Downhill Time Trials

So last week I went to InterBike with Boyd Cycling. It was a pretty cool experience, really a thing I always see on all the bike tech sites out there but finally going there is a totally different experience. First of all, the coverage that all the online venues covering the event combined don’t even begin to scratch the surface of the number of exhibits there. It’s pretty overwhelming. For instance there are foreign sections, China, Japan, Italian “villages” that essentially get no media coverage. There was a HUGE e-bike section of the show as well (which also seemed to be the best funded). However the best section, in my opinion, was the “Urban” village. This encapsulated everything from custom cruisers, fixies, to folding bikes. By far these were the most creative and off the wall exhibits and products.

Our booth was tucked into the “Triathlon” section…..yeah yeah. I spent most of my time hand modeling for BikeRadar in the booth:Boyd Eternity Hub
Tubeless Nut

Hand ModelAnd also showing off our one gimmick:

Boyd Cycling Wheelset

Climber’s Wheelset

Yes the most entertaining part of the show for me was to tell people to go pick up our “Climbing Wheelset”. Weighing in at 15 lbs, this thing could serve as a flywheel for an old school steam tractor. There’s a lot of hype around 3D printing right now and a lot of questions were fielded at the show about why we didn’t go that route. The reason is two fold: 3D printing is finite and not continuous. This means that the finish for a curved surface would be stepped surface which would require further finishing (another possibility for imperfections). Additionally 3D printing is typically done with plastics which do not carry high loads well (think spoke tensions and tire pressure).

Why does all that matter? The Aerodynamics of bicycle wheels is converging onto a single (correct, sorry reynolds) design. This means that the variation between the best aerodynamic wheel-sets are getting smaller and smaller. Aerodynamics is VERY sensitive to small variations. Something like 20 psi vs 100 psi in a road tire or low tension (bent) spokes could also greatly alter aerodynamic drag results. So by doing a solid Aluminum wheelset in the wind tunnel we could model a REAL wheel.

Why go through all this trouble anyway? If you see a wheel company showing their slick carbon wheel in the wind tunnel, it means they’re testing a finished product (cough #AeroIsEverything cough). It’s well known carbon molds are very expensive, and if you’ve made the mold, you’re pretty much married to the shape you created, so you’re either wasting money and translating that stupidity to high costs to your customer, or you’re just going with a bad design. This prototyping allows us to make small design changes or evaluate several design at a relatively low cost before making the costly investment in a mold.

Mistakes are how you learn, so it’s better to make i

Bike Wheel Wind Tunnel Testing

Aluminum Prototype in A2 Wind Tunnel

nexpensive small ones than expensive big ones.

Also see my other post (excessive rant) on why Wind Tunnels are absolutely necessary.

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Why I kinda hate NAHBS

First of all let me say I love NAHBS, the bikes that are showcased there aren’t as much bikes as they are pieces of expression. Each one as unique as the builder that made it. They’re pieces of art made in the medium of the bicycle. I personally take the bikes as that.

I love these kind of bikes, my favorite bike is steel, but the fact of the matter is that no matter what you do, there are limitations to the metal bikes. There is good reason why top cyclists all race on carbon, why all new aircraft are almost 100% composite, etc, it’s just better for the application. If Eddy Merckx were racing today (for some reason we seem to romanticize that era in an Amish sort of way), he would be on a carbon bike from Asia. These craft bike thrive in areas where absolute performance of the frame isn’t as important, Cross, city bikes, Fat Bikes, etc.

NAHBS is absolutely part of the larger “craft” movement. And it’s interesting where “craft” industries really thrive. There are some cases where you pay more and legitimately get a better product, like food and beer. These industries make more practical sense because large producers use cheaper inputs (ingredients, processes, etc) to make a uniform and inexpensive product. There are other cases where you’re not necessarily getting a better (functionally speaking) product, but something more unique and artistic, like the stuff at NAHBS. You’re paying just as much for your bike to be produced with cheaper materials and older production techniques, not because you’re interested in functionality, but because you want the bike an expression of yourself.

Once carbon production has become easier and cheaper, you’ll start to see more ‘craft’ carbon shops coming into the NAHBS sphere as well. This is because steel or aluminum isn’t the heart of the NAHBS, it’s just the medium. It is relatively easy for an individual to master the art of building a metal bike, which means that bike is the individual’s creation and expression, thus most bikes at NAHBS are metal. Carbon bikes are more complex.

It takes a team to build a carbon race bike, not an individual. This means that an individual’s vision must match up the other people working on the bike, there is not yet room for much expression. This does not mean that the Engineer creating material layups is not a master of their craft, or the factory worker who must meticulously set up the layups is not passionate about their work, or that the designer who creates the paint scheme does not have vision, but these people must come together to create a single vision for a product that is beautiful AND functional. Just because you don’t know the names of the people who built the bike doesn’t mean they are not craftsman.

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Wind Tunnel vs. CFD

So after getting a prototype made up we finally made it to the wind tunnel yesterday up in Charlotte. The A2 wind tunnel is a bit of a commercial wind tunnel, renting out wind tunnel on a time basis. If you read any cycling publications you’ve seen its fans as backdrop for any number of “Aero” tests. It was a really nice facility. It was an open circuit wind tunnel that was sized almost perfectly for bicycles (although maybe a bit small for cars). It was a really professional facility.

We ran our prototype vs a few of the top aero wheels currently in the US with VERY good results, but we can still use a little refinement.

