# Dropper for kid (I know, I know...)



## Feldybikes (Feb 17, 2004)

So, part of me feels silly for even bringing this up, but silly kids bikes is what this forum is all about, so I'll just embrace it :thumbsup:

When I built my son's bike, I put on a QR seat clamp to make it easy to move up and down. Alas, he often doesn't want to bother raising and lowering it even though I'm the one doing it for him. I put my old gravity dropper post on it (27.2 seat tube) and the range of height works quite well. The issue is that he's not heavy enough to drop the dropper. Does anyone have experience with one that works? The KS Lev is non-adjustable, as is the Thomson (which, at 5" travel, is probably too long anyway). I think that leaves X Fusion or PNW Components. But not sure whether those will work for someone who's maybe 50 lbs after some ice cream.

Any experience out there?


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## jestep (Jul 23, 2004)

How much post is currently exposed and how much post can fit in the frame? 

I think a problem you're going to run into is that most droppers are 350 - 400mm total so the seat may be too high even if the post is inserted all the way.

Specialized does make a 50mm 27.2 post but I think the shortest total length is 350mm. The KS 27.2 is 100mm which is under 4" of travel.


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## Feldybikes (Feb 17, 2004)

The current post is a 375mm gravity dropper descender. The issue isn't height (but as mentioned before, might be with a Thomson), the issue is something that will work with a very low spring force such that 50 lbs can lower it. Some air posts are non-adjustable for spring pressures. Others have a lower limit, though I'm not sure what happens if you go below that limit other than maybe a very slow return speed.


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## silvascape (Sep 11, 2014)

My sons new Norco Fluid 24 came with a dropper post. He is not tall enough to use it yet but has tried it out and he is heavy enough to make it work easily - he weighs 22kg (48 lbs). The post is described as JD Tranzx dropper post with remote. You would need a different diameter though as it is 30.9mm


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## RMCDan (Feb 28, 2008)

jestep said:


> How much post is currently exposed and how much post can fit in the frame?
> 
> I think a problem you're going to run into is that most droppers are 350 - 400mm total so the seat may be too high even if the post is inserted all the way.


Good point. I've been pondering adding a dropper to my son's bike too. I'll have to measure his post to be sure but I cut a considerable amount off it from stock and it's probably under 350 mm.



jestep said:


> Specialized does make a 50mm 27.2 post but I think the shortest total length is 350mm.


I hadn't heard of that one. Looks like it's meant for weight-weenie XC racers and costs $450. That's not happening. What I need is a 50 mm or 75 mm eTen.


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## jestep (Jul 23, 2004)

Feldybikes said:


> The current post is a 375mm gravity dropper descender. The issue isn't height (but as mentioned before, might be with a Thomson), the issue is something that will work with a very low spring force such that 50 lbs can lower it. Some air posts are non-adjustable for spring pressures. Others have a lower limit, though I'm not sure what happens if you go below that limit other than maybe a very slow return speed.


I see now, sorry I misunderstood the actual problem.

I think most of them can operate at 20 psi as far as specs go, but I wouldn't think there'd be a problem with lower. I think the primary concern would be lowering the pressure too much that either the friction of the shaft prevents it from raising or it just takes forever to return to the up position.

Have you called KS's or Thomson or Rockshox support on it? I would definitely see what they consider the actual minimum usable pressure because I'd bet it's lower than what the specs list. I use the LEV and as far as it being possible, you can change the pressure to whatever you want, so that post is definitely adjustable, it would just be a matter of how low it can go and still function effectively.


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## the.vault (Oct 11, 2006)

Feldybikes said:


> The current post is a 375mm gravity dropper descender. the issue is something that will work with a very low spring force such that 50 lbs can lower it.


Gravity dropper is small company. I'm pretty sure I've seen them with their kids at races. They might have a lighter weight spring option if you ask them.


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## BullSCit (Mar 26, 2004)

Thanks for asking this question, as I was going to ask the same thing in a couple of months, when my kids will hopefully be long legged enough to use my 27.2 Gravity Dropper.

And my kids are the exact opposite, when they were on their smaller bikes, they would want me to move the saddle up or down on every little climb and drop. Just kind of ruins the flow of a ride, and would love for them to have the ability to easily do this themselves.

Regarding Gravity Dropper, wonder if the pull knob on the post itself version would be any easier.


