What Is Aero in Cycling? Aerodynamics Explained

August 24, 2023

Updated October 2026. First published August 2023.

Aero in cycling means reducing aerodynamic drag: the resistance of the air pushing against you and your bike. On flat roads above about 15 mph (24 km/h), drag is the biggest force you fight, so a more aerodynamic rider goes faster for the same power, or holds the same speed for fewer watts.

Key takeaways

At 20 mph (32 km/h) on the flat, roughly 80% of your effort goes into pushing air out of the way. By 25-30 mph (40-48 km/h) it approaches 90%.
Drag force rises with the square of speed, and the power needed to beat it rises with the cube. Aero gains are worth the most watts when you are going fast.
Your body causes around 70-80% of total drag, so position and clothing matter more than frames or wheels.
The number to track is CdA (drag area). For flat riding, what decides your speed is your power divided by your CdA (W/CdA).
Test, do not guess. The fastest position and kit differ from rider to rider.

What does "aero" mean in cycling?

"Aero" is short for aerodynamic. An aerodynamic rider or product lets air flow past with less resistance. Two things create that resistance. Pressure drag comes from the air piling up in front of you and leaving a low-pressure wake behind you, and it is the larger of the two. Skin friction drag comes from air rubbing along surfaces such as fabric, helmets and tyres, which is why fabric texture and fit can change your speed.

How much of your effort goes into drag?

The faster you ride, the bigger the share. The figures below come from a simple model of a rider and bike (80 kg combined, CdA 0.32 m², flat road, still air). Real-world numbers move with your size, position, wind and road surface, but the pattern matches published research, which puts aerodynamic drag at around 90% of the mechanical power needed on level ground once speeds pass roughly 50 km/h.

Speed	Share of resistive power spent on aero drag (modelled)
15 mph (24 km/h)	about 73%
20 mph (32 km/h)	about 83%
25 mph (40 km/h)	about 88%
30 mph (48 km/h)	about 92%

The rest goes mainly on rolling resistance. Our aero calculator lets you put in your own numbers.

Why speed makes drag so much bigger

Drag force increases with the square of speed. Because power is force multiplied by speed, the power needed to overcome drag increases with the cube. A 10% increase in speed means about 21% more drag force and 33% more power to overcome it. Going from 30 to 40 km/h means roughly 78% more drag force and about 2.4 times the aerodynamic power.

This is why aero savings grow as you speed up. Cutting your drag area by 10% saves roughly:

3 watts at 20 km/h
11 watts at 30 km/h
25 watts at 40 km/h

(Modelled for a CdA of 0.30 m² and an 80 kg rider and bike.) Slower riders still benefit, since drag is the main resistance above roughly 15 mph, but the watts saved are smaller.

What is CdA, and what is a good number?

CdA, or drag area, combines your drag coefficient (Cd, how slippery your shape is) with your frontal area (A, how much of you the wind hits). A lower CdA means less drag at any speed. Coaches and testing services commonly quote ranges like these for road riders. They are indicative, not a standard, and vary with your size and kit:

Position	Commonly quoted CdA (m²)
Road bike, hands on the hoods	about 0.32-0.40
Road bike, in the drops	about 0.28-0.35
Time trial or triathlon bike	about 0.20-0.26

One rider's numbers can move a lot with small changes. In a single-rider wind-tunnel study of an elite triathlete (Barry et al., 2015), the hands-on-hoods position measured 0.343 m², standard drops 0.332 m², a crouched drops position 0.306 m², and the hoods with forearms held level 0.295 m². Your own results will differ, which is why testing matters.

To see what a CdA difference means in watts: holding 40 km/h on a flat road takes roughly 305 W at a CdA of 0.32 and roughly 245 W at 0.25, a gap of around 60 W (modelled).

On flat and rolling courses, speed is governed more by W/CdA than by raw power. A rider who gives up a few watts for a meaningfully lower CdA often comes out ahead. On steep climbs, speed is low and gravity dominates, so weight matters more than CdA.

Where does the drag come from?

The rider accounts for around 70-80% of total aerodynamic drag on a typical road bike, by most estimates. The bike, wheels and components make up the remainder. That split tells you where to look first: position, then clothing and helmet, then equipment.

