Designing the perfect bicycle race bottle: Engineering in hydration
In the world of professional cycling, attention to detail can make the difference between victory and falling behind— and that principle extends all the way to the water bottles clutched by the riders. Far from being simple vessels, these bottles embody a sophisticated interplay of ergonomics, aerodynamics, and cutting-edge engineering, design considerations that ultimately influence hydration, rider comfort, and even performance over grueling race stages. Today, the development of such seemingly ordinary products relies heavily on modern simulation technology.
Bottle squeezing simulation for the perfect race bottle
The newest release of Simcenter STAR-CCM+, version 2506, brings a significant innovation to this domain with Enhanced Linear Hex Elements. This enhancement revolutionizes simulation efficiency for thin-walled structures like bicycle bottles, providing more than three time the speed for structural simulations and with that providing also a substantial speed-up for Fluid-Structure Interaction (FSI) scenarios. As a result, engineers can rapidly iterate on their designs, achieving the ideal balance of weight, flexibility, and performance needed for elite competition, helping riders stay hydrated without missing a beat.
Designing a cycling bottle that excels on all these fronts requires a meticulous approach. Factors such as bottle shape, wall thickness, material choice, and nozzle design all directly impact not just the user experience, but the product’s manufacturability and cost. Mistakes in this phase can become expensive fast, as the production of advanced extrusion blow molds can reach €10,000 or more per piece.
That’s why simulation platforms like Simcenter STAR-CCM+ are indispensable in today’s product development. By modeling a bottle’s structural response to hand pressure, engineers ensure that each bottle is light, resilient, and fits seamlessly into a rider’s hand and bottle cage. Activating the software’s fluid and FSI capabilities, designers can further refine flow characteristics, ensuring every squeeze delivers instant, effortless hydration with minimal strain, stage after stage.
A solid grip
One of the first considerations when designing a drinking bottle is how it feels in the rider’s hand. Grip is essential — cyclists must be able to grab, squeeze, and return the bottle to its cage almost without thinking, especially when fatigue sets in towards the end of a long stage. The side walls need to be as flexible as possible to allow an easy squeeze. The bottom needs to be stiffer so that the bottle springs back into its original shape to fit tightly into the bottle cage. The top of the bottle—which connects to the lid—must always remain sturdy to avoid fluid leakage.
To simulate real-world use, we look at a typical squeezing event: a cyclist compresses the bottle by 10 mm on each side in just 0.15 seconds, holds that grip for 0.2 seconds, and then releases it. (We can safely ignore the pinkie finger in the load distribution, since, as any close observer of cycling will notice, it doesn’t contribute much.) Accurately capturing this interaction is crucial for delivering a product that performs under racing conditions.
Simcenter STAR-CCM+ Structural Mechanics provides all the tools needed to simulate this kind of squeezing action and analyse how wall thicknesses influence the required force. According to ergonomic studies and published literature, most users find squeezing forces between 10 and 20 N comfortable during repeated use, while forces above 30 N are regarded as noticeably hard and uncomfortable. For a typical racing bottle design, our structural simulations show that a side wall thickness of 0.6 mm results in a squeeze force of roughly 8.6 N—well within this comfort zone. Reducing the wall thickness by just 0.2 mm more than halves the required force; increasing it by 0.2 mm nearly doubles it. This highlights how crucial wall thickness selection is for an ideal bottle design.
Accurate bending with enhanced linear hexahedral elements (Hex8E)
Modeling the bending deformation of such thin-walled structures requires appropriate mesh elements. Here, hexahedral element meshes are ideal. The new enhanced linear hexahedral elements (Hex8E) introduced in Simcenter STAR-CCM+ 2506 deliver nearly the same quality of bending simulation as higher-order Hex20 elements, but at the far lower computational cost of standard Hex8 elements. In comparison, using standard Hex8 elements in such bending-dominated problems can lead to strong locking effects, resulting in a predicted squeeze force up to 2.5 times higher than reality. Enhanced Hex8E elements, on the other hand, not only provide accurate results but also speed up the simulation—three times faster in this case and up to seven times faster for larger structures compared to Hex20 elements.
