More Luggage, Less Air Resistance? – FORK BAG / 01

Guest post by Patrick Zasada, who conducted the aero test of the CYCLITE FORK BAG / 01.

Fork bags have a poor reputation in the performance segment. And rightly so! Anyone preparing a gravel bike for longer tours knows the problem. At some point, there is no longer enough space in the saddle bag, frame bag and handlebar bag. So additional luggage moves to the fork. This is often practical, but rarely a good idea aerodynamically.

On the fork, bags sit very far forward in the airflow. They are hit directly by the air, increase the frontal area of the bike and sit in an area where the airflow is already strongly influenced by the front wheel and fork. Classic round fork bags work well as storage space, but aerodynamically they often act like a brake in the wind. They protrude sideways into the airflow, have an unfavorable shape and rarely integrate cleanly into the system of bike and rider.

That is exactly why the starting question for this test was so interesting. What happens when a fork bag is not designed like a round drybag, but as a wedge-shaped, narrow bag that sits close to the bike? Can such a shape reduce the usual aerodynamic disadvantage? Or is an aerodynamic fork bag ultimately an impossibility?

The surprising answer is: In the tested setup, the CYCLITE FORK BAG / 01 was not only faster than a classic fork bag. The complete system of rider, gravel bike and CYCLITE FORK BAG / 01 was even measurably faster than the reference setup without fork bags.

Why aerodynamics matter even at lower speeds

Bikepacking is always a compromise. You need storage space, but you also want as little weight as possible, good accessibility and as little aerodynamic disadvantage as possible. Especially over long distances, air resistance quickly becomes a decisive factor. Not because every bikepacker is racing, but because air resistance continuously costs energy over hours and days.

Depending on system weight, tire choice and riding position, air resistance becomes the largest resistance on the bike from around 20 km/h. On a normal gravel bike, this already requires around 45 to 50 watts at 20 km/h. As speed increases, this power demand rises extremely quickly. At 30 km/h, around 145 watts are already required to overcome air resistance.

Put simply, aerodynamic power demand increases approximately with the cube of speed. This means that a small aerodynamic issue may still seem manageable at low speed, but at higher speed it very quickly costs a lot of power.

At the same time, aerodynamics should not be underestimated at lower speeds. Although the percentage share of air resistance in total resistance is lower, you also spend significantly more time on the route. As a result, the absolute time saving can still be very large. On a 100-km course, a 3 dm² better CdA can save around 4 minutes at an average power of 250 W. At an average power of 100 W, the saving on the same course can even be closer to 5:30 minutes. You are slower overall, but the aerodynamic advantage acts over a longer riding time. That is exactly why aero is not only a topic for fast road cyclists, but also for bikepacking and long distances.

Why standard fork bags are aerodynamically difficult

Classic round fork bags have several disadvantages. They sit in an exposed position, they are usually relatively wide, they have a round cross-section and they generate turbulence. These are disturbed air regions in which the airflow no longer moves cleanly along the bike. For a bicycle, this usually means additional drag.

Of course, every bag initially creates additional frontal area. A fork bag does not simply disappear from the wind. The decisive question is therefore how it changes the overall airflow pattern around the bike. In the end, everything influences everything else. Fork, front wheel, tires, legs and luggage all sit in one shared airflow. A bag can therefore add drag in one place and reduce drag elsewhere. What matters in the end is the balance of the complete system.

What was actually measured in the test

The test was therefore explicitly not about evaluating a single bag in isolation. What was measured was the complete system of rider, bike and bag configuration under real-world conditions. This is important because the so-called CdA is always a system value.

In simple terms, CdA describes the total aerodynamic area. On the one hand, it includes the frontal area, meaning how large the system appears from the front. On the other hand, it includes shape quality, meaning how well or poorly the air flows around this system. A smaller CdA means that less power is required at the same speed. Or, conversely, that you ride faster at the same power.

Three setups were tested. First, a reference setup without fork bags, but with ballast to keep the system weight constant. Then a setup with classic round fork bags with a comparable packing volume of 3 liters per bag. Finally, the setup with the CYCLITE FORK BAG / 01. The system weight was controlled and kept as constant as possible so that the difference would not be caused by more or less weight, but by the aerodynamic effect of the respective configuration. Therefore, both bag setups were packed so that they had the same weight.

When one setup is heavier than another, rolling resistance also changes. It would then be unclear whether the differences came from aerodynamics, weight or the analysis. That is why the reference setup without fork bags was ridden with ballast. This keeps the question cleaner.