A2 Wind Tunnel, Aero Rim Prototype

Our Uber Lightweight Prototype Rim in the Wind Tunnel

On the way back from the wind tunnel I had some good car time to think about why my CFD was missing some important things that we were seeing in the model. That’s when I stopped at a bike shop and happened to start talking to a bike builder and we got on the topic of CFD and wind tunnels. I mentioned that we did CFD analysis on a bunch of rim designs before heading to the wind tunnel with a prototype, he looked at me incredulously that we would even consider wasting our time at a wind tunnel when we could just model everything in CFD.

I just about threw a chair at him.

Yes computers now are very powerful, and a lot of CFD out there is VERY good at approximating scenarios. But, CFD will never replace a good wind tunnel test, ESPECIALLY with something like bicycle components. There are a few reasons for this.

First of all is Reynolds number similarity in the wind tunnel, which basically means matching accurately simulating flow phenomenon in a wind tunnel. Essentially you want your Reynolds Number and Mach number to be similar between your model in the wind tunnel and real life. For aircraft and rockets, this is very difficult. You cannot put a 1/50 scale aircraft in a wind tunnel and run it at flight speed, that would reduce your Reynolds number by a factor of 50 relative to real world, changing all the flow phenomenon. Your alternative is to increase airspeed by 50 times, this obviously is very difficult to physically do for any flight type air speed, but it will also entirely change the mach regime your model is in, rendering your model useless. Bicycles on the other hand are VERY easy to put in a wind tunnel. You can put full sized models in a relatively small tunnel, then run them at real world air speeds, giving  you essentially real world drag results.

Second is that fluid flow, specifically turbulence is INCREDIBLY complex:

“I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic” – Horice Lamb (1932) British applied Mathematician

 

“Perhaps the biggest fallacy about turbulence is that it can be reliably described (statistically) by a system of equations which is far easier to solve than the full time-dependent three-dimensional Navier-Stokes equation”  – Peter Bradshaw Professor of Engineering @ Standford University

It might seem that bicycles, traveling at a relatively low speed of 20-30 mph are simple things, but the fact of the matter is that there are a ton of very complex things going on in the bike system. Take spokes for instance. They are not simply wires traveling through air, they are rotating, and they are small relative to the rest of the system. This means that they create entirely different types of flows than the rim. There’s also the interface of the rotating wheel and the fork, the stationary ground. Don’t even start on the body of the cyclist (which accounts for 80-90% of all drag anyways).

The solution to this is approximation. In every field of complex engineering we try to break up the model in to manageable parts, then figure out the interactions between these parts. Currently I’m modeling the rim shapes in a 2 dimensional domain. This has some very obvious shortfalls, but to run an accurate model of a 3D rotating wheel (just the front), is beyond the computational power that I, and probably most bike companies, have on hand. It is a light model that allows us to run through a relatively large design space with essentially a souped up gaming computer. That’s one of the reasons why we go to the wind tunnel in the first place, to refine the CFD. Yesterday I found out that my model was predicting the performance of some of the wheels incorrectly, and now that I have other data to reference the CFD against, I can refine the model.

There’s nothing wrong with approximation, it is how design is done. However if you forget that the model within your computer is just a model, you will make missteps or worse. CFD a.k.a Cleverly Forged Data, Colorful Figure Delivery, etc is great for marketing, it shows that you have made the steps to improve your product methodically. However it is very easily altered to suit your needs, I can make a CFD model show that our product is better than brand X easily with the right assumptions and models. You will never have a fully realized fluid model of a bike or any other complex design, in sports or aerospace. In order to close the gap between the simplified CFD world we work in and the real time gains on the road, the wind tunnel will never be replaced.

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Taking a break from the Cube-Farm

I know I know, JUST had a post extolling the greatness of commuting by bicycle to work and how it can save you SO much time in training that you can race the Pro/1 division while working a full time job.

Well I just quit my engineering job.

Alright just kidding…I didn’t really quit, but am going on a “Leave of Absence” to focus on cycling and today is my last day.

This had been brewing  for a long time. After a lot of discussion with family, friends (thanks for putting up with all my fretting), and co-workers I finally took the deep breath and had the talk. I had been going back and forth with work a few times about ways to make this work: through either part time, or remote work, but ultimately it was decided that LoA was the best route for everyone.

My co-workers/managers was actually very supportive of me taking time off (contrary to any nightmares I had before talking to them). They didn’t find it that odd that I wanted to leave my engineering desk job to try my hand at being a professional athlete. I didn’t want to have to describe how much less glamorous being a professional cyclist is than being say a pro baseball player, but hearing them say that made me feel pretty good regardless.

I’m really happy and excited about this, I’ll really be able to focus on the cycling 100%.

I’m also pretty psyched to be doing it with the Smart Stop guys too. The team camp gave me a lot of good vibes about the guys on the team and the goals they’re trying to accomplish.

So today is my last day in the cube farm for a while. Tomorrow I’m flying out to Arizona for the Tucson Bicycle Classic, then it’s off to San Dimas, followed by Redlands!!

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Some Perspective (not bike racing)

Awesome video, narrated by Neil Degrasse Tyson who is a generally awesome dude, about why we still need NASA and space exploration: to gain some perspective

It’s sad that the most visible thing NASA is doing now is transporting retired space shuttles around for cool photo ops:

In related space news Promethious continues to astound with how little Hollywood knows about how space travel actually works. Here’s a trailer…I’m going to warn you it’s pretty intense and scarry:

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