This is the response from my LBS
Yes we would be able to fit this for you. The Stages power meters are supplied as a left hand crank assembly. You will therefore need the matching Shimano 105 5700 chainset to match, as the power meter you have won’t fit onto the Rotor crank. We can order Shimano 105 5700 series chainsets, though they are a discontinued item so availability is limited. Also having looked at the component spec of you bike and compared it against that on the Cervelo website, I assume that your bike is a 2016 model Cervelo S2? If this is the case, the 2016 bike uses Shimano 105 5800 series. Whilst you could fit the older 5700 series 105 crank to the bike, you have to bear in mind that 105 5800 series is 11spd, whereas 105 5700 series is 10spd. You can use a 10spd crank and chainrings on an 11spd system, but gear shifting performance will be impaired and the system will often be quite noisy in use. The other part you will need is a replacement bottom bracket as your Cervelo uses a PF30 bottom bracket which a Shimano crankset will not fit. You can use a 3rd party adapter system to allow the fitting of Shimano bottom brackets to a PF30 bottom bracket shell, however in our experience these tend not to work too well and have a habit of creaking as you are introducing a further interface between the bottom bracket shell and the bottom bracket itself. What we would recommend is the fitting of a PF30 to Shimano Fit bottom bracket from Wheels Manufacturing. These bottom brackets are press fitted into the frame before a centre connection tube is then screwed together which locks the bottom bracket securely in place. We have recently fitted a few of these bottom brackets to Bianchi bikes we stock that also use a PF30 system, and they have been trouble and creak free.
Given all of the above our recommendation for proper running of the bike would be to fit a Shimano 105 5800 series crank and the appropriate Stages power meter to match. Although we don’t keep Stages power meters in-stock we may be able to get a-hold of them as we do have contact with Stages supplier. You would then need to purchase the matching crank and the bottom bracket to suit. There are many options available for the crank and bottom bracket, so price does vary. Cranks are between £124.99 and £139.99 depending on gear ratio chosen. The Wheels Manufacturing bottom brackets are between £69.99 and £99.99 depending on whether you opt for angular contact or hybrid ceramic bearings. The 105 5800 Stages power meter is £499.99 assuming we can order them.
