The Win Tunnel - Explaining Time Saved Over 40km

In this episode, Mark and Chris explain the logic behind our metric of time saved over 40km.

[@adiorthotos]

Hey hey hey, math DOESN'T suck! And I'm sure you love it to, you wouldn't be doing this if not. So don't just try to be cool and bash the things you love.

[@MITaerobike]

We were just kidding. We love math. I was a mathlete and will always be!

[@finh94]

Please do the maths video

[@Matt-uf2nc]

make video with the numbers!

[@TeslaOsiris]

I would like to hear about how stem stack height impacts efficiency.

[@bigbetter769]

This video is great! Thanks for taking the time gents!

[@ryanrearick5843]

Thanks guys! These videos are awesome!

[@AdamWarrix]

How much aero drag do gloves make? I heard a rumor that gloves can cause as much drag as a non - aero front wheel. Of course, there is a wide range of gloves from aero lycra gloves to touring gloves. Do you think you could test this?

[@MITaerobike]

on the list!

[@nikiforosparaskevopoulos1699]

nice videos you guys.i watch the win tunnel videos since they came out and you have an excellent interaction with the people about new requests/ideas they have.nice work , you really love what you are doing and this is to be mentioned ! ''Thumbs up for fluid mechanics

[@lindqvistelias]

Love your videos, keep it up!

[@richtinsley6262]

Very informative, as usual! My question would be... Riding with a tail wind, at what point would it be better to get into a more aero position? If a more upright postion catched more of the tailwind? I would assume that when you're speed matched the tailwind an aero postition would be better

[@MrChangCJ]

wait i thought it meant that if a person puts out a constant wattage to complete a 40km TT on both trials, the difference it time taken before and after shaving would be that "time saved over 40km"

[@psychosis7au]

You do really good videos, keep it up.

[@chewingthehandlebars]

I don't necessarily want a video, but would love a white paper or similar explaining the testing protocol please.

[@MITaerobike]

we were going to do that for this one but it was just too much for one video. We'll do a separate video on this, what we're measuring in the tunnel, etc.

[@LAShooters1]

Thanks for the explanation.

[@EK1H]

Descending is it faster to have feet level and both knees tucked inwards or one leg extended and the other bent with one knee tucked in. Also, if you can feel drag pulling on your shoulders/jersey and adjust posture of your back/shoulders to stop that feeling, is it actually faster.

[@mariozavala93]

These videos are awesome! I actually want to be in your position work wise, what major should I follow ? Currently going for aerospace engineering.

[@MITaerobike]

Chris Yu majored in Aerospace - BS, MS, and just got his PhD this week! Congrats, Chris! I majored in mechanical engineering but worked at a wind tunnel as an undergrad.

[@joshajohnson]

Great video Guys, explained it very well. Any chance for the video with the maths?

[@climbrnoob]

what is the difference between wearing sunglasses and without and a visor on an aero helmet TT helmet and without?

[@stevo8266]

How about testing the aero impact of different head positions when on the Shiv? I've wondered what the impact is (if any) when I tilt my head down to give my neck a break compared with the normal position (with an Evade helmet of course!)

[@pranksterdk4574]

Can you guys make a video about how aero the venge is in a cross wind??

[@SCOOPSLEGEND]

I want to know what positions are faster for crits like when I go in a break, should I just stay on the drops or should I go simulated aerobar position with my hands more central above the bar and my elbows resting on the bar. #aeroiseverything

[@FrekeOne]

brilliant! Congrats on the ph.D.!

[@Byron-Munton]

please can you test the pros and cons of different depth road wheels.

[@andrewschlicht1787]

Could you do a test of oval chain rings vs circular chain rings?

[@effehz]

I don't think I've ever seen a discussion about how different pedaling cadences can save time? Would a lower cadence be faster because you don't disturb the airflow as much as if the legs are moving fast?

[@cathyy5125]

Math does NOT suck!

[@tonyohalloranOfficial]

Could you do a test into aero overshoes please.

[@MIT2004]

Where can I buy that cool black Specialized polo shirt?

[@tk38]

Can you do the numbers version.

[@Catcrumbs]

The SI requires a space between the number and the unit and further specifies either a solidus, horizontal line or negative exponent to be used to indicate the division of unit symbols. Please re-read the SI Brochure to avoid such mistakes in future.

[@ThemCubes]

Can you actually show us the math for calculating how specific things like shaving legs/race wheels/aero helmet save specific amounts and save certain numbers of watts?

[@jcleary2001]

How much more aero is a tt skin suit compared to road apparel? Thanks

[@sambroomhead6506]

Is it true that an aero seat post makes as much difference aerodynamically as the position of your little finger?

[@zacharymoon4008]

shaving legs had a huge impact on aerodynamics, and as a triathlete i used to shave my arms for the swim, so would it make any impact on the bike?

[@jyflyn]

Could you test a beginners road bike maybe the specialized sectuer or the allez with all the spacers, so that it is setup like a real beginner road bike, and than test it against an really aggressive postition without spacers and than this bike against a venge. that would be really interesting because i ve got an beginner road bike with spacers and it would be nice to see how much faster i would go with an agressive position on a venge! #aeroiseverything

[@alongeller2102]

What do times equate to in CdA?

[@hedleykerr3564]

Chris and Mark great job on all the video's I really enjoy all the data and myths that have been put to rest on certain things! I didn't really see a cat. that this would fall under but I would like to see some figures using different crank lengths! M y guess would be there some benefits to riding with shorter cranks say 167.5 to 175mm? I know there a lot of variables in there dealing with physiology of the cyclist but it would be still interesting! Thanks Hedley

[@Christri]

Pedals. Now that Speedplay is coming out with an aero pedal, and have claimed aero benefits on their other pedals, can you test the difference in the major players?

