I committed to something today. I ordered a Sram S950 (S900 compact crank version). This is a huge departure from the SRAM Rival. The S900 has two carbon fibre crank arms and an aluminium spider. This will allow me to answer the carbon fibre fatigue question. That is, does carbon fibre crank arms exhibit a change in the stress-strain slow as they fatigue and will it result in non-linear and hysteresis effects.
It will be getting instrumented as one of the beta units. I am trying to track down a used Quarq Cinqo Saturn or an SRM unit that used the S975 crank. This would allow for the first two crank based power meter comparison! If anyone out there wants to lend me their Cinqo Saturn spider I’d appreciate it. However, I very much doubt anyone is going to loan me a 1500 dollar piece of hardware so that I can take it apart. I’ve seen some old SRM wired units going for 500, but all have been Dura-Ace. So if I find one at a reasonable price I’ll try and pick it up in the coming months. Then that will mean that some lucky person in the beta will get two power meters to trial. Whoever that might be (Ray perhaps?) will be provided with a custom logger for their bike that can log two power meters at the same time. Unless, one is a wired SRM and then I’ll have to work something out.
Here is where I am stuck. To test the carbon fiber fatigue theory which I’ve talked about, I need some very heavy usage. I can do this in two ways. Artificially with an MTS machine, or through a lot of logging of real world usage. One is fast, and one is cheap. Both are good. The old adage of pick 2 holds valid.
Specs:Sram S950: 170mm, Compact 50/34, GXP BB