Lab-based Position Optimisation
Nick's Giant Trinity Advanced Pro build is a perfect example of the position optimization process for time trial application. From the outset, we had to address the equipment choices that are integral in delivering the final end goal of an aerodynamically efficient riding position, sustainable for race duration, while hitting the realistic power/duration targets.
The build of a TT bike is a complex process, taking time to assemble and integrate the wiring and junction box. Getting the basics right from the start of the build process is key to utilizing this time effectively.
The shape of Zipp Vuka EVO 110 extensions allows for the maximum height gain while providing more purchase for the hands, thanks to the flattened top profile. The modern “ergonomic ski” shape of the Zipp Vuka EVO 110 is more favourable for promoting a consistent position than that of the traditional ski-bend extension.
The PRO Aerofuel saddle suits the moderate to narrow pelvis type, with sufficient width to support the pelvis and sufficient pressure relief to reduce compression of soft tissue structures. The blunt nose design allows freedom within the UCI regulations, while achieving the desired position over the bike.
With previous fit data from road bike positioning, we knew that Nick would benefit from the use of 165 mm cranks. With aero testing on the cards, the Verve InfoCrank was suggested as the unit of choice, due to the known accuracy and reliability aspects.
A Look at the Kinematic Data
Cleat setup and pedal interface aside, bike fitting always starts with finding the appropriate saddle position. Saddle height and saddle offset are easily defined using 3D kinematic analysis techniques, analyzing joint angle, joint position and centre of gravity measurements.
Nick’s saddle height of 706 mm provides an average peak knee extension angle of 142 degrees. The appropriateness of saddle height always needs to confirmed with ankle joint kinematics and overall lower limb symmetry. Nick’s prior fit data was used to inform the decision to go with 165 mm cranks and this is confirmed in the most recent captures on both bikes. The average peak knee flexion angle for Nick’s fit is 112 degrees, in line with our target for an optimized position.
A saddle nose offset of 11 mm provides a knee (joint centre) over pedal spindle measurement 45 mm in front of the pedal spindle. In combination with an aggressive (TT) position, this places Nick's centre of gravity 113 mm in front of the bottom bracket. This is typical of a UCI legal time trial position, with a forward position being favourable for maintaining an aerodynamic position (position consistency).
Successful TT positioning heavily relies on the adjustability of the front end and the Giant Trinity Advanced Pro offers all that is required here. Independent adjustments for pad stack, pad stance and pad fore-aft are vital for achieving a position the athlete can relax into. The outcome can be viewed in the torso and upper body kinematics. A trunk inclination angle of 13 degrees has been achieved with 115 mm of elbow pad drop, while a pad reach measurement of 564 mm has facilitated a shoulder angle of 79 degrees.
The UCI rules have been applied, with a height gain of 88 mm to the extremity of the extensions. Nick is able to fully take advantage of this height gain, evident in the forearm tilt angle in the order of 20 degrees. Nick’s bridged hand position sees the right hand placed on top of the left, contributing to a slight difference in forearm tilt.
You cannot argue with Nick's attention to detail and the finish of the build. Clever integration of the eTap blip box and wiring make for the cleanest possible front end. Grip tape covers the forward contact points which makes for a very effective slip-free solution.
What's next in the position optimisation process? Track aero testing, refining Nick's position with aero techniques and equipment optimisation. Stay tuned!