Stefan Christ and his team of engineers in Grenchen, Switzerland have a happy knack of simplifying complexity. It’s a pleasing trait whose advantages are not lost on, say, BMC Racing’s Rohan Dennis.
The few, subtle modifications made by Christ and his colleagues to their already impressive BMC trackmachine TR01 were enough to provide the Australian with a machine on which he could travel 52.491km in an hour, sufficient at the time to break the Hour Record.
It says much for Christ’s design that such a specific application was far from his thoughts when he was tasked by the Swiss federation with designing a single bike for use in all disciplines in the omnium. That the same machine proved suitable, with only the smallest adaptation, for a task as specific as the Hour is a testament to its ingenuity.
Christ is as rational as one would imagine a Swiss engineer to be. Putting Dennis on BMC’s trackmachine TR01 and not its road-going sister, the timemachine TR01, was, he shrugs, a straight forward decision; never mind that none of the recent slew of Hour Record holders before or since have ridden a track bike (all rode modified road time trial bikes).
“The decision was pretty easy for us,” he says, gesturing at Dennis’ machine, brought into the quiet anteroom of BMC’s Grenchen HQ in which our interview takes place, and propped against a wall. “From a pure front-end, aero performance point of view, we were convinced that the trackmachine was the better choice.”
That suitability, specifically, lies in the tube shapes. Those of the trackmachine TR01 have a profile designed to perform at “zero degree yaw angle,” Christ explains. Put simply, there are no crosswinds in a velodrome, and the tube profiles have been optimised accordingly.
There’s more. Look closely at the tubes and you’ll notice a low ridge. This is a “tripwire”, moulded to disturb airflow. If this seems counterintuitive (“aerodynamic” designs are smooth skinned, right? Surely air should be allowed to flow unimpeded where at all possible?) it is because engineers have learned that by initiating turbulence they are able to exhibit some level of control upon it.
“Instead of letting the profile by its shape define the point where the flow goes from laminar to turbulent, you can create a small turbulence boundary layer. By that you can delay where the air really starts to separate,” Christ explains.
Of the two people involved in this conversation, it’s fair to say that I am the more impressed. “It’s pretty old now,” Christ shrugs. Tripwire technology was first used on gliders, he continues, whose comparatively low speed offered an obvious application to bicycles. Now the concept is widely used, including by Mavic on the tyres supplied with their CXR wheels.
I look closer. The tripwires on the front of the fork blades are easy to spot, now I know what I am looking for. I fail to notice them on the chainstays, and for good reason: the concept works only on tubes that “see the wind”; that is to say, the vertical, rather than the horizontal.
Aero is not enough
The track bike’s superior aerodynamics were only one reason Dennis used it to set his Hour Record, however. Stiffness was the other. Its frame is 1lb heavier than its road-going sister. The pound was “spent” on stiffness, Christ explains.
The UCI applies the same 6.8kg minimum weight requirement to track and road machines. The absence of brakes and transmission from the trackmachine TR01 allowed BMC to use more of the same high modulus fibre in the construction of the frame. “It’s one of the few bikes so far that I have developed where weight was not one of the top three targets,” Christ says with a grin.
“It’s basically more material. We use the same high modulus composite fibres as on the time trial version, but everything is thicker, across the bike. All of the tubes contribute to the overall stiffness. You get much more direct energy transfer to the track. We can say clearly that the track-dedicated pursuit bike is stiffer than a road time trial bike.”
While this much is obvious even to the layman, the advantage to handling is not so readily apparent. Most riders will ascribe a bike’s handling (or lack of) to its geometry. The specific demands of riding a bike at speed on a banked oval, however, bring the frame’s construction into play.
“You can imagine that a frame that is weak in torsional stiffness means that you have to oversteer more. When I ride a TR01, the first thing that I realise, compared to other bikes, is that it’s so precise, and this is purely linked to stiffness. I think Rohan benefitted from this as well: he broke the record using less energy to hold the line.”
He makes a final point on weight before we leave the topic: the raison d’etre of most endurance events, and the Hour Record in particular, is maintaining speed, rather than acceleration (“Steady wins the race,” as Mark Walker, Alex Dowsett’s coach, once told me; ironically, immediately after his rider had beaten Dennis’ record). Christ concurs. “It’s different when you go to high acceleration disciplines like the sprint, it [weight] may play a role, but maybe stiffness is still more important.”
No bar to progress
The centerpiece of Christ’s design – and the aspect that met a design brief for the cash-conscious Swiss federation that might be summarised as “build us one bike to rule them all” – is the ingenious cockpit.
Handlebars can be swapped from ‘drops’ to ‘skis’ in less than two minutes, courtesy of a 10mm Allen bolt in the back of the stem. Additionally, there is an impressive range of adjustment: as much as 90 degrees in the vertical axis (the stem can flipped too, for a negative rise, or spacers added) and 40mm in the horizontal. For a federation unable to equip each athlete with his own bike, and forced instead to follow a policy of share-and-share-alike, such broad parameters are essential.
