I bought the SRM second hand, it was fully functional, however, I can tell it has been used a lot. Maintenance history unknown, I was anticipating how on that really important time trial I would lose power data.

Well it was less dramatic than that, one autumn day it simply took 15min till the SRM paired up and the next day I got no response at all. Couple of rides before that I would notice the 3s average power acting weird ( dropping to 100-150W when I was doing a steady 220W average) on some occasions. That should have rang a bell that I need to look into changing the batteries.

Being the DIY type and training with power junkie I set up on replacing the batteries ASAP!

SRM Batteries

SRMs come with two types of batteries – a round lithium cell (mostly older wired units) or 1-2 square 3.6V lithium thionyl batteries. These batteries have extremely low rate of discharge so can be stored for 10 or so years. On one of those lazy weekends I should have opened up my powermeter to see which type it required so when the time came I wouldn’t have to lose a week of having no power data. I always learn the hard way…

My wireless SRM Dura Ace requires 2xLTC-7PN-S4 batteries. The LTC-7PN-S2 is the exactly same unit, however, the wiring terminals are longer and not straight. You can cut and bend them yourself so either type works fine.

In Europe you can find them here under Lithium Primary cells.

In the US here (or Google: LTC-7PN-S4)

DIY SRM Battery Change

Remove the crankset from the bike; unbolt the chainnrings (the small ring holds the plastic cover down)

With a small screwdriver pry the plastic lid open (there are small indentations at each corner.) start with one side and gently go around.

Carefully lift the plastic lid (some SRM units have wires connected to the lid, DON’T break them!). In my case the lid is not connected to anything so it comes right off. Vóila you see the  two yellow batteries. Notice how the wires are pressed against the walls of the SRM. That is why they need the black plastic sleeves.

Slide off the plastic sleeves of the wires; Using a soldering iron disconnect and remove the old units

Adjust (cut/bend) the terminals on your new batteries to match the old ones.

Re-solder (RED is “+”; BLACK is ground) and slide the plastic sleeves back over the wires. This one was actually tricky since the terminals need to bent towards each other so that they are not touching the walls of the SRM. I couldn’t get the plastic sleeves back on, however, there is about 1-2mm gap between the solder joint and the metal frame. The black plastic cap holds the batteries down so they shouldn’t be moving back and forth. If it ain’t broken don’t fix it.

If you have a small magnet at hand you can “wake-up” the powermeter and see if it can be paired to your computer. Simply move the magnet back and forth the two long blue components.

Follow the first steps in reverse order to re-assemble the crankset. Wipe off any dust/road grit from the rubber O-rings (and add some silicon grease) to ensure that no water can get inside your precious powermeter.

Re-check if the slope is what it used to be (in my case 18.0Hz/Nm). The zero offset value was around 630-650 before the battery change. It was 555 immediately afterwards. I check it before every ride and will report if anything changes over time. UPDATE: After my first ride I checked the zero offset a couple of times (Garmin Edge 500 updates it as well). It started at 559 and finished at 628, so overall the SRM is back to it’s pre-battery change state.

Re-install the crankset and go ride!

Total time was about 1h, since it has been a while that I have used a soldering iron and also getting the battery terminals bent the right sway took some fiddling. It is a tight space packed with (sensitive) electronics so I was overly careful not to break anything or tear any wires.

It was quite easy to do, just remember to take your time or you risk damaging a very expensive unit.

Good luck!

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The beauty of training with a power meter is that it forces you to keep a detailed training diary. The more data you have, the better. So at the end of season it is good to look back into the mountain of numbers and see what worked and what didn’t.

Below is the Golden Cheetah Performance Manager Chart following my 2012 cycling season. More detailed information on the terms can be found here. In general the chart describes the following: fatigue (pink), freshness (yellow), and overall fitness (blue), in addition the light pink bars represent how hard I worked each day.

The second image is a grayscale version of the first showing the periodization. The bulk of the training was Base training (green), followed by a Build phase (Yellow), finished off with a final Maintenance and Taper (red) for peak condition around the Bulgarian National Time Trial Championships. The last part represents rebuilding my base fitness (green) and taper again (red). For more information on training periodization click here:

If you just consider the Performance Manager it looks like the perfectly scheduled season. Fitness went high while at the end I traded some fitness in order to get high freshness. However, there is more than meets the eye. Below you can see the relationship between my season fitness (blue) together with what Golden Cheetah calls Aerobic Power (5,10,20,30,60min peak power).  Addtionally you can see that my Functional Threshold Power changed from 325W to 350W mid season and all the training zones shifted accordingly. You can see that the overall trend for the Aerobic Power peaks is going down weeks before I was supposed to be peaking while fitness remains high…***

Hmmm…Why is that?? During the Build period intensity went high as expected, combined with a race or more every week required me to take more rest days, therefore the time spent riding was lower as shown in this next graph. What happens when you take days off and train less? That’s correct, you lose some of your condition. This is sometimes wrongly attributed as “peaking too early.” As described in my engine analogy here, you simply lose volume so as that happens you have to work harder to obtain the same power, until you need to work way past the redline.

