Why test bike wheels at 30 mph if I only ever ride 20??

I’ve heard this more then a few times:

“How many people ride at 30 mph? I’m not riding in the Pro-Tour, why do I care if a wheel is faster at 30 mph if I’m riding 20 mph?”

Because you care about aerodynamics, that’s why. And 30 mph is how you determine what is Aerodynamic.

In all of the analysis we’ve done CFD domain run speeds were set at 30 mph. Not only is this the de-facto industry benchmark but it gives you a nice representation of the developed flow structures.  Reynolds Number, which is a non-dimensional indicator of how a flow behaves (mainly laminar flow vs. Turbulent) is the indicator for which kind of flows you should expect for a given object flying through the air. For bicycle wheels the flow ranges from 11,000-650,000 (20mm rim @ 20mph and Full Disc at 30mph). Flows (of any kind, water, air, gas, etc) transition from smooth/mathematically predictable structures, called laminar, to unpredictable Turbulent flows around Re’s of 2000-4000.  Reynolds Number Turbulence Developement

This is sufficiently high to place wheel aerodynamics in the fully developed turbulent region of air flow (i.e. Re>4000). This means that flow structures remain relatively constant throughout interested flow speeds and Drag will scale directly with a square relation to velocity. This means that in the drag equation F_d=\frac{1}{2}\ \rho\ C_d A\ v^2.

The 1/2 *rho *Cd * A term will remain constant for a range of velocities.

At low speeds the spread between different wheel manufacturers is very small, meaning experimental or computational error noise would make it difficult to determine which wheel design is in fact better. A higher wind speed amplifies these differences in order to actually see what wheel is faster.

The other takeaway from this to be aware of is that at low speeds a lot of wheels are ESSENTIALLY the same, Aero Performance Wise. This is why we took a multi-disciplinary approach to designing wheels; including features such as tubeless technology and wider rims.

VeloNews Wheel Drag Plot

The plot above is from actually a pretty good VeloNews test on wheel performance (usually they’re fairly half ass-ed). Notice that the largest discrepancies among top Aero wheel brands is 25 grams at best (8 pennies weight worth of force for those keeping track). At lower AoA’s (where you spend most your time riding) this difference is smaller, additionally at 20 mph that drag spread drops down to 4 pennies worth of drag (~12 grams). At which point wind tunnel measurement inaccuracies start becoming a significant part of your delta. Not to mention things like atmospheric conditions (in an open wind tunnel like A2), manufacturing imperfections, and tire wear can all play a pretty big role in affecting your measurements.

In the end performance always comes at a premium. You CAN  drop $2500 on a wheelset that is sometimes 3 grams faster than the competition, but as an informed cyclist you shouldn’t feel obliged to. It’s not going to hold ANYONE back (unless your last name’s Froome). Instead, maybe just go out and ride a little more.


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.


What is this…a Time Trial for CARS?!

It’s July, that means hours streaming the Tour de France through some pirated grainy feeds…AND a lot of bogus Aerodynamic information, including an ESPECIALLY ugly looking Giro helmet:Rohan Dennis Tour de France Time Trial

After the opening TT it’s important to remember the importance surroundings play on the Aerodynamics of a cyclist.A Center for Ants


Obviously drafting a car gives you a huge advantage, but a car drafting you? It turns out you can get a SIGNIFICANT advantage from a follow vehicle. Current UCI regulation is 10 meter minimum distance.

Bert Blocken has a great course on coursera.com about mostly cycling and some city/urban aerodynamics. You can check it out here.

He also recently published a research paper about the effect of follow cars in a TT situation.

When a body is moving subsonically through a fluid, an area of high pressure is created in front of the object as the air rushes to get out of the way of the moving body. Behind a body is an area of low pressure, this is basically the mechanism that creates pressure drag.

