We looked at the aero vs. weight question way back in 2006, which is what's presented below. Recently we checked the same question with data from modern frames, and while we're too busy engineering the next generation of Cervélos to update this presentation, we can tell you the results are still within 1% of these old numbers. Enjoy.
To answer the weight vs. aero question, we need to look at two issues:
- What are the weight differences between aero and non-aero frames?
- Does the aero advantage outweigh the weight advantage in various scenarios?
Step one: Ignore manufacturers’ claimed weights. They often weigh super small frames, with no paint, hangers, bolts – or simply make up a number. Here are the results from two magazines that verified frame weight.
The first is VeloNews, which weighed five supposedly 900 gram ProTour road frames.
The second is a TOUR (Germany) test of TT/Tri frames. To be fair, TOUR normalizes on size 57cm, slightly above a reasonable “average” size for quoting weights.
Look at the column above labeled "Claimed weight." This may look like a wide range of weights, but the difference in actual weights is often tiny, less than the weight of an energy bar. This is caused by their tube shapes, which are not solely focused on light weight (like for example the R3’s Squoval tubes) but also on (the appearance of) being aero. Even for road, aero doesn't have to mean heavier. In fact, the full-aero Soloist Carbon is lighter than several of the non-aero “900g frames” from the table of road frame weights. And the SLC-SL is lighter still. An aero frame designed with attention to weight is often lighter than a “light” frame.
But what if both the aero and the light frame are optimized? The Cervélo Soloist and R3 ranges offer us that comparison. Both are designed with the same tools, stiffness philosophy, stringent safety standards and attention to detail. The only difference between them is the ultimate aero vs. ultimate lightweight focus.
The weight delta between a Soloist Carbon (SL) and an R3 (SL) is approximately 150g.
What does 150g really mean?
150g on a 1000g frame sounds like a lot, but of course we are not accelerating or climbing with just the frame. At all times, we also have the other bike parts and, more importantly, the rider, to deal with. If we assume a 7kg bike and lithe 50kg (110lb) rider, the 150g frame weight savings only represent an overall weight savings of 0.26%. These savings are indicated above in red.
For a heavier 100kg (220lb) riders, it’s even less: 0.14%.
What are the aero savings?
On to the difference in drag between a good aero frame with narrow tubes and a frame with more voluminous tubes optimized for low weight. Similar to the weight delta, the drag difference is large between just the frames, but much smaller when looking at the drag of bike and rider combined. Lowering Cd by 0.009 on an overall Cd of 0.60 works out to a savings of 1.5%. A Cd of 0.60 is a good number for a rider on a road bike; while around 0.5 would be good in the aero bars on a TT bike.
So what is more important, saving 0.26% in weight or 1.5% in drag?
Naturally the answer depends on where you ride. On the flats, where aerodynamics can be up to 90% of your resistance, saving 1.5% in drag is the answer. But if you are one of those rare riders who only ride up crazy climbs like the Mortirolo (and take the gondola down), take the 0.26% weight saving.
But where is the tipping point?
"Col de la Tipping Point"
How steep does a climb have to be before the weight savings trump the aero gains? As we saw before, the answer depends on the rider weight and speed, as a faster rider would encounter higher aerodynamic forces while the gravitational forces stay the same. For an average, 250 Watt rider, the tipping point is around a 5% slope, for a good pro who puts out 400 Watt, it’s at 8%.
What's an 8% climb?
Alpe d’Huez has an average slope of 8%. So for a pro on the ultimate climbing terrain, the aero bike is just as fast as the light bike! That’s of course if this aero bike is a Soloist Carbon and the light bike is a Cervélo R3 or a Scott CR-1 Limited. Most “light” bikes would actually be slower, even up Alpe d’Huez. More later about the SLC-SL case. On top of that, the aero frame saves you energy on all the flats, up moderate climbs and on descents.
That’s nice for Frank Schleck, but how about us 250 Watt riders?
If we just want to climb Alpe d’Huez, saving those 200g would be worth it as the tipping point is at 5%. But for a course with climbs and descends it is more complicated.
Let’s look at the 2007 Etape du Tour, held on one of the toughest stages of the Tour. Our model predicts a time of 8h 00m 35s (including turns, stops, group riding) for the aero bike. This is 35sec faster than the light bike with the same 250W rider – despite the very hilly course.
So, can you have your cake and eat it too?
Comparing actual, not claimed weights, the R3/R3 SL and select others save you some real weight. But as we saw, most other “super-light” frames aren’t really that light. As a result, you can get an aero frame that weighs just as little as one of these “super-lights”. Or get an SLC-SL and clearly beat 99% of the frames on weight yet be fully aero. Fittingly, when Frank Schleck won the 2006 Tour stage to Alpe d’Huez, he was on an SLC-SL.
For the absolute lightest without sacrificing stiffness or strength, you can't do better than our R-series bikes. They also fits wide tires, even some cyclocross tires.
So they are designed to be:
Strong and ideal for bad conditions:
- Victory in the toughest race, Paris-Roubaix, with the lightest frame under the heaviest rider (Fabian Cancellara seen on the right in the above image)
Light yet stiff in bottom bracket and torsion:
- Lightest and stiffest frame in the ProTour
- Winner of the TOUR test of ProTour bikes
- Winner of stiffness-to-weight tests published by our competitors!