Interesting. I’ve seen a few posts but not about eTap indicating you can sometimes run a 30T on a short cage if you adjust the B screw. Others have indicated it’s not possible with eTap.
A 130BCD SRAM crankset is the only one that has 53/39. Their 110BCD starts smaller. But, yes, if I could go larger than 28T, I’d be less concerned about only 34T in the front.
A bike shop responded to my inquiry with:
“I talked to SRAM this morning and they mentioned eTap was designed and tested for use with SRAM Red 22 Cranks and Chain. The issue is the Crank ramps as they are designed around the SRAM Red Chain. I asked them about using other cranks, and it was mentioned to me use of the product out of the intended design could void the warranty.
Bottom line is it will work with other cranks, but not as well as it was designed.”
In my view this response avoids my question because, while I understand the whole “ramps” issue, all the derailleur does is push the chain in a direction. And unless I’m mistaken, it has nothing that engages the chain like a ramp. But a 3rd party ring on a SRAM crank as also suggested might fit the “not as well” criteria which I understand might mean “noisy” or not as smooth shifting.
And my interest in this arrangement is simply that I’m used to 53/39 which is fine for my typical race. My plan is to do SavageMan 70 next year — also in Garrett County. If you see here: https://www.vtsmts.com/savageman-elevation-profiles/ you’ll see that Westernport averages 12% but has a segment that’s 31%. Climbing that looks like this: https://www.youtube.com/watch?v=E3Hv1v9gE_w
So being able to switch rings to something with 34T or less would be helpful.
