Aero shoes? Up to 12 watts saved in shoe choice...

Ian Kurth

Admittedly, I have paid NO attention to drag forces related to my cycling shoes. However, this post got my attention... Up to 12 watts in shoes choice (and probably more compared with other shoes)? Very interesting.

http://www.thomasgerlach.com/2016/05/fastest-ironman-bike-shoes-aerodynamics.html

Dave Tallo

Huh. Got my attention as well. Thanks for sharing this.

Al Truscott

Two comments:

• The potential savings from your feet is compounded by the facts that they are (a) moving (not static like arms), (b) out in the wind, not protected by anything in front of them and (c) facing at least twice as much air as the rest of you d/t (a)
• BUT, not this comment in the Gerlach notes: " It tested 4 watts faster at 0 degrees of yaw, and 12 watts faster at 10 degrees of yaw!!! This is at wind tunnel standard testing of 30mph with two data points at each wind angle." (his bold, my italics) With the geometric, not arithmetic increase in resistance with speed increase, the real-world (i.e., what I might experience @ 18 mph, or Dave T @ 22 mph in an IM) will be significantly less than 12 watts gained.

thekidduxc

Posted By Al Truscott on 10 May 2016 10:21 PM

Two comments:

• The potential savings from your feet is compounded by the facts that they are (a) moving (not static like arms), (b) out in the wind, not protected by anything in front of them and (c) facing at least twice as much air as the rest of you d/t (a)
• BUT, not this comment in the Gerlach notes: " It tested 4 watts faster at 0 degrees of yaw, and 12 watts faster at 10 degrees of yaw!!! This is at wind tunnel standard testing of 30mph with two data points at each wind angle." (his bold, my italics) With the geometric, not arithmetic increase in resistance with speed increase, the real-world (i.e., what I might experience @ 18 mph, or Dave T @ 22 mph in an IM) will be significantly less than 12 watts gained.

Interesting post, but I agree with Al there seems to be some practical real world application missing from this study.

Chris Ciannella

All the pro cyclists wear shoe covers during their time trials......

Ian Kurth

I pinged Heath Dotson, and Brian Stover - the guys who run aerocamp and who did the actual testing in this case. I asked if they have enough data points to make a recommendation. At this point, they still have a small sample size, but in each case where the participant tested shoes similar in design they have seen an aero benefit. Not one has tested worse. The opinion from boys running aerocamp at this point is that these type of shoes at worst will be aero neutral, and likely will provide a benefit.

I appreciate Al's comments regarding the practical applications and practical significance regarding speed etc. I guess my main suggestion is that attention to shoe "areoness" is prudent. If one is in the market for new shoes - pay attention. Similar to using latex over butyl as tubes are necessary equipment and it makes sense to choose a faster tube - shoes are a required equipment. All other things being equal (and obviously they currently aren't as the profiled post requires a Hobby Lobby visit and glue gun etc to unleash one's inner craftiness) attention to shoes choice with respect to drag is important.

Gabe Peterson

Interesting that the Giro Empire with shoe laces is the fastest shoe. I have the MTB version of the shoe. It takes a good minute to lace them up properly. Not sure how that would work for transition.

I remember hearing in a podcast somewhere that shoes are the next frontier for aero products because they churn through the air, similar to how shaving your legs can save watts.

Rich Stanbaugh

I find that it helps me to think of "'time savings" rather than "power savings" when evaluating wind tunnel results. It is an interesting fact that some aero improvements actually have a larger "time reduction" at lower speeds than they do at higher speeds. The reason is that the course is always 112 miles regardless of speed. So, by virtue of the fact that slower riders are on the course longer than faster riders, the net time savings will be bigger for the slower rider.

