Lee,
These are great questions. Yes the setup on the 2nd set of shoes for TT/Tri may differ from your road shoes in several ways. Since the pelvis in the aero position is rotated forward and down the ischial tuberosities narrow and place more weight distribution on the pubic rami and perineum area. Therefore the stance width or "Q" factor may change since you are not sitting up and wide as in a road position, and canting levels may be less. You may desire a narrower stance to relieve tension of your abductors (inner thigh). What is becoming more normal in TT/TRI now is to look at placing the pedal farther back on the shoe (via speedplay extender plates) to put the axle underneath the knee more and deactivate the calf and reduce radial and axial forces (rolling)of the ankle foot relationship. This along with the correct arch support via a custom insole can create a more favorable torque profile perfect for steady state riding and in some cases can reduce hip and knee angles (and the distance they travel) that allows more aero positioning without a loss of power. Add a rotor ring with the correct phasing in the powerband for your most efficient sustainable power production.
There are several methods to finding the best case placement of the cleat, but you would need to quantify how much steady state versus undulation your riding entails (speed changes as well as terrain), as well as intensity and duration. If you were to graph power based on placement, the farther forward the cleat the higher the spike, whereas moving the cleat back creates a spike not quite as high as the forward position it is several times wider which means that the ability to sustain a high workload. The difference is the use of the foot as a rigid lever and the different muscular recruitment, especially the calf.
The old way of placing the center of the spindle under the ball of the foot has changed whereas the axle centerline is now advised to be between the junction of the 2nd and 5th toes at their respective bases. This was to reduce pressure on the bones of the foot. Besides the "ball of the foot" is usually 3cm due to the curvature and angle of the foot depending on toe up or toe down pedaling styles.
While you know I am happy to do this for you, here is the way I would advise you to baseline the cleat position. Keep in mind this is not addressing cant or orientation/rotation. Use your powermeter to determine at a set speed(kph)if you can drop a few watts out by fore/aft positioning from the baseline.
1. Sit on a table with bare feet. Have a partner mark the center line of the (side) of the ball of your foot with a pen while your feet are suspended. (The foot is often on an elevated position and not one of 90 degree dorsiflexion as in standing.)
2. Take a thumbtack (point bent over)and place longways over the penmark. Affix with tape.
3. Carefully slide your foot in the shoe. Have your partner feel and place a mark (on the outside of the shoe) on top of the thumbtack. It is best to continue it to the sole of the shoe. Chalk or a grease pencil/china markers works well. It is not abnormal to not have the lines match up from left to right due to variances in your feet.
4. Next set the cleat centerline behind the drawn line based on the below:
Shoe Size 36-38 7-9mm behind the line
Shoe Size 39-41 8-10mm behind the line
Shoe Size 42-43 11mm behind the line
Shoe Size 44-45 10-12mm behind the line
Shoe Size 46-47 11-14mm behind the line
Shoe Size 48-50 12-16mm behind the line
Try this out and let me know how it goes.
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