44 vs 40cm bars in the wind tunnel

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user83843
Posts: 56
Joined: Mon Mar 07, 2022 9:14 pm
Location: Idaho

by user83843

Thought I'd share an abbreviated summary from part of a recent test at local uni's wind tunnel

Same rider on two identical team bikes, save for varied handlebar / hood orientations
Many runs with the two bars linked below in the aero hoods (only) positions

bar 1: https://www.competitivecyclist.com/spec ... -handlebar
bar 2: https://www.competitivecyclist.com/east ... ar-eas0140

- 44cm s-works bars hoods straight .247 cda
- 44cm s-works bars hoods turned inwards (40 degrees ) .244
- 40cm easton aero bars hoods straight .243 (~2w improvement vs 44cm inward across runs at 40kph, attributed to flat top aero bar portion vs round)
- 40cm easton aero bars hoods inward (statistically insignificant vs 40cm straight)

with the hoods on the narrower easton bars turned inwards we would expect an additional ~2w savings vs straight, so this was somewhat of a surprise. however this setup was not ideal for our 182cm / 70kg rider's geo

test was part of a larger study on domestic elite racing aero trends and changing preferences that'll likely be published on researchgate next yr, but also helpful info for our team in prep for a stage race with bad roads / significant elevation - two factors that often impact bar choice

nothing new here, just confirmation of improved cda for inward hoods (regardless of bar profile) when in the aero hood position for riders selecting wider bars for climbing, sprinting, etc

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Ronin416
Posts: 398
Joined: Mon Aug 27, 2012 5:46 pm

by Ronin416

user83843 wrote:Thought I'd share an abbreviated summary from part of a recent test at local uni's wind tunnel

Same rider on two identical team bikes, save for varied handlebar / hood orientations
Many runs with the two bars linked below in the aero hoods (only) positions

bar 1: https://www.competitivecyclist.com/spec ... -handlebar
bar 2: https://www.competitivecyclist.com/east ... ar-eas0140

- 44cm s-works bars hoods straight .247 cda
- 44cm s-works bars hoods turned inwards (40 degrees ) .244
- 40cm easton aero bars hoods straight .243 (~2w improvement vs 44cm inward across runs at 40kph, attributed to flat top aero bar portion vs round)
- 40cm easton aero bars hoods inward (statistically insignificant vs 40cm straight)

with the hoods on the narrower easton bars turned inwards we would expect an additional ~2w savings vs straight, so this was somewhat of a surprise. however this setup was not ideal for our 182cm / 70kg rider's geo

test was part of a larger study on domestic elite racing aero trends and changing preferences that'll likely be published on researchgate next yr, but also helpful info for our team in prep for a stage race with bad roads / significant elevation - two factors that often impact bar choice

nothing new here, just confirmation of improved cda for inward hoods (regardless of bar profile) when in the aero hood position for riders selecting wider bars for climbing, sprinting, etc
Thanks for the confirmation.

Coupled with elbows bent at 90 degrees vs slight bend would be a substantial savings.


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Nereth
Posts: 250
Joined: Wed Jan 18, 2023 10:18 am

by Nereth

user83843 wrote:
Wed May 24, 2023 11:34 pm
Thought I'd share an abbreviated summary from part of a recent test at local uni's wind tunnel

Same rider on two identical team bikes, save for varied handlebar / hood orientations
Many runs with the two bars linked below in the aero hoods (only) positions

bar 1: https://www.competitivecyclist.com/spec ... -handlebar
bar 2: https://www.competitivecyclist.com/east ... ar-eas0140

- 44cm s-works bars hoods straight .247 cda
- 44cm s-works bars hoods turned inwards (40 degrees ) .244
- 40cm easton aero bars hoods straight .243 (~2w improvement vs 44cm inward across runs at 40kph, attributed to flat top aero bar portion vs round)
- 40cm easton aero bars hoods inward (statistically insignificant vs 40cm straight)

with the hoods on the narrower easton bars turned inwards we would expect an additional ~2w savings vs straight, so this was somewhat of a surprise. however this setup was not ideal for our 182cm / 70kg rider's geo

test was part of a larger study on domestic elite racing aero trends and changing preferences that'll likely be published on researchgate next yr, but also helpful info for our team in prep for a stage race with bad roads / significant elevation - two factors that often impact bar choice

nothing new here, just confirmation of improved cda for inward hoods (regardless of bar profile) when in the aero hood position for riders selecting wider bars for climbing, sprinting, etc
the 0.001 Cda change between 44cm inwards and 40cm straight, is less than a watt at 40kph, no?