Coggin has a rule of thumb that:  0.1 lbs (50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr - I have modeled this online and come up with numbers that are essentially the same, within rounding error)

I used an online modeling tool with actual numbers for me riding my Shiv, and assuming that a 5w drag reduction at 30mph is ≈ reducing CdA by 0.005m^2. Here is roughly how it translates:

Nominal Speed		w/ 5w Drag Reduction		Savings over 112 miles
30.00 mph		30.06 mph		27 sec
25.00 mph		25.05 mph		32 sec
20.00 mph		20.04 mph		40 sec

 

Ian Kurth

Gabe-
The shoes were modified to address the lace up issue. The tongue was removed, and elastic speed laces were installed. In addition, Thomas Gerlach mentioned he "drilled" into the heal to be able to place rubber bands. He claims he can get in and out as quick as his tri specific shoes. I don't recall drain holes in the soles being addressed...

Ian Kurth

Rich -

Superstar mathlete! I am subcontracting all real world math problems and their practical applicability to YOU! Good stuff!

Thanks!

Rich Stanbaugh

Thanks Ian - another interesting thought - a reduction in CdA of 0.005 (5w drag reduction) is about the same of reducing your area that impacts the wind by 7.7in^2.

Think of that as a square ˜ 2.5" per side. Most of us have a lot of free time by really focusing on cleaning up our bikes, no gels taped to the cross bar, etc.

Dave Tallo

Posted By Rich Stanbaugh on 11 May 2016 11:03 AM



Thanks Ian - another interesting thought - a reduction in CdA of 0.005 (5w drag reduction) is about the same of reducing your area that impacts the wind by 7.7in^2.



Think of that as a square ≈ 2.5" per side. Most of us have a lot of free time by really focusing on cleaning up our bikes, no gels taped to the cross bar, etc.

Amen.  Or, rolling our shoulders and tucking our heads. 

Todd Glass

Funny, I have been wondering about the possibilty of adding aero boot covers.  For example, could they be worn over the top of the shoe up to the staps and under the shoe past the cleat.  Then once foot in and on bike could you roll them up.   I have not had time to see what the impact of weraing them over 112 versus the time it would take to get them on.   If you add up enough Watts you will certainly see some difference.  How much,  i don't know. 

Dave Tallo

Posted By Todd Glass on 11 May 2016 02:39 PM
Funny, I have been wondering about the possibilty of adding aero boot covers.  For example, could they be worn over the top of the shoe up to the staps and under the shoe past the cleat.  Then once foot in and on bike could you roll them up.   I have not had time to see what the impact of weraing them over 112 versus the time it would take to get them on.   If you add up enough Watts you will certainly see some difference.  How much,  i don't know. 

Todd- a few things to look at:

1. Orca RS1 covers. They look easy (ish) to get on and off.
2. Velotoze. See http://bikeboard.at/show_bericht.php?ber_id=6197&dsw=1. It's in German, but the numbers are clear enough.

JeremyBehler

I'd seen similar data in the past, and actually used shoe covers at IMWI this year. It's impossible to say how much it helped, but I can tell you it certainly didn't hurt as they were very easy to peel down and get in /out of. Maybe 1-2 seconds cumulative. This may be different if it's a race where they don't allow you to have shoes pre-mounted in the pedals.  Attached is the fuzzy screenshot from Finisherpix

There was a similar thread going around regarding the aero benefit of calf sleeves so to my non-scientific mind the logic should carry over.

William Jenks

I agree that this is something that can't possibly be wrong in theory, but that the magnitude needs careful examination.

moetai@gmail.com

Isn't the 30mph a "relative speed"? thus kinda more achievable: you ride @18mph in a 12mph headwind=30mph of relative speed...

Brent Bills

David, yes the wind speed is relative. The wind doesn't care if you are stationary with it blowing 30 mph or if the air is still and you are biking 30 mph. In a wind tunnel you are stationary. Therefore on a windy course you would see far greater advantages to being aero.

Brian Quarton [OLD]

Another lace option is to take the shoes by the Boa guys at the expo in Kona and get a free upgrade? You may lose a bit in aerodynamics, but gain in convenience and efficiency? Then you don't have to bother with the covers. Not sure I would cut the tongue out until I saw how they felt. The wires are not forgiving.