Helmet field testing? CdA impact

[ed72]

Aurelian Bonneteau must have tested many helmets before attempting his world record run

What really shocks me of his record photos is how much skin he exposes. Skin is incredibly slow. Tons of wind tunnel data, Chung testing data, anecdotes from top Ironmen, and when was the last time we saw a TdF TT winner exposing much skin. Perhaps the airflow is so disturbed from the legs that arm coverings do not matter. Who knows. I just try stuff and test. If it is faster, it is faster.

 

[ed72]

I am almost expecting my Giro to be faster with the shield now because of a more recline position would seemingly benefit the tight shield over the less tight but narrower profile of glasses. I lowered the seat in the rear and raised it on the front using rubber and neoprene washers. The rear is lowered 1 inch and the front is raised 3/8 inch, so my angle is quite a bit more reclined. I also lowered the stem by using a different fork that was slammed. What a difference in handling with the new fork......floppy, floppy, floppy.....now I know what you mean.

I did figure out the Ventist pad power robbing issue.....some of my kit slides on that pad. When I wear the "slippery" kit, I can't make as much power. My arsh moves all over the place.

 

[cpml123]

I looked into getting a Casco speediro helmet before. I don't think they can be shipped to US officially because it's not certified by helmet folks here. Darn...

 

[Osiris]

$500 when I was looking but.....that was 14-18 months ago. I think there is a newer version available. Larry's testing was good enough for me in terms of speed but the close fit of the shield is too much a liability for a lowly randonneur like me.

I was intending to retest helmets with and without visor today but had to take care of my MIL with Alzheimers. I have large and also a medium Giro Vanguish. One of them will get modified with an attached mirror and tons of reflective tape. I need to replace the Bell Star, after 25k miles, it is ruined.

http://www.casco-helmets.co.uk/Casco-SPEEDtime

I tried to order one from that website, but it appears that they only ship within the UK.

 

[Osiris]

What really shocks me of his record photos is how much skin he exposes. Skin is incredibly slow. Tons of wind tunnel data, Chung testing data, anecdotes from top Ironmen, and when was the last time we saw a TdF TT winner exposing much skin. Perhaps the airflow is so disturbed from the legs that arm coverings do not matter. Who knows. I just try stuff and test. If it is faster, it is faster.

I'd be interested to know what his M5 is like to ride. Can he actually see what's ahead of him, or does that not matter if you're just going in circles? In that extreme horizontal posture, I would think a different helmet shape might be more aero.

 

[ed72]

I just remembered that I have a cone shaped TT helmet....the tail kind. Surprisingly, the headrest fits just inside the helmet and the tail rests onto the tailbox. Might be fast. (I know that goes against conventional benthood)

I decided to do a comparison 10 miles each direction at 23 mph. One round trip with the Vanquish and shield and one roundtrip without the shield and just the Shimano glasses. In my new reclined position, the medium Giro Vanquish shield fits flush to my face whereas the Large provides more room between the shield and face (glasses can fit inside there). Unfortunately, I flatted due to a slit casing and since it was 90F plus and humid, I only tested the medium helmet with shield. Basically, I bagged the last 22 miles of a 65 miler.

The good news, it only took me 140-145 watts to go 23 mph on average. So, I am just under last year's numbers in terms of drag...I wore the fancy clothes and cleaning the bike up yesterday. I'm not seeing any way for a 6'4'' 200 pounder to do 24 mph on 14-150 watts unless it is on one of Osiris's super bikes and maybe dual disc wheels at that!! The slight additional recline that I dialed in might not be worth it, I felt under powered and the seat was uncomfortable on my derriere.

I hope to get some better testing time.....need calm day and time to do it.

 

[Osiris]

I just remembered that I have a cone shaped TT helmet....the tail kind. Surprisingly, the headrest fits just inside the helmet and the tail rests onto the tailbox. Might be fast. (I know that goes against conventional benthood)

I tried that with my TT helmet as well, but I couldn't get it to work No matter how I positioned my head, the the tail of the helmet would scrape against the rear tire. Very disappointing.