Rider position: the biggest free gain

For road riding, the general rules are to get low and narrow:

Bend your elbows and tuck them in, rather than riding on straight arms.
Lower your torso and keep your back flat.
Shrug your shoulders forward and slightly up to narrow your frontal profile.
Tuck your head so it sits inside the outline of your shoulders rather than above it.
Ride the drops, or the hoods with bent elbows and forearms close to level, whichever tests faster for you. In the Barry study above, the level-forearm hoods position was the lowest-drag road posture for that rider.

Small changes add up. A 2025 CFD study of a time trial position (Maddocks and Walker) found that narrowing the elbows alone cut the rider's drag area by around 4%.

These changes cost nothing. An aggressive position can feel less powerful at first, and some riders find their output recovers with time, but you can only confirm that for yourself by checking both power and speed. Keep a position you can hold, because a position you abandon after ten minutes saves nothing.

Aero kit: what the testing shows

Clothing is the cheapest place to find aero gains, but published numbers vary widely with the baseline garment, the speed and who ran the test. Here is what independent researchers and our own wind-tunnel testing have found:

University testing. Researchers at NTNU compared jerseys and bib shorts on a mannequin and a rider. The best jersey saved about 8 W at 50 km/h against their baseline kit, and the best bib shorts about 5 W.
Aero socks. Former Zipp technical director Josh Poertner has said the best aero socks can be worth 12-15 W at 30 mph in a wind tunnel. Our own testing points the same way, with smaller numbers. In March 2025, independent consultancy ATP Performance tested socks at the Silverstone Sports Engineering Hub with one rider, and our One Aero Sock saved 4.1 W at 40 km/h, 3.3 W at 45 km/h and 3.4 W at 50 km/h compared with a standard sock. At 30-35 km/h the gain was around 1 W or less. Rule 28 funded the test, and savings vary by rider and speed.
Base layers. Speed range matters. In tunnel testing at Silverstone with Olympic track sprinter Jean Spies, our high-speed base layer saved about 5 W at 50 km/h, 14 W at 55 km/h and 24 W at 60 km/h compared with our original lower-speed base layer. It was slower than the original below about 50 km/h, which is why base layers are designed for specific speed ranges.
Overshoes. In 2024 tunnel testing at Silverstone with one rider, our One and Neo overshoes were 7.4 W and 9.1 W faster than the previous generation at 40 km/h, and 9.2 W and 11.8 W faster at 45 km/h.

The practical lesson is that riders in loose or old kit have the most to gain. Three things matter whatever you choose:

Fit. Wrinkles create drag. In the NTNU study, a jersey one size larger cost about 14 W at 50 km/h, which the authors put down to more wrinkles on the side panels. The same study found that tightening one jersey's pocket band added wrinkles and probably drag. Aim for smooth, not as tight as possible.
Fabric and sleeves. Textured fabric reduces drag most at higher speeds, and longer sleeves increased the benefit in the NTNU tests.
Heat. Aero helmets, long socks and shoe covers can limit how well you shed heat in hard efforts, so match kit to conditions.

Browse our men's and women's skinsuits and aero base layers, aero socks and overshoes, aero gloves and aero jerseys.

Bike, wheels and tyres: what has changed

Frame shape, integrated cockpits, internal cable routing and minimal bar tape all help. The biggest shift in recent years is the move to wider tyres and wheels designed around them:

Wider tyres are now mainstream. One rear tyre measured 33.65 mm at the 2026 Tour de France. Wider tyres add frontal area, but Zipp's Nathan Schickel says reduced rolling resistance now outweighs that penalty. Balancing aero, rolling resistance and weight is still rider-specific. You can compare options with our rolling resistance calculator.
Rim and tyre work as a system. Brands now sell wheels designed around a specific tyre width, and aero-shaped tyres are on the market. In wheel maker Parcours' 2026 tyre tests, measured tyre width drove aero performance below 10 degrees of yaw, which its data suggests covers about 89% of ride time, and aero-shaped tyres stood out mainly above that.
There is no simple rim-to-tyre ratio. A 2025 wind-tunnel test of nine deep-section wheels by wheel maker AeroCoach found no simple relationship between external rim width relative to tyre width and aero performance, though it used a single 28 mm tyre. Test the actual combination where you can.
Cockpit and helmet. In a 2024 interview, Poertner reported 25-28 W from a good aero flat-top handlebar in a 30 mph wind-tunnel test, 12-15 W from an aero road helmet, and 30 W or more from a time trial helmet compared with a road helmet. These are one expert's indicative figures, and results depend on the rider.

