CdA is equal to about .10 mph and or 13 watts saved?
Can anyone confirm that?

2) With running laps for testing, yesterday I scrubbed several runs due to cars. The cars were coming in the opposite direction, but due to the location, they were usually traveling less than 15 mph. Did I need to stop those runs, or would even a slow moving car displace enough air to corrupt my data?

Robb

Hypothetical: my rollout for my 23mm GP4000S IIs on my Zipps is 2136mm. If I were to adjust that to 1068mm and put a magnet opposite my existing magnet, could I get higher resolution speed data? At the top of my new "half-pipe" I'm usually only doing about 5mph. This lets me turn around without using the brakes.

While I've got you here:
-is there anything out there I could use to automatically start/stop my Garmin? Like some sort of a wire I could ride over that would send a start/stop signal?
-any tips for surveying a course?

2 magnets does work. Not tried it with Garmin myself. There could be a small problem if they're not exactly a half turn apart (for speed in particular).

I can't think of anything that'll auto start stop a Garmin apart from the autolap marker. That's a geofence type thing and may not be too great for this. If you've got a GLONASS/GPS unit (510 onwards) give it a try maybe.

As for course surveying, I'm not sure what you mean. If you mean to generate a topographical map, I can get pretty good elevation plots these days. I'd love to say buy my system, but they're not for sale I'm afraid.

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Developing aero, fit and other fun stuff at Red is Faster

I'm having a problem with my data in that the starting and ending elevations don't match and it's very annoying. I've never had this happen before. The ending elevation is consistently lower than the start elevation by about 5' and that's on a course that's barely half a mile one way. Using a Garmin Edge 1000.

If this has just started, have you moved your Garmin? You may be getting a pressure difference with a stagnation component now.

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Developing aero, fit and other fun stuff at Red is Faster

Depends on the speed sensor and head unit you're using but, yes, it's possible to do this. First, flip from mph to km/h. For some head units this will get you a bit more resolution. Second, two magnets may limit your top end speed accuracy. Reed switches do take a little bit of time to re-open, and the original PT hub started to get wonky speed readings up above 60 mph (that's about 14 wheel revolutions per second), so if you put two magnets on one of them you might get wonky readings above 30 mph (~50 km/h). I haven't gotten above 80 km/h on my current generation of PT so I don't know if this is still the case.

Topcon GPT-3000.