On the positive side you can see that the last part of the season although I had lower fitness, my Aerobic Power was close to the levels at the end of the previous period. Base training paid off.

Next season, my racing calendar would look similar, so couple of things I would pay attention to:

1. Maintain my Aerobic Fitness once intensity becomes high; 1x2h at low intensity weekly should be sufficient, maybe even replace a higher intensity training.

2. Specificity; my priority goal was a TT, so I should train towards than one event, including practice time trials instead of focusing on fitness alone.

***Right at this time I switched from a Powertap to an SRM power meter. I found it strange that numbers were becoming lower (the SRM should be ~5% higher because it has no chain friction losses as compared to a hub power meter). I naively attributed the downward pattern to possible calibration issues.

Conclusions

• Base training is immensily important
• If you want to improve you need to learn from experience and yes, from mistakes.
• It is a constant feedback between you, the power meter and the data. Data should be viewed as a whole.
• Trends sometimes start unnoticed and cannot be fully evaluated until the dataset is complete (at the end of season for example). Therefore past experience and knowledge already out there is important. If you start noticing decline in power numbers over time, go back and reevaluate what is your training lacking? Are you overtraining? Are you recovering enough? Are you sick?
• Trends can and do explain your performance. Numbers don’t lie!

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Fitness and Equipment

I completed a solid 8 weeks of base training starting January and I have done a number of Time Trials going through the 5 week Build phase, leaving me with a 4-5 weeks to work on any weaknesess/bike fit/etc and taper. My race power numbers were all around my FTP – 350-355W. I did experiment with pacing and did blow up in one race, so I am aware of my limits. I made some significant position changes for my last race which I think cost me about 10-15W. It is a lower and narrower position so it is a good trade-off. Sustaining 330-335W for the 40K is a very reasonable goal.

I also bought a second hand SRM crank power meter so I can use a rear disc rather than my 32 spoke Powertap wheel. I got a HED3 and a HED Stinger Disc used so I have one of the fastest wheel combinations available. I changed the original lighter tyres with ones with some puncture protection as an extra safety measure. I have a narrow range 11-23 cassette installed and ready to go.

Furthermore after months of waiting and promises I finally have a real TT bike: a Cervelo P3, rather than an converted road bike with clip-on aerobars. One small addition, the frame developed some cracks around the seatpost opening. The shop called Cervelo and this seems to be a problem they have seen before, also online forums have some P3 owners with similar issues. Most likely it is just cosmetic paint cracking, however, I will have to keep an eye on it, especially be aware of the seatpost slipping down. This is a literally ‘make it or break it’ situation. I did get the green light from Cervelo to go and ride, what would happen in terms of warranty remains to be seen. Nonetheless, the bike is FAST, there is no doubt about it and quite comfortable. The small cracks aside, it lives up to the hype surrounding the Cervelo P series of bicycles. Ideally I would have liked to have longer time to get used to it, however, 10 or so days should be enough to let my body adapt.

I also found aerodynamic shoe covers and although my team skinsuit did not arrive in time (sponsor issues), I have a an unmarked black one which I will be using for the race.

Overall unlike my previous races I have world class equipment so I will not be at a disadvantage before even getting off the starting line.

Other

I am completely unfamiliar with the course. From previous years it was an out and back race on the highway outside the town of Sliven. I do not think it will be very technical or involving significant elevation changes. If marked properly I should be able to focus entirely on pedaling hard, rather than missing a turn. Another more significant aspect is the weather. I am expecting temperatures in the 30-35C degrees range. Here in The Netherlands, jokes aside, the mercury rarely creeps above 20C, on a good day. Wind conditions should not be worse that what I have been getting here. I am going couple of days in advance to recon the roads and to get used to the heat. Hydration will be key. Also it is a 2300km drive from The Netherlands to Bulgaria. I am planning of taking my time and doing it in 3 days, stopping by my parents house in Sofia for a day, before heading for Sliven. I will do some short (30-45min) workouts in hotel rooms/parking lots on the Tacx to keep my body into ‘race’ awareness.

This would be my first experience of a high-caliber race, I hope not the last one. There probably will be some Continental PROs mixed with fast club racers. Any unforeseen circumstances aside I am excited and looking forward to setting some personal best numbers. I will post an event recap after the race.

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