Per pound spent, position and clothing usually beat new wheels or frames. Equipment makes sense once those are sorted.

Drafting: the biggest aero gain in racing

Riding behind other riders is the largest single aero saving in racing. Earlier work on small in-line groups put a following rider's drag at roughly 50-70% of a solo rider's, a saving of about 30-50%. A 2018 wind-tunnel and CFD study of 121-rider pelotons (Blocken et al.) found that riders in the mid-rear of the bunch can face just 5-10% of an isolated rider's drag. Drafting also helps uphill: van Druenen and Blocken (2021) found a power saving of over 7% for a following rider on a 7.5% gradient at 6 m/s, with larger savings as speed rises.

For more on racing and aero, see how to ride faster in road races, how to ride a faster time trial and how to ride faster on gravel.

How to measure your aerodynamics

General rules are a starting point. To find what works for you, measure it. There are three common routes:

Field testing. The Chung method (virtual elevation) uses a power meter, speed sensor and altimeter on a repeated loop to estimate CdA, and lets you compare positions or kit in a single session. Pick a calm day and a loop you can ride without braking. Wind, slope and sensor error can easily swamp small differences, so repeat runs before trusting a result. Our free Aero Calculator estimates your CdA from your average power, speed and weight for two positions or kit choices and shows what the gap is worth. It is a simplified method that assumes flat ground, no wind and steady effort, so use it to compare two setups on the same day, not as an absolute number.
Aero sensors. Devices such as the Notio use an air-speed probe to estimate CdA. In a 2023 study of 17 professional riders on an indoor velodrome, the device's CdA values were consistent with a standard virtual-elevation method, but the direction of change between positions differed, which could lead to different recommended setups. Use sensors to compare, and confirm important decisions another way.
Velodrome or wind tunnel. Controlled conditions give the cleanest comparisons of position and equipment, at a cost.

Whichever you pick, change one thing at a time, and repeat tests to understand your own noise before trusting a small difference.

Frequently asked questions about aero in cycling

What does aero mean in cycling?

Aero is short for aerodynamic. In cycling it means reducing the air resistance acting on you and your bike. Because air resistance is the main force you fight on flat roads at speed, a more aero rider goes faster at the same power or uses fewer watts to hold the same speed.

How much of my power goes into aerodynamic drag?

On a flat road in still air, roughly 80% of your resistive power at 20 mph (32 km/h), rising towards 90% at 25-30 mph (40-48 km/h). At lower speeds the share is smaller, but drag is still the main resistance above about 15 mph (24 km/h). Climbing and headwinds change the balance.

What is CdA and what is a good CdA?

CdA is your drag coefficient multiplied by your frontal area, expressed in square metres. Lower is better. Commonly quoted figures for road riders are around 0.32-0.40 on the hoods, 0.28-0.35 in the drops, and 0.20-0.26 in a time trial position. Your own best number depends on your body, position and kit.

Is aero worth it if I am not a fast rider?

Yes, though the watts saved are smaller. Aerodynamic drag is still the main resistance above about 15 mph (24 km/h), so a lower CdA helps on flat and rolling roads. The biggest gains in watts go to riders going faster, but free changes like position and well-fitting kit are worth making at any speed.

What is the cheapest way to get more aero?

Change your position first. Getting lower and narrower, tucking your elbows and head, costs nothing and often saves more than any equipment. After that, well-fitting aero clothing is typically the best value, and wheels or a new bike come last, once position and kit are sorted.

Does aero clothing really make a difference?

Yes, though the savings depend on the garment, the speed and what you compare against. One university study found the best of its test jerseys saved about 8 W at 50 km/h. Fit matters because wrinkles add drag: in that study a jersey one size larger cost about 14 W at 50 km/h.

Are wider tyres slower aerodynamically?

Wider tyres add some frontal area, but wheel brands such as Zipp argue that the lower rolling resistance now outweighs that, and road racing has moved to 28 mm and wider. Wheels and tyres are designed together as a system, so choose a rim and tyre width that suit each other and test the combination where you can.

How can I measure my CdA?

The most accessible method is field testing with a power meter using the Chung (virtual elevation) method, which lets you compare positions and kit in one session. Aero sensors, velodrome sessions and wind tunnels are other options. Test in calm conditions, change one variable at a time and repeat runs, because wind and slope can distort results.

Sources

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