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Live chat replay: Cervélo’s aerodynamicist Ivan Sidorovich

Ask questions of the engineer who cheats the wind on March 27, 1:30 p.m. EDT

The Cevélo P5 is the bike Ryder Hesjedal rode to his Giro d'Italia victory in 2012
The Cevélo P5 is the bike Ryder Hesjedal rode to his Giro d'Italia victory in 2012

The air is always in your way. One man who tries to beat this invisible bit of resistance that every cyclist faces is Cervélo’s aerodynamicist, Ivan Sidorovich. He started with the company roughly four years ago. In that time, he’s developed Cervélo’s in-house computational fluid dynamics system, a computerized wind tunnel that allows the company to develop wind-cheating designs. He worked a bit on the company’s S5 aero road bike, but was instrumental in the development of the P5 time trial bike, which Ryder Hesjedal rode to victory in the final stage of the 2012 Giro d’Italia.

Join us Wed., March 27, 2013 at 1:30 p.m. EDT when we host a live chat with Sidorovich. Find out how he can make you go faster. Bring your questions about air foils, aero bikes and beating the wind.

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Replay of the live chat with Cervélo’s aerodynamicist Ivan Sidorovich

Wednesday March 27, 2013
1:25
Canadian Cycling – Matt: Hello everyone. Welcome. We’ll be starting in a few minutes.
1:26
ivan sidorovich: Hi everyone
1:29
Canadian Cycling – Matt: Hey folks. It’s good to see that some of you are ready with questions. We’ll get to some of them after an intro to Ivan and a few of my questions.
1:30
Canadian Cycling – Matt: All right. Let’s get going…
1:31
Canadian Cycling – Matt: Since Cervelo’s inception, the company has been defined by innovation. It’s focus on aerodynamics for time trial and road bikes is part of that innovation. Today, we have a member of the Cervelo team, Ivan Sidorovich. He’s the company’s aerodynamicist. We’re going to discuss some of the work he does to cheat the wind.
1:31
Canadian Cycling – Matt: Welcome Ivan. Thanks for joining us.
1:31
ivan sidorovich: Nice to be here!
1:31
Canadian Cycling – Matt: First, Ivan, can you tell me a bit about how you became interested in aerodynamics?
1:32
ivan sidorovich: Since I was very young I’ve been fascinated by airplanes and going to the airport was my favorite pastime, that is the reason why I became and aerospace engineer with specialization in aerodynamics.
1:33
Canadian Cycling – Matt: What is some of the work you did in the field before coming to Cervelo roughly four years ago?
1:34
ivan sidorovich: My first big break came when Chrysler hired me as a power-train CFD analyst. With a bit of spare time on my hands, I decided to enroll on a par-time masters program where I performed the aerodynamic analysis of a Chrysler sedan.
1:35
Canadian Cycling – Matt: So you’ve moved from cars to bikes. How do you like working on the two-wheeled machine?
1:37
ivan sidorovich: To be able to a part of the whole process, from ideation, to design, to CFD and wind tunnel design to a final product has been very rewarding.

I’m not just one more cubicle!
1:39
Canadian Cycling – Matt: Nice that sounds like a cool environment. You’ve mentioned CFD. Can you tell us a bit about computational fluid dynamics? How do they factor into the design process?
1:40
Canadian Cycling – Matt: While Ivan is composing his reply, I’ll share a few pictures of the new Project California bike, the Rca.
1:41
ivan sidorovich: At the core, CFD is a numerical method that allows a solution to the fundamental fluid dynamic equations. In this manner, we can simulate “real” physical condition in a virtual environment. Which allow us to tinker with crazy shapes and concepts before we go to the wind tunnel for final validation.
1:41
Canadian Cycling – Matt: So CFD helps you design for the wind tunnel? You still test in the tunnel afterwards?
1:42

Ryder Hesjedal riding Cervelo’s Rca

1:43
The head tube of the Rca in profile
1:44
ivan sidorovich: Both tools have advantages and disadvantages. CFD is good at testing “out of the box” ides. However, when it comes to swapping components (wheels, forks, etc) and final checks as well as competitor benchmarking, the tunnel is unparalleled.