I decided to do a comparison 10 miles each direction at 23 mph. One round trip with the Vanquish and shield and one roundtrip without the shield and just the Shimano glasses. In my new reclined position, the medium Giro Vanquish shield fits flush to my face whereas the Large provides more room between the shield and face (glasses can fit inside there). Unfortunately, I flatted due to a slit casing and since it was 90F plus and humid, I only tested the medium helmet with shield. Basically, I bagged the last 22 miles of a 65 miler.

The good news, it only took me 140-145 watts to go 23 mph on average. So, I am just under last year's numbers in terms of drag...I wore the fancy clothes and cleaning the bike up yesterday. I'm not seeing any way for a 6'4'' 200 pounder to do 24 mph on 14-150 watts unless it is on one of Osiris's super bikes and maybe dual disc wheels at that!! The slight additional recline that I dialed in might not be worth it, I felt under powered and the seat was uncomfortable on my derriere.

That sounds very efficient to me. I never do any tests at 24 mph, but on a 12 mile TT a couple of weeks ago I averaged 25.2 mph @ 205 watts on the M5. Last Friday on the same segment with the M1, I averaged 26.8 mph @ 192 watts. The 12 mile segment is ideal for testing because it's shaped like a big U, so the effect of any head/tail wind should be canceled out. That same day on the M1 I rode a 1 mile segment where I averaged 32 mph @ 272 watts, but that was going in one direction, so it's not a number I'd put any faith in. It does give me hope that there will come a day when I'll be able to do a 10 mile TT @ 30 mph, though.

I'm told that this particular trail is slated to become part of the X-Florida route once a connecting segment is completed, so there's a chance I'll be able to partake in that event. If/when I do, I want to be as aero as possible because that 170+ mile ride is going to be a killer for someone with my lousy endurance.

 

[ed72]

Last Friday on the same segment with the M1, I averaged 26.8 mph @ 192 watts

Thanks for that benchmark. That is right at what my target was in terms of aero improvement. It shows me that I was a bit aggressive in my goals. I have a few small gains to make.....remove front light, remove tail light on rear stay, remove mirror, etc. Small beans. The tailbox sits high on my modified Thor seat. The upper edge is 2 inches higher than my shoulders......two bricks in the wind. Even with the best of the best helmet and little tweaks, ain't getting as fast as your ride.

 

[ed72]

It is easy to get CO2 out of wack but I actually think in the other direction.

This is one of the studies that got me to think about dead space, CO2, and my overall strategy of "easing" into a threshold effort. There is another set of studies showing the VO2 response of supine vs upright exercise, the supine response is much slower. This means it is very easy to fool yourself in the first 1-3 minutes into using anaerobic energy but once the aerobic system comes on line so to speak, your legs are already toast.

I never found research studying the effect on chemorecptors. I found that intense VO2 max intervals would leave me with an intense hypoxic feeling; and, merely sitting up would resolve that feeling more quickly than laying down on the seat. So, I concluded it was more geometry than biochemistry.

The average values of at each intensity were slightly higher in the sitting position compared with the supine position, but not significant. The average values of (Fig. 2) and (Fig. 3) at each intensity were also higher in the sitting position compared with the supine position. In particular the differences were significant from before the warming-up period to 3 minutes after exercise started.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4316495/

https://www.ncbi.nlm.nih.gov/core/l...to zoom&p=PMC3&id=4316495_jjpta-1-13-g002.jpg

 

[Osiris]

Thanks for that benchmark. That is right at what my target was in terms of aero improvement. It shows me that I was a bit aggressive in my goals. I have a few small gains to make.....remove front light, remove tail light on rear stay, remove mirror, etc. Small beans. The tailbox sits high on my modified Thor seat. The upper edge is 2 inches higher than my shoulders......two bricks in the wind. Even with the best of the best helmet and little tweaks, ain't getting as fast as your ride.

Here's another benchmark that might be useful. At the end of Friday's session I was feeling pretty drained, so for the remaining four miles back to the parking lot I just took it easy, keeping my speed between 24-25 mph. Strava shows my average speed on that segment as 24.6 mph @ 142 watts. That was on the M1. In this speed range, I estimate that my M1 has a 1.6-1.8 mph advantage over my M5 at the same power level, so that may give you some indication as to what you can expect from your M5 at 24 mph.

