Gravel build - Power !!

Installing the crankset also means installing the powermeter.

In this case a 6800 Stages Gen2, remanufactured for Gen3 (thank you Stages for making this happen) in left-side only option.

I assembled everything on the bike, tried a spin test and ... "ffftttttt ffftttt ftttt" 

????????????

!!!!!!!!!!!!!!!!!!!!

?????????????

Took a closer look and ... the HORROR, the DRAMA, the TRAGEDY ! 

The battery door is scraping the chainstay !!!!!

How/Why can this happen you ask ?

Well... This is a Gravel bike, so maximum tire clearance is wanted, that can still fit a road crankset.
The specification for the chainstay / crank clearance is of around 6mm or so.

So, if you use tighter manufacturing specs/etc, you can tap into that "hole" and use it.

In the frame, this space was used to make chainstays larger, so you can fit larger tires, so you can have more FUN.

In the crank, this space has been used to add a pod that will allow you to measure power/cadence.

So... TWO components tapping into the same space, and it is now gone...

OPEN has a nice explanation about this that I am going to copy to illustrate :

Some power meter design conflict with the desire to have the most tire clearance.
The reason this is tricky is:

• As you know, the UP/UPPER has the most tire clearance of any performance frame that fits regular road cranks. And that is the defining feature, more clearance = more fun.
• It's also crucial that we can fit road cranks, if you use mountain bike cranks you do create more clearance but you give up efficiency due to the bigger Q-factor (in plain English, you ride like a duck). Less efficient, less aero, less speed. And that would not be acceptable, as we want you to be able to ride with your roadie friends on your UP (or at least go their speed even if you don't want to ride with them). The UP should be ultra-performing on- AND off-road, not forcing a choice between the two.
• Anyway, lots of space for the tire and insisting on running narrow road cranks means there is not much space for the chain stays. To make the chainstays as big as we can, we do two things:
  1) drop the driveside chainstay, which has become one of the defining (and most-copied) features
  2) focus on very tight tolerances in production to reduce the space between crank/chainrings and chainstay
• This second part is very important. To give you an idea, the standard clearance in the bike industry in that area is 6mm, we use 2mm in some areas. That 4mm extra is huge when you're chainstays go from 10mm to 14mm. Taking wall thickness effects into account it more than doubles the stiffness of the tube.
• Problem is, some power meter manufacturers have also been eyeing that 6mm gap and decided to stick a measuring pod on the crank to take advantage of it. That doesn't work for us, if we allow that clearance, the UP would go from fitting 2.1" tires to fitting 1.8" tires or we would have to sacrifice BB stiffness, and both of those are features we and our customers love. Nobody has ever done an epic offroad ride and concluded "that was great, but I would have enjoyed it more if my tires were skinnier and my bottom bracket more flexible."
• If the pod poses a problem with the outboard position of our chainstays depends on how thick the pod is and where it is located. Around the pedal, we have pretty normal clearance (5-6mm) since that is no longer a critical area for chainstay size, but closer to the rings it gets a lot tighter.

With the reasoning explained, time for the solution :
1- Buy a different powermeter ( Right side, axle placement, pedals, etc)
       - Not desirable due to €€€€ost.
2 - Delrin shim
       - In my case the pod was just grazing the chainstay, not hitting it, so a small spacing should be sufficient.

24mm ID spacers available in 0.5 or 1mm should allow some clearance and are not big enough that I run out of axle or splines do not engage properly.


I tested with a single 1mm spacer, and result is

Free spinning !!! No more fttt fttt fttt

I tried also 2mm and still had proper spline engagement and locknut was good,but seemed to be "too much" clearance, so I am considering 1.5mm to be on the safe side,although 1mm looks pretty good unless there is a lot of flex somewhere under power. (The additional 0.5mm is for flexing).

1.5mm should not be noticeable on Q-Factor, centering, etc, and can easily be compensated in the cleat if needed. 

 Additionally, I have replaced the HollowtechII bolt, with a GOLD one !!!

*UPDATED*

So, my OCD made sure I changed this to 1.5mm spacing.

Here you can see the delrin spacers on the spline. (I left separated so you can see the thickness from the side.

Plenty of engagement left, so no issues with adding 1.5mm, well within tolerances.

Should have "plenty" of clearance now for any twisting under load.