Proper position = more aero than any frame set.

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Jim Manton / ERO Sports

Ok, it's going to take some time for me to wrap my head around the Felt aero head tube concept, then.

Are you saying that 111mm of 3cm diameter head tube has less drag than 111mm of 2 NACA0030 (or NACA0012 for non-UCI) aero risers? Is there any public data on this?

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AndyF
bike geek

The Cervelo P5 white paper has some mention of finding that going wider on the head tube got more aero with the Zabriskie Mannequin aboard.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Additionally - I sometimes find that having to use low stack bars precludes the use of a BTA (if the rider also has narrow elbow position). Not having the BTA may force bottle on to the frame which wipes out a lot of frame design gains. Would rather have low stack frame and ability to use bars (not that there are many good bars) to accommodate rider specifics taking both position and fuel carrying into account.

Bingo.

Since Superdave is awesome and responds to this thread (notice no other manufacturer of bikes is responding but certainly watching), let's use the old B-Series geometry as an example. When you combined the old geometry with a low-stack Devox bar, well, even I have to admit that combination was a pretty long/low for most people. But hey, that B-16 with the high-stack aero bar, and basically two top caps (low and high were included, which is also pretty awesome of Felt by the way)...now that was a bike I could fit to almost anyone (and did). Would I sometimes need a low-stack aero bar for that bike? Sure, sometimes, but that would then be the outlier.

Unfortunately, manufacturers have now raised the stack of their frames AND combined that with high-stack aero bars. That was just too much. Properly fit, these bikes fit the outliers, the rest just simply can't get low or long enough. Give me the old geometry (B-Series or Cervelo P-Series) with a Bayonet III bar - I'm in fit heaven. If you need higher, I'll pedestal them up to get them there, no problem (most bars are more aero when pedestaled anyway).

Again, the problem is not with the manufacturers; they are simply producing bikes they can sell. The reason they need to build them higher is where the problem lies, and that's with the bike shops who fit these bikes. Bad bike fit is to blame. Turning bike fit into a marketing and sales tool, that's the problem. If good fits were being conducted, and demand for lower-stack bikes rose, manufacturers would happily build them. Simple.

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Jim Manton / ERO Sports

I hear you. I want to get lower on my SC7... already at -25 degree and eeing a -35 stem. A Small frame would require a longer stem than I'd prefer. The longer the stem, the more weight over the front wheel and you handling get a little wonky and you lose more braking performance.

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TrainingBible Coaching
http://www.trainingbible.com

Yes, I totally agree. Thank you, SuperDave, for sharing your knowledge. It might get challenged, but it is very much appreciated!

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AndyF
bike geek

I wouldn't say you lose nothing by pedastaling armrests, you keep a very low base bar position. Also, you make it so that consumers need to pic a certain style of aerobar. There is also the whole aesthetics thing, which is important to lots of people(have you ever seen a nosecone shiv setup really high...shudder)

You imply that anyone who isn't slammed on a p4 is a parachute. Many of us have proportions which allow us to ride very complimentary basebar and aerobar positions on normal stems on middle stack bikes with a flat back and turtled head. Ever seen Rapp on his tall/narrow shiv?

The point is that pretty much all the bikes fit the same. The only difference is aerodynamics and price. How many more bikes with the same characteristics do you need on the market?

Rapp has really long legs and barely fits on Shiv. He is one of very few people I've ever seen who has a decent fit on a Shiv. You're using one example to represent many.

How about you post your pic and drag numbers?

They would sell another bike to me if they made long and low. My profile pic shows me in my very comfortable long and low position and although I've not done the wind tunnel or Chung'd I am confident that it's pretty fast. Because I haven't been able to find long and low to facilitate my 51.0 cm stack and 48.0 reach, I haven't upgraded my 51 cm P3C. I use a 135mm -35 degree stem to get my pads that low and the USE Tula bars have the pads as low as I can get them. As others have mentioned I've looked for a P4 and also have some interest in the Norcom Straight, 48cm NP3, Giant Trinity, and Felt DA with 0 rise stem but I think that is what we I am limited to at this time. I agree with others who have argued that it is hard to justify spending money to replace the P3C when the gains would be marginal at best. At this point I am waiting to see what Giant does with their new TT frame.


Regards.

Jack,

This is exactly how the DA is configured. The Bayonet handlebars are flippable. The low downward sloping position is for a lower "drops" hand position on the brake levers and the high position is intended to replicate the "hoods" position for the brake levers. The bar is symmetric so it offers two hand positions in one bar. It's also modular in construction so we've configured it so it can be made in widths as narrow as 30mm or as wide as 48cm. It has even been reconfigured with "drops" like a road bar for use on the track w/o brake levers.

But in the case of low-head tube, thin arm rest/extension risers you are only looking at ways to reduce frontal area specifically but these efforts do not increase lift at yaw typically. You need a sail or surface area to get lift and minimizing said surface area has marginal benefits for high-yaw condition rides/athletes i.e. most triathloners.

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

the head tube is the part of the frame that the fork steering axis passes through. I think you are thinking of steer (steerer) tube.
(28.6mm O.D. convention)

The head tube on the IA is not round and closer to 200mm at its widest point, not 30mm.
Look for a link to the patent applications. I don't think we're openly sharing this data; in fact, I think we're protecting it.

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

Can we call it a head tube assembly? Or head tube interface? This: http://upload.wikimedia.org/...ame_met_balhoofd.JPG


Ok, but the question in my mind still remains: more head tube or aero risers? How can NACA aero risers not be more aero than almost any other shape?