One thing I became aware of but didn't have the opportunity to test was that sitting with my head off the headrest may be causing a significant amount of drag. Unfortunately lying all the way back causes the lip of the visor to cut right across my field of vision, so I've developed the bad habit of holding my head up slightly. When I relaxed and put my head all the way back, I noticed a couple of times that my speed began to creep up to ~25 mph. Now this could be due to other variables like very mild wind gusts or slight changes in slope, so I'll have to run some tests to account for that. A high speed coast down test would be ideal for this purpose, but suitable hills are scarce in this part of the state.

By the way, I'm only 6'-0" and 165 lbs, so would that difference in our size and weight make these sorts of comparisons worthless? The size of the rider makes a pretty big difference in drag on an upright, but I'm not sure how much difference it makes in a supine position.

 

[Osiris]

This is one of the studies that got me to think about dead space, CO2, and my overall strategy of "easing" into a threshold effort. There is another set of studies showing the VO2 response of supine vs upright exercise, the supine response is much slower. This means it is very easy to fool yourself in the first 1-3 minutes into using anaerobic energy but once the aerobic system comes on line so to speak, your legs are already toast.

I can certainly relate to that! It would certainly explain the mysterious drop in power I always experience after the first mile of a hard 2-4 mile effort, followed by the gradual increase in power after another half mile or so. On shorter runs of 1 mile or less, there is no noticeable drop in power, unless of course I go much too hard at the very start.

Fascinating article. I'm inspired now to run some 5 minute interval tests on my trainer, comparing my performance on the M5 to that on my upright. In 1 minute max efforts, the difference in power production on the two platforms is enormous.

 

[ed72]

I've contemplated head and neck position. If you look at Larry or any of the fast guy's like aurelien bonneteau during a TT, the chin is tucked to the chest. For aero purposes? Some have said it is for better breathing but I am not so sure on either account. The receptors that control breathing are located just below the chin area and are sensitive to stretching. I know that I am faster with my chin down and straight thorax. I don't know why. Aero? I also haven't experimented carefully.

 

[Osiris]

I've contemplated head and neck position. If you look at Larry or any of the fast guy's like aurelien bonneteau during a TT, the chin is tucked to the chest.

It doesn't look that way in these photos (Matthias Konig obove and Bonneteau below).

 

[ed72]

The top photo shows a clear wrinkle of skin/fat below the mandible......This has to be due to tucking the chin towards the chest.

The second photo can be seen the apparent lack of cervical lordosis, also suggesting a conscious effort to push the chin towards the chest.

Maybe I am wrong or maybe they are putting their necks into flexion to be able to see where the heck they are going. LOL. Trust me these are not normal neck positions of a person in rest, I spent the last two years getting PT and Chiro 2-3 times per week on my neck.

I have noticed an increased topspeed during Chung testing when pull my neck in....recumbent turtling position.....but it also impact my shoulder width making it narrower.

There is an obvious reason these racers hold there head/helmet like that, I am not sure why.

It doesn't look that way in these photos (Matthias Konig obove and Bonneteau below).

 

[Osiris]

The top photo shows a clear wrinkle of skin/fat below the mandible......This has to be due to tucking the chin towards the chest.

The second photo can be seen the apparent lack of cervical lordosis, also suggesting a conscious effort to push the chin towards the chest.

Maybe I am wrong or maybe they are putting their necks into flexion to be able to see where the heck they are going. LOL.

That's all I thought it was. I've been comparing those photos to to my own to see if I can spot the difference with respect to chin positions, but I can't see anything. Hard to tell in my case though, due to the beard.

I've spent a lot of time searching the net trying to find anyone in the US (or who exports to the US) who sells Casco Speed helmets, but no luck. Local bike shops have been of no help either. I've seen time trialists in the area wearing these, so they must have a source somewhere.

I just did a group ride on my upright and realized that at ~31 mph, even my most aero roadbike helmet creates too much drag. I could hear the wind whistling as it passed through the openings, and I felt the helmet pulling on my chin strap. No telling how much drag is being created, but it's too much. I need that Casco Speed helmet.

I'm really intrigued by those photos of Konig and Bonnetaeu. Notice how Bonnetaeu is able to keep his hands clear of his thighs, even with his right leg at full flexion and both arms almost fully extended. I tried to emulate his pose on the trainer, and it proved to be physically impossible for me. Maybe he has very unusual proportions that enable him to do this. The angle between his femur and thorax is also much greater with his pedal at TDC than Konig's is. I wonder why that is. In my case that angle is roughly 90 degrees on the M1, which completely rules out a low hand position like those shown in the photos above.