So YES, we cannot skip the tunnel, we need both tools to work in harmony.
1:44
Canadian Cycling – Matt: Thanks Ivan. And now, let’s take some for our readers’ questions.
1:44
Comment From Guest
Hi Ivan, How important are aero wheels for improving the aerodynamics or speed of a bike?
1:45

Cervelo’s Project California bike: the Rca
1:47
ivan sidorovich: In addition to the frame, aero wheels are very important for performance. If you compare a trainer set of wheels to a dip rim, the advantages can be in the order of 100g or more which translates into 10w of power savings.
1:47
Comment From Brian Crounse
How confident are you that wind tunnel findings are relevant to on-road conditions? I’ve done some bicycle-relevant tunnel testing (wheels); results always seemed very sensitive to details that may or may not be representative of the real world. How do you validate wind-tunnel findings?
1:49
Canadian Cycling – Matt: While Ivan answers Brian’s question, I’ll post some of Cervelo’s data on aero performance of frames.
1:49

Aerodynamic drag comparison: Cervelo Rca and others
1:52
ivan sidorovich:
Our wind tunnel protocol stipulates that we test with a dummy, that is, we are trying to test rider+bike. In addition, we also tested a moving legs mannequin that confirms that DZ’s fixed legs position best represents the overall moving legs cycle. So we are making the right steps towards translating wind tunnel data into road data.
1:52
Comment From Howard
Every bike company claims that theirs is the fastest bike and has wind tunnel data to back it up. How does “Joe Shopper” know what to believe or what to look for in those numbers or test protocols?
1:53
Canadian Cycling – Matt: While Ivan answers Howard’s question, I just want to add to his comment above. Ivan referred to DZ. Does anyone know who or what DZ is?
1:54
Canadian Cycling – Matt: Bueller?
1:54
Comment From Guest
foam DZ, the Stable Zabriskie dummy
1:54
Canadian Cycling – Matt: That’s right, Guest!
1:55
Comment From Guest
Jimm Matin’s “Validation of a mathematical model of cycling power” has proven wind tunnel valid to real world riding.
1:56
Canadian Cycling – Matt: They have a dummy of David Zabriskie to substitute for a real rider in the wind tunnel.
1:56
ivan sidorovich:
To me it comes down to the level of precision that your tools have. We take pride in the amount of R&D work that we do. In fact, some of this R&D work included testing several wind tunnels. I cannot comment on other wind tunnels performance, but I can say that we test in the best tunnel for bicycle aerodynamics, that is LSWT in San Diego.
1:56
Comment From Craig
Does a water bottle in a cage on the downtube make a frame more or less aerodynamic?
1:57

The down tube of the Cervelo Rca
1:58
Comment From Brian Crounse
Why is drag vs. yaw so asymmetric? (re: graphic @ 1:49)
1:58
ivan sidorovich:
Rarely a bottle on the DT will improve aero but if the frame is design correctly it can certainly minimize the penalty. That is the case of the S5 and P5.
1:58
Andre: Brian, the drag is asymetric because of the drive train on one side of the frame.
1:59
Comment From Jim Gourley
The data from the P5 white paper indicates an approximate 5% improvement over competing superbikes. Previous manufacturer white papers claim similar improvements. As the absolute drag numbers decrease, so does the relative 5% improvement. Are we reaching the most optimized design?
2:00
Canadian Cycling – Matt: Wow. These are some really great questions. Thanks folks. We’ll try to answer as many as we can.
2:01
Comment From Jim Gourley
The bike equivalent of “Moore’s Law,” so to speak…
2:02

The Cervelo P5 time trial bike
2:02
ivan sidorovich:
It is true that as you get more familiar with the technology that you have, you tend to reach a plato in terms of performance. However, I don’t think that we reach that level yet. In fact, we are in the infancy period of what CFD can do for us. Also, there are more an exciting technologies coming up that will certainly help to elevate the glass ceiling.
2:03
Canadian Cycling – Matt: More exciting technologies? Can you tell us what they are?
2:03
ivan sidorovich: nope, sorry!
2:03
Comment From Simon at The Tri Store
Theoretically, how much better could a frame outside of the Luddite UCI regulations, be?
2:03
Canadian Cycling – Matt: Ah. Top secret, eh?
2:05
Canadian Cycling – Matt: Simon, I’m guessing you are referring to the 3:1 rule? That the depth of a tube cannot be more than 3x its width.
2:05
ivan sidorovich:
You guys are putting me on a tight spot here, but the logic is there. Less restrictions, more room to explore, more aero…
2:05
Comment From Bob
Which will make me more aerodynamic on the bike, good aero wheels or an aero helmet?
2:06
ivan sidorovich:
I’d go for wheels, for sure!
2:06
Canadian Cycling – Matt: Ivan’s being diplomatic! The UCI regulations are the rules designers must play by. The metaphorical tennis net.
2:06
Comment From Brian Crounse
Who has the 2nd-most aero frames? (I presume you’d say Cervelo is the best)
2:08
Comment From Simon at The Tri Store
yes, aerodynamically and wind ‘handling’, so 3:1, double triangle and so on
2:08
ivan sidorovich:
All I know is we have the fastest frame, who cares about the second.
2:08
Canadian Cycling – Matt: Bah-boom!
2:09
Andre: How much of a difference will aerodynamics play when riding in a pack?
2:10
Andre: What I mean is, does riding in a pack negate much of the advantage one gets from an aero frame like the S5?
2:11
ivan sidorovich:
Just because your effective wind velocity is diminished by the “drafting” effect, it does not mean that airspeed is zero. In fact, it will still be significant so aero road bikes like the S5 will still give you a significant benefit.
2:11
Comment From Jim Gourley
I thought it was interesting that you have an automotive background. I assume you’re familiar with the Kamm effect designs evolved by Ford, which other car makers adopted and Trek copied on the Speed Concept. Simon Smart has also gone with “chopped off” airfoil designs, but Cervelo maintains the superiority of NACA profiles and seems to have succeeded with the P5. Is a traditional NACA airfoil the optimal shape, or have we just not found the right way to improve on it yet?
2:15
Canadian Cycling – Matt: To Jim’s question: the discussion is about the airfoil shape, like a traditional airplane wing, and the truncated airfoil (Kamm tail).
2:16
ivan sidorovich: Long answer, here it goes.

