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Some random wind tunnel observations and datapoints
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Thanks to the folks at Faster, I got a few insights on positioning and gear. A few big lessons (which may or may not apply to anyone else):

1) My seat was too low. I guess I should have listened to Dan Empfield. Maybe some of you remember this thread:

Slowman says Jens' seat is too LOW...


In the intervening decade, I reverted to my old, bad ways and lowered it again. Aaron suggested raising it 2 cm. Hmm. Same as Dan.


2) More drop isn't always better. How your body achieves that drop matters. I went from ~14cm drop to ~10 and ended up with less drag. That's really big, because for me, 4cm less drop also means ~15 watts more power output.

3) Helmets really, really matter. In my case, the difference between two aero helmets was over 100 grams of drag.

4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.

5) Q-factor matters, though not as much as hoped. I switched from ~160 to ~130, which saved ~50 grams at 0 deg; 34 grams at 5 deg; but actually increased drag 19 grams at 10 deg. Maybe some smarter folks than myself can interpret that.
Last edited by: jens: Mar 15, 17 9:12
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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Jens, Thank you for posting this. I really enjoy your posts and have gotten a lot out of them. Much appreciated.
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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jens wrote:

Thanks to the folks at Faster, I got a few insights on positioning and gear. A few big lessons (which may or may not apply to anyone else):

1) My seat was too low. I guess I should have listened to Dan Empfield. Maybe some of you remember this thread:

Slowman says Jens' seat is too LOW...

In the intervening decade, I reverted to my old, bad ways and lowered it again. Aaron suggested raising it 2 cm. Hmm. Same as Dan.


2) More drop isn't always better. How your body achieves that drop matters. I went from ~14cm drop to ~10 and ended up with less drag. That's really big, because for me, 4cm less drop also means ~15 watts more power output.

3) Helmets really, really matter. In my case, the difference between two aero helmets was over 100 grams of drag.

4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.

5) Q-factor matters, though not as much as hoped. I switched from ~160 to ~130, which saved ~50 grams at 0 deg; 34 grams at 5 deg; but actually increased drag 19 grams at 10 deg. Maybe some smarter folks than myself can interpret that.

One thing I'm starting to appreciate is just how individual aerodynamics is. For me, the delta between my slowest helmet and my fastest helmet was 27 grams and the majority of my helmets were within 10 grams of each other. My Virklon sleeved tri suit was actually *slower* than my sleeveless Kiwami tri suit by 25 grams. Sorcery I tell you!

Just a random thought, the people at Faster, A2, etc. should consider tracking body morphology to see if there are any trends.

WTB: TriRig Omega SV (not x). PM me if you have one :)
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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Great post, thanks for sharing! Can you expand on the aero helmet testing? Did you test head down and head up positions? Did you only test two helmets, or was that the delta between best and worst?

Also, I'm curious how they determine increased power output from positional changes. Do you just do a max effort in each position?
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Re: Some random wind tunnel observations and datapoints [chrisgrigsby] [ In reply to ]
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chrisgrigsby wrote:
Great post, thanks for sharing! Can you expand on the aero helmet testing? Did you test head down and head up positions? Did you only test two helmets, or was that the delta between best and worst?

Also, I'm curious how they determine increased power output from positional changes. Do you just do a max effort in each position?

I only tested two helmets and just in the position I would actually ride in -- low, but eyes up the road. I suspect helmets are highly individual. I previously compared notes with an Olympian who had tested the same two helmets as me and had precisely the opposite results(!).

The drop/power differences are based on my own long-term experience. I'm probably an an extreme example in this regard. Even with the clown cranks, going from a road position to 14cm drop decreases power over 30 watts.
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Re: Some random wind tunnel observations and datapoints [GreenPlease] [ In reply to ]
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The problem with body morphology is that it's hard to categorize, because numbers alone wouldn't do; it'd be more about proportions and shape. I seem to recall Steve Hed (or maybe Cobb, crap I'm getting older) hypothesizing once that high hands worked better depending on the riders hips size.
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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jens wrote:

Thanks to the folks at Faster, I got a few insights on positioning and gear. A few big lessons (which may or may not apply to anyone else):

1) My seat was too low. I guess I should have listened to Dan Empfield. Maybe some of you remember this thread:

Slowman says Jens' seat is too LOW...


In the intervening decade, I reverted to my old, bad ways and lowered it again. Aaron suggested raising it 2 cm. Hmm. Same as Dan.


2) More drop isn't always better. How your body achieves that drop matters. I went from ~14cm drop to ~10 and ended up with less drag. That's really big, because for me, 4cm less drop also means ~15 watts more power output.

3) Helmets really, really matter. In my case, the difference between two aero helmets was over 100 grams of drag.

4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.