With these advancements, engineers can efficiently explore and optimize the tactile experience of the bottle—making sure it’s easy to squeeze, quickly rebounds, and maintains its integrity ride after ride, all while accelerating development cycles and minimizing costly prototyping errors.
1: Diagram Comparing thicknesses with 0.6mm Hex8 vs Hex8E vs Hex20, and then 0.4mm and 0.8mm Hex8E as a function of time, together with Finger motion
2: Normalized solve times for structure-only simulation with varying number of processes (NP)
Understanding the Fluid-Structure balance
A particularly critical factor in water bottle design is the amount of pressure a rider must exert to get water flowing. At the tail end of a grueling race, Tour de France cyclists have limited energy to spare, and the last thing they need is to struggle with a stubborn bottle. It is vital that bottles require as little force as possible to deliver a satisfying water flow. Not only does this minimize the time riders spend drinking—time during which their focus is inevitably split from the road—but it also reduces physical strain, allowing them to maintain maximum concentration and performance until the finish line.
When the bottle is squeezed, both the water and the trapped air pocket inside are compressed, resulting in a flow of water out of the nozzle. The exact behavior—how much water is expelled for a certain squeezing force—depends not just on the applied hand pressure, but also on the intricate relationship between the nozzle geometry, bottle wall flexibility, and the ratio of air to water in the bottle. This interplay of structural and fluid dynamics is complex and cannot be fully captured without a comprehensive multiphase Fluid-Structure Interaction (FSI) simulation.
One of the significant advantages of using Simcenter STAR-CCM+ for this process is its seamless integration of structural and fluid modeling. To transition from a structural simulation to a full FSI setup, only the fluid domain needs to be defined and added to the previously established structural model. Advanced features like dynamic stabilization, FSI traction residual, and dynamic stabilization residual ensure that simulations remain robust and accurate, even under the fast, transient loads experienced during real-world bottle use. Importantly, as pressure builds within the bottle, it not only drives fluid out, but also increases the needed squeeze force and also causes further deformation of the plastic structure—making a two-way coupled FSI approach essential for realistic results.
The results of such FSI simulations, as shown in diagram 4, illustrate a key point: in addition to the force needed just to deform the plastic, riders must also overcome fluid resistance as water is forced through the nozzle. In this case, the force needed to squeeze the bottle with fluid inside is more than 4 times higher than without the fluid in place. For truly optimized performance, both the structural design of the bottle and the geometry of the nozzle must be considered together, ensuring maximal water flow at the lowest possible squeezing force.
3: Water Mass Flow as a function of Squeeze Force from FSI simulation
From Design to Manufacturing
Once the optimal design for the cycling bottle has been finalized, attention turns toward manufacturing—specifically, ensuring that the desired shape and carefully chosen wall thicknesses can actually be achieved in production. With the finite element–based computational rheology capabilities of Simcenter STAR-CCM+, engineers can simulate the blow molding process itself. This capability allows for the virtual prediction of material flow and the resulting thickness distribution within the final bottle—long before any physical tool is cut.
In the latest release, Simcenter STAR-CCM+ 2506, new contact modeling features have been introduced—enabling simulation of interactions between the expanding bottle and the mold during forming. This ensures that critical geometric features and thicknesses are faithfully reproduced in manufacturing, helping to minimize costly trial-and-error iterations on the shop floor. By seamlessly integrating product design and process simulation, Simcenter STAR-CCM+ accelerates innovation from the digital workspace to real, race-ready products.
Racing to the top – One perfectly engineered squeeze at a time
So as the grand peloton races across France this July, every squeeze of a water bottle is backed by sophisticated engineering and simulation. What appears simple at first glance is, in reality, the result of advanced digital design and optimization, supporting the world’s greatest athletes in their pursuit of victory, one perfectly engineered squeeze at a time.