The method behind the outdoor aero test

The test was carried out as a standardized outdoor aero test according to the Aerotune protocol. A flat, low-traffic test route was used for this, on which each setup was ridden several times in both directions. This out-and-back principle is a central part of the method. Outdoors, wind is never completely absent. But it can be mathematically controlled much better when the same route is ridden in opposite directions. What acts as headwind on the way out partly acts as tailwind on the way back. With several runs, wind influences can be classified much more reliably. Using a clean combination of parameters, this can be mathematically filtered out much more accurately. Explaining this in detail here would go beyond the scope of the article. Anyone who wants to explore it in more depth will find the test protocol linked below, where the exact method and the mathematical-physical principles are explained in more detail.

Among other things, power, speed, system weight, tire pressure, air pressure, temperature, humidity and ambient conditions were measured. Speed was recorded with a speed sensor because GPS can be too inaccurate for this type of analysis. Even small time delays or position errors can distort the calculation. In addition, the rider position was stabilized using aerobars so that head, shoulders, arms and upper body remained as consistent as possible.

Even small changes in head position or elbow position can have a greater effect than some equipment changes. That is why, in an outdoor test, not only the software matters, but also the discipline during execution.

The method is not a wind tunnel test and is not intended to be one. Outdoors, there are always more influences than in a laboratory. At the same time, an outdoor test has one major advantage. It measures the bike under real riding conditions, with real pedaling motion, rotating wheels, real body position with balancing movements and natural airflow. For bikepacking setups, this is exactly what matters, because bags, rider and bike also interact in reality.

The result was much more surprising than expected

The expectation before the test was relatively clear. Classic round fork bags would probably slow things down significantly. The CYCLITE FORK BAG / 01 should likely perform better thanks to its narrow and wedge-shaped design. It would have been realistic to expect that it would slow the system down less than a round bag. In the best case, one might have expected a largely neutral result. But that is exactly not what happened…

The reference setup without fork bags achieved a measured system CdA of 32 dm² in the test. The setup with classic round fork bags came in at 37 dm². This is a clear increase and confirms the general skepticism toward round bags on the fork. The CYCLITE FORK BAG / 01, however, measured 29 dm², placing it below the reference value without fork bags.

This difference can be translated into power and riding time. At 33 km/h, the setup with the CYCLITE FORK BAG / 01 required 190 W in the model. The round standard fork bag required 229 W at the same speed. In the tested setup, this results in a difference of 39 W in favor of the CYCLITE FORK BAG / 01. Compared with the reference setup without fork bags, the advantage of the CYCLITE configuration was around 15 W at 33 km/h.

For a 100-km round course with 780 meters of elevation gain and an average power of 200 W, the model calculated an advantage of 4:23 min per 100 km for the CYCLITE FORK BAG / 01 and therefore around 0.7 km/h more speed. The round fork bags cost almost 7 minutes over 100 km.

Why these numbers cannot be applied universally to every bike

As strong as the measured values are, they should be interpreted carefully. The test shows what happened in the tested setup. It was a gravel bike with the rider positioned in the aerobars, an additional full frame bag for the ballast and exactly these bag positions. With a different rider, a different fork, a different tire width, a different body position or another combination of frame bag and front luggage, the result may be different.

Aerodynamics is always system behavior. A bag is not just a single object in the wind. It interacts with everything that happens behind it, next to it and above it. That is exactly why it is so interesting that the CYCLITE FORK BAG / 01 did not merely slow the tested setup down less, but measurably improved the complete system.

The possible explanation is not in the bag alone

At first glance, the result seems counterintuitive. How can an additional bag be faster than no bag? After all, it adds area. This is exactly where one has to distinguish between an individual component and the complete system.

A single bag cannot have “negative area”. It takes up space and is hit by the airflow. Within the complete system, however, it can change the airflow in such a way that less drag is created elsewhere. For the CYCLITE FORK BAG / 01, one plausible explanation is the changed airflow in the area of the fork, front wheel and legs.

The bag sits comparatively narrow on the bike. It does not have a classic round cylindrical shape, but a flatter, wedge-like form. This could redirect the airflow more favorably than a round bag. A calmer flow region could form behind the bag. During pedaling, the legs are partly located exactly in this area. If less disturbed air hits the legs there, the drag of the complete system can decrease.

This is not directly proven flow visualization. The test measured the resulting total drag, not the exact airflow made visible. The explanation is therefore a plausible interpretation of the measured values. What is certain is the measured system effect. The exact reason for it remains a fluid-dynamic hypothesis.

Why round fork bags perform significantly worse in comparison

The comparison with the classic round fork bag is particularly interesting because the packing volume was comparable. So this was not about a large bag versus a small bag, but about two different concepts for similar storage space.

Round bags make sense from a packing perspective. A drybag is simple, robust and flexible. Aerodynamically, however, the round shape is difficult on the fork. A round cross-section promotes flow separation. This means that the air is not guided cleanly along the surface, but separates earlier and creates an unstable vortex region behind the bag. In addition, the effective frontal area is often larger because the bag protrudes more to the side.