For Dennis, however, it was not a consideration. Christ knew his man’s position: the stem was flipped to deliver a completely horizontal position, and the bolt discarded in favour of a more permanent solution. “When it was fixed, we glued it together, and made a nice transition between the bar and the stem.” This simple modification (and others, which we will come to later) was made in-house, at BMC’s prototyping facility in Grenchen, next door to Christ’s office.
“Basically, we tried to save a little bit more of the aerodynamic performance. Up to here…” Christ rests the edge of his hand on the end of the top tube, just behind the stem, “…it’s all standard.
“Then we glued the components together and shaped them a little bit. The handlebars are a standard 3T Brezza Nano that we covered a little bit in the middle. This is the only modification we made [to the cockpit].
“The good thing is there is no UCI homologation process for the handlebar and stem,” he continues. “It just has to be 3:1. We also did not have to go through the whole homologation process for the frame, where other companies who made on-road bikes, had to get the product homologated, and on top of that, based on the rules, would be forced to make it commercially available, which I doubt that they will.”
He chuckles at this last observation; an engineering gag.
If the only modification required was subtle and easily achieved, that is all to the good for a project, which, if not entirely last minute, left little breathing space. Christ’s team in Grenchen got the nod on returning to their desks in January, immediately after the Christmas and New Year break.
“Basically, we got the final call when we came back from the new year holiday. But were lucky in that we had a product that was usable. Also, having the prototyping facility next door and the track across the road made it all easier.”
Christ is diplomatic when I ask if his team tested the modifications before sending the bike to Dennis. There is “a broad range” in ability between an engineer who rides the nearby track in his lunch break, and the elite rider targeting an Hour Record. “We all ride on the track, but riding as a professional is something different,” he says.
Instead, Dennis hit the track in earnest on a regular TrackMachine TR01 shortly after winning the Tour Down Under in January. The sessions were enough to confirm the position into which his the handlebar and stem should be glued on the prototype bike awaiting his arrival in Grenchen. “The only surprise was that he had a cockpit that was stiffer and faster. In terms of position, he knew what he was getting.”
The final modification was to the drivetrain. “One thing we didn’t want to change to a track set-up was the crank. From a pure stance point-of-view, he was used to the road,” Christ explains.
“Having the crank the same as the road, the chainring was 6mm further outboard, which with a regular sprocket for the track, you would be outside of the thread. Because the chain line had to be perfect, we machined a sprocket. We made 14t and 15t, so he had a choice. “
Christ opted also to equip Dennis’ bike with a Shimano Dura-Ace road chain, rather than the more bulky items typically found on track bikes, and made the change after seeking advice from the Japanese giant. Interestingly, Sir Bradley Wiggins opted for the same solution to set his record, though his Dura-Ace chain was subject to modifications of its own.
Having machined sprockets for Dennis, it seemed only polite to program the CNC machine to produce some new 56T chainrings, too. As a final touch, BMC 3D-printed an attachment to hold Dennis’ SRM power meter, positioned on the back of the seatpost (regulation prevents him from seeing the data during the attempt).
Other details? Dennis stands 182cm in his socks, and rides a medium frame with a stack height of 506mm and a reach of 408mm (“He’s pretty tall”). His crank length is 175mm. The 3T Brezza Nano bars are a minuscule 300mm wide, but, as Christ points out, an endurance rider only uses the base bar to get up to speed.
He is more reticent on the topic of Dennis’ rolling stock: “We should not talk so much about the wheels,” he chuckles, refusing to be drawn further on make or model.
“He was testing two different set-ups, and in the end, the front and the rear were not the same brand. We had two pairs of each brand, and we masked them; just neutral. That was never a big discussion.” He does confirm that Dennis used track-specific wheels. “From his former career on the track, he knew what to expect.”
With so much preparation and a favourable outcome (Dennis’ mark of 52.491km ws comfortably further than Brändle’s 51.852km), what does Christ remember of the occasion?
“We knew at the time it would be a bit easier, since we had a bike designed for the purpose, but honestly we didn’t put too much into how they [Dennis’ rivals] solved things as we had a different base line.”
Expect to see the trackmachine TR01 used in anger next year at the Olympic Games in Rio. The bike was designed with this in mind, after all, and Christ is confident that the Swiss have a young, strong, and fast-developing team capable of surprising more established nations.
The bike, at any rate, will be up to the task. Dennis has proved as much, and so too, more recently, has Stefan Küng, who in February was crowned world individual pursuit champion.
“From a sporting perspective, it made sense to develop this, but I have to say from a commercial point of view, it’s a product that you would not develop. It is not big business,” he says. “On the other hand, it’s a good development, because it is less time sensitive. A good track bike remains a good track bike, as long as the rules don’t change.”
Christ allows himself another chuckle at this last observation. If Christ embodies the layman’s perception of the Swiss engineer- rational, thoughtful, highly intelligent – his bike certainly embodies the perception of Swiss engineering. The trackmachine TR01 is advanced, yet beguilingly simple. Dennis and Küng are unlikely to be the only riders to appreciate its qualities.
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