[@107443838]

How about a video in attachments to a road bike like bottle cages, bottles, saddle bags, frame mounted air pumps etc

[@jtmuso]

But the aero saving in watts against speed is not linear and therefore the savings of the slower rider will not ever ‘catch-up’ with the faster rider because the efficiency savings are too small. You said the saving was 1w at 25kph vs 20w at 50kph and therefore the 25kph rider will have to ride for days to make up the gains. Correct me if I’m wrong

[@biranfalk-dotan2448]

Please do produce another video explaining the math. I (and others) don't actually believe that math sucks, and it is certainly necessary to justify your claim. Betz's law describes the power applied by wind to a stationary object (which is equal to the power a moving object applies to stationary air), and power is proportional to the cube of speed (v^3). Using time saved over 40 km rather than a time/time measure only introduces a factor of 1/v, which certainly does not cancel v^3. So, power saved over distance is proportional to v^2. I don't know what function relates power and time over 40km, but time saved must approach zero at very low speed because rolling resistance plays a proportionally larger effect (frictional resistance is normally assumed to be constant, i.e. nonvariable with time). Time saved must also approach zero at extremely high speeds, because at "P=infinity" there is no time left to save. Therefore, this function must have at least one peak in the middle. Your claim amounts to this: the range of speeds in which aerodynamic considerations are significant is on the downward (higher power, speed) side of such a peak. I don't know, but I intuit that this is false because otherwise aerodynamics would be of similar importance when climbing, which they are not.

[@gappahuchon6251]

Shoe covers please !

[@TheTonicro]

cool stuff

[@ChrisSchroedercyclist]

can we get a video with all the math it will make it a lot easier to understand

[@jinnshi240]

Aero is everyone's!

[@corentinoger]

This is a clever way to cancel out the "square law" nature of aerodynamic drag. Too bad it doesn't work with weight gains.

[@BenBlizard]

Do the math video.

[@RodrigoDeJaneiro]

Please do share the numbers... Even on your video you say that the rider doing 25kph will save more time than the rider doing 50kph, so.... how can you say that the metric 'time saved over 40k' is an absolute metric for all the riders?? You just showed that the total savings over 40k IS dependent on the speed. Would a better metric be time savings over 40k @ 40kph, then you can extrapolate, if I go at 25kph, then I know i'll save a bit more or if I go at 50kph, my total savings will be a bit less?

[@searay3340]

Sorry, this calculation is totally incorrect. In your example 10 times 1 watt is more than 5 times 20 watts ?! You are making a linear calculation on ( parabolic ? ) progressive data. For example, a car that is driving at 120 km per hour uses more fuel than the same car that is driving 60 km per hour over the same distance !

[@tuffhawk13]

That's why the metric is time saved rather than watts saved. Assuming all variables are the same--wattage, rider weight, gradient, distance, etc--except for aerodynamic drag, you are able to quantify time savings. Since 40k is long enough to be meaningful to most riders, but short enough that the variability of outcomes is fairly limited regardless of rider speed, the metric "time saved over 40k" is a useful metric. For example, if you were to set your wattage cruise control at 180w for 40k with hairy legs, then recover, shave your legs, and do the exact same course at the same wattage, you'd finish the course 70 seconds faster. If Bradley Wiggins were to let himself go for a few months, ride the same course at 360w, recover, shave his legs, and redo the course at 400w he'd finish 70 seconds faster than his previous effort as well. Because looking at savings this way is linear, it means the same thing for you as it does for Sir Wiggo, even though he's still finishing 12 minutes ahead of you on both rides.

[@searay3340]

Greg Thompson Wrong, because the effect of air resistance at 40k/hour is at least 3 times higher than the resistance effect at 25k/hour. The saving for Wiggo would therefor be much higher, but he benefits during a shorter period of time from it. The speedfactor is only 1,6 ( 40 didvided by 25 ) but the resistance fcator is ~ 3,4. A person of about 75kg needs about 90 watts to ride 25k/hour and needs about 305 watts to ride 40k/hour. The air resistance increases exponentially, therefor you cannot use a linear comparison.

[@djconnel]

The standard model is wind power, and wind power savings, are proportional to the third power of speed, which implies doubling speed (25 to 50 kph) increased by a factor of 8 (for example, 1 watt to 8 watts) the power savings from a given aerodynamic aid. This is just an approximation but generally appears to work fairly well in data I've seen for cycling. So 1 to 20 W seems unrealistic: I'd like to know where Specialized got that number.

[@searay3340]

Well one thing I know, if you do like 25 km an hour, there is no point in shaving ur legs for sure.

[@nickluhr381]

Searay The reason the faster rider has a bigger wattage savings is the same reason that rider DOESN'T get a bigger time savings for a given ride distance. Watts saved at higher speed allow an exponentially smaller increase to speed (and time savings) when compared to watt savings at lower speed.

[@klawrence029]

thumbs down for saying math sucks. I thought you were engineers? btw - more than half the cyclists I know are engineers

[@flocci22n]

Math sucks, then immediately shows graph.

[@okram69]

"... and oddly enough the slower the speed the greater the time saved over that distance." really meaningless lol at 25kmh 5min saved in 100min = 5/100= 5% time saved. at 50kmh 4min saved in 50min = 4/50= 8% time saved. better: "... and not surprisingly the slower the speed the SMALLER the PERCENTAGE OF time saved over that distance."

[@TeslaOsiris]

I would like to hear about how stem stack height impacts efficiency.