On the back of an unfortunate incident that led to me no longer owning my Emonda, (apologies to anybody who buys my now stolen broken bike from Gumtree), I’ve had the opportunity to experience what it’s like to ride a bike at the other end of the spectrum. The slick and highly aerodynamic Cervelo S5 is a bike so far away from the rounded lightweight climbing machine that I’ve been accustomed to that I think the only real similarities that can be made are that they both still have two wheels.
Up until now I had always had the mentality that it was your legs and body that made all the difference when it comes to riding faster, and that aero bikes were designed purely for marketing purposes. That they were made to convince cyclists that they need one extra bike (which we always do) in their garage. That the number of grams of drag saved was just a fancy phrase that weak riders would be drawn in by, in the hopes that it might get them that bit closer to the pro peloton. Why would I need to save Watts anyway, when I can just get stronger instead?
Well, that mindset went completely out of the window within the first few kilometres of riding the S5 because, to put it simply, it is an extremely fast bike. Every road I went down, regardless of wind direction, I seemed to be riding a couple of mph more than usual.
Of course, part of the speed increase will be a result of the aggressive geometry, a design feature that defines the aero bike genre. Compared to the Emonda, the head tube length of the S5 at 155mm is 15mm shorter and the combined length of the reach and stem makes you feel like you’re being forced into Graeme Obree’s “Superman” position. Up to 85% of the drag experienced by a cyclist will come from the rider alone, so a forced reduction to the rider’s frontal area will no doubt be a significant factor in reducing drag.
However, quite fascinatingly Cervelo claim that the S5 can save up to 32W in comparison to “typical” road bikes. That’s 32W in the bike alone! It’s interesting that Cervelo doesn’t mention what bikes they were comparing to, “typical” is definitely quite vague, but it’s probably safe to assume that these “typical” bikes were not far off the Emonda’s design, because the large round tubing doesn’t entirely lend itself to being aerodynamic. 32W is definitely a figure to be cautious of (fancy marketing phrases etc), but if the bike were to save only half that, I would still consider it an impressive saving.
With the combination of aggressive geometry and blade-like aerodynamics, the claimed reduction in drag is certainly verifiable, at least in perceived effort, when you ride the bike. If only my power meter hadn’t been on my late Trek then I may have been able back this claim up with cold hard numbers…
All this Formula 1 style aerodynamically designed geometry must come with some sort of weight penalty though, surely? Well, yes, but it’s not nearly as drastic as one might think. Both the Cervelo S5 and the Cannondale SuperSix have a claimed weight of just under 8kg, depending on which combination of tires, pedals, bar tape, etc. Initially, that sounds quite a lot, especially considering that most high-end bikes around that price mark will be much closer or even less than 7kg. I, for one, would previously quite happily open my wallet for upgrades that would result in a slight weight reduction; but it’s a number that I think I’m beginning to accept.
After only riding the S5 for a few days, I’ve covered just about 2000m of elevation over a wide variety of gradients, and the weight difference is only really noticeable once you start tipping over the 10% mark. And I mean, only slightly noticeable in the same way that having a full water bottle feels slightly heavier. For me, at 70kg with previously a 7.2 kg bike an increase of half a kilo represents a 0.6% increase in system weight. For any rider that isn’t competing at a high level within the sport, I think it would be a pretty poor excuse to use for a bad segment time.
Even crazier still, Cannondale actually claim that the SystemSix is faster than a climbing bike for gradients up to 6%. The S5 is obviously not the same bike, but the design is very similar, and for those low gradients it holds its speed just as efficiently as on the flats. In fact on a recent ride out I managed to smash some of my previous uphill PB’s by quite a substantial margin; most of that will probably have come from an increase in fitness, but it certainly proves that the bike doesn’t hold you back.
Overall, I can safely say that my opinion on aero bikes has drastically changed. Its clear from my experience that their drag-reducing characteristics can be realised by the amateur and weekend warrior, and are not just part of the ‘marginal gains’ category that only the pros benefit from. The manufacturers will obviously squeeze as much from their tests as they physically can to beef their numbers up, but regardless, it’s now clear to me that there is truth behind it all. Aero bikes do allow you to ride faster for less (Watts, not money).
Will I be buying one? Perhaps, because on 90% of roads they’re exceptional. But irrespective of the wind tunnel science and CFD testing, I’ll still be looking for something a little lighter when it comes to the hill climbs.
- Cervelo S5 Tech Paper: https://www.cervelo.com/media/gene-cms/s/5/s5_tech_paper_2.pdf
- Cervelo S5 White Paper Executive Summary: https://www.semanticscholar.org/paper/Cerv%C3%A9lo-S5-White-Paper-Executive-Summary-Aero/8062f7d98509d9ad95faff521cd50e4534ea1591