5) Q-factor matters, though not as much as hoped. I switched from ~160 to ~130, which saved ~50 grams at 0 deg; 34 grams at 5 deg; but actually increased drag 19 grams at 10 deg. Maybe some smarter folks than myself can interpret that.

Cool.
But you had something janky in the link to the old 2007 thread, so I took the liberty of posting it below. It's too good of a thread for folks to not be able to just click :-)
http://forum.slowtwitch.com/forum/?post=1324075



http://bikeblather.blogspot.com/
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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Thanks for sharing... nice insights.

"Too Low/High" is always possible... it all depends on what point you are referencing as the "start"

I found my saddle could be raised 1cm with no effect on aerodynamics, but some relief in the hip angle. Front end was the same... dropping 20mm of spacers was almost the same as higher, dropping 40mm of spacers was worse than higher. Like all things aerodynamics... it depends.

Helmets only mattered a bit (comparing only the ones I would have guessed were fast) but skinsuits mattered a lot, even among some of the faster (or so I thought) TT options.

My Blog - http://leegoocrap.blogspot.com
Podium Sports Racing - http://www.podiumsportsmed.com/team/
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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jens wrote:

Thanks to the folks at Faster, I got a few insights on positioning and gear. A few big lessons (which may or may not apply to anyone else):

1) My seat was too low. I guess I should have listened to Dan Empfield. Maybe some of you remember this thread:

Slowman says Jens' seat is too LOW...


In the intervening decade, I reverted to my old, bad ways and lowered it again. Aaron suggested raising it 2 cm. Hmm. Same as Dan.

Did you test different saddle heights in the wind tunnel?
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Re: Some random wind tunnel observations and datapoints [Andrew Coggan] [ In reply to ]
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that's what I want to know too +1

when I did, lower saddle was much faster
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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How many grams of drag did you have total? I'm curious what 100 grams of drag difference in helmets works out to be percentage-wise.

How many runs did you do total?

How much less drag did you have at 10cm of drop versus 14cm?

Regarding the increase in drag at 10 degrees of yaw on the Q-Factor change, did that increase occur at 10 degrees both left and right? Is it different drive-side versus non-drive-side?

Travis Rassat
Vector Cycle Works
Noblesville, IN
BikeFit Instructor | FMS | F.I.S.T. | IBFI
Toughman Triathlon Series Ambassador
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Re: Some random wind tunnel observations and datapoints [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
Did you test different saddle heights in the wind tunnel?


Not in isolation. We raised the saddle by 2cm and bars by ~6cm at the same time. We made the latter change by switching from FSA Vision bars to 3T Aura Pros and adding a bunch of risers. Average drag was slightly (30grams) lower.

So no apples to apples --or even fruit to fruit-- comparison. More like fruit to vegetable. ;-)
Last edited by: jens: Mar 15, 17 9:34
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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jens wrote:
Andrew Coggan wrote:
Did you test different saddle heights in the wind tunnel?


Not in isolation. We raised the saddle by 2cm and bars by ~6cm at the same time. We made the latter change by switching from FSA Vision bars to 3T Aura Pros and adding a bunch of risers. Average drag was slightly (30grams) lower.

So no apples to apples --or even fruit to fruit-- comparison. More like fruit to vegetable. ;-)

So you don't know if raising your saddle hurt your aerodynamics. Do you know if it increased your power?
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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did you test the aura at the baseline as well or just completely wholesale nothing to compare swap?
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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Interesting results. Thanks for sharing. I wanted to add a couple points from my two trips to Faster with Ventum over the past two years.


jens wrote:
2) More drop isn't always better. How your body achieves that drop matters. I went from ~14cm drop to ~10 and ended up with less drag. That's really big, because for me, 4cm less drop also means ~15 watts more power output.

This was my experience as well. Raising my pads 1 cm lowered drag. It also felt significantly more comfortable and powerful. This small change allowed me to shrug my shoulders and turtle my head more naturally.

jens wrote:
4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.

My most surprising result was that my Kiwami ITU suit tested about the same or significantly faster than two sleeved suits. Neither fit really well and both had wrinkles in the shoulder area, which may explain the poor results. I'll be sticking with ITU suits until I can show that the benefits of sleeves outweigh the disadvantages for me (heat, effect on swim, slower T1...).

CodyBeals.com | Facebook | Twitter | Instagram | Strava
Ventum | Skechers | Martin's | EAS | STAC | Alto | Pioneer | Bliiq | Keystone Communications
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Re: Some random wind tunnel observations and datapoints [Cody Beals] [ In reply to ]
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Cody Beals wrote:
Interesting results. Thanks for sharing. I wanted to add a couple points from my two trips to Faster with Ventum over the past two years.

jens wrote:
4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.

