Kids on dropper posts - minimum rider weights?

i know, if my pressure is low on my one up, the return speed is super slow
Brand x do kids specific, i think pnw do too?

I used a 70mm drop Pro gravel post for my 9 year old nipper's bike, worked a treat and gave him a load more confidence.

It was 27.2 and had external routing so fits pretty much any frame, I had to shim it but for a kid's use that works fine.

My son (9) has a brand-x one on his bike. Made to work at lower pressures so all 30kg of him can push it down and up. He loves it and it has transformed his riding.

Synchros have a kids post too but could be a rebranded post, I haven't looked closely.
My kids have always just had fox transfers on their bikes, starting on the 24" transition ripcord.. #2 was at that point (and still is) an absolute sparrow and has never had an issue with dropping the transfer post under his slight weight.

Another +1 for the brand x one. Works well. Probably the cutest bit of bike gubbins I've ever seen apart from a Frog mini tadpole.

My 10yo quickly got the idea with the kids dropper to the point that I'm immediately discounting any future bike/frame that does not have dropper routing. Sadly that also narrows the choices some what.

My eldest has such long legs for her (fairly tall for 9.5) height that I think she could fit a 150mm dropper on some of the short seat tube bikes I’ve been looking at (like the Vitus Nucleus). I didn’t know kids droppers existed but 70mm is quite short for legs that are already 28” long!

https://thebikedads.com/kids-dropper-posts/ recommends the ks lev as working on low pressures. If you're trying for 150mm be really careful of insertion depth as most kids frames probably aren't deep enough (especially with the extra length of internal cable dropping out)

the brand-x one looks good, shame its internal routing as most kids bikes probably aren't drilled for it..

I'm intrigued that folks don't just take a drill to the (side of the) seat tube?

Or if it's internal routed just send the cable down the down tube and around the bb?

I agree 70mm isn't long, but I'm also not exactly "sold" on the usefulness of a dropper, having learned the trade entirely without one.

I’m intrigued that folks don’t just take a drill to the (side of the) seat tube?

my kids 20" bike has a 250mm seat tube. that brandx dropper is 315mm total length, lets say 80mm is above the seatpost (70mm drop + 10mm collar). That leaves exactly 15mm from the centre of the bb to get a cable out, with a reasonable curve of cable. lets assume the bb is 15mm wide at the middle, you might be able to run the dropper slammed if the routing was external, but with internal routing you're going to need at least 50mm for the cable exit noodle thing and a reasonable amount of cable curvature to make it round the bb. My kids not tall enough for 130mm of seat post showing, so its a non-starter.

Giant's droppers support internal and external routing from memory, it'd be nice if these did too

Or if it’s internal routed just send the cable down the down tube and around the bb?

That's what I did on her orbea mx 24 except on the inside you could use the lower cable port to drill into the seat tube (funky shaped down tube).

I could not get daughter to put the saddle down for some sections but she was complaining about the saddle getting in the way. Dropper at 70mm has solved both. I would rather it was 100mm drop or a bit longer overall as we are currently above the min insertion point by 2-3cm :eek. This is ultimately going to limit the life of the post for her (we have a second child that will get use from it though).

Droppers have made a big difference confidence-wise for my eldest (10yo). