After chainring bolt failures and entire squads puncturing almost simultaneously, I thought the Tour de Romandie prologue had thrown up all its surprises. Then this new time-trial bike from BMC popped up in one of the photographer’s galleries as I searched for a photo of Rui Costa.
While most of the Tudor Pro Cycling Team riders raced with the current BMC Timemachine 01 Disc (see below), Tom Bohli raced on a stealth-looking new rig we have not seen previously.
The new frame shares more than a resemblance to the bike BMC developed and unveiled in partnership with Red Bull Racing (RBR) last year but with a few key differences.
The similarities include the new head tube profile. While the existing Timemachine was somewhat ahead of its time with a deeper head tube bridging the top and down tubes, the new bike adopts the angular and tapered profile of the RBR bike.
The bayonet-style external steerer of the current Timemachine (TM01) is dropped in favour of an internal design that is topped and tailed with an integrated stem and a wide stance, shelf-like fork crown. This headtube and fork design closely mimics that of the RBR bike, but from the photos we have seen the new UCI legal bike actually features a much deeper fork crown shelf and fork legs.
The base bar on the new bike seems to sit somewhere between the dropped bar of the existing TM01 and high and forward base bar on the RBR offering.
The RBR downtube position opened the gap between front wheel and the downtube compared to the exisiting TM01, which effectively wrapped the downtube around the front wheel profile. Tom Bohli’s new TM01 shows BMC has seemingly further increased the gap between the front tyre and the downtube.
Narrowing this gap and effectively wrapping the downtube around the front wheel has long been considered to provide the most aero-efficient design. BMC (and others, most notably Merida) has seemingly taken a different approach, separating the two structures. I’m no aerodynamicist, but my best guess is BMC feels the separated design offers some improvement either by positioning the downtube to work independently in reattaching airflow off the front wheel, or in offering a route for airflow to escape through at anything other than zero degrees of yaw.
The downtube width also varies from the wider section where the head tube flows off the fork, to a narrower midsection, before finally flaring out again where BMC has integrated a
fairing proprietary aero bottle design. This downtube profile, integrated spares box/bottle, and huge bottom bracket area are all borrowed from the RBR design.
The new bike clearly differs from both the RBR and the TM01 as we move towards the rear. Perhaps most obvious is the shorter chainstays, but more interestingly is the new top tube. The front portion of the top tube on the new UCI-legal bike is very similar to that on the RBR, but the rear portion tapers to a much flatter profile from about midway along the tube to almost entirely flat as it meets the seat tube. This is in stark contrast to many time trial designs, which effectively fill the top tube to seat tube junction as much as possible.
With no comment from BMC on the new bike, we can only speculate as to the benefits of the new slimmer design, only possible thanks to the UCI’s decision to drop the minimum 25 mm tube thickness down to just 10 mm. Clearly, the new design will provide a weight saving simply due to their being less frame. Presumably, the new design introduces some intended flex which should help with both comfort and frontal impact tests. Integrating this design and profile into the top tube presumably has little to no aero penalty as the top tube matches air flow. We will have to wait for an official comment from BMC, in the meantime, call me old-fashioned but I like the huge aero-looking tubes on time trial bikes.
BMC has dropped the twin-position seat post option with the current TM01, which offered both UCI-compliant saddle setback and the more forward positions popular in triathlon.
The seat tube itself seems a carbon copy of that on the RBR bike. However, it seems BMC has tweaked the junction with the seat stays ever so slightly. The new stays look shallower and actually meet at the front of the seat tube.
Last but not least, BMC have moved the rear wheel into the same time zone as the rest of the bike, opting for much shorter chainstays than those seen on the RBR bike unveiled last year.
We have requested more information from BMC and will bring it to you as we have it, which presumably will coincide with an official launch of this new frame.