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I recently explained why aero bikes have taken over the Tour de France, even on the hardest mountain stages.
Modern aero bikes are remarkably light. And because the UCI requires race bikes to weigh at least 6.8 kilograms, a climbing bike is often not allowed to use its biggest advantage. When two legal bikes weigh essentially the same and one is more aerodynamic, the choice seems obvious.
Then Isaac del Toro delivered one of the most noteworthy recent Tour wins aboard a climbing bike, taking Stage 2 on Colnago’s lighter V5Rs.
His teammate and race leader Tadej Pogačar finished second on the more aerodynamic Y1Rs. Same team. Same roads. Two different bikes. The supposedly less efficient one crossed the line first.
So was my reporting about aero bikes wrong?
No. But Del Toro’s choice, and his victory, shows why the fastest bike on paper is not automatically the best bike for every rider, on every stage, doing every job.
The numbers matter.
So does the person riding the bike.
Del Toro’s Bikes Do Not Weigh the Same
Colnago’s Y1Rs is the company’s more aerodynamic race bike. The V5Rs prioritizes low weight.
For some Tour riders, the difference between an aero bike and a climbing bike mostly disappears once both are built to near the UCI’s 6.8-kilogram minimum. That is a reason aero bikes have become so common on mountain stages.
Del Toro’s two bikes are different.
According to Colnago head of product Davide Fumagalli, Del Toro’s V5Rs weighs 6.8 kilograms in race trim. His Y1Rs weighs about 7.1 kilograms.
That means the V5Rs retains a real advantage of roughly 300 grams, or about two-thirds of a pound. This is not a comparison of bare frame weights. It is the difference between his complete race bikes.
But that still does not make the V5Rs automatically faster.
The Y1Rs creates less aerodynamic drag. It can save energy on flatter roads, rolling terrain, descents, and faster climbs. Those small savings can accumulate for hours before the race reaches the section that ultimately decides the result.
Weight may win the climb.
Aero can still win the ride.
The Rider’s Job Changes the Answer
When I asked Fumagalli last year how UAE decides between the Y1Rs and V5Rs, he outlined three primary considerations: the rider’s role, the specific performance demands of the stage, and the energy the bike can save before the decisive moment.
A rider expected to spend much of the day working at the front is an obvious candidate for the Y1Rs. His most important work happens at high speed, where aerodynamics matters most. Carrying a few hundred additional grams up the final climb is less important if his job is already done.
Del Toro’s role is different.
Fumagalli said Del Toro’s decisive efforts are usually concentrated into relatively short climbing sections. At lower speeds and on steeper gradients, the Y1Rs’ aerodynamic advantage becomes less significant while the V5Rs’ lower weight becomes more useful.
But weight is only part of the reason Del Toro chooses it.
Fumagalli said Del Toro particularly values the V5Rs’ stability and handling. That is why he sometimes chooses it not only for summit finishes, but also for rolling and selective stages.
That complicates the tidy aero-versus-weight argument.
Del Toro is not simply looking at the stage profile and choosing the slightly lighter bike whenever he sees a mountain. He is choosing the bike whose behavior best matches how he expects to race that day.
“In the end, marginal gains are not just a number measured in a wind tunnel,” Fumagalli told me. “They are the result of a much more complex equation—one in which the most difficult variable to quantify is always the rider.”
Feel Is Not the Opposite of Performance
Cycling’s hard data can tell us a lot.
It can measure drag. It can calculate how much time 300 grams costs on a steep climb. It can estimate the energy an aero frame saves over a stage.
But a bicycle is not raced by a calculation.
It is raced by a person who must position it in a nervous peloton, throw it into corners, follow wheels on descents, react to attacks, and commit when the race begins to break apart.
A bike that feels stable and predictable may allow a rider to brake later or hesitate less. A bike that feels more responsive may encourage a sharper acceleration. A bike a rider trusts may leave more attention available for the race instead of the machine underneath him.
Those effects are difficult to isolate and measure. That does not make them imaginary.
Del Toro gives away some aerodynamic efficiency when he chooses the V5Rs. But Stage 2 demonstrated why that does not necessarily mean he is giving away performance. On a course packed with short climbs, descents, corners, and accelerations, the lighter bike’s handling—and Del Toro’s confidence in it—may have mattered more than its wind-tunnel deficit.
That does not mean feel always defeats physics.
It means feel is part of the physics once a human being gets involved.
What Del Toro’s Choice Means for You
The lesson is not that climbing bikes are secretly faster. It is not that aero equipment is overrated. And it is certainly not that you should buy whatever bike Del Toro rides.
The lesson is to define what “best” means for you.
Start by comparing complete bikes in your size. A 300-gram difference is a different decision than a three-pound difference. Do not assume every aero bike is heavy or every climbing bike is dramatically lighter.
Then consider the complete ride. Fast group rides, exposed roads, rolling routes, and long periods at higher speeds usually favor aerodynamic efficiency. Long, steep climbs give lower weight a better opportunity to matter.
But also pay attention to how the bikes feel.
Which one fits you better? Which one encourages you to stay in an efficient position? Which one makes you more confident on a descent? Which one disappears beneath you instead of demanding your attention?
Those are not frivolous questions. They affect how you ride.
I still believe aerodynamics is the better default when the goal is covering a complete ride as quickly and efficiently as possible. Del Toro does not disprove that.
He demonstrates that the calculation does not end with the wind tunnel.
The fastest bike may be the one that produces the lowest modeled time. The best bike may be the one that feels right enough that you can actually use what it gives you.
Sometimes those are the same bike.
Sometimes they are not.