 

[ed72]

I hear you on the hand position. No luck for me either. I "think" part of why they can bring their arms in so tight lies in the length of the back half of the bike and less seat drop from the BB. Larry's special (does he call it Frankenstien?) seems to have a much longer back end than stock, his arms and shoulders seem much more streamlined on that bike....my estimation of his CdA on it is pretty special, too.......not as slippery as your M1 but getting there.

Dead still calm today. I wore my standard kit today and did some light tempo work, 10.xx miles in 22:21 (27.3 mph ave) on 219 watts in one direction and 9 miles at 25.7 mph at 209 watts and 126 BPM HR. (there is a net 40 foot rise upriver or 40 foot fall down river with about 250 feet total climbing/descending). A little less slippery than the other day, but no fast socks, skinsuit, etc today....just my regular Assos shorts and jersey. Medium Vanquish helmet. No chance yet to do official Chung testing. It seems the large Vanquish (which tested slower with shield than with glasses alone) fits much tighter to my face, there really isn't much gap. The shield hits the cheeks whereas with the large, I can wear glasses under the shield. Since the helmet has very good cooling, it is a keeper for my uses.

Check Amazon UK for the Casco Speedtime helmet. Amazon and one retailer in Germany has one. I do wonder if I had such a helmet if I could break 4 hours for 100 miles. Maybe.

 

[Osiris]

I hear you on the hand position. No luck for me either. I "think" part of why they can bring their arms in so tight lies in the length of the back half of the bike and less seat drop from the BB. Larry's special (does he call it Frankenstien?) seems to have a much longer back end than stock, his arms and shoulders seem much more streamlined on that bike....my estimation of his CdA on it is pretty special, too.......not as slippery as your M1 but getting there.

Based on Larry's write-up (posted on another forum), the "Frankenstein" bike didn't work for him at all. It was definitely more aero than his V20, but he claims that his power output on it was so much lower that the improved aerodynamics didn't compensate for it. I was thinking about that when reading the article you posted earlier.

There are a couple of interesting things to note when comparing the picture of Konig to Bonneteau. First is that Bonneteau's hip angle is much more open with the pedal at TDC. Either his cranks are very short, or his legs are extraordinarily long. You can see how that affects his hand position. The picture shows that the top of his thigh at full flexion doesn't even reach his knuckles, whereas in Konig's case, the top of his thigh overlaps his entire hand and even part of his forearm. That was the big problem I had with the gunner grips that my M1 came with. It meant that at any moment one of my thighs could strike one of my hands while pedaling and cause the front wheel to jerk to one side. I believe that's what led to the two crashes I had. Now if I could position my hands the way Benneteau has them, I'd be a lot more aero without incurring any risk of a thigh/hand collision. The trouble is that the frame geometry on my M1 and M5 just don't allow for that type of position.

Dead still calm today. I wore my standard kit today and did some light tempo work, 10.xx miles in 22:21 (27.3 mph ave) on 219 watts in one direction and 9 miles at 25.7 mph at 209 watts and 126 BPM HR. (there is a net 40 foot rise upriver or 40 foot fall down river with about 250 feet total climbing/descending). A little less slippery than the other day, but no fast socks, skinsuit, etc today....just my regular Assos shorts and jersey. Medium Vanquish helmet. No chance yet to do official Chung testing. It seems the large Vanquish (which tested slower with shield than with glasses alone) fits much tighter to my face, there really isn't much gap. The shield hits the cheeks whereas with the large, I can wear glasses under the shield. Since the helmet has very good cooling, it is a keeper for my uses.

Check Amazon UK for the Casco Speedtime helmet. Amazon and one retailer in Germany has one. I do wonder if I had such a helmet if I could break 4 hours for 100 miles. Maybe.

No joy with Amazon UK. I tried ordering the Casco, but I kept getting a message saying they couldn't deliver the item to any of the US addresses I tried. As an alternative, I've been looking at the Oakley ARO7 helmet. It's available in the US and currently on sale at Biketiresdirect.com for $375.96.