So how does a car help a rider from behind? The high pressure area in front of a vehicle (or even other rider) for that matter, acts to fill the low pressure region behind a cyclist. This acts almost as a fairing, increasing the pressure on the back side of the cyclist, reducing drag. A picture from the above mentioned paper gives a better example.followcar

The high (red) pressure area acts to fill the area behind the cyclist (which is pretty clear to see when the car gets real close). The effect is even noticeable at smaller distances:followCarDraftAs you can see here, the benefits get pretty drastic below 8 meters (26 feet). I took a quick look at the Tour de France prologue using a simple F=1/2 Cd A rho v^2 calculation for force then converting to power. Based on this calculation, Dennis put out 492 watts (neglecting drive-train/elevation losses) for almost 15 minutes over 13.8 km’s.

A car at 10 meters (UCI legal limit) give’s you a 0.23% advantage. Let’s say his car was only 2 meters closer, giving him double the car draft advantage of 0.45% (Thus a 0.22% difference). I’ll factor this in as a reduction of the CdA term and keep the wattage for Dennis constant for the calculation…

Given this ONLY 0.22% reduction in drag, Dennis would’ve saved a whopping 10 SECONDS!!!!!!

In a short TT decided by only 5 seconds across the top 3 riders…any team manager in their right mind would get FINED TO DEATH in order to drive as close to their rider as possible.

This isn’t even taking into account video moto’s…which somehow are above UCI rule and can drive as close to riders as they please (in front or behind).

So pay attention at the next short TT in this year’s tour to see if each respective DS is doing their jobs correctly (rider safety be damned!!!).


-This analysis is quick and dirty, CdA values are VERY approximated


-TOTALLY neglecting acceleration

-Drive train losses neglected

-However the actual wattage produced by Dennis may be different, the benefit should be roughly the same since we are not looking at that side of the speed equation



Another Wind Tunnel Cross Wind Caveat

Ok I like to rag on wind tunnel and CFD results. Don’t worry yet, this is a less math intensive post than my last post about Wind Tunnel Cross Winds. The relative ease with which you can drop a couple hundo for a few hours on the wind tunnel to get some pretty graphs, or possibly even less on some CFD results (which have the possibility of being even more wrong), means it’s easy to BS your way to a marketing “Aero” bike or component.

One of the frequently mis-understood…or unreported (ignorance or deception, depends on the company) is what speed you’re actually riding at in a wind tunnel.

Now I guess I don’t know for sure, but I’m almost 100% certain EVERY wheel company uses a bit of trigonometry to help their high yaw angle drag values…which is essentially fine as long as you’re comparing apples to apples.

Here’s a screen shot from a report we got from the A2 wind tunnel in Charlotte (which A TON of bike companies use).



What you see here is a set of runs across yaw angles. Take a look at the “Tunnel Section Speed” column. The velocity is kept relatively constant through the range of yaw angles, this is done because wind tunnels are huge machines where it makes a lot more sense to turn a small bike wheel than change wind speeds. Anyway if you remember your high school trig, you should be thinking it’s off.

Bike Wheel Cross Winds

If you’re riding a bike at 30 mph (yes I know it’s fast for me too) with no cross wind, you’re seeing 30 mph of airflow. However if you’re riding your bike at 30mph and see a 5mph cross wind, the TOTAL wind you’re seeing 30.5 mph. When you get bumped up to 10mph cross wind, your total is 1.5 mph faster than 30. This may seem small, but it’s an important distinction to make when the drag difference between brands of wheels is on the order of a couple grams.



Using the standard drag equation and assuming Cd is going to be roughly the same between 30 and 31 miles per hour, so drag is going to scale by the square of velocity. So a Zipp 303 w 60 grams of drag at 15 degrees angle of attack is now bumped up to 64 grams. Insignificant, but it is the order of difference between top bicycle rims on the market if you’re splitting hairs.

So…while this isn’t something that is necessarily a make or break proposition. This CAN make a difference in the game where a gram here and there matter.


Snake Alley 2015

Snake Alley, for anyone coming up cycling in the MidWest has a special significance. No other crit really compares to the Snake’s 0.8 mile course: a twisted brick road that climbs out of the Mississippi river valley followed closely by a technical descent on some classically terrible MidWest pavement. It falls somewhere closer to a CX race than any other crit out there. The list of former winners reads like a who’s who of regional and national crit racers. You always love the courses you win on, but I’ve loved snake alley since the first year I did it in 2008 and made it only 5 laps or so (Dewey Dicky “won” that year). No other race requires as much, strength, tactics, technical skills as Snake Alley (yeah I realize CX checks off these boxes as well). Other crits may claim to be the hardest crits but they’re wrong.

