Login required to started new threads

Login required to post replies

Prev Next
Results from Helmet Field Test - Did I Learn Anything?
Quote | Reply
So I wanted to find out if my new(er) Giro Aerohead was faster than my old Selector. I perhaps should have read up on the Chung Method first, but I just devised my own simple test:

I did a coast down a hill of about 0.96 miles. I had the finish marked with a line on the road, and two lines at the start - the first was where my front tire was when I took my one and only pedal stroke of the entire test - with the right pedal in the 3 o'clock position I stood on it with my body weight to get rolling. I clipped my right foot in and got in aero position. Slowly I rolled to the second line, about 25 yards away, where I started my clock. Then when I got to my finish line, I hit lap.

I tried to maintain my true Ironman position the whole time instead of my best possible position that I will try to use when I'm confident I won't run into anything - so looking forward enough to see the road but with that stretched feeling in my neck of trying to keep my head out of the wind as much as possible. First test was with the aerohead and I alternated each test, for 4 tests total, 2 with each helmet.

Results:

Run 1: Aerohead, 104.60 seconds
Run 2: Seletor, 101.55 seconds
Run 3: Aerohead, 102.17 seconds
Run 4: Selector, 102.63 seconds

Aerohead Average: 103.39
Selector Average: 102.09
Difference, 1.3 seconds, advantage Selector.
Paired, single-tailed T-Test result: 0.29

Bad photos:


she got me going for the brake at the end of the test





I feel like over such a short test, a 1.3 second difference is a big deal, IF it is real. There was not much wind. Differing initial velocities could have a big effect on the results, even though I tried hard to control it. On the second aerohead test, a "right power meter missing" warning came up and I felt I had to clear it because I was not sure my lap button would work if I did not. I did that from the aero position and the head unit is right between my hands, so I did not really have to move much. On the second selector test, I mimicked the same motion at the same spot in the course to try to keep things consistent....


For so few datapoints, the results of the t-test do not seem awful, but certainly not something one could go publish a paper off of.


So... Did I learn anything?

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
Hello RowToTri and All,

Pictures can lie ..... but your Selector matches your back better in the pic.

Your chin position seems close to the same in both pics.

Cheers, Neal

+1 mph Faster
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
I would have liked to have seen more samples, especially given the fairly significant variance sample to sample.
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [gary p] [ In reply to ]
Quote | Reply
Me too... All I could do though.

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [nealhe] [ In reply to ]
Quote | Reply
True, but the areohead isn't really designed to be a back-matching hemlet. It's supposed to be fast with your head in all sorts of positions.

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
i'd be inclined to view run#1 as an anomaly as its so different to the others. excluding that, call it a wash between the other 3.
so no, i don't think you learnt anything except:
  1. its hard to control all variables - you did a pretty good job but maybe need 3 runs per helmet so as to be able to more clearly identify anomalies and have at least 2 runs left after excluding them
  2. there's probably minimal difference between the 2 helmets (for you at least)
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [pk1] [ In reply to ]
Quote | Reply
It seems like my results could largely be explained by initial velocity - however this is GPS speed so it could easily be off by 1mph. But this seems fairly compelling.

Run 1: Aerohead, 104.60 seconds , Vo = 7.83 mph
Run 2: Seletor, 101.55 seconds , Vo = 8.75 mph
Run 3: Aerohead, 102.17 seconds , Vo = 8.41 mph
Run 4: Selector, 102.63 seconds , Vo = 8.16

I'm coming to the conclusion that this test probably does not have high enough resolution to find the difference in these helmets. Does that mean the difference is too small to matter or just that the test is not adequate?

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
Hello RowToTri and All,


Sounds like you do not have confidence in the tests ...

Perhaps time for wind tunnel or velodrome testing.

Or just wear the one you prefer for fit and ventilation .... (looks don't count in helmets)

Cheers, Neal

+1 mph Faster
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
I hate to say it but you probably didn't learn anything. I'd try again with a much larger sample size. Be mindful of what your reaction time likely is (starting/stopping the clock) and how that adds noise to the data. A big source of error in testing like this is slight variations in how your feet are positioned. You might think they're positioned the same every time but subtle differences can have a big impact.

WTB: TriRig Omega SV (not x). PM me if you have one :)
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
I think you learned how hard it is to do field testing.

Brian Stover
Accelerate3 Coaching
twitter & IG = @accelerate3
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [desert dude] [ In reply to ]
Quote | Reply
Ha! True!

So how about this - Taking a snapshot of the data between two easily definable points during the fastest part of each run. Because of the cubic relationship of speed to drag, this will minimize the influence of the different starting velocities. It also eliminates errors in my button pushing accuracy, especially when looking at speed. Because the garmin is only taking a datapoint every second, just looking at time might give skewed results (though the data points line up close to the center of the roads surprisingly well in each file) but I can also look at average speed over each interval.




