Aero bikes are for sprinters, and climbing bikes are for climbers, right? Well, that depends.
Peter Sagan won his third stage at the 2018 Tour de France on his Specialized S-Works Venge. That’s not much of a surprise: Sprinters have long embraced aero bikes to get them to the line quickest. Conversely, climbing specialists have mostly avoided these heavier bikes at the Tour. When going uphill, lighter is faster.
Not so fast. (Forgive the pun.) For the vast majority of riders, those of us not racing through France this July, an aero bike might actually be the better tool, even on some climbs. But there is a reason you won’t see the likes of Romain Bardet or Chris Froome ditching their featherweight climbing rigs any time soon.
First, consider what actually constitutes an aero bike: a frame built with truncated airfoil shapes, mated to deep-profile wheels, and integrated cockpits. Those elements combine to reduce drag at various yaw angles you’ll encounter in real-life riding situations.
Next, consider a climber’s bike: It has a frame built with mostly round or slightly shaped tubes, mated to low- to mid-depth wheels, and far less integration. All of those elements combine to make the lightest bike possible (while meeting the UCI’s 6.8kg minimum weight rule, though production bikes are often much lighter than that). Climbers’ bikes are perhaps the most likely to stick to rim brakes for the foreseeable future in the pro peloton, again to shave grams.
However, those two categories are beginning to overlap. Now, you can find a few crossover bikes that feature aerodynamic touches while maintaining the overall look and feel of a climbing bike. Take BMC’s Teammachine SLR 01, for example. While the truncated airfoil shapes aren’t as pronounced as they are on something like a Trek Madone, they’re still there to help reduce aerodynamic drag. It’s likely we’ll see more of this crossover type of bike in the near future.
That’s because, as it turns out, the benefits of aerodynamic tube shapes outweigh the light weight of a climber’s bike, even on the majority of climbs. When Cannondale engineers were designing the new SystemSix aero bike, they quickly realized that riders would benefit from aerodynamic tube shapes on climbs up to a 6 percent gradient.
“For most people, aerodynamics is the most important design constraint,” says Nathan Barry, Cannondale’s road design engineer. “If you want to design an ultra-lightweight bike that’s five kilos or something, you’re not going to be able to have tubes that are as deep as we have on SystemSix. Now that doesn’t mean that bike is going to be faster most of the time. In fact, it’s going to be slower most of the time unless you’re going up a very steep hill. For most people, aerodynamics is the most important design constraint, so you can add a little bit of weight to that system in order to reduce its drag. We’ve talked about what the performance gains are. For a bike like SystemSix, that tipping point is around 6 percent grade.”
So why aren’t the pros giving up their less aerodynamic climbing bikes anytime soon? Those guys are most likely to encounter steeper grades with regularity. Stage 12‘s finish on Alpe d’Huez averages right around 8 percent and kicks up to 13 percent in places. Monte Zoncolan averages 11 percent and maxes out at an astounding 22 percent. Even Mont Ventoux averages right around 8 percent grade.
It’s clear that a climbing bike would benefit riders on long stretches of steep climbing.
Couldn’t a climber like Rafal Majka outfit his Venge with superlight components to combine aero and light weight? Yes, he could, but it wouldn’t quite reach that 6.8kg mark — and every detail matters for Tour de France riders.
But for the rest of us, it’s likely an aero bike might be a more appropriate choice than a climber’s bike. If you still love the feel of a climber’s bike, you’re in luck: The categories are melding rapidly.
“Within the 6.8kg rule, with the Venge we’ve got pretty close to one bike that can do it all,” says Eric Schuda, road product manager at Specialized Bicycles. “Our teams do have Tarmacs still, and they’ll ride them on the mountain stages or the ones that have the key climbs because it still is a lighter bike.”
But it’s only a little bit lighter — about 300 grams. Schuda says comfort wasn’t a design goal of the new Venge; it was all about weight savings while maintaining aerodynamic advantages. That meant tailoring the truncated airfoil tube shapes to shave weight wherever possible and measuring that against the aerodynamic trade-offs. “We knocked 460 grams out of this Venge,” he says of the new bike. “And the comfort goes up significantly as a side benefit.”
In other words, the Venge comes close to giving the rider all of the advantages of the Tarmac — Specialized’s all-around bike — and all the advantages of its aero lineup.
But it’s still only close. There will always be a tradeoff between aerodynamics and light weight, simply because the most aerodynamic shapes require that materials be added to the frame. A full airfoil — one that is not truncated, or chopped off at the rear end — would certainly add the most aerodynamic gains. But that comes at a cost, both in added weight and ride characteristics. A full airfoil would essentially act as a sail in crosswinds, making the bike difficult to control. It also reduces lateral stiffness, which in turn leads to pedaling power loss.
So for now, you’ll still need to choose between aero bike and climbing bike. Fortunately, the choice should be somewhat easy: If you routinely climb pitches that are steeper than 6 percent or thereabouts, a climbing bike is probably your best tool for the job. For just about everything else, an aero bike probably benefits you more. Of course, if you’re looking to conquer all types of terrain, perhaps consider something that bridges the gap between the two categories.
Fortunately, that group of bikes is growing in size every year.