The above is a slightly odd set of results to me. You got 0.003m^2 off Cda from turning the bars inwards, but only an additional 0.001 from being in presumably a similar position, but with now an aero profiled handlebar. Then moving in a further few cm did nothing. So the implication is that moving inwards from 44-40 or whatever the "44cm bar, hoods inward" position was, did a lot, moving from 40 -> 30-something did very little, and the aero handlebars did very little at all in the first place.

Could be a function of reaching a point of diminishing returns with narrowness (accompanied by a spike in effectivness as the arms get in front of hte body?). Could be measurement (read: rider position) error. Weird that the aero profile bars don't appear to do much.

I'm looking forward to hopefully reading the full paper.

maxim809
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by maxim809

I'm curious what happened to the rider's position for the 4 setups.

One philosophy is to control as much as possible for position, including head position, shoulder, grip, for all the bars. Even if it means the rider may not be riding in their preferred 'natural' position for the sake of controlling the experiment.

The other philosophy is to change the bars, but allow the rider to self-select whatever position they find most comfortable for each setup. This has the advantage of producing results that will better match real world riding.

Yaw data would also be helpful. I'm assuming those CdAs are averaging, or are these CdA at 0°?

Many more questions like how many runs per position. What positions were tested, (90°, sitting up naturally in the hoods, in the drops, etc), and if multiple positions, how did they each fare.

But yeah also looking forward to the full paper as well.

user83843
Posts: 56
Joined: Mon Mar 07, 2022 9:14 pm
Location: Idaho

by user83843

Rider was tested with the two bar configs in one position only - aero hoods with 90 degree arms / back horizontal, at 40kph on a non TT road setup. Avg cda values.

1x aero hoods straight 40cm aero bars
1x aero hoods inwards 40cm aero bars
1x aero hoods straight 44cm round bars
1x aero hoods inwards 44cm round bars

We were correct that 40cm aero bars (straight or inward hoods) would be faster than 44cm round bars with inward hoods, however the diff was less than anticipated (.0015 or ~2w)... due mostly to the rider's shoulder width and way that the hand/wrist/forearm interacted with air flow around the cockpit, minimizing the impact of flat aero bar tops.

Manuf most often test equip using mannequins (or just the bike / frame with cockpit). Different wind tunnel designs and protocols, many with conflicting results. Some are even using CFD programs. All problems that often lead to incorrect (unrealistic) cda expectations IRL. another part of the study will deal with the disparity between such results vs tests with conti level riders in motion. Perhaps this research will help pave the way to rigorous standardization for wind tunnel testing protocols and greater transparency.

usr
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Joined: Thu Mar 25, 2021 5:58 pm

by usr

Nereth wrote:
Thu May 25, 2023 2:55 am
Could be a function of reaching a point of diminishing returns with narrowness (accompanied by a spike in effectivness as the arms get in front of hte body?).
Sounds plausible to my ears. That threshold might get considerably less pronounced with a yaw sweep if they only tested frontal?

On the other hand the threshold might be more from posture than from flow direction: hand movement translating almost 1:1 into elbow movement at wide hand separation values (angle between forearms not changing much) and almost 1:0 into elbow movement at closer distance between hands (angle between upper arms not changing much)

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robbosmans
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by robbosmans

Surely you have some pictures or something documenting the different positions?

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JayDee81
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Location: Czech Republic

by JayDee81

Normally I would expect that with the wider bars the rider would be a little more leaned forward because of the additional reach. Was this controlled somehow?
Also the Easton one has 5 mm more reach and 4° flared drops.

usr
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by usr

Why would wider bars imply more lean? We are not talking about any "jesus bars" on MTB that are so much wider than a pair of shoulders that the lateral shift in hand position with cause a change in the horizontal arm angle that would fall anywhere close to the steep part of the cosine function (or of the sine, depending on what line you use as reference)

TobinHatesYou
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by TobinHatesYou

A narrower hand position causes the scapula to flare out a little bit and the shoulders to roll forward, increasing a rider’s reach requirements. Additionally, turned in shifters results significantly reduces the “grip reach” (BB-to-horns distance.) When I moved from 40cm bars with fairly straight levers to 38cm bars with severely turned in levers, I also had to switch from a 120mm stem to a 150mm.

