Helmet field testing? CdA impact

[ed72]

Has anyone done Chung field testing on helmets? I know it is a long shot....

I own a few helmets, the Bell Star is fastest but am wondering if the Giro Vanquish or the Casco Speed might be faster. Neither are cheap. I know the Chung method will allow me to determine which is best but hoping to keep costs somewhat in line.

Has anyone done any sort of testing on the Giro Vanquish? Maybe even coastdown? There is a lot of DF testing out there but it isn't likely applicable to the bent position.


Thank you. Ed

 

[cpml123]

I am guessing Bell Star is also the warmest. I have one, and it's gets hot above 75 deg outside.

 

[ed72]

I am guessing Bell Star is also the warmest. I have one, and it's gets hot above 75 deg outside.

Compared to the Laser Z1 Mips, it is warmer but the ability to open and close the vents while wearing clear eyewear under the shield allows one to ride in the rain while the strategic placement of tape on the shield keeps sunlight above the horizon out of my eyes. The Bell is cooler than the Specialozed Evade, at least to me. Another TT helmet wont clear the headrest and was a silly waste of money

 

[Balor]

Casco Speed

You can buy Casco Speedairo replicas for peanuts from Ali that seems pretty much the same externally.
Optics undoubtedly suck in comparison, but a cheap way to get a test of aerodynamics at the very least. I have one, and I kind of like it - except the fact that the visor is not magnetic. If it was, it would be a perfect helmet for my needs.

 

[Balor]

Anyway, how about a shaved head and no helmet for a boost in aerodynamics?
Head is usually the last place to get damaged in a cycling accident on a bent, and I've had my share of those.
Wouldn't leave home without on if riding DF, of course - it proved itself invaluable a few times already.

 

[ed72]

Balor....thanks for the tip as always on Ali

WRT shaved head, there isn't much left to shave. LOL.

When I added the Bell Star, the improvement over my standard road bike helmet was noticeable but suspect the new Giro or the Casco would be faster. I never made any precise measurements but it is faster....I used to be able to feel the helmet lip at the forehead pulling away on the old helmet. I have about 15 different equipment, clothing and position changes identified to test using the Chung protocol. It is a silly goal but I want to see how much time I can chop off my 10 mile TT route but figure free speed is free cheap. It just isn't easy to find. It takes some effort. The A in CdA needs some work.

 

[Balor]

Yea, kind of like this:
https://ru.aliexpress.com/item/Cost...e-Helmet-Casco-Speed-Airo-RS/32821344544.html

You can search for 'TT helmet' or 'aero helmet' lot of designs (some are crazier then the other) crop up.
You can buy a heap for peanuts, test ride them and get the real deal of the ones you like. If you care enough .
I'm yet to find a Lazer alternative with a buckle that does not interfere with a head rest. Fortunately, soft cushion of M5 headrests is forgiving of those buckles.

 

[jond]

Bontrager ballista was best aero style helmet according to wind tunnel testing on a df when I did my research. I have it and it’s not hot compared to my giro air attack shield which was the first but ran last in the test.

Of course the helmet is oriented differently on our recumbents and the shield just works seemingly on the giro.

Talk to LarryOz he has tested various helmets on coast downs etc.

 

[Balor]

By the way, among those I've tried, this type of helmet from Ali works the best with a head rest:

https://ru.aliexpress.com/item/2017...-da-Ciclismo-Cascos-Ciclismo/32801876412.html
It is also *looks* decently aero.

 

[ed72]

Bontrager ballista was best aero style helmet according to wind tunnel testing on a df when I did my research. I have it and it’s not hot compared to my giro air attack shield which was the first but ran last in the test.

Of course the helmet is oriented differently on our recumbents and the shield just works seemingly on the giro.

Talk to LarryOz he has tested various helmets on coast downs etc.

Thanks, I read his report from a few years ago. His Casco was 0.18 mph faster if I recall but he had some fogging issues. Thanks

 

[ed72]

By the way, among those I've tried, this type of helmet from Ali works the best with a head rest:

https://ru.aliexpress.com/item/2017...-da-Ciclismo-Cascos-Ciclismo/32801876412.html
It is also *looks* decently aero.

