Chasing maximum cycling performance hinges on a critical issue in the philosophy of bike design. Which matters more: lightweight or aero?
Cyclists and engineers grapple with this age-old question, navigating the delicate balance between shedding grams for uphill slogs and making the bike and rider as slippery as possible to prioritize aerodynamics on flat terrain.
The higher the speed, the more important aerodynamics are. On the other hand, the steeper the gradient of a climb, the more important weight savings become.
Therefore, there’s a tipping point speed or gradient between the two, where the balance shifts from one to the other.
For professional cyclists, this tipping point is typically at gradients of around 7.5%. Because amateurs ride more slowly, the tipping point is also lower, typically at around 4.5%.
As a result, in the majority of cycling situations, aerodynamics are more important than weight.
However, this is a massive simplification, and there’s much more to explore about how to prioritize these two factors to suit your riding and even to support your strategy in a bike race through your equipment choices. In this guide, we’ll be covering:
Lightweight Vs Aero On Flat Terrain
Jean-Paul Ballard, an experienced aerodynamicist and engineer with over 14 years in Formula One, co-founded Swiss Side. He brings a wealth of knowledge in aerodynamics to cycling.
Ballard highlights, “From speeds as low as 9 mph (15 km/h), aerodynamic drag is the primary resistance a cyclist faces.”
The general belief is that for mountainous rides, lighter gear offers the most advantage.
But what about when riding a gran fondo or a hilly sportive at an average of 16 mph (25 km/h)? Does aerodynamics or weight play a more significant role?
To illustrate his point, Ballard shares a specific case study:
“Consider a simulation of a 75 miles (120 km) route with 3,280 feet (1,000 meters) of elevation, ridden at an average speed of 16 mph (25 km/h). For an 80 kg cyclist on an 8 kg bike, the average power output is about 150 W.
“Let’s compare the effects of a 5% aerodynamic improvement on the bike against a 5% reduction in the bike’s weight. This scenario is like choosing between a lightweight set of climbing wheels and a set of aero wheels.”
So, in this scenario, which option yields more time savings?
Reducing aerodynamic drag by 5% leads to a time saving of 3 minutes and 30 seconds, whereas reducing weight by the same percentage saves only 20 seconds.
In other words, on relatively flat ground, aerodynamics are much more valuable to cyclists than weight savings.
Lightweight Vs Aero On Climbs
Except for scenarios like a mountain summit finish or an uphill time trial, an aerodynamic bike is almost always the faster option across an entire stage.
This holds true even when riding in the protection of the peloton, where the reduction in drag remains significant and beneficial.
To put this into perspective, Ballard notes that for professional cyclists, the tipping point where bike weight becomes more critical than aerodynamics is on climbs with an average gradient of 7.5%.
For amateur riders, this threshold is lower, around 4.5%, due to their generally slower speeds.
These insights, however, are broad generalizations. The specific gradient at which weight trumps aerodynamics varies by individual.
Nevertheless, the overarching evidence indicates that only in uphill time trials or races ending at a summit does a lightweight, less aerodynamic bike setup become advantageous.
The importance of bike weight is primarily in acceleration and on exceptionally steep climbs. Its impact is often exaggerated in road biking.
Why is this the case? Weight is a tangible factor. Lifting a bike immediately reveals its lightness. It’s a common experience for many cyclists.
In contrast, identifying an aerodynamic bike is less straightforward. Assessing aerodynamic efficiency requires more complex methods like wind tunnel testing or computational fluid dynamics (CFD) software.
Unlike weight, aerodynamics isn’t something you can easily gauge by simply picking up a friend’s bike before a ride.
What Are Aero Bikes?
Aerodynamic bikes prioritize minimizing wind resistance. They aim to be as streamlined as possible since 85% of the resistance a cyclist faces is their own body.
To reduce this resistance, aerodynamic bikes often feature a shorter head tube, leading to a lower frontal profile.
Along with a shorter head tube, aerodynamic bikes usually have a longer frame reach, measured horizontally from the bottom bracket axle’s center to the head tube. This reach provides insight into the bike’s design purpose.
It’s crucial to differentiate between frame reach and rider reach. Rider reach is the distance from the saddle tip to the handlebar center and can be adjusted with a longer stem or more saddle setback.
The aggressive geometry of aerodynamic bikes may pose a challenge for riders lacking the flexibility or core strength to maintain the intended position.
Without the ability to comfortably achieve this lowered position, the aerodynamic advantages diminish, and there’s a risk of injury.
Aerodynamic bikes also push the boundaries of UCI regulations with tube profiles adhering to a 3:1 ratio – for every centimeter in depth, they can be up to three centimeters long.
These tubes are designed to cut through the wind with a tapered leading edge and sculpted tail. Sometimes, the tube ‘tail’ is truncated, simulating a sculpted tail in varying wind angles.
The frame shape of these bikes is notably aggressive and angular. Unlike the sloping top tubes seen in lightweight and endurance bikes for added comfort, aerodynamic bikes often feature straight, flat top tubes.
This design shortens the distance from the seat tube junction to the seat, enhancing stiffness and reducing frontal profile.
However, the extra material needed for these aerodynamic forms typically makes these bikes heavier than their lightweight counterparts, even with similar geometry and specs.
Time trial bikes are the most aerodynamic of all, but are only legal for time trial stages, not in regular racing.
Perhaps the most visual demonstration for cycling fans of the tipping point between lightweight and aero is on hilly time trial stages, such as Stage 16 of the 2023 Tour de France.
Tadej Pogačar started the stage on a time trial bike, before a frantic pre-planned switch to a lightweight road bike as the course reached a major climb.
