FLO Cycling – How Much Drag Does a Clydesdale Build Add to Cycling Wheel


Back in November, when Chris and I went to the A2 Wind Tunnel to test the new FLO 45, 60, 90, and DISC, we decided to study a few things we’ve thought about over the years.  Today’s article looks at the difference in aerodynamic drag between a standard build and a clydesdale build wheel.  

Testing at the A2 Wind Tunnel
If you are interested in our other studies from the A2 Wind Tunnel, please be sure to check them out. 

Does Tire Pressure Change Aerodynamic Drag?
Aerodynamic Difference between Sapim CX-Ray and Round Spokes
Does Covering the Valve Cutout on a DISC Wheel Matter?

What We Tested
When you order a clydesdale wheel set from us, you get a different rear wheel.  All of our front wheels are built with 20 spokes in a radial lacing pattern. Since the rear wheel is the only wheel that is different, we tested the difference between a standard rear wheel and clydesdale rear wheel in the A2 Wind Tunnel.  The specs of each build are as follows.

Standard Build: 24 spokes, two cross build, on both drive and non-drive side
Clydesdale Build: 28 spokes, three cross build, on both drive and non-drive side

Here are the details of the test.  

1.  We wanted to maximize the spoke length in the wheel to find the largest difference in drag possible.  We used rear FLO 30s for the test because they are our shallowest rim, and as a result, have the longest spokes.

2.  The wheels were built with Sapim CX-Ray spokes.

3.  We used the same Continental GP 4000 S II tire in a 23mm size to test both wheels.

How We Tested the Wheels
It’s important to define how a test is performed in a wind tunnel.  There are countless variables, and if you are not clear about the test, the results are not very clear.  Here is how we tested the wheels at the A2 Wind Tunnel.

1.  Tare was calculated and removed from all tests.

2.  Each wheel was swept from 0-20 degrees of yaw, in 2.5 degree increments.  The drive side of the wheel was opened to the airflow as the angle increased from 0-20 degrees of yaw.

3.  The same tire was used for each test.

4.  Each measurement was taken twice and averaged. 


5.  All tires were inflated to 95 psi and calibrated with a digital gauge.

The Results
The results were surprisingly similar.  The yaw vs. drag graph below shows the rear FLO 30 standard build vs. the rear FLO 30 Clydesdale build.


To determine what this means from a time perspective, we calculated the time savings for each wheel when compared to a Mavic Open Pro with 32 round spokes.  The Open Pro used the same Continental GP 4000 S II tire in a 23mm size.  The time savings were calculated using our Net Drag Reduction Value formula.  We developed this formula after collecting 110,000 live data points with a custom built data logger that was mounted to a bike.  If you’d like to learn more about this process be sure to check out the Five Part Series.  


We can see that the difference over a 40km and an Ironman is 2 seconds and 6 seconds respectively.  In the grand scheme of things, the difference is very small.  

Should You Be Worried About Using a Clydesdale Build
Now that we know the aerodynamic difference for a Clydesdale build is nothing to worry about, let’s look at the most common questions we get when we recommend someone moves up to a Clydesdale build.  

How much more does the Clydesdale build weigh?

The weight difference is about 30 grams.  While 30 grams may seem like a lot of weight, the time difference from a weight perspective is pretty much 0 seconds.
  
If you find yourself contemplating the Clydesdale build, and are worried about weight or aerodynamic losses, do yourself a favor and size up.  While I have not studied the difference in power transfer between the two builds, I would wager a bet that a heavier rider losses more time due to inefficient power transfer from being on a wheel that is not strong enough for them.  On top of that, you’ll have a wheel that will stay truer longer, and maintain it’s warranty with us. 

I hope you enjoyed this article.  Please feel free to comment and ask questions below. 

Take care,

Jon

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16 Comments

  1. Still curious what the aero penalty of a 25 mm tire is. They ride so much nicer! Any plans to test this or have you already and I just missed it? Love my Flo 60 and 90.Looking forward to trying out a disc this year.

    Thanks,

    S.

  2. tclimber,

    We did study it. In fact we studied 20 different tires during our last trip to the A2 Wind Tunnel. We are still working on the report and will have it up shortly. The 25mm GP4000s II was one of the tires we studied, so you'll get to see exactly how much of a difference it makes.

    Take care,

    Chris

  3. I'm interested too. But my 23 on your wide rims has the contact width of a 25 and feels very much like it a 25 on a more narrow rim. I'm content.

    Jordan

  4. Are the Clydesdales stronger with laterial forces? I'm thinking of putting a FLO 60 on the rear of a Catrike 700 trike. The rear wheel on a trike take a lot of laterial pressure. I'm really in enjoying my FLO 60 and 90 on my Bacchetta.

  5. Steven,

    Thanks for writing. Yes the Clydesdale wheels are stiffer both radially and laterally. Based on your email conversation with my brother, you will want to use the clydesdale build for your Catrike 700.

    Take care,

    Chris

  6. Thanks for the great article.
    Do you think that, as rear wheels residing in turbulent air, the time difference is likely to be smaller than what your results would indicate?

    Regards,
    Donald

  7. Donald,

    It's really hard to give you an exact answer because every bike and rider will create a slightly different aerodynamic system. For example, what frame is the athlete using, what size is the frame, how are the athlete's legs shaped, how is the athlete fit on the bike etc, are all potential things that could change the results. In this particular case we are looking at a difference of 2s over a 40km race and 6s over an Ironman when comparing aerodynamics of strictly the wheel. If I had to guess, I would think the time savings would be a little less with a full bike/rider system. If you are a clydesdale athlete, I'd personally focus on getting the wheel that is properly built for your size before worrying about the 2-6s. You'll not only have a wheel that is designed to handle your load, but keep your warranty as well.

    I hope that helps,

    Chris

  8. Since the wheel was rotating you captured rotational as well as translation drag? Can you share these different darg numbers for this test and any others for which you have them?
    Thanks,

  9. If you only measure translational drag then the differences between wheels is not accurately portrayed, particularly when it comes to your disc wheel which shows only an 8 second difference to your 60mm carbon clincher for a 40k TT. See https://docs.google.com/spreadsheets/d/1i8RmF35eOmEgDNmcfagy0UGl0JGRYsDn0WXRAL94hu0/edit#gid=0.
    Disk wheels have rotational advantages that are huge compared to wire spoke wheels, and rotational advantages are present at all yaw angles as opposed to translational advantages.

  10. KenF,

    Rotational drag or watts to spin is certainly a component. This study was designed to show the difference in translational drag. We are looking at measuring watts to spin numbers for all wheels.

    Take care,

    Chris

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