I feel like the time needs to be taken to determine optimal fit for each setup.

pmprego
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by pmprego

TobinHatesYou wrote:
Thu May 25, 2023 11:29 am
A narrower hand position causes the scapula to flare out a little bit and the shoulders to roll forward, increasing a rider’s reach requirements. Additionally, turned in shifters results significantly reduces the “grip reach” (BB-to-horns distance.) When I moved from 40cm bars with fairly straight levers to 38cm bars with severely turned in levers, I also had to switch from a 120mm stem to a 150mm.

I feel like the time needs to be taken to determine optimal fit for each setup.
you kinda of moved from a 40cm bars to a tt-like position thus the huge increase in reach.

splzd
Posts: 140
Joined: Tue Jan 28, 2020 11:11 am

by splzd

user83843 wrote:
Thu May 25, 2023 7:19 am
1x aero hoods straight 40cm aero bars
1x aero hoods inwards 40cm aero bars
1x aero hoods straight 44cm round bars
1x aero hoods inwards 44cm round bars

How can you be sure which of the two changes (handlebar width and profile) the changes found are due to? Shouldn't you also test:
  • aero hoods straight 40cm round bars
    aero hoods inwards 40cm round bars
    aero hoods straight 44cm aero bars
    aero hoods inwards 44cm aero bars

TobinHatesYou
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by TobinHatesYou

pmprego wrote:
Thu May 25, 2023 1:52 pm

you kinda of moved from a 40cm bars to a tt-like position thus the huge increase in reach.

It was both an increase in my reach needs and a decrease in effective grip reach. Turning in the grips brought them closer to the tops/stem by about 2cm.

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maxim809
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by maxim809

user83843 wrote:
Thu May 25, 2023 7:19 am
Rider was tested with the two bar configs in one position only - aero hoods with 90 degree arms / back horizontal, at 40kph on a non TT road setup. Avg cda values.

-snip-

Perhaps this research will help pave the way to rigorous standardization for wind tunnel testing protocols and greater transparency.
Thanks for the clarification! Def agree on greater transparency.
JayDee81 wrote:
Thu May 25, 2023 9:00 am
...because of the additional reach. Was this controlled somehow?
TobinHatesYou wrote:
Thu May 25, 2023 11:29 am
A narrower hand position .... increasing a rider’s reach requirements.
-snip-
I feel like the time needs to be taken to determine optimal fit for each setup.
Yes, so what JD and THY bring up are getting at what I was subtly poking in my initial reply.

When you change the bar, it will absolutely have an impact on the rider's position. In an extreme case, this can negatively impact the rider's final head position as far as head position is concerned. Not only for the valid reason on scapula that THY brought up, but also because of what can happen around the shoulders, elbows, wrist, etc which are all complex systems without a formula.

So two ways to control:

1. Optimize for Rider Fit
2. Optimize for Bike Setup

Or something in-between. Which philosophy the protocol is designed for, can produce totally different results and takeaways. In the "Optimize for Rider" scenario (which I what I am actually more a fan of, because it represents real world riding) it may not be enough to simply swap out the bars. You may need to adjust Stack and Reach to do what is best for the rider, as a First Order.

Second order is to quantify Power to CdA in the new position, and the time to exhaustion in this position (basically, can the rider sustain it).

Third order is to consider Handling for this new position. Which steps into the hairy realm of Qualitative analysis.

Even before all that, it's necessary to have the Rider under Test perform calibration in the tunnel. Such that for each run, the position they hold is validated to be repeatable and consistent. Without this, the data has risk of being dominated by Rider induced noise. Example is if the head position is inconsistent, you will be measuring the deviations in head position rather than the bar you are trying to isolate. If the rider's head is introducing ±5w of noise (10w peak to peak), then it is not possible to distinguish 2w of improvement or regressions, because the 10w of noise will dominate.

But anyway.

Lastly, agreed -- mannequin sounds great on paper, but in practice has flaws.

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