That being said, Pogačar was blown away by Vingegaard on the stage, despite the Dane sticking with his time trial bike throughout!
What Are Lightweight Bikes?
Lightweight bikes aim to be as light as possible while maintaining a balance in performance features.
Positioned between the specific characteristics of aero and endurance bikes, lightweight bikes are often the preferred choice for General Classification riders and team leaders. They strike a balance in comfort, stiffness, and handling.
While they aren’t as comfortable as endurance bikes, they generally offer more comfort than aero bikes.
In terms of handling, they’re comparable to aero bikes but are more agile due to their reduced weight.
The design of lightweight bikes focuses on slim tube profiles that balance stiffness and durability without adding unnecessary weight. This slimness allows for some flexibility, absorbing road vibrations for a smoother ride.
To optimize the balance between lightness and strength, these bikes often feature enhanced stiffness in key areas like the bottom bracket, seat tube, head tube, and chainstays, achieved through specific carbon types or additional fiber layers.
While lightweight bikes may not be as rigid as aero bikes, their stiffness-to-weight ratio is more favorable.
Aero bikes, with their thicker tubes, are stiffer but heavier. Lightweight bikes manage to offer comparable stiffness with slightly less weight.
The geometry of lightweight bikes varies among manufacturers, depending on their range of models.
Some, with separate lines for aero, endurance, and lightweight bikes, may lean towards a more aggressive geometry for their lightweight models. Others might offer a more relaxed geometry, especially if they lack a dedicated endurance bike in their lineup.
As modern-day all-rounders, the geometry of lightweight bikes can vary widely.
What Do The Pros Choose?
Professional cyclists like Jumbo-Visma’s Vingegaard, sponsored by Cervélo, have the advantage of selecting their equipment according to the race stage.
For instance, at the start of this year’s Tour de France, Vingegaard rode the Cervélo S5, an aerodynamically optimized road bike with features reminiscent of the Cervélo P5 time trial bike, emphasizing its focus on cutting through the wind efficiently.
However, Vingegaard switched to the Cervélo R5 for high mountain stages, a lightweight climbing bike.
Though it still integrates aerodynamic elements, this bike veers towards a more traditional design, prioritizing low weight and high stiffness for better performance on long climbs.
It’s also worth noting that strategic concerns might see a pro cyclist opt for a lightweight setup for climbing, even if the stage as a whole may favor an aero bike.
This is because the most decisive moments of racing are likely to happen on climbs, especially on their steepest sections. Therefore, they may choose their equipment to prioritize performance in those crucial moments of racing, rather than the stage as a whole.
You’d be most likely to see this situation on a stage that’s largely flat, but features a major climb (or multiple climbs) at the end, especially if it includes a summit finish.
Weight Vs Aerodynamics in Bike Wheels
As for wheel rim depths, pro riders face a similar dilemma between deeper rims, which are heavier but more aerodynamic, and shallow rims, which save weight at the expense of aerodynamic efficiency.
As a result, pro cyclists will often adapt their choices of wheels depending on the terrain of the stage they’re racing.
Wheel Choice For Mountain Stages
Wheels with depths of 35 mm or below are ideal for steep climbs due to their lighter weight.
Wheels in the 30-35 mm range used to be considered “mid-depth”, but with advancements in carbon fiber technology, they offer similar lightness with improved aerodynamics and are now at the shallow end of the range of wheels typically chosen for road bike racing.
Wheel Choice For Hilly Stages
Wheels in the 35-50 mm depth range are highly versatile and popular in modern professional cycling.
They balance well on both steep and gentle slopes, offering better aerodynamics for higher speed and acceleration.
For those who prefer not to switch wheels often, a wheelset in the middle of this range is a good all-around choice.
Wheel Choice for Flat Roads
Wheelsets with a depth of 50-65 mm are mainly designed for flat roads, providing enhanced speed and stability with improved aerodynamics.
To counteract crosswind effects, some models use a combination of shallower front and deeper rear wheels.
Wheel Choice for Time Trials
Lastly, wheels with a depth of 65 mm or more are less common, and typically reserved for triathlons or time trials.
Some may even use disc wheels, pushing the philosophy of deeper rims to its natural limit.
Focused solely on aerodynamics, these wheels are heavier and less comfortable, requiring skilled handling due to their susceptibility to crosswinds.
Weight Vs Aerodynamics For Casual Riders
Many casual riders believe that aerodynamics only matter if you’re riding at high speeds.
This perception suggests that aerodynamics is a concern exclusive to those who are always pushing their limits in terms of speed.
While it’s true that drag becomes significantly greater at higher speeds, it’s a misconception that only fast riders reap the benefits of aerodynamic enhancements.
Jean-Paul Ballard explains, “Drag increases with speed, as it’s tied to the square of velocity. However, faster riders spend less time on the course and encounter a narrower range of wind angles.
“Our simulations show that slower riders can actually save more time overall.
“Since they’re on the course for a longer duration, they benefit from aerodynamic improvements for an extended period.”
We’d love to hear about your experiences and choices
It’s clear that the choice between the two is not just about speed or comfort; it’s about understanding your riding style and the terrain you’ll be conquering.
From the in-depth insights of expert Jean-Paul Ballard to the strategic choices of Tour de France winner Vingegaard, we see that the decision is as much about personal preference as it is about technical specifications.
Whether you’re a casual rider discovering the benefits of aerodynamics at lower speeds or a competitive cyclist weighing the advantages of a lightweight bike on steep climbs, your experience is unique.
Have you tried both aero and lightweight bikes? Did you notice a significant difference in your rides? Do you adjust your bike or wheelset depending on the route?
Share your stories and tips in the comments below!