It’d been a few years since racing the QuadCities races; the old mail in registration was gone and replaced with snazzy USACycling Online registration, but otherwise it was all the same. The Burlington road race, another unique race kicked off the series on Friday. A claimed 95miles that was actually 105miles of sitting in and letting a large field pull you a long with full road enclosure makes the race feel like a much bigger deal. I had a pretty singular focus on Snake Alley, but David Goodman went on the solo insane ride of the day, dropping his DraPac breakaway companion and soloing for the last 40 miles of the race (and would’ve won too if the race actually ended at 95). Thankfully Andy Scarano got a free ride in a breakaway all the way to the finish thanks to Goodman and took the sprint for the win.

I didn’t even bother registering for Snake Alley online and got number 115. The rest of the pre-reg’d 706p boys were only slightly better in the 100’s, which meant last row starting position in the only crit in America where starting position matters (except for Andy who got a call-up thanks to his win the day before). Thankfully for us, starting call up was not quite as hectic as in years past and a few of us were able to pull some curb hopping shenanigans to get to the halfway point in the pack before the start.

The race went off and we were able to make it up the Snake the first time without dropping a chain or getting bogged down enough to walk (the one thing that can REALLY kill your race there). After a few laps of hard work I made it up to the front with Thomas and Andy. A couple guys were knocked out with mechanicals in the first half but things mostly stayed together. A few attacks split a group of 10 or so off the front with all the big contenders. At about 11 laps to go I attacked with old MWCCC rival Isaac Neff and we were shortly joined by Chris Winn out of Colorado. We started working well together and Isaac fell off leaving just two Chris’ leading the race. We worked together seamlessly keeping our gap at 15 seconds, which can be very short or very long at Snake Alley. I kept on expecting a group to come up lead by Holloway but the disorganization behind allowed our gap to continue to grow.

Great shot attacking up #snakealley with @isaaclneff @pocsports @raleighbicycles @stansnotubes @guenergylabs

A photo posted by Chris Uberti (@cuberti) on

With 3 laps to go we had 30 seconds and our victory was all but sealed, deciding how to finish was a little more difficult. I knew he was a CO guy and probably had lots of horsepower and figured I could take a sprint. With one lap to go he attacked going into the Snake, I tagged on without too much difficulty, and countered going over the top, which he tagged on to as well….so sprint it was. Again a little overconfident (and slightly mistaken about the distance from the last corner to the finish) I lead it out going through the last corner. I’m pretty good at longer sprints, but this was LONG.

  The #snakealley bike throw. Just a hair #cycling #sprinting #winning great racing with @Chris_winn   A video posted by Chris Uberti (@cuberti) on

In the end it was literally a pixel width on the official’s camera that decided it.

Snake Alley Bike Throw 2015

You cant tell until you put the vertical ruler on the screen

It was a great race that could’ve gone either way with the slightest difference in wind direction, but a pixel is really all you need.

There is maybe only one other race in America that would mean as much to me to win, but everything else is leagues behind. I only half-jokingly told my teammates that I could quit racing after that win and be happy with it (walk out while you’re ahead). That’s not going to happen for a while, but that’s how much it meant to me after the turbulent past few months.

After snake alley I packed up and left Iowa, skipping the third and fourth race of the series. I had just visited my family the week before Snake Alley and needed to get back home. I was starting work at a new (old) job at the Engineering company I previously worked for doing gas turbine heat transfer work. While most cyclists look at a regular desk job as a death sentence, I’m looking forward to it. Aside from actually enjoying engineering, going back to work is a good return to a more regular life/training schedule. As ridiculous as it may sound, I sort of didn’t enjoying just being a pro cyclist. When all you have to do is ride, eat, and rest, it’s a lot of fun for a little while but eventually you feel a little unfulfilled and gets progressively hard to actually motivate yourself to put in hard work to progress, I’m just not wired that way. If you’re in the trenches of a pro team you’re only as good as your last result and that’s not what I want my life to be all about.