I’ve been trying to find an answer to this but without any success.
Does anyone know the proper torque spec to attach the bike with thru-axle to the Wahoo Kickr?
This is likely more about your bike and stock thru axle than the trainer. Some axles have an actual torque spec on them. Lacking that, I think contacting the bike maker is the more likely place to get the related answer.
At least part of that question is because there are different thread specs for the axles (at least 3 and maybe more?, between brands and even some models within brands) which very likely have different values related to thread strength.
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There isn’t one. Generally tight. Nothing is mounted in Tension, nor has any stretch to it.
The end caps - the tq isn’t critical. They’d just need to stay on the trainer (do they even have threads)?
The rear axle - neither the threads nor the axle stretch, so no tq measurement. The bolt is mounted in shear and supported by the cups on the outside of the endcap, so again not a critical tension.
Generally, of common materials, only steel and titanium bolts have torque specs. This is because you are stretching the bolt like a spring, as they are springs. Aluminum doesn’t really stretch/elongate that much before the life of that fastener goes way down, what you do here is just put a little torque on the bolt, then rotate it a pre-defined number of turns - the number of threads engaged determines the proper clamping load. The TA is usually Aluminum engaging an Aluminum nut/insert on the other side. The TA has a shoulder at the end of the threads to stop you from over tightening it, but it’s held in place by the (spinning) friction of those threads, not a clamping pressure like on a normal bolt.
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