Honestly curious how you were able to average 25mph on 232W. What kind of setup did you race with?? Impressive as hell.

I'm planning on riding at 265W (3.7 w/kg) for my 70.3 in June and BBS was saying I'd ride a 2:17 (1900ft elevation gain on rolling terrain).

Could be many things.

Your power could have been off.

Your inputs for other things (Crr) could have been off.

Or, the estimated wind conditions used by BBS could have been very different from the actual wind conditions.

That wind estimator is, in my opinion, the weak link in BBS for estimating actual time. It's still very useful for generating general power plans.

Prior to the race BBS had me at 25.7mph on 250w. Based on my training rides I thought that was a little high but doable with full race setup. With the actual weather from the day in there now it seems to have gone wonky.

I feel like I'm fairly slippery just from slowtwitch knowledge (and help from Dan on fit), but I haven't been to the tunnel or anything.

I don't have any real good side photos from the race unfortunately. I have one from the side from a previous race that's similar to a bigfoot photo. Here's that and a photo from the front. I've kept the bike extremely clean. No bento no nothing other than a bta bottle and bhs bottle.

First thing I thought was my powermeter was whacky, but after this thread looks like it's probably fine.

http://forum.slowtwitch.com/...n/accuracy_P6269776/

I don't think it's the Crr, I haven't messed with it and BBS seemed relatively accurate previously.

The wind conditions looks correct, just not sure why it computes my actual CdA for the ride at .3 when the bike is setup with CdA of .23.

It really looks like it's something wrong with BBS but maybe I'm missing something.

Yeah, their CdA estimation is still "Beta" too.

I think once we (hopefully) start integrating zero-yaw wind data from all these new wind sensors under development into .fit files then BBS will be able to do a lot. And of course other programs, but it'll help BBS "close the loop" between predicted and measured performance. Right now the CdA in BBS is a giant fudge factor unless you have a good estimate from another source, whether Aerolab or a real wind tunnel.

I had the same issue when trying to find the CDA of my athlete from Galveston.

his CDA is pretty much known to be a .225. So I thought I'd use the Beta from BBS. It spit out something like .18

When preparing for this ride, the wind condition gave us a drag of a .29 cda which I had to adjust back down.

Your speed to power looks pretty close to where he was and we are confident with his prior testing of .225 cda.


When consulting with someone else regarding this issue, they noted that their are things that BBS would have a hard time accounting for such as braking in a race or the slingshot effect you get from passing someone... but yes, I noted the same issue as you.

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COROS Sports Science

Great info! Thank you!

Hey Sean. That does seem really wacky. I'll take a look but something must have gone horribly wrong math wise!

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Founder: BestBikeSplit
Amazonian

For reference on the Beta Aero stuff we are not doing a great job isolating the outliers and clustering yet (have some new automated things in the work(. When you have a lot of data it tends to workout much better. In Sean's case it sounds like the Time Analysis tool is behaving funky so will dive into that as well. Ideally the data would look something like below.

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Founder: BestBikeSplit
Amazonian

Taking a quick gander It does seem like with extreme yaw angles (average yaw of 30 degrees....geez) we may need to adjust our TA tool. The CdA being used in the model was ~ .23 but the equation we are using the TA tool is a bit different (and seem at extreme yaw angles is not handling it correctly). Im curious if you use the new Aero Analyzer feature on your race file what number it comes up with.

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Founder: BestBikeSplit
Amazonian

Thanks for looking into it. I will try that tomorrow and let you know.

It came up with 0.1828

Well at least it's consistent... ha. So you would expect CdA to drop with yaw till there is a stall angle, so I'm now leaning towards our wind model being quite a bit off. I have some other data form the race so I'm digging into that now as well.

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Founder: BestBikeSplit
Amazonian