Finding Free Speed: My Latest Aero Testing at Silverstone

A few months ago, I headed down to the Silverstone Sports Engineering Hub to dive back into the wind tunnel and see what gains I could still squeeze out of my position and kit. It had been five years since my last tunnel session, and with a whole host of new products hitting the market—and a few positional tweaks I’d been wondering about—it felt like the right time to get some fresh data.

The Goal

While I’ve already been to three different wind tunnels over the years and have a good understanding of what works for me positionally, there were still a few extremes I hadn’t tested. The plan was to explore some deeper saddle-to-pad drops and then move on to helmet and skinsuit testing. Everything was geared toward finding that sweet spot between aerodynamic efficiency and power output.

The Baseline: Back to 2015

To give some context, back in 2015 at Drag2Zero, we established that:

• A -95mm saddle-to-pad drop gave me a CdA of 0.19225 @ 50kph / 72kg / 5° yaw

• A more aggressive -135mm drop gave a better CdA of 0.18603 under the same conditions.

Image of -95mm saddle/pad drop from D2Z in 2015

The -135mm setup was clearly faster aerodynamically, but I found I could produce more power with the slightly higher stack of the -95mm setup. So for years, that’s the position I stuck with.

But here’s the thing: I’d never tested what happens between those two drops—or beyond.

Tunnel Setup and Strategy

We kicked things off with my baseline kit:

• Helmet: Giro Aerohead

• Skinsuit: Kalas

• Overshoes: Imp Sport

  
  

Baseline -95mm saddle/pad drop

From there, I worked through 10mm increments of saddle-to-pad drop, starting at -145mm (as low as my bike setup allows) and moving up to -85mm. The aim? To find the position that offered the best trade-off between reduced drag and sustainable power output.

Each run was carried out at a test speed of 50kph (this is basically the wind speed blowing into your face in the tunnel), and each run has 2 tests, one test at 0 degrees YAW and one test at 5 degrees YAW, I've taken the average of these for results.

A test at 5 degrees YAW is used as we rarely see a direct headwind or tailwind when racing, and there is some sort of cross wind most of the time, the 5 degrees YAW test helps to account for that.

Positional Testing

Here’s the sequence I tested:

• -145mm

• -135mm

• -125mm

• -115mm

• -105mm

• -95mm

• -85mm

  
  

After cycling through all these, -125mm felt like the sweet spot. It gave a good aerodynamic return without compromising power too much.

Helmet Testing (and a Note on Aesthetics)

Once we’d locked in the -125mm position, I moved on to helmet testing. From past experience, I don’t usually see big changes between helmets—likely because my head stays well within the silhouette of my torso—but it's still worth validating with data.

Tested helmets included:

• Rudy Project Wingdream

• Sweet Protection

• MET Drone

• HJC

• Kask Mistral

  
  

The Rudy Project Wingdream came out on top, offering a 2-watt improvement over my baseline Giro Aerohead. Paired with a longer reach setup, it netted me an additional 6-watt gain — proving that small changes in posture and equipment really do add up.

That said, I’ll be honest: the Rudy doesn’t look great from the side. In fact, it's probably the worst-looking helmet of the bunch in profile. But this just goes to show — aero doesn't care how good you look. When performance is the priority, looks sometimes have to take a back seat.

Rudy Wingdream at -125mm saddle/pad drop

Skinsuit Testing

With the best position and helmet sorted, we moved on to skinsuits.

• HUUB TT suit (no aero base layer)

• Rule 28 suit (with aero base layer)

• Kalas (baseline)

  
  

The Kalas suit remained the fastest overall. The Rule 28 setup came in about 2 watts slower, and the HUUB was 8 watts off.

Interpreting the Results

One thing to note is that CdA values from Silverstone are slightly inflated due to the bike holding stanchions—they likely add about 0.02 m² to the numbers. With that in mind:

• Starting CdA: 0.2016

• Final tunnel CdA: 0.1943

• Real-world CdA (adjusted): ~0.1816 → 0.1743

  
  

Estimated Equivalent Power improvements

Change	Equivalent Power Gain
Lowering front end (from -95mm to -125mm)	~7W
Rudy Wingdream helmet	~2W
Increased reach	~6W

Total gain: ~15 watts

Estimated power loss due to lower position: ~5 watts

Net real-world gain: ~11 watts

Takeaways

This session was a great reminder that aerodynamic testing is always evolving—even when you think you’ve got your position dialed. Small changes, especially when compounded (position + helmet + suit + reach), can add up to big real-world gains.

In a sport where free speed is gold dust, that ~11-watt net gain could make all the difference in a time trial or triathlon bike leg.

Huge thanks to Michael Charlton for assisting with equipment changes.

If you're serious about performance, I can’t recommend structured wind tunnel testing enough. Just make sure you go in with a plan, a priority list, and a stopwatch—every second counts.

If you have any questions or need any help with your own testing, feel free to reach out, happy to help.