My most surprising result was that my Kiwami ITU suit tested about the same or significantly faster than two sleeved suits. Neither fit really well and both had wrinkles in the shoulder area, which may explain the poor results. I'll be sticking with ITU suits until I can show that the benefits of sleeves outweigh the disadvantages for me (heat, effect on swim, slower T1...).

I had the same thing happen with my Kiwami ITU suit except my sleeved kits actually fit really well with practically no wrinkles.

WTB: TriRig Omega SV (not x). PM me if you have one :)
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Re: Some random wind tunnel observations and datapoints [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
So you don't know if raising your saddle hurt your aerodynamics. Do you know if it increased your power?

Since we tested "the whole system" rather than that specific measure, there's no way to say what raising the saddle by itself did. Power is definitely higher. But even that is reflective of a whole system change (i.e. less drop). Maybe in a week, I'll try dropping both the bars and the saddle back down 2cm and do a few power tests.
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Re: Some random wind tunnel observations and datapoints [Cody Beals] [ In reply to ]
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If you haven't read Cody's wind tunnel article it's a great read. I frequently find myself going back to it for reference.



Cody Beals wrote:
Interesting results. Thanks for sharing. I wanted to add a couple points from my two trips to Faster with Ventum over the past two years.


jens wrote:
2) More drop isn't always better. How your body achieves that drop matters. I went from ~14cm drop to ~10 and ended up with less drag. That's really big, because for me, 4cm less drop also means ~15 watts more power output.

This was my experience as well. Raising my pads 1 cm lowered drag. It also felt significantly more comfortable and powerful. This small change allowed me to shrug my shoulders and turtle my head more naturally.

jens wrote:
4) Skinsuit matters. A slightly baggy one vs. better fitting swiftspin was worth around 70 grams.

My most surprising result was that my Kiwami ITU suit tested about the same or significantly faster than two sleeved suits. Neither fit really well and both had wrinkles in the shoulder area, which may explain the poor results. I'll be sticking with ITU suits until I can show that the benefits of sleeves outweigh the disadvantages for me (heat, effect on swim, slower T1...).
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Re: Some random wind tunnel observations and datapoints [Cody Beals] [ In reply to ]
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regarding aero suits, how far and what would your limit on budget be to get two suits made custom to you, measured to your body in your chosen position on the bike?

Anne Barnes
FIST/SICI/FIST DOWN DEEP
Live Grit
anne@livegrit.com
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Re: Some random wind tunnel observations and datapoints [ABarnes] [ In reply to ]
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ABarnes wrote:
regarding aero suits, how far and what would your limit on budget be to get two suits made custom to you, measured to your body in your chosen position on the bike?

It depends
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Re: Some random wind tunnel observations and datapoints [James Haycraft] [ In reply to ]
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haha, excellent response.
ok, more exact question: if I was a BioRacer Speedsuit provider, would you come to chicago to get it fitted? two suits, with or without longsleeves, plus a little bit of time with me for about $2k.

Chicago is really nice this time of year. :)

Anne Barnes
FIST/SICI/FIST DOWN DEEP
Live Grit
anne@livegrit.com
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Re: Some random wind tunnel observations and datapoints [ABarnes] [ In reply to ]
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It's more a $/watt question. If this custom designed GUARANTEED watt savings at the rate of say...$100/3-5w then I might consider it.
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Re: Some random wind tunnel observations and datapoints [jens] [ In reply to ]
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Thanks for sharing.

I wonder if people ever measured the drag of a racenumber with a belt which you have to wear at nearly every triathlon. Whether that deletes the advantage of a suit over two-part wear for example.
Related to that: I watched the WC Kona carefully again on youtube, but I didn't see any belts with numbers, also not with the AG, am I blind or do you not have to wear a number on the bike in Kona?
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Re: Some random wind tunnel observations and datapoints [longtrousers] [ In reply to ]
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You don't have to wear it in most IM races in North America.
Other parts of the world I am not sure. For example I think France requires it
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Re: Some random wind tunnel observations and datapoints [longtrousers] [ In reply to ]
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longtrousers wrote:
Thanks for sharing.

I wonder if people ever measured the drag of a racenumber with a belt which you have to wear at nearly every triathlon. Whether that deletes the advantage of a suit over two-part wear for example.
Related to that: I watched the WC Kona carefully again on youtube, but I didn't see any belts with numbers, also not with the AG, am I blind or do you not have to wear a number on the bike in Kona?

Many years ago I tested race number position (belt) on my tri bike at a2, there was a 5 watts difference between low on my back and high (like a hr strap high) on my bike) and about 8w difference wearing it on my front (low back was best)

Wearing on a 2pc tri kit was worse than on a one piece (an old LG two piece and a 1 pc Desoto, both 2010'ish neither with any kind of sleeves)

Draw from that whatever (if anything) you would.

My Blog - http://leegoocrap.blogspot.com
Podium Sports Racing - http://www.podiumsportsmed.com/team/
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