I think that the best way to answer the question is to think of the bike as country that has very different geographical regions such as rain forest, desert and tundra. If you were to travel to all of these destinations on one trip you would not take just one set of clothing, you need several.

This is exactly the situation within a bicycle+rider system like the P5, we have different regions and we need different types of airfoils depending on the “weather” conditions, as an example , P5 sections are not the same in the head tube (full foils), down tube (full top, truncated bottom), seat tube (fully truncated) . What is important to know is that we did our work and we chose the foils best suited to the flow conditions, hence maximizing performance.
2:16
Canadian Cycling – Matt: Nice. That’s a great answer.
2:17
Comment From Howard
Simple one here – Does aero trump weight?
2:18

The Cervelo Rca in the wind tunnel with the David Zabriskie dummy
2:19
ivan sidorovich:
Well, I’m bias towards aero, so I’m the wrong person to ask.
Aero is always on, so aero over weight all the way!
2:19
Canadian Cycling – Matt: Great. One more question from a reader. Jim asks: “Some folks here may not realize that there are different forms of CFD. There are various ways to tackle creating the “mesh structure” of a bike model and then calculating the airflow around it. Do you think that the greatest improvements in bike design lay in more powerful computers or refining the way we crunch the equations?”
2:21

Aero features of tube shapes
2:22

Aero features of the Squoval down tube
2:23
ivan sidorovich:
With regards to the hardware, yes, computing power has become cheaper, hence allowing us to crunch very big cases in a shorter time frame. However, not all CFD codes are the same. The better your CFD solver the better your solution will be in terms of results and ease of use.
So you need both, a good CFD solver (we have the best in the market CCM+) and a powerful computer.
2:24
Andre: One more from a reader, Brent, he ask “I believe I read an article by someone at cervelo that level thumbs and arms on a TT bike were most aero. My own experience is showing that its more comfortable to turtle head with hands up more (not extreme praying mantis but up) and wondering if they still find that. Seems most P5 riders are level hands… Is arms and thumbs flat universally faster, or does it matter more how the body reacts to positions?”
2:25

The head tube of the Cervelo Rca
2:27
ivan sidorovich:
You have to remember that aero is a combination of various factors like comfort (you need to finish the race), they type of add-on you have (bottles, fuel, computers, etc) and so on.
In general it is a good setup but I would say that riding position is a case by case approach.
2:27
Canadian Cycling – Matt: To add to Ivan’s comments on CFD. In a earlier discussion we had Ivan mentioned that CDF allows them to protype designs more quickly. Take more risks and be more creative.
2:28
Canadian Cycling – Matt: That’s all the time we have folks. A big thank you to Ivan for chatting with us. And thank you for all of your questions. Be sure to tune in for future discussions here at Canadian Cycling Magazine.
2:29
Canadian Cycling – Matt: Thanks Ivan.
2:29
ivan sidorovich:
Thanks, it was very nice to talk to all of you and hoping that you keep enjoying he Cervelo experience
2:29
Comment From Jim Gourley
thanks Ivan!
2:30
Andre: Thanks everyone for joining us!

Writer: Canadian Cycling – Matt

Live chat with Cervélo’s aerodynamicist Ivan Sidorovich
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