Team GB’s London 2012 Olympics bikes – Part 2

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Team GB’s London 2012 Olympics bikes – Part 2

Forks and cranks make a difference

Posted 7 August 2012

If not quite all-conquering, Team GB’s cyclists have been beyond dominant at the London 2012 Olympics. What part of their performance differential over the opposition may be credited to the UK Sport bikes used for the majority of their rides – and all of them on the track – is debatable and, given that the UCI’s stated aim is to ensure “the primacy of man over machine”, should be minimal.
 
However, given the attention to detail lavished by UK Sport’s cycling team on every detail that might affect ultimate performance, it is highly likely that the machines that carry the riders have been developed, within the limitations of the UCI’s regulations, to something near perfection.

Victoria Pendleton’s wide-crown fork; pic by Sportivephoto.com

 
It is a matter of record that a band of engineers known as the ‘Secret Squirrels’ has spent countless hours poring over such pressing questions as with which grease and with how much (if any) to lube the various bearings, so we may assume that greater issues deemed, going by developments in the cycle industry, to be of even more vital importance to the cycle’s performance have been thoroughly assessed by the same furtive nut-hiders.
 
On that basis, several design features that may be assessed from a look either at the UK Sport Commercial Opportunities page or at the bikes themselves are worthy of comment. Of course, there’s a lot that Team GB won’t reveal and the level of secrecy surrounding the squad’s technology is such that even the regular Mavic wheels used since Beijing are covered up between races.
 
Some details, however, may be gleaned from even a brief perusal of the page. For example, UK Sport’s Track Chainset, available in lengths from 165mm to 175mm, is stated to be twice as stiff as the comparable Shimano Dura-Ace model and nearly 200g lighter. It uses a ‘custom oversize’ bottom bracket and will only fit the Mk2 Track Frame, which presumably has a suitable bracket shell. There’s a Mk2 Aero Road/TT frame that might also take the chainset.
 
These are exciting figures indeed and would be trumpeted by any series manufacturer. Just how the chainset is made will be familiar to attentive viewers of the BBC’s Olympic cycling commentary. Chris Boardman revealed that the carbon-fibre composite is wrapped around a metal mandrel before being placed in the female mould. The whole lot is heated to cure the resin and the metal melted to get it out.
 
How is this done? There are several metals with exceptionally low melting points such as Field’s metal, which is a eutectic (lowest melting point) alloy of bismuth, indium and tin and melts at 62degC. Which of these metals is used depends on the cure temperature of the resin; if the metal must stay solid during cure, one with a melting point a few degrees higher will be used. Post-cure, it can be melted out without overheating and damaging the composite to leave a hollow structure with precise internal and external dimensions.
 
Of more immediate interest is the selection of forks shown on the page. There are basically three models: Pursuit, Sprint and Road/TT. The first can also be used for bunch racing and must, therefore, be available with or without the crown drilled for a brake bolt. It looks to come from the same mould as the Road/TT model, with the latter sporting different machined aluminium dropouts to afford the required offset. Their steerer tube “tapers” to 1” and so, presumably, is fatter where it meets the crown.
 
One might ask why, given UK Sport’s attention to detail, the Road/TT fork sticks the brake on the front of the crown where it meets airflow. Two likely explanations present themselves: either the team’s studies have shown that there’s not enough of an aero benefit to make designing a fork with concealed brake worthwhile, or the work required to develop and build such a fork is beyond the means of a small team making parts on a small scale. Maybe it’s a bit of both – or maybe there’s no significant benefit to be had from concealing the brake either within or behind the fork, since the only parts that stick out beyond the silhouette of the fork are the ends of the two arms. Let’s just say the issue was not big enough to bother Bradley Wiggins on his way to TT gold.
 
Perhaps the most impressive of the three fork models is the Sprint, which features a massive, almost cyclo-cross-style crown so wide that the legs slope inwards towards the dropouts. It is said to be designed for some of the world’s most powerful bike riders, of which there can be no doubt, and to give precise steering even at 70kph and under the 2.5g loads imposed by the banking of the velodrome.
 
Interestingly, this fork was used by the men’s and women’s team pursuit squads; both need excellent aerodynamics. There’s no obvious reason, other than improved aerodynamics, why the women’s squad, whose members are unlikely to trouble the fork’s structural integrity, should choose it over the Pursuit fork, so we may reasonably infer from this that the design offers lower air drag, perhaps by allowing the air to pass more freely between wheel and fork legs.
 
Sadly, the same gap would need to be filled by any front brake acting on the rim, so the fork is unlikely to see road action any time soon. Maybe it is just waiting for a suitable disc brake.
 

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