I'm going to check it, eventually

Thanks Balor. I am finding that this aero testing is not so quick to do on the road. Unless it is calm, the results are not as conclusive for small gains. My half pipe is one mile long with a top speed of 38 mph at the bottom but five runs takes about 15-20 minutes due climbing. One run of a baseline and two equipment changes takes about an hour and then time to analyze. I am starting to get an appreciation for the work Larry did on his testing. I am probably fast enough for a randoneur and why bother.....? If I get my weight to where it should be and if I can drop another 0.01 m^2, I can lumber along 1 mph faster on my modest 140 watts. You know what that means on a long event. My biggest likely gains would be to shave and to trim the aero belly but I like to eat. I'm still dithering around with wheels, tires, clothing, and positioning. Pedaling with knees slightly out causes a rather large increase in CdA (for me). Paradoxically, narrow hands is slower than slightly wider position (for me). These effects are much larger than 0.18 mph. My strategy was to pick up the low hanging (and free) fruit before buying any stuff. Since my mother in law moved (she has Alzheimers), I haven't been able to test as much as desired. I am now thinking to just shotgun my approach. Instead of making changes one by one and carefully comparing to a baseline control, I would just guess and make all the changes. I've managed to get from about 0.200 to around 0.163 CdA with educated guesses. The gains are now very small and difficult to be 100% sure of an improvement without sufficient replicates. Stupid stuff like how you hold your head, hands, etc. make a difference. Or one aero covered rear wheel is faster than the other (surprise....404 is faster than HED Belgium covered although the exact amount would take a careful look at calibration of the powertap hubs). It looks like Larry gained 0.025 m^2 with just a helmet, so, it is probably well worth the money to buy me a batch of helmets.

 

[Balor]

Or one aero covered rear wheel is faster than the other (surprise....404 is faster than HED Belgium covered although the exact amount would take a careful look at calibration of the powertap hubs).

How wide are rims in relation to the tires? I guess you know that for a full benefit from a disk you must have it actually a bit wider than the tire in the area of rim/tire interface, and if you want a nice, fat tire, not a skinny 23mm, that dictates a rim that is at least 30mm wide! Covering an MTB trail 29er wheelset seems a good idea (and I intend to do just that eventually).

 

[ed72]

How wide are rims in relation to the tires? I guess you know that for a full benefit from a disk you must have it actually a bit wider than the tire in the area of rim/tire interface, and if you want a nice, fat tire, not a skinny 23mm, that dictates a rim that is at least 30mm wide! Covering an MTB trail 29er wheelset seems a good idea (and I intend to do just that eventually).

Same 25 mm GP4000sii reflex on both the wider HED Belgium Plus and the narrower Zipp 404. I had thought the seemingly puffier rim/tire profile on the Zipp would be slow. The transition from the aerojacket cover to the Zipp has less of an angle than the transition to the less deep HED rim, I suppose this must be it although the actual tire width is 29.6 mm on the HED Belgium Plus and 25.7 mm on the Zipps. These are older, narrow rimmed Zipps. I am just going to trust published wind tunnel data for the front wheel. I do have a 23 mm tire for the rear Zipp to test but I really don't want to get too skinny of a tire plus it is a Supersonic and then I am guessing what the Crr change would be and changing one variable of a time is easier for me. I could be wrong but same tire and also same latex tube and same pressure. The reason I use the steep half pipe in a neighborhood is the high speed should give more aero sensitivity in the data and the slow hill and slower flat part should let me tease out the Crr. I can actually get 1 mph difference in top speed at the bottom just with position. Surprising to me, it looks like the Crr is just over 0.005.....maybe 0.0055 on this road and 0.0043 on a really smooth, one year old asphalt road. Actually shows how important rolling resistance is for us mere mortals on real roads, anyway.

 

[Balor]

I suppose this must be it although the actual tire width is 29.6 mm on the HED Belgium Plus

Isn't it only 25mm wide externally? And it puffs up a 25mm tire up to nearly 30mm? That's huge!.. well, in my case a 21mm internal width rim puffs up a 23mm tire to 26mm.
Should actually work because I have full suspension, though it undoubtedly makes the bike less aero overall than a set of wheel covers... it was never intended to be a 'fast' bike truth be told, being able to cruise at 24mph was a totally unexpected bonus, and I'm very interested how far I can take it.

