Hi, first post and a new bike to boot. I’m wanting to buy the X- Brand dropper post for my Trek X-Caliber 8, I’ve just measured from the seat rails to the top water bottle mount (which also sits inside the tube) and its around 38cm, the total length of the dropper post is 41cm for the 125mm version. I am I looking at this wrong or won’t it fit to my desired height?
Not sure what model year you have but the current version of the bike is touted as dropper-compatible. It probably doesn’t matter anyway as the screws that hold the bottle mount to the frame usually don’t go all the way through.
You can check how far your current seatpost goes down as that may give you a very quick answer. Otherwise, see if you can find some paper that’s long enough and roll it (cylindrical) to the width of your post and see if it slides in as far as the post. Alternatively, contact Trek directly with the exact specs and they’ll tell you.
I’d be shocked if there’s only one brand that fit. You can always contact Trek to be certain. With a dropper all you’re looking to do is get the seat out of your way and/or lower your center of gravity as you move around the bike esp. on more technical downhill sections. You may well find the 120mm drop sufficient.