The data from this section:


Run1: Aerohead, 53.2 sec, 36.2 mph
Run 2: Selector, 50.92 sec, 38.1 mph
Run 3: Aerohead, 52.68 sec, 37.1 mph
Run 4: Selector, 50.75 sec, 38.2 mph


Time difference: 2.1 seconds
Speed difference: 1.5 mph


t-test for time: 0.026
t-test for speed: 0.083


This data seems much more compelling to me. Might I be getting something wrong in the analysis?



-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Last edited by: RowToTri: Oct 8, 17 21:00
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
Visually, on you, the aerohead sits up much higher than the selector, so I wouldn't be surprised if the selector is faster.

The aerohead seems to be designed for a different neck / head position.

That said, this might all be due to the MIPS system adding extra height / size of the helmet. If you are using a L Aerohead, it's physically larger than the M/L Selector.


Last edited by: bloodyshogun: Oct 9, 17 5:33
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
How are you doing a T-test with only two runs per helmet?
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [awenborn] [ In reply to ]
Quote | Reply
I'm just using g the Excel function for it. I was wondering if it was valid with so few points... But a quick Google search did not give me a minimum number of data points.

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [bloodyshogun] [ In reply to ]
Quote | Reply
I'm using medium in both- the selector is actually a little more comfortable. A large aerohead was more comfy but just huge.

I can hold that low head position for short periods of time but I have to keep poking my head up to make sure I won't hit anything. When I'm passing (which I'll probably do a lot of in the first hour) or descending or on a twisty bit of road I hold my head like in my pictures.

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
From my increasingly faint memories of my student years and doing manual T-Test calculations, I always used a method involving the Mean and Variances of the two series of measurements, the latter of which required at least three measurements, but it seems that there are methods of doing it with just two, so you can probably ignore me!

You should totally give the Chung method a try though, it's easy enough once you get your head around the theory and should give you much more reliable data.
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [awenborn] [ In reply to ]
Quote | Reply
easy you say?

the hard part is finding the no wind "half pipe" to ride on, or so I'm told.

awenborn wrote:
From my increasingly faint memories of my student years and doing manual T-Test calculations, I always used a method involving the Mean and Variances of the two series of measurements, the latter of which required at least three measurements, but it seems that there are methods of doing it with just two, so you can probably ignore me!

You should totally give the Chung method a try though, it's easy enough once you get your head around the theory and should give you much more reliable data.

Eric Reid - AeroFit
- Aerodynamic Optimized Bike Fitting
- Retul Pre-Purchase Bike Fitting
- Triathlon Coaching and Nutrition
Ask me: Scody Optimized Speed Suits | CeramicSpeed Oversized Pulley Systems | HUUB Skinsuits and Wetsuits |
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [ericMPro] [ In reply to ]
Quote | Reply
ericMPro wrote:
easy you say?

the hard part is finding the no wind "half pipe" to ride on, or so I'm told.


No wind, no traffic, representative road surface, no potholes, not-too-short, not-too-long and nearby... piece of cake!
Last edited by: awenborn: Oct 9, 17 5:28
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [awenborn] [ In reply to ]
Quote | Reply
So I went to analytical cycling, put in the average grade, crr, air density, weight and played with frontal area and Cd until I got the average speeds with each helmet. I'm thinking that the absolute CdA might not be exactly right, particularly because the grade for the run is not constant - but intuitively it seems like the difference in CdA between the two might be somewhat accurately calculable.

The result was that the Selector gives me an improvement in CdA of 0.012.

When I then plug that in with a flat road and my ironman power, it gives a increase in speed of 0.8 mph.

Obviously that is massive - not really believable. But I'm starting to feel confident that the Selector is indeed faster for me.

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
imo short answer...yes, you learned something.

You need to do A LOT more runs to try to eliminate variables in roll down tests.

My Blog - http://leegoocrap.blogspot.com
Podium Sports Racing - http://www.podiumsportsmed.com/team/
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
You shouldn't be using a t-test for n=2. And use of a one-tailed test is a clear no-no. Not that it actually matters in this case. Just for the record. Good luck with testing!
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [nealhe] [ In reply to ]
Quote | Reply
nealhe wrote:
Hello RowToTri and All,

Pictures can lie ..... but your Selector matches your back better in the pic.

Your chin position seems close to the same in both pics.

After some field testing (2 x 2 sessions of 5 loop Chung/VE) of similar helmets, I can say that "matching my back" was ~.005 slower. I never did update this thread though. http://forum.slowtwitch.com/...t_P6332571/#p6332571
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
you learned you cannot use GPS for speed no matter how much you want it to work, get a speed sensor that measures actual relative(relative even if not 100% accurate between runs, ie 4.6rpm is 4.6 rpm of wheel) speed
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [jeffp] [ In reply to ]
Quote | Reply
Do you not think average speed over 50+ seconds measured by gps would be relatively accurate?

-------------
Ed O'Malley
http://www.motivengines.com
@EdwardOMalley
Quote Reply
Re: Results from Helmet Field Test - Did I Learn Anything? [RowToTri] [ In reply to ]
Quote | Reply
no.

at 40mph over 50sec you are still +/- 0.25mph so for 2 runs you could be as much as 0.5mph off if everything else was perfect
Quote Reply

Prev Next