 

[ed72]

29.6 mm is the width of the 25 mm nominal GP4k sii on the HED Plus rims, I don't know the internal width of the rim itself but they are pretty wide. I have to adjust the brake cable to use them. With butyl tubes, they don't puff up as much. I once made these measurements.....maybe around 1 mm less width.

 

[Gary123]

being able to cruise at 24mph was a totally unexpected bonus, and I'm very interested how far I can tak

It would be unexpected for me also, impossible in fact.

 

[Balor]

It would be unexpected for me also, impossible in fact.

Well...
https://www.strava.com/activities/1725029972/

Admiteddly, I'm getting about 1 "free" mph from passing traffic + the road is very flat and very good (especially by local standards), my suspension I've spend so much resources and 'brainpower' on is totally lost on that road.
Plus, I'm talking about not *easy* cruising speed, but near FTP level effort, which I loath to work at of late. It seems I went low-carb way too late - I'm talking with an endocrinologist, and it seems I'm on a verge of type 2 diabetes based on my bloodwork. I wonder if my resistant obesity is the culprit or a symptom... but I digress.

Back to the aero bits.
My front wheel - 26" 40mm tires (24 spokes, but 2mm) are not the pinnacle of 'aero' to be sure, though rolling resistance seems surprisingly decent (Vittoria tire).
I have a spare wheelset with very cheap hubs, but nice i23 WTB tubeless rims, 23mm inner width, 30mm outer width.
Well, 23mm rated UST tubeless Schwalbe Ultremo (very old, got it for free from a buddy who was clearing out his parts bin) is about 27mm wide on that rim (though 21mm high), and it makes for pretty much PERFECT tire/rim interface if you ask me - rim a bit wider then the tire, tire pretty much 'blends in' into the rim. (For 28mm tires, Enve makes high-profile carbon rims with actually 25mm inner width).
I can email you the pics how it looks like on the rim if you are interested, Ed. Covered, it seems like pretty much a perfect aero disk wheel... if aerodynamics was ever predictable, that is.

I don't like the hub much, but it spins relatively well after I've adjusted the cones, and I cannot care less about it's weight.

 

[Gary123]

I'm envious. I may have to do some "testing". My fastest setup was bacchetta with seat slammed back and spinergy wheels with 23's. Now I'm a little scared of old spinergy rev X's and cruzbike is faster climbing although average speed is about the same. I'm usually in the 18-19 range unless I'm killing myself.

 

[Balor]

I'm envious. I may have to do some "testing". My fastest setup was bacchetta with seat slammed back and spinergy wheels with 23's. Now I'm a little scared of old spinergy rev X's and cruzbike is faster climbing although average speed is about the same. I'm usually in the 18-19 range unless I'm killing myself.

Well, it took me about 4 years of 'bent adaptation', experimentation and actually diving head-first into esoterica of frame design and bicycle dynamics, so I guess some positive results are no less then deserved . My first bent was (also DIY, of course) RWD Azub Max clone I was about HALF as fast on compared to my fairly upright chinese carbon niner with 2.35" tires, and any uphill was a pure torture. It was very good that I found out about MBB bents and was able to get one (imperfect though it was).
I was always heavy but relatively powerful - which is still nothing compared to Ed's achievements, 54 hours PBP is something I can only dream about...
My own 600k took 36 hours and my butt "said": Never again! At least, not on upright.

I also have some room for lowering the seat, but I'll have to switch to a 3D printed mount... and I might start getting interference with lower 'lip' of the seat - due to very low bb that I actually require so not to get numb feet.

 

[ed72]

Balor makes an important point about adaptation. Everyone talks about getting bent legs, but it is more complicated and it does take time.

I have researched and experimented with a variety of different training techniques. Anyway, it has taken me one full year of hard work and I am still not to my upright power levels but lots of progress. I can cruise easily at 24 mph, it only takes around 180-190 watts depending on clothing, temps, and humidity. 180-190 watts is simple on an upright for me but it only gets me around 20 mph. 180-190 watts was nearly impossible for me on a bent six months ago. Between different training techniques and improving my aerodynamics a lot, I went from 26:20 to 22:05 on a 10 mile time trial. It has been a lot harder than expected but then again I did have shoulder rotator cuff surgery and also major sinus surgery, too.

Edit: Shoulder and neck issues keep me off a Cruz, I know it would climb better but reaching for the bars would be too painful. I think the V20 would be a better PBP bike but I'll make due on what I have in August 2019 at PBP.