Advertisement

Sign up for our newsletter

Advertisement

Aero vs. lightweight bike: Which is better for climbing?

At what gradient does a lightweight bike and kit become more effective than an aero setup? Cyclist goes in search of the tipping point

Jamie Wilkins
30 Nov 2022

The benefits of lightness when riding uphill have been appreciated since time immemorial, and by now we all know how valuable aero gear can be at saving time on the flat. But in between there must be a crossover, so where is it and what can it tell us about optimising our equipment choices?

‘It’s an interesting question,’ says renowned aerodynamicist Simon Smart of Drag2Zero, consultant to WorldTour teams and here to provide his expert insight. ‘I get asked about this a lot.

The aero effect is quite small at climbing speeds and most of your work is against gravity. On the other hand, when you consider total system weight, including the rider, the extra weight of the aero setup isn’t that much either.’



It’s often suggested that aero trips over into the need for lightweight at around a 5% or 6% gradient, so to test that theory, and to examine the differences aero or lightweight setups can make, we sourced some of the fastest and lightest kit around and went pedalling off up a 6% climb. Here’s what happened…

It was important that both sets of kit be fully committed to their respective roles – no all-rounders. We scoured the market and these items are either best in class or very close to it.

The lightweight setup

The Specialized S-Works Aethos is the perfect lightweight bike for this experiment, solely focussed on its job of skipping up big climbs, with round tubes and not a single aero feature. This one is a top-spec custom build with SRAM Red eTap AXS belonging to a staff member of Specialized France.

The Assos Superléger clothing collection is designed for hot days, steep climbs and also indoor training. It’s so minimal that the jersey has no zip and only one pocket, reducing its weight to 90g. Giro’s Empire SLX II shoes are among the very lightest currently on sale, as is the Poc Ventral Lite helmet. It’s a winning mountain setup.

The aero setup

In the aero corner, the BMC Timemachine is as focussed on drag as the Aethos is on gravity.

Every element is shaped to slip through the air, right down to the down tube and integrated bottle cages, designed to direct air around bottles.

It comes on do-everything 50mm wheels so, for the purposes of this test, we fitted a set of mighty Zipp 808 Firecrests, 82mm deep and 2,015g in weight. The result was an aero monster of 8.18kg, almost 2kg up on the Aethos.

Every piece of aero kit is equally single-minded: Suplest Aero shoes reduce drag with a lace cover and weigh 128g more than the Giros; the clever ribbed fabric of the Rule 28 socks saves further watts for 26g extra; and the recently launched Giro Eclipse Spherical helmet is claimed to be one of the fastest on the market, but carries an extra 98g compared to the Poc.

Finally, there’s the Le Col × McLaren Project Aero speedsuit, an incredibly advanced (and expensive) one-piece road suit with two pockets. It’s claimed to be the fastest such suit in the world, yet a little awkwardly it’s actually 30g lighter than the Assos jersey and bibshorts combination.

But that’s near unavoidable given that speedsuits don’t have bibstraps nor extra hems and seams.

Method: Ride up a mountain

Our test segment was the top 5km of the Col d’Aubisque on the eastern side. It’s an ideal gradient, a near-constant 6.3% with the bonus of being bite-your-fist beautiful. It’s also conveniently close to my guesthouse (ahem, Escape to the Pyrenees).

Each run began and ended at precise points, starting from stationary but clipped in with a brief trackstand. Timing was by the computer’s lap button as I could press it at pretty much the same place, whereas the GPS accuracy of a Strava segment is more dubious.

I rode to power, averaging 300W for each run. Doing this blind is impossible, of course, but by staring at my computer like Chris Froome and watching live power, lap average power and lap normalised power on a dedicated screen, it’s as straightforward as can be to control both average power for the run and smooth power distribution.

I stayed in the saddle and on the hoods throughout, trying to maintain the same body position, and carried nothing with me. Each bike got two runs for validation.

It was essential to control as many variables as possible, so the two bikes were set up with identical fit measurements and were fitted with Pirelli P-Zero Race 26mm tyres (208g each) and Maxxis Ultralight inner tubes.

Tyres were inflated to 90psi (front) and 95psi (rear). Additionally, each bike was cleaned and silicone-polished to give an equal finish, and the drivetrains were removed, run through an ultrasonic cleaner and relubricated with Squirt wax. If that sounds like a lot of work, it was.

Favero kindly supplied a set of Assioma Duo power pedals (302g), which were ideal as they could easily be swapped between bikes, plus they boast +/-1% accuracy and temperature compensation to account for any temperature changes over the test period.

While this was a test of a theory, not the bikes themselves, it’s important to note that the precise results will apply to these setups only. Different aero or lightweight products will give their own outcomes. However, the trends seen here will apply in most cases.

Here's how it went


Both runs on both bikes went smoothly. I pedalled continuously, tried to hold the same position, took the same lines and averaged the same power. As close as it’s possible to get in the field, this felt like a fair test.

