What dropper post fits my bike?
It doesn't depend on a single thing, it depends on three: 1) the diameter of the seat tube (30.9, 31.6 or 34.9 mm — you can go up with a shim, not down); 2) the maximum travel that fits, limited by the available insertion and the stack of the post, NOT the nominal travel on the box; and 3) the routing of the cable, internal or external. Measure all three before buying: with that you won't go wrong.
The most expensive mistake is buying by travel ("I want a 150") without checking whether it fits. Here's the right order.
The three conditions, in order
1 · Diameter. Read the engraving on your current post or measure the inside of the seat tube. The three standards are 30.9, 31.6 (the most common) and 34.9 mm. You can fit a thinner post with a reducer shim, but never one thicker than the tube.
2 · Travel that fits. Here's the detail almost no one explains: a dropper needs a minimum length inserted inside the frame. The real usable travel is limited by the available insertion (how far it drops before hitting a bend, a pivot or the bottle cage) and the stack of the post (what it takes up between the collar and the saddle rails). The number on the box is the ceiling, not what fits.
3 · Routing. If your frame is set up for internal cable, use an internally actuated dropper; if not, it runs externally. Getting this wrong leaves the post unmountable or the cable exposed.
Key facts
What it pairs with
To close the purchase without surprises you need two sibling entries: the diameter 30.9 / 31.6 / 34.9 and, above all, how to measure the insertion and the stack. That measurement is what really decides the travel that fits you.
Send us your bike model and your saddle measurement and we'll tell you the maximum travel that fits you. Message us on WhatsApp
Frequently asked questions
What does it depend on whether a dropper fits my bike?
On three things: the diameter (30.9/31.6/34.9), the maximum travel that fits (limited by insertion and stack) and internal or external routing.
Why can't I run whatever travel I want?
Because the post needs a minimum length inserted in the frame. If the tube is short or has a bend, the whole thing won't fit; usable travel is limited by the insertion, not the box.
How do I know the diameter?
Read it on your current post or measure the inside of the seat tube. You can go up with a shim (30.9 in 31.6), never down.
Related
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