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AndyF
bike geek

When I started on Slowtwitch some 13+ years ago I knew it all. Now that I've got 13 more years of experience and knowledge, I'm convinced I know very little.
Sometimes there are constants, like this gem:

SuperDave

Feb 26, 03 8:12

Post #10 of 11 (897 views)
Re: For your $3000...? [denewone] [In reply to] Edit | Delete | Quote | Reply

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If your price tag is $3000, start there and work backwards. Perhaps you can afford a P3 frame with HED wheels, if that is $2300, you may be able to finish off the bike if they built it with 105, and FSA cranks. The premium frame and wheels are going to make the greatest gains in your time, riding on a Dura Ace brakeset or front derailleur just makes you pretty. The components are going to wear out part by part and you can make the switch to Dura Ace then, a small outlay of cash at each occurrence. A good pro shop would be willing to not just switch components to make the bike fit, but make the bike fit your budget. Gurus are pretty, Cervelos are fast.

SuperDave
In many other cases what I thought to be a rule (less is more) is often just a much too narrow view of a much larger topic (more is less). I've learned this in many subjects such as tube shapes, training volumes, etc...
I'd encourage challenging any/everything you read that contradicts what you know, think you know, or felt was obvious or an unwritten rule.

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

I totally agree, SuperDave. But data is the only thing that changes my 30 years of experience at this point.

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AndyF
bike geek

Think about this one, given identical equipment otherwise, what do you think is more aerodynamic on a -20, 0, 20 yaw sweep at 40kph:

58cm XL IA with zero arm rest/extension risers:


Or a 54cm with ~40mm of risers to get the same pad stack and rider position:


-SD

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https://www.kickstarter.com/...bike-for-the-new-era

Totally agree and IMHO I think is a hugely overlooked aspect. There are many bikes you can get long and low (particularly classic P3, QR Illicito, QR CD0.1..) on but weight distribution is a very very valid point.

90% of the brain's activity is used to balance your body within the gravitational field of earth. If your body is distorted mechanically (off balance), it begins to effect the other 10% of the brain's activity, which controls all the other body functions such as breathing, digestion, or thinking.
The less work muscles pertaining to posture and balance have to do on the bike the more one can focus and control the muscles providing power / movement in cycling this is why core stability is paramount to good cycling technique. It is important to bear in mind that many professional cyclists inevitably acquire this “on the job” through years of acclimation, as opposed to specific training.
You are looking to avoid several conditions that can occur whilst cycling, these being “Lower Crossed Syndrome” as proposed by physical therapist Vladamir Janda (a combination of tight hip flexors and a tight lower back, paired with weak abdominals and weak gluteals) and “Upper Crossed Syndrome” (excessive weight bearing forward leading to a tendency for the elbows to lock up in order to bear the body weight and greater loading being placed upon the neck and shoulder musculature).
Evidence of prolonged isometric contraction in postural muscles due to excessive weight bearing over the front of the bike in upper body, is never a good thing, especially in females, why?.... Sherrington’s law of reciprocal innervation states that for every neural activation of a muscle there is a corresponding inhibition of the opposing muscle.

Many years ago Dan / Slowman proposed some % split front vs. back in terms of weight distribution that I think are spot on guidelines and I'd go as far to suggest that that thinking probably influenced some the geometry design in early QR bikes....

My 2c.....

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David T-D
http://www.tilburydavis.com

Need more details. Lots of geometry is changing between those 2 setups. Rider or riderless? The same negative forearm angles? The same bikes as in your pics? Even the brakes?

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AndyF
bike geek

I wish I had seen this further back in the year, not a great time to get a new fit before IMAZ. I am sure I will be scheduling something at the beginning of the year... I want to try to get lower, as I think it will be more comfortable and faster.

100% the same rider position
same saddle height
same pad stack, same pad width

The photos were just for reference to get you an idea of the differences between a flat-stacked bar on a big head tube and one with 40mm of risers on a 4cm lower head tube to give the same resultant bar height.
Apples to apples on the component spec and rider position, the only thing that would change is the frame size and arm rest and extension riders; other equipment stays constant.

Essentially I'm asking if you think the smaller bike/head tube has less drag. I think that is what you are saying when you ask for a low frame with lots of aerobar riser/pad stack. And you are probably right when most frames are concerned, certainly you'd be right in the case of the photo you shared.

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

It's *almost* what I'm saying. I'm saying that you leave all the other geometry the same so that stems and bar lengths don't change. The only element I would like to see different is the height of the head tube. I'd like to see a low frame stack, leaving all other bike dimensions the same (seat tube angle, top tube length, etc..) With that lone change, I'd like to compare how a tall head tube compares to more armpad riser stack. Preferably between +/- 7deg yaw. (Remember, we measure yaw "in the wild".)

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AndyF
bike geek

Never underestimate interference drag. The Speed Concept doesn't use a monoraiser just for show.

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____________________________________
Pain is inevitable. Suffering is up to you.

Just to answer your very legit question... I would say the smaller head tube setup would do better at low yaw, while the taller head tube has more sail effect going on, so it will do better at higher yaw. Let's see how I do! :-)

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AndyF
bike geek

Nailed it.

There is also the interference referenced above and when you decide to go to risers you need to use lots of them (depending on many factors such as hand position) to achieve the gain you are talking about.

You need enough separation that the air sees a blob of hands/arms and a nice clean airfoil, not a big blob with the lower half having clean fast air. Lift in the y-vertical direction doesn't help you :)

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

Ok, so those are some real nuggets of wisdom, SuperDave. For anyone out there who want to be faster, this is information you can really use!


I'm thinking that this is the reason we often see that a little uptilt on the forearms, when used with armpad risers, really helps lower aero drag. You're moving the hands out of the airstream that's hitting the risers, maybe, SuperDave?

Thank you for your valuable insight. I certainly will use it with my own testing, and it gives me some interesting ideas for track pursuit, too.

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AndyF
bike geek