While there were moments when the bikes felt different, the experiences of riding the climb on each were ultimately very similar. I couldn’t feel whether more of my energy was being used against gravity or air resistance, dependant on the bike, only that for a given effort I was moving at a certain speed.

This similarity of feeling is compounded by the testing controls. Staying seated at a constant power limits opportunities for the setups to differentiate themselves in terms of feel.

When you stand on the pedals, the Aethos scampers up steep grades like a squirrel up a tree – a sensation the Timemachine doesn’t elicit. But sat down and churning out equal power, the respective sensations of equipment performance are near indistinguishable.

Some of the differences when it comes to kit are slightly more tangible, however.

The most noticeable contrast is in the helmets. The aerodynamic Giro is 98g (47%) heavier than the Poc Ventral Lite, and I could just about feel it. However the 64g per shoe difference between the Suplest Aeros and Giro Empires wasn’t detectable.

Clothing is trickier. The aero speedsuit is actually a little lighter than the separate – albeit ‘superlight’ – jersey and bibshorts, which fit closely and don’t flap. But being skin-tight is only the beginning of clothing aerodynamics, and the Le Col speedsuit achieves its speed with advanced fabrics and crucial seam placement.

Again, I couldn’t feel these things working, but it’s well established that skinsuits are faster.

The very close times between runs indicates that our testing protocols worked well. The lightweight setup posted identical times and the aero setup deviated by just two seconds (a 0.2% variance).

Averaging the aero times to 15:25 gives us a win for the lightweight setup by 15 seconds, which over 5km is a 1.5% advantage.

However, to dig a little deeper we went back to Simon Smart, who did a range of calculations based on our results and some very well-educated estimates of the total system drag of each setup, and broke down the outcome: ‘Out of your 300W, around 16W went on rolling resistance and, on the lightweight setup, around 24W is aero drag. The rest, 260W, is climbing drag, working against gravity.

‘The aero setup saves around 20% of the work against the air, so 4.8W, while the 2.2kg weight penalty costs around 8W, so it’s a net loss of 3.2W.’

While those numbers are estimates based on experience and expertise, that 3.2W loss of the aero setup would tally with the idea that the lightweight setup was marginally faster uphill.

Conclusion: Have we found the tipping point?

Based on the supposition that the steeper the climb, the more gravity plays a role, the very close times we recorded seem to indicate our 6.3% climb is right around the crossover point where aerodynamics gives way to lightness as the primary concern for a fast time uphill.

Of course the optimum setup would combine the best of both worlds, taking aero gains without weight penalty. As such, a speedsuit would likely be an easy free-speed win.

The proportional relationship of aero and weight is far from linear, however, and the most effective products are the outliers from that line, those which combine most of the lightness with most of the aero. This all-rounder concept is everywhere in road cycling right now.

So, given all this, what would Smart choose to ride up our climb? ‘I’d take a 40-50mm wheelset and a minimal aero road bike, such as the Specialized Tarmac or Scott Foil, or a lighter semi-aero option such as the Scott Addict.

Still, you have to think about the rest of the course and what time you might gain back on the descents or flats.’

That’s valuable insight we would all do well to keep in mind, especially those of us who tend towards aero obsession or weight weeniness. In fact, it sounds like a fascinating premise to test at another time…

Aero vs. lightweight: The full setups

Aero setup

Bike: BMC Timemachine 01 Two, 56cm, 8.18kg (7.90kg stock)
Wheels: Zipp 808 Firecrest
Helmet: Giro Eclipse Spherical, 308g
Glasses: SunGod Airas, 33g
Speedsuit: Le Col x McLaren Project Aero, 189g
Socks: Rule 28, 56g
Shoes: Suplest Aero, EU45, 626g
Total kit weight: 1,212g
Total equipment weight: 9.39kg
Total weight (inc 74kg rider): 83.39kg, (2.7% heavier than lightweight setup)

Lightweight setup

Bike: Specialized S-Works Aethos, 56cm, 6.19kg
Helmet: Poc Ventral Lite, 210g
Glasses: Poc Elicit, 23g
Jersey: Assos Equipe RSR Superléger S9, 90g
Bibshorts: Assos Equipe RSR Superléger S9, 129g
Socks: Assos RS Superléger, 30g
Shoes: Giro Empire SLX II, 45, 498g
Total kit weight: 980g
Total equipment weight: 7.17kg 
Total weight inc 74kg rider: 81.17kg

Results

Col d’Aubisque, final 5km, 6.3%

Aero run 1: 15:26, 300W average power, 17.3kmh average speed
Aero run 2: 15:24, 300W average power, 17.3kmh average speed
Light run 1: 15:10, 300W average power, 17.6kmh average speed
Light run 2: 15:10, 300W average power, 17.6kmh average speed

click to subscribe

Thanks

Big thanks to Simon Smart at Drag2Zero for his expert insight; Billy at Specialized France for the loan of his personal S-Works Aethos; Favero for the excellent Assioma Duo power pedals; and Pirelli for supplying the P Zero Race control tyres. Ride the Col d’Aubisque and many others with Escape to the Pyrenees.

Photography: Chris Storrar

Read more about: