Helmet Aerodynamic Testing Part 1: Evade v Aerohead v Podium TT

Helmet Aerodynamic Testing Part 1: Evade v Aerohead v Podium TT

X3 has a new toy – I mean, high-precision instrument – the Notio Konect aerodynamic sensor. This device mounts to the bars of your bike and collects atmospheric (air pressure, wind speed / direction, humidity) and kinematic data (vertical oscillation and long-axis pitch) as you ride. It combines these streams with power and ground speed from other on-bike sensors to calculate aerodynamic drag. This is awesome!

It’s awesome because it enables coaches, fitters, and athletes to make informed equipment and rider position choices based on field testing in real-world environments. I’ve been calibrating it and performing informal testing for three weeks now. This is my first controlled test.

Here goes.

 

  1. The Purpose Statement

To test the affect on aerodynamic drag of three helmets: the Specialized Evade gen 2, the Giro Aerohead, and the Smith Podium TT. Also to test the affect of head position using each of the helmets.

 

  1. The Test

This is my first go at controlled, outdoor aerodynamic testing so the primary objective is to create a protocol that can be repeated for subsequent test runs and come up with a control set of testing kit. Having a control kit will allow me to run future experiments with a decent expectation of reliable, repeatable results. Here’s what I mean.

Today I want to see how the above-mentioned lids stack up against one another. But today’s results are specific to today’s conditions! Wind speed, direction, air pressure, humidity, road conditions all affect aerodynamic drag. That means that the CdA (Coefficient of Drag x Area) value measured today for a given setup will likely be slightly different tomorrow. What will remain the same – or essentially the same – is the difference between the setups. That is if helmet A tests faster than helmet B by 10%, it’s fair to conclude that A will be faster by roughly 10% on most days. Helmet A can then be my control helmet.

Now if I want to see how helmet C stacks up against helmet A (or B), and if I plan to test helmet C in the future, I will have to test C against my control (helmet A). That way, I can confidently assess how C stacks up with B or any other helmet I tested against that control.

Science!

The test protocol itself is straightforward.

  1. Find a stretch of straight road with no traffic lights or other interruptions that will allow for a steady effort of roughly 5 minutes. The road ideally has a slight, steady grade. This is not essential, but it cannot have too steep a grade at any point along its course.
  2. Record equipment setup for future repeatability. Mine here was:
    • Bike: Garneau TR1, M, narrow pads, stem slammed, 10mm pad riser
    • Aerodynamic Sensor: Notio Konect
    • Wheels: FLO Gen 2 carbon clinchers, 60F 90R
    • Tires: Vittoria Corsa G+
    • Tubes: Latex
    • Pressure: 105F 110R
    • Shoes: Sidi Genius 5 Road
    • Legs: not shaved, tall socks
    • Kit: X3 Team Castelli short-sleeved tri suit
  3. Warm up, then perform ‘out and back’ repeats for each helmet or position. That is, 5 minutes out, quick turn-around, 5 minutes back. That’s one test.
  4. I tested the Evade and the Aerohead in both comfortable head positions and low / turtled positions. I tested the Podium only in the low / turtled position as I was running low on time and had testing the other positions in a previous round. So 5 test runs in total.

 

  1. The Helmets

I am not intending this to be a helmet review post. I’ll post my thoughts on each of these bean-toppers separately. Instead, I’ll write a very quick summary of each for sake of context.

  1. Specialized Evade Gen 2
    • Aero road helmet,
    • Lightest and best-vented of the bunch
    • No visor. Shimano rimless cycling sunglasses instead
    • At home on a road ride as much as a long-course TT
    • $260 CAD
  2. Giro Aerohead MIPS (not the Ultimate version)
    • Dedicated TT helmet
    • Decent ventilation and excellent visor
    • Quiet for a TT helmet
    • $300 CAD
  3. Smith Podium TT
    • Dedicated TT helmet
    • Very light for a TT lid and well vented too
    • The red visor lens really makes colours pop
    • Loud at high speeds and certain head angles
    • $440 CAD

 

  1. The Results
HELMET HEAD POSITION AVERAGE CdA
Specialized Evade Gen 2 comfortable 0.301
Specialized Evade Gen 2 low 0.275
Giro Aerohead comfortable 0.277
Giro Aerohead low 0.264
Smith Podium TT low 0.278

 

  1. The Unexpected, the Caveats, and the Conclusions

The most satisfying aspect of testing is encountering unexpected results. Here are two highlights.

  • Specialized’s Evade is a VERY fast road helmet. In this testing it was as fast as the Smith Podium with the same head position. Given how much lighter, better vented, and more comfortable it is than any true TT helmet, it should certainly be a lid to consider.
  • The effect of head position is substantial! In my case – and I expect in most cases – a lower head position is significantly faster than a higher one. My high head position tested between 5% and 10% slower than my lower position! That’s a substantial difference given that in involved no equipment changes.

It is important to recognize two critical provisos to this data.

  • This testing is highly individual. Your ‘low’ head position is likely different than mine. Your shoulder width, back angle, stack vs saddle height are all different. Aerodynamics are fickle and generalizations are typically less than accurate. The only way to know which helmet or which position works for you is to test it!
  • I must admit that my error bars for this test are likely large. I only performed one out-and-back for each test. Notio recommends two or three. The more passes, the smaller the error.

For my own personal use, I’d stick to the Aerohead for shorter, more intense efforts and likely go with the Evade for really long or very hot events.

  1. The Next Steps

I plan on testing stack height next. I’m not super happy with my overall CdA values and would love to get to a number below 0.25.

If you have equipment you want me to test, or want to test your own setup, please send me a note! Remember: #aeroiseverything!

 

4 Comments
  • Kevin
    Posted at 17:34h, 23 August Reply

    Would be interesting to see how it compares to a STAC virtual test. Let me know if you need any test dummies! Also something I thought about, do you think the sensor works with a front hydration system like ones on the Scott Plasma and now aftermarket versions of that, the PD Aeria? Wonder if the sensor would get confused with something blocking the wind form certain angles.

    • admin
      Posted at 14:29h, 24 August Reply

      This is something that we’re speaking with STAC about actually. The pitot tube on the sensor needs to be unobstructed from the front and the sides, so some builds with integrate front hydration setups may be a little more tricky. However the folks at Notio have built in quite a bit of calibration into the system, so I’m confident that if we can find a place to mount the sensor, we can make it work.

  • Jon Watkin
    Posted at 16:38h, 30 August Reply

    Can you elaborate on which power meter you used and what margin of error you are placing on the results? What is Notio Konect’s accuracy on CdA?

    • admin
      Posted at 11:13h, 31 August Reply

      Thanks for the note Jon.

      I was using Powertap’s P1 pedals for the test. As for your question about the margin of error, the honest answer is that I do not know. The testing protocol from Notio is robust, but I did not have time to make multiple passes with the same setup (which is what they recommend) to average out the errors. I do believe that a true margin of error will be hard to calculate when you’re doing a field test. There are just too many uncontrollable variables: wind gusts, vehicles, subtle changes in position, etc. I can’t imagine that you’ll ever attain the precision of an indoor wind tunnel / virtual wind tunnel (CFD) / or track testing when you test outdoors. I’d argue though, that the utility of outdoor testing is the very fact that it is real-world. So you get inherent feedback on how sustainable a position is as you test it – there’s utility in that! So at the moment, I’ve been using the Notio to test setups / positions / equipment against one another. I have more confidence in saying that A is faster than B by some percentage than claiming firm CdA numbers for A or B.

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