The measured values match this interpretation. The setup with round fork bags measured 37.10 dm² and was therefore significantly above the reference setup without fork bags. At 33 km/h, this meant 229 W in the model instead of 205 W without fork bags. Compared with the CYCLITE FORK BAG / 01, the difference was as much as 39 W.

Shape, position, attachment, load and bike geometry all play a role. However, the test shows very clearly that a classic round fork bag creates significantly higher air resistance, while the CYCLITE FORK BAG / 01 can make the complete system aerodynamically more favorable.

Why watt figures are not meaningful on their own

Watt figures are tangible, but they always depend on the selected speed. An advantage of 5 W at 40 km/h can be greater than an advantage of 7 W at 45 km/h. That is why the CdA value is more relevant for the technical assessment.

CdA is the aerodynamic fingerprint of the complete system. The smaller this value, the less power is needed at the same speed to overcome air resistance. In the test, the CYCLITE configuration measured 29.00 dm², the reference setup without fork bags measured 32.05 dm² and the round fork bag measured 37.10 dm². The difference between CYCLITE and the reference was therefore around 3 dm². Between CYCLITE and the standard fork bag, the difference was even 8 dm².

For long distances, this is relevant. On the bike, it means that you either need to produce less power at the same speed or ride faster at the same power. Over a longer bikepacking trip, this difference quickly adds up to several hours. Especially for riders spending long days on the bike, the benefit is not only more speed, but also less energetic loss.

How reliable is an outdoor aero test?

Outdoor aero tests must be carried out carefully and interpreted cautiously. Small differences can be influenced by wind, rider position, rolling resistance, temperature, measurement variation or traffic. That is why this test did not rely on a single run, but evaluated six valid measurement runs per setup.

The variation was comparatively low. For the reference setup without fork bags, the combined total error was ±0.38 dm². For the round fork bags, it was ±0.43 dm². For the CYCLITE FORK BAG / 01, it was ±0.32 dm². The measured differences between the setups were significantly larger than this variation. That is exactly why the result is not just a small numerical deviation, but a clearly recognizable setup difference.

Nevertheless, the classification remains important. The test does not replace a wind tunnel and does not show high-resolution flow visualization. But it does show very well how complete setups behave under real riding conditions.

Why the result is so relevant

Many products are described in terms of weight, volume and material. Anyone riding long distances feels not only every gram, but also every unnecessary watt lost. A bag can be light and still slow. It can offer a lot of volume and at the same time continuously cost energy. That is exactly why the relationship between packing volume, weight and aerodynamics is so important.

The CYCLITE FORK BAG / 01 weighs 224 g and offers 3.1 l of volume. These numbers alone, however, do not describe the decisive point. The bag becomes interesting because it creates storage space in an aerodynamically critical position without behaving like a classic brake in the tested setup. On the contrary. The measurement shows that its shape and positioning can create a positive overall effect.

This changes the perspective on fork bags. Usually, the trade-off is: more storage space on the fork costs aerodynamics. With the CYCLITE FORK BAG / 01, the trade-off looks different.

Conclusion

So do fork bags generally have no major aerodynamic disadvantage? That is exactly what the data does not show. The classic round fork bag was significantly slower in the test. The more important insight is that the shape and system integration of a fork bag are extremely decisive.

With the CYCLITE FORK BAG / 01, this exact combination seems to work. The bag sits narrow and close to the bike, integrates better into the area around the fork and front wheel and apparently changes the airflow in such a way that the additional drag was not only reduced, but overcompensated in the tested setup. The result is a lower measured total CdA than in the reference setup without fork bags.

This is aerodynamically remarkable because it contradicts the usual gut feeling. More luggage normally means more drag. Here, the test shows that a well-integrated component can improve the complete system.

Fork bags are considered aerodynamically critical for good reason. Classic round bags hang in an exposed position in the wind, increase frontal area and often generate additional turbulence. The test fundamentally confirms this skepticism. The round standard fork bag was significantly slower in the tested setup than the reference without fork bags.

However, the CYCLITE FORK BAG / 01 behaved differently in this test. In the tested setup, it was not only significantly faster than a classic round fork bag with comparable packing volume, but also faster than the setup without fork bags. In the 100-km forecast at 200 W, this resulted in a calculated advantage of 11 minutes per 100 km compared with the classic 3 L fork bags, and an advantage of just over 4 minutes compared with the setup without fork bags.

The most likely explanation is that its narrow, wedge-shaped form, sitting close to the bike, has a favorable effect on the airflow in the area of the fork, front wheel and legs.

For performance-oriented bikepacking, this is an exciting insight. The CYCLITE FORK BAG / 01 creates additional storage space on the fork and, in the right setup, can be aerodynamically more favorable. Above all, the test shows one thing: a fork bag does not have to be a necessary evil. If shape, position and system effect are right, it can become part of a faster ultra-cycling setup.

View test report