Thinking about getting the wean a dropper for his bike if I can find one cheap enough, but am not very bright and can’t work out if it’s possible.

His weenie Trek can take 200mm in the frame.  Which leaves him with 140mm showing outside the frame when in it’s lowest position (the only way to get it lower would be to cut the post).  I guess he has it showing around 170mm when he has it in the high position (ie when riding easy stuff or uphill)

So I guess I need something that is a maximum of 370mm long when extended (200+170) – any longer than that and it won’t fit far enough into the bike for him to straddle.

And I assume I only need around 100mm of extension, which would mean that his low seat position was 70mm lower than the lowest which the rigid one currently reaches.  Which would be spot on.

See, I’ve even managed to confuse you, I’m so shit at this.

Have I got the numbers right?  Does a seat post exist that is 370mm or less for non stoopid money?

cheers

What are you asking?

If there’s 200mm available inside the frame and 170 is needed above at the highest, then 370 is your minimum size.

Don’t forget that there’s around 1″ of collar to account for so if you wanted the full number then it would be

370 – (200″25) = 145

If it’s a stealth dropper then you need to leave space for the linkage under the lower too.  If it’s external that issue goes away obviously.

Is it a good idea buying the exact size currently needed for something like a dropper for a kid who is growing?  It’s possible to not use the full extension of a dropper so I’d buy something overlong and teach kid to use it appropriately.  Is weight an issue?  Is the kid heavy enough to knock a dropper down or not be disturbed by it when it extends?

Back to your 370, there are KS Lev’s and Reverbs in that ballpark that could be picked up SH if careful.

Have you looked at the Oneup dropper? Custom sizeable through use of shims you can tailor make.