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Where are you measuring to on the seat post/saddle? The accepted reference point is the seat rails, so is that 5.5" (140mm) from the top edge of the seat clamp to the saddle rail?

You also don't mention if the frame has cable routing for an internal dropper or not? If you need an externally routed dropper this will eat into what you have to play with.
^^^THIS^^^ is where I was going to go with my response.

Based on your post and some quick searches, it appears you need a 30.9mm internally routed post that will allow for 140mm from the bottom of the collar/top of seatpost clamp to the seat rails in the extended position while requiring less than 135mm of insertion to do so. For the most part, what you are looking for is a unicorn and you'll have to go to really short travel.

From what I can tell, the following brands have nothing that will meet your needs...
PNW, OneUp, TranzX, KS, BrandX, Bike Yoke, Crank Brothers, Fox, Race Face, Rockshox, SDG, e*thirteen, DT Swiss, Thomson, Ultimate USE, Manitou, Ritchey, FSA, Easton, X-Fusion, Pro Bike Gear... I think you get the idea.


The 9point8 Fall Line R 275x75 comes really close, but still appears to exceed your maximum dimensions slightly.
 

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For the most part, what you are looking for is a unicorn and you'll have to go to really short travel.

The 9point8 Fall Line R 275x75 comes really close, but still appears to exceed your maximum dimensions slightly.
The Brand-X kids dropper is close, total post length is 315mm, so with a slightly shorter crank and the lowest profile saddle available...
 

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I just looked at a picture of the bike (https://s7d5.scene7.com/is/image/Specialized/145014?bgc=0xF1F1F1&wid=1600&hei=900&$jpg$) and assuming the cranks are 170mm I'd estimate 8" of available seat tube. I struggle to believe that Specialized would have made a bike, with internal dropper routing, that couldn't fit a dropper!

OP - there's no chance you're basing your measurements off the 300mm seat post so if you've got 150 sticking out there must be about 150 you can't see?
 

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I'm beginning to see the issue. 5.25+5.5=10.75 seat post length -> 275mm. That is a very short dropper. On the ETEN internal 27.2 300 with 65 drop you can get about 40 mm (1 1/2") of effective drop. Probably not worth it for the significant weight penalty. I think they make that part in a 30.6, they have a lot of skus.

I use my 3" dropper as a quick fit device as my kids all want to swap on to my bike and they can set the seat height themselves with it. It is slightly useful on the steeps, but 150mm would be more useful. It just won't fit.
 

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I'm beginning to see the issue. 5.25+5.5=10.75 seat post length -> 275mm.
See my last comment, I might be wrong but I'm thinking maybe the OP is measuring the amount of seat post visible and subtracting it from the total length of the seat post and those are the measurements he's giving us.
 

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The Brand-X kids dropper is close, total post length is 315mm, so with a slightly shorter crank and the lowest profile saddle available...
I actually own and installed the BrandX Kids dropper on my son's bike. If the OP's measurements are correct, it will not work. The seat will be more than 1.6" higher than the current position. The post also has an 40kg (88 lbs) weight limit.

Shorter cranks and lower profile saddle are both great tips. I've used the lower profile saddle to fit my youngest on his 16" pedal bike and shorter cranks to better fit my wife to hers. Even with both, you'd probably be really hard pressed to make up for the additional post length.
 

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Just looking at the picture you can see it has a ‘kinked’ seat tube, so there’s no way you’ve got 15” of insertion to play with, I just think it’s more than the ~5” the OP is referencing.
Exactly this. Not a chance you have 387mm of seat tube. That is the total distance from the center of the bottom bracket to the top of the seat tube measured in a straight line. I looked pretty extensively yesterday and couldn't find any published data (from Specialized or reviews, etc) that listed the actual available insertion depth. The best info we currently have to go off of is the OP's 5.35" measurements.
 

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There's no way the OP's gf is on a size small bike and can use a 300mm+ dropper.
I don't think he's saying he needs a 300mm dropper, from the info provided the total space he has to play with is less than 300mm and is trying to find a dropper that is less than 300mm from the seat rail clamp to the bottom of the actuator.
 

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9point8 can shim their 325-75mm down to 325-55mm. Fall Line Dropper Post
I think 9point8 has the best solution, but I don't think a 325x75 Fall Line shimmed down to 55mm is it. Even if the total length is reduced to 305mm.

OP stated he had 5.5" from the post clamp to the rails and 5.25" of insertion depth. Based on this information and using 9point8's terminology, this equates to the following...

Total Post Length: ~273mm
Lower Tube Length (Max Insertion): ~133mm
Bottom of Collar to Seat Rail (Total Length - Lower Tube Length): ~140mm

The Fall Line R in 275x75 is the only post I could find anywhere that was close to meeting these requirements. Close enough that it should absolutely be usable. It also maintains the longer 75mm stroke rather than being cut to just 55mm.

Total Post Length: 275mm (+2mm)
Lower Tube Length (Max Insertion): 139mm (+6mm)
Bottom of Collar to Seat Rail (Total Length - Lower Tube Length): 136mm (-4mm)

It appears that in a worst case scenario (the Fall Line R can't be bottomed out), you'd have 6mm of the lower tube above the seat clamp. However, the collar to seat rail distance is 4mm shorter. Therefore, the seat will sit 2mm higher than the current static post. This should absolutely be doable for the OP, if the info they provided is correct. The good news is, it will only cost them $400 to find out. ;)
 

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Discussion Starter · #36 ·
I'm beginning to see the issue. 5.25+5.5=10.75 seat post length -> 275mm. That is a very short dropper. On the ETEN internal 27.2 300 with 65 drop you can get about 40 mm (1 1/2") of effective drop. Probably not worth it for the significant weight penalty. I think they make that part in a 30.6, they have a lot of skus.

I use my 3" dropper as a quick fit device as my kids all want to swap on to my bike and they can set the seat height themselves with it. It is slightly useful on the steeps, but 150mm would be more useful. It just won't fit.
you on to right track! worth is doesnt matter if she wants it she gets it. just got to fins one. im thinking externally routed would save some space
 

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Discussion Starter · #38 ·
I think 9point8 has the best solution, but I don't think a 325x75 Fall Line shimmed down to 55mm is it. Even if the total length is reduced to 305mm.

OP stated he had 5.5" from the post clamp to the rails and 5.25" of insertion depth. Based on this information and using 9point8's terminology, this equates to the following...

Total Post Length: ~273mm
Lower Tube Length (Max Insertion): ~133mm
Bottom of Collar to Seat Rail (Total Length - Lower Tube Length): ~140mm

The Fall Line R in 275x75 is the only post I could find anywhere that was close to meeting these requirements. Close enough that it should absolutely be usable. It also maintains the longer 75mm stroke rather than being cut to just 55mm.

Total Post Length: 275mm (+2mm)
Lower Tube Length (Max Insertion): 139mm (+6mm)
Bottom of Collar to Seat Rail (Total Length - Lower Tube Length): 136mm (-4mm)

It appears that in a worst case scenario (the Fall Line R can't be bottomed out), you'd have 6mm of the lower tube above the seat clamp. However, the collar to seat rail distance is 4mm shorter. Therefore, the seat will sit 2mm higher than the current static post. This should absolutely be doable for the OP, if the info they provided is correct. The good news is, it will only cost them $400 to find out. ;)
yeks on the price do you have a link?
 
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