Finding out what size post you need for your new dream build can leave you scratching your head (I know I have got in a muddle over it), so I decided to make a little calculator to takeaway the guesswork - scroll down to use it.
The diagram shows a hardtail, but will work for any bike (shock horror, even e-bikes).
Essentially, your new post length (C) should be less than or equal to the max post insertion of your frame (B) plus your collar to bum distance (A-D).
C ≤ B + (A-D)
If you don't have your new frame and/or post in hand you probably don't know your collar to bum distance, so you can work this out by subtracting the seat tube length (found on the geo chart) from your saddle height (BB to saddle rails).
It's also worth noting that if you are planning on changing crank lengths on your new build, this should be taken into account. If you are going 5mm shorter on your cranks, your seat will need to be 5mm higher.
Max Seatpost Length Calculator
Calculating: C ≤ B + (A - D)
In short: find A, B & D, then plug them into the calculator above to get C.
| A | Saddle height: Measure on your current bike from the center of the BB to the saddle rails. |
| B | Max post insertion: Get this from the geo chart of your new frame. |
| C | Extended post length: This is what we are trying to find out. |
| D | Seat tube length: Get this from the geo chart of your new frame. |
Now go forth and build with confidence!