 

[ed72]

Bonneteau supposedly rode 130mm custom cranks and is also very tall with longer than normal legs, so, your observation would seem correct. I have no where to put my hands either; however, with my new more reclined position (1 inch lower in the rear and about 3/8 inch higher in the front of the seat), it "feels" like I make less power. I need to do an FTP test but my fatigue level is kind of high and am loathe to do it. This was one of the reasons I did two different submaximal steady state efforts the other day. It is pretty easy to do a regression analysis to find one's approx. FTP and in fact Golden Cheetah does that but the data it had was noisy. It was giving me an FTP of 354 watts which is much too high. I did a steady effort for 10 miles at one heart rate and then another higher rate, it estimates me at 274-280ish watts with the more reclined seat. I had been suspecting my FTP was closer to 300 watts now. I might raise the seat back up and try it again. I did my 10-12% climb with the lower seat and that is where I really noticed it seemed like i made less power. I caught a roadie and he was like, "wow, a recumbent on this climb" but truth be told, I struggled a bit. My best on an upright for that climb was 4:04 and my best on a bent is 4:58. It took my 6:03 although I was not killing myself, it felt very hard. I supposed I could have done a 5:30.....this would suggest a 10% loss in power or something like that. A loss of 10% power but with 10% lower CdA won't be noticeable on the flats, in fact, you'd still be faster and I suspect larry would have been faster on the track with the laydown position but could be wrong. I think I might have this "problem".........do you know how much power Larry reported to lose with the frankenstein bike?

 

[Osiris]

I couldn't be sure from the photo, but Bonneteau's cranks did look unnaturally short. Just look at the height of his right knee at maximum flexion; the knee cap is only slightly higher than his head! When you think about it, that small amount of knee bend must give him a big aero advantage.

I ran an experiment on my upright today that bears out what you report about hip angle. I had always suspected that I made more power on the uprights when I sat up with my hands on the hoods rather than down in the drops, so today I went up my favorite test hill where I always try to hold the highest average power I can manage until I reach the top. My previous record was ~460 watts on the upright with my hands in the drops, and ~395 watts on the M5. Today I managed to average 516 watts with my hands on the hoods, and it would have been even higher had I not miscalculated the starting point of the segment. A 56 watt difference is huge, and I can really tell the difference when I change my hand position from the hoods to the drops; it suddenly feels as if my quadriceps have no leverage, and my glutes are being asked to take up the slack, which they're just not capable of doing.

In anticipation of buying a new aero helmet, I also did a short but steady run at 27 mph. Now I have the data I need to tell me how much the choice of helmet really matters. Next, I'll do the same segment at the same speed wearing my LG time trial helmet and see what kind of wattage reduction I get. If I'm going to shell out 400-500 bucks on a new helmet, I want to make certain it's money well spent.

Larry posted his write-up on the "Frankenbike" on a racing forum I've since been banned from, so I can't go back and look it up. What I remember him saying was that it was indeed much faster at the same power level than the V20 out of the gate, but that only lasted for a short while until his heart rate began to climb much higher than he was used to and the effort became impossible to sustain. I think he gave up riding it after that and focused all his efforts on the Arrowhead. Larry sent me some spreadsheets where he'd recorded his results on various recumbents, testing different wheels and tires, etc., but the Frankenbike isn't mentioned anywhere. That suggests to me that his performance on it was so poor that he'd simply written it off after the first experience. Nevertheless, I'd love to get a test ride on a radical design like Bonneteau's M5, if only to satisfy my own curiosity.

 

[ed72]

Helmet selection is a tough one if you read wind tunnel testing results....mostly from Triathlon racers. What works on one rider doesn't work on another, which of course makes the tunnel testing more cost effective since they have helmets there for you to test. Easy to spend a ton of money on helmets, I have about $1200 of them sitting on my workbench. I suspect my Giro Vanquish with the vent holes taped over would be a pretty fast helmet. You might laugh but I keep duct tape on the bike for a variety of emergency purposes like taping the helmet vents in rain to keep me warm or to fix a broken tailbox mount (with help from zip ties) on a 300k ride

In terms of money spent, a helmet is usually a good value for speed on an upright although good data from bent riders is scarce. IIRC, Larry got like 0.3 mph at around 26 mph with helmet choice.....that is huge.