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## Feldybikes (Feb 17, 2004)

jestep said:


> I use the LEV and as far as it being possible, you can change the pressure to whatever you want, .


Unfortunately, unlikely the larger diameter ones, the 27.2 is non-adjustable.



the.vault said:


> Gravity dropper is small company. I'm pretty sure I've seen them with their kids at races. They might have a lighter weight spring option if you ask them.


Good suggestion. I had looked on their site where they list all the parts, but probably worth a follow-up.



BullSCit said:


> Regarding Gravity Dropper, wonder if the pull knob on the post itself version would be any easier.


I've got the pull-knob (Descender) post. It's not that easy to operate. I think having the handlebar lever would be easier for him (assuming he could lower it at all).


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## Francis Cebedo (Aug 1, 1996)

Difficult problem to solve but very important quest. When my kids where finally old enough (long enough legs) to use a dropper. Their reaction was the same:

"DAD? Why you been holding out???"

It is just an amazing tool for kids. It is a bigger game-changer for them than it is for us.


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## Delgado (Sep 9, 2016)

Maybe the Giant Contact Switch dropper? There's a 375mm length, 75mm drop version (30.9mm dia.). Not sure what the drop weight would be though.

Aliexpress has it cheap for $150 if u don't mind waiting for it to come from China.


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## POAH (Apr 29, 2009)

Lewis has a KS lev DX on his ripcord 100mm


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## Southbound (Oct 17, 2016)

Gravity dropper spring tension is adjustable. Turn the hex head on the bottom of the seat post in the loosen direction.


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## RMCDan (Feb 28, 2008)

Delgado said:


> Maybe the Giant Contact Switch dropper? There's a 375mm length, 75mm drop version (30.9mm dia.). Not sure what the drop weight would be though.
> 
> Aliexpress has it cheap for $150 if u don't mind waiting for it to come from China.


Ugh, that would be perfect except I need a 27.2.


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## jestep (Jul 23, 2004)

I haven't looked at the schematics, but is there any way to install an air port in the top of the LEV 27.2 in the same place where it is on the normal LEV? You could use something like the valve/fill nipple found in a SID or other air forks.

I can't believe they didn't make that one adjustable. What happens if it loses pressure over time, are you just SOL on a $300 post?


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## Feldybikes (Feb 17, 2004)

I check with GD and no, they don't carry any lighter springs.



Southbound said:


> Gravity dropper spring tension is adjustable. Turn the hex head on the bottom of the seat post in the loosen direction.


Thanks for the suggestion, yes I already tried backing off the preload and still too tight.

As for changing the air pressure in the Lev 27.2, there



jestep said:


> ... is there any way to install an air port in the top of the LEV 27.2 ...


There's a brilliant and extensive thread on servicing the "non-serviceable" cartridge on the Lev which includes instructions on how to pressurize a 27.2 using a basketball needle and some electrical tape. However, this is not a direction I want to go unless I happened to find a Lev 27.2 lying on the ground. Having serviced the larger diameter post, it's already a PITA without having to deal with not really having an air port.


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## Steve-XtC (Feb 7, 2016)

But the KS LEV is only available in: 
30.9mm
31.6mm
34.9mm


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## Feldybikes (Feb 17, 2004)

You should probably send them an email to update their website 

LEV 272 | KS Suspension


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## GSJ1973 (May 8, 2011)

Feldybikes said:


> You should probably send them an email to update their website
> 
> LEV 272 | KS Suspension


Wow, 532 gram dropper seatpost.


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## Steve-XtC (Feb 7, 2016)

Feldybikes said:


> You should probably send them an email to update their website
> 
> LEV 272 | KS Suspension


Update somewhere on the website as I copied and pasted .... as nothing to do with the kids bike I'd like a 27.2 dropper myself but the Thompson is more expensive than I can justify to myself over the TMars I have.

Both of which are in the same ballpark as my frame weight!

Sent from my iPhone using Tapatalk


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## FrankZappa6 (Aug 9, 2010)

I'm using this one on my Karate Monkey to aid with getting on an off the bike with a Thule Ride Along Mini front mounted kiddie seat. Others have pointed out that it bears a strong resemblance to the PNW model.

Using a bathroom scale as a force gauge, it takes 40-50 lbs to get it moving then it drops to 30-40 lbs for the first 1-2 inches. The resistance then builds for the final travel and peaks at about 60 lbs near full compression.

