We’re at a point with carbon fiber bicycles that most dedicated cyclists have had a chance to own one or two of them and get a feel for the material’s strengths and weaknesses. Compared to what was achievable in 1999, what we can expect from a carbon creation 15 years down the road might be compared to the difference between Genesis’ first album and The Lamb Lies Down on Broadway. That first album showed almost no promise, and unlike those debuts that announced the arrival of a great new talent, it didn’t hint at the talent that would later compose classics like “Supper’s Ready” and “Back in NYC.” Honestly, the best carbon fiber bikes on the market in 1999 weren’t much better than the best stuff available in 1992.
The emergence of the aero road bike is a sign that manufacturers were beginning to run out of challenges. How much lighter than 800 grams do you want your frame to be? How much stiffer do you want your bike to be? Making them impervious to dings isn’t sexy, so the next big challenge was to make them faster in the only other way possible: Hide them from the wind.
While it’s true that everyone from Look to GT had done aero road bikes in the 1990s, meaning Cervelo didn’t create the category, but they legitimized it. Cervelo was the company that stepped forward to push the aero road frame not as an oddball alternative, but as a whole category. The Specialized Venge, the Giant Propel, the Felt AR and numerous other bikes owe their existence to the fact that Cervelo pushed the aero category with the relentless intensity of an addicted gambler at the slots.
Count BMC among those who need to give Cervelo a nod. The TMR01 is based on BMC’s time trial frame (the TM01 Time Machine) but with a few tweaks for drop bar use.
As far back as 2008 I started hearing from product managers and engineers that all the significant gains bike companies would make in terms of creating bikes that would allow riders to go faster than with the previous designs would come in aerodynamics. Honestly, at the time, I didn’t really believe them. And then one product manager took the time to walk me through the cost of carbon fiber, the way it escalates as you push weight down, an examination of the parts that can practically be made from carbon and the exponential curve of cost bikes would undergo if we started trying to produce 8-lb. bicycles.
And because wind resistance is a squared function, as we’ve learned to eat better, train better, go faster, the bigger the role aerodynamics can play. But aero road bikes pose a more vexing problem than just minimizing wind resistance so we can go faster.
The Old Saw
The standard criticism of bike reviews is that every bike is torsionally stiff but vertically compliant. It became a joke because the observation was made too often, too easily, awarded to bikes that didn’t do anything particularly well. So while the phrase was cheapened through overuse, the bike industry’s wolf crying, it never stopped being a mix of qualities worth pursuing. Some bikes are truly more comfortable while offering great out-of-the-saddle stiffness. I bring this up now because of the problem the inverse causes.
Some years ago I reviewed the Cervelo SLC-SL, a bike that became the benchmark for what an aero bike could achieve with respect to aerodynamic performance. It was a bike that would make the aero skeptic in anyone scratch his (or her) head. The bike was undeniably quick. The bike was as unsteady under sprints as a giraffe on muscle relaxers. Worse, it was less comfortable than riding bare rims over the Carrefour de l’Arbre. I’ve ridden bikes made from Columbus’ legendary Max tubing, stuff that yielded under weight in the same way that a skyscraper does, which is to say that while engineers can tell you they sway in the wind, it flexes not a bit if you run into it. Yeah, it’s like that.
Aero road frames face yet another issue. To make them stiff enough to be worth riding, they usually end up weighing as much as an aluminum frame and riding with the same corpse-like feel.
From an engineering standpoint, making the perfect aero road frame is the holy grail of carbon fiber use. How do you make a bike that seems small to the wind, remains light enough to climb well and not feel like wood and yet can be sprinted on without pounding you into schnitzel?
What I’ve learned from the engineers I’ve talked to is that they’ve learned down tubes and bottom brackets can be wider than previously thought. BB30 and other bottom bracket standards have allowed them to make the BB area even bigger, lending leaps in stiffness. They’ve also learned that you don’t need to make the top tube airfoil shaped. Hell, it doesn’t even need to be perfectly level. If you’re willing to get fancy with the layup schedule and use more high-modulus carbon fiber, you can gain ride feel and stiffness, though that will drive up the cost of the frame through materials and labor.
I’ve liked the BMC bikes I’ve ridden, but my opinion has been they’ve been better at the enthusiast end of things than at the racy end. I like the Team Machine, but when compared to similar racing bikes, the handling was a bit more relaxed and required a bit more input from the rider. Aggressive it was not. The Gran Fondo was, by contrast, one of the best grand touring bikes I’ve encountered. The fact that you can easily mount 28mm tires in it makes it all the more marketable.
When I first looked the TMR01 over I wondered just how aero it would be, based on the many funky shaped tubes. I saw the possibility for a lot of turbulence. A product team can talk Kamm tail this and NACA airfoil that, but ultimately the design is either fast or not.
The TMR01 uses some shapes that may look familiar, but others that don’t. One of the more unusual features of the tube shapes are a number of stepped profiles, in essence small grooves running lengthwise along many of the tubes. What they do is make the boundary layer better follow the tube profile, preventing some of the laminar separation that makes round-tube bikes slower. It is most apparent on the down tube, seat tube and seat post.
The TMR01 also takes the unusual step of integrating the brakes into the frame in a way that almost nothing else on the market does. The brakes are small linear pull (“V” brakes) units; the front is housed beneath an aerodynamic cover so that only the brake shoes protrude, while the rear is mounted beneath the chainstays. The cables are routed internally, cleaning up the front end of the bike for a much less turbulent attack. The “Hinge” Fork provides some of the same tripwire benefit found on other tubes and it is through that structure that the front brake cable is routed in order to keep it out of the wind.
The seat stays attach to the seat tube at the height of the rear wheel’s brake track, thus giving the air coming off the seat tube and seat post free passage. And while the tube profiles for the down and seat tubes are elongated (the seat tube does feature a rear wheel cutout), they are still short enough that the bike is UCI legal.
In talking to a couple of engineers at the competition I heard that while the TMR01 doesn’t have the swoopy look of the Cervelo S5 and some other competing bikes, in testing proved it to be a surprisingly wind-neutral machine.