Project Praying Mantis

We’ve recently had Tom Vickery in for a triathlon fit as the first part of his journey towards Challenge Roth, Europe’s biggest long course triathlon.

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efore the fit Tom said “Step 1 on the journey to next year is looking at what big dramatic changes can be done. I wanted to make changes now to have plenty of time to adapt to them before they are put into action next year. If done well, one of the biggest of changes which can deliver the greatest gains is the bike setup.   

I’ve been riding the same Cervelo P2 for many years now. When I rock up at races It feels like I’m on an old vintage classic when compared to today’s hyper bikes. My old faithful P2 has served me well and I don’t have any intention of retiring it soon. But there are still gains to be had here without changing the bike. In the past I have always set my own TT positions; which basically involved me tinkering here and there and trying to make myself as low as possible. The net result being riding the bike with a slammed negative 17degree stem. I would typically spend winter breaking myself trying to make it work.

We started the fit by looking at Tom’s current position in action. The slammed -17 degree stem makes the bike look awesome in transition, however lower may not always be better. There is a limit to how much you can bend at the hips before you start hitting the end of the range over the top of the pedal stroke. Going lower than this sees greater reductions in power production and the back to round. It also forces the shoulders to stretch down to the bars (protract) which opens up the frontal surface area to the wind.

Drag (CdA) is made up of two aspects 1) the drag coefficient (Cd) which is how slippery the object is and 2) frontal area (A). By protracting the shoulders (stretching down to the pads), it opens up the frontal surface area. In addition, the open and low hand position scoops the air that is hitting the hands and forces it up into the chest where it gets trapped in the crotch area like a parachute. In addition, to be able to see, the head has to lift up into the air stream to see down the road, increasing the frontal surface area and causing drag behind the head.

As you can see from the 2 above pictures from CFD analysis on a pro triathlete performed by STAC ( https://www.staczero.com/vwt ), a head that is held up in the air stream causes the air to separate from the back and creates a huge amount of turbulance that continues a long way behind the rider. In addition, the air is forced between the hands and head then has to force its way around the hips (the red areas on the top picture).

Next was an initial scan with the STT 3DMA motion tracking and a body assessment to find Tom’s tightnesses and weaknesses. This revealed a lot that could be done to stabilize his feet which was causing a lot of the knee movement, particularly in his right knee. We made a set of custom footbeds and made a big change to his cleat position to help stabilise the foot. The goal is to not only be faster on the bike, but also reduce the load on the calves and deliver his foot to the run in as fresh a position possible.

Tom was already interested in the recent trend towards a high hands “praying mantis” style positions. This type of position was first used by Flyod Landis in the mid 2000s and the UCI (the governing body for cycling) quickly bought in a rule to ban it (the top of the extensions can now be no more than 10cm above the pads). I have a general rule of thumb “If the UCI ban it, it must be fast”. That is why I am not always looking at the pros for inspiration to the fastest possible TT positions as they are working with one arm figuratively tied behind their back (though if it was literally tied behind their back it might be more aero…….).

Disciplines like UK time trialling and triathlon have much more open rules when it comes to position set up and are not restricted like the pros. On the UK time trial scene, there have been some balletically fast position coming out of wind tunnel and track testing using this style of position.

It can also be sustainable and has been used by a number of Ironman athletes.

So what’s the theory behind this position? The way that I describe it is that we are using your hands to influence the air flow up stream and then “hide” as much of the body as possible behind the low-pressure pocket created them. The air is forced up and over the head/shoulders and down and out between the legs. With the hands at the same height as the hips, more of the air is forced out and around the hips. It’s similar to the way that a swimmer will use the lead hand to punch a hole in the water in free style.

But that’s only one aspect of the changes that we made to Tom’s position. To allow the body to drop down behind the hands without closing off the hips and compromising the power production, the elbow pads needed to be raised. This allowed Tom to comfortably retract his shoulders and drop his chest down, reducing his frontal surface area.

When comparing the before and after positions, despite the elbow pads being 45mm higher, Tom’s head and back are lower than before with a flatter posture.

Next up was to refine the position and posture with the BioRacer Aero green screen system. This is often referred to as a “virtual wind tunnel” but let me clarify a few things. Is it a wind tunnel? No, it is measuring one aspect of the drag calculation mentioned before (frontal surface area) and making assumptions about the coefficient of drag. Therefore, the numbers may not be watt perfect but it is a great tool to demonstrate how small changes in posture can make big changes to frontal surface area and therefore drag. This is why professional teams like Team Sky use it to make initially changes to position and posture so they don’t waste expensive wind tunnel time. First thing to do is select area to be measured and tell the system which bits are green. It then tracks the surface area of the non-green bits.

First, I got Tom to purposely ride in an unaerodynamic posture: shoulders protracted and head up in the wind. Once we had this saved as a reference posture, he drop his chest and head down into a “comfortable aero” posture. This saved roughly 20-25 Watts at 40 kph or 1:30-1:45 min over a 40km time trial. Next, we moved to an actively more aggressive aero posture working on both head and shoulder posture. This saved a further 12-17Watts or roughly a minute over a 40km time trial.

Finally, I got Tom to sit up on the base bars to show how important it is to stay in the aero tuck. This would cost him over 7 minutes every 40km and demonstrates why a long distance aero position must be sustainable. Making a position so low that you have to spend periods out of the aero bars to stretch doesn’t make sense. Having the pad position higher and actively getting small and aero means that Tom can stay in the aero bars and stretch (as in the first position) and still be 4 minutes per 40km faster than if he comes out of the aero bars to stretch.

Next we made a small change to the width of Tom’s pads that allowed him to narrow his shoulders slightly. This tweaked another 6 watts reduction. And finally, we tried a secret posture (that I’m not going to share) which saved another 8 watts.

Has this worked? I’ll let Tom tell you “The 3D motion capture re-enforced the reasoning for the changes made and the Bio Racer green screen helped to further refine the fit. When you can see how your knee tracks through the pedal cycle before and after it gives you confidence that positive changes have occurred. I went into the fit happy just to go as aero as possible and not worry about being comfortable (I thought I’d just have to get used to it!), but Ben actually made the position a lot more comfortable. My power numbers are also higher and I can’t feel as much wind on my face so I must be punching a smaller hole in the wind than before. This can only mean one thing. I’m going to be going faster next year, so Andrew Diplock and Barney Palmer will have to keep dreaming if they want to take my king of Cambridge Triathlon Crown!

Want to get your tri or TT position dialled in for next season? The TT fit with BioRacer Aero is a 3 hour session that costs £250. Give the shop a call on 01223 500502 or email bikefitting@primocycles.co.uk.

 

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