Obviously, YMMV but the price was right. It took about a week to show up.
Best,
FZ6


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## Feldybikes (Feb 17, 2004)

FZ6 -

Thanks for pointing out the Tranz X post and especially for measuring the activtation force. I did a bit of searching and found the manual for that post









and it seems it has a preload adjust on the bottom. I take this to mean it's probably a coil spring inside?? Have you messed with this at all? Your force measurement puts it right on the line of not being able to work.


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## FrankZappa6 (Aug 9, 2010)

Well, I took my TranzX out and put a socket on that nut to see what would happen. It basically unscrewed the bottom cap out of the outer shell. I think the only thing that nut does is hold the bottom cap onto the inner shaft. Here's a pic. 








To disassemble further, one would have to remove the nut. The problem is, everything is heavily lubed and the shaft turns with it. There's no squared off flange for a wrench and I couldn't get the nut loose. I didn't want to put a set of vise grips on it.

I could be wrong, but my impression is that a 50 lb kid could probably get about half the travel out of the post if they had a good bounce going in. There is an initial resistance to overcome and the force definitely stacks up as the hidden spring compresses.

Thanks for posting the manual. I don't recall seeing an English version. Good luck in your quest!
FZ6


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## lixxfe (Apr 19, 2012)

*Lighter springs for GD*

I have 2 Gravity Dropper posts, in 27.2". One is 2" stroke, 325mm Length, the other is 3" stroke, 300mm Length (yes, shorter length on the longer stroke unit).

The spring in the 325mm unit has dimensions: 
Free Length = 9.25" length
Wire Dia.= 0.073"
Spring Outer Dia. = 0.85"
#active coils = 24

Using the spring rate calculator at https://www.thespringstore.com/spring-calculator/spring-rate-calculator.html and assuming music wire for the material: 
Spring Constant, k = 3.6 Lbs/in.

Minimum Preload when installed = 4.0"
Spring Force at top of stroke = 3.6*4.0 = 14.4 Lb.

For the spring in the 300mm unit:
Free Length = 8.00"
Wire Dia. = 0.072"
Spring Outer Dia. = 0.85" 
#active coils = 21
Spring Constant, k = 3.9 Lbs/in.
Minimum Preload when installed = 3.2"
Spring Force at top of stroke = 3.9*3.2 = 12.5 Lb.

I ordered two of these to stack together to reduce the spring force: https://www.leespring.com//product_spec.asp?partnum=LC067K10S&springType=C&subType=

Specs:
Free Length: 4.00"
Wire Dia. = 0.067"
Spring Outer Dia. = 0.845"
Spring Constant, k = 4.5 Lb/in. 
(#active coils not specified, but I counted 12/each)

Two of these stacked together halves the spring constant, so:
k= 2.25 Lb/in.

When installed in the 325mm length GD:
Min. Preload = 2.5"
Spring Force at top of stroke = 2.25*2.5 = 5.6 Lbs.

So about 2.6x less Spring Force (top of stroke).

My calibrated hand says this is about right.

The reduction in effort to drop the seat is very noticeable.

The only issue is the springs cost about $10/each, and there is $50 minimum from Lee Springs (unless you pay $20 handling fee).


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## Feldybikes (Feb 17, 2004)

FZ6 - thanks for the disassembly. I may still give that a short since the post is relatively cheap and it has a remote. I"m not highly confident it'll work for the kid, but maybe still useful as a backup for me.

lixxfe - good idea on the aftermarket springs. Looks like I could something similar from from MSC, though there's a 10 spring minimum which is 5x more than I need.


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## lixxfe (Apr 19, 2012)

The MSC spring would offer some benefit. Spring constant for two is higher at 2.85 Lb/in, vs 2.25 Lb/in for the Lee springs. Even at qty. 10, cheap enough to take a chance and try, I reckon.


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## iamkeith (Feb 5, 2010)

lixxfe said:


> I have 2 Gravity Dropper posts, in 27.2". One is 2" stroke, 325mm Length, the other is 3" stroke, 300mm Length (yes, shorter length on the longer stroke unit).
> 
> ...
> 
> I ordered two of these to stack together to reduce the spring force: https://www.leespring.com//product_spec.asp?partnum=LC067K10S&springType=C&subType=


Thanks for posting this! And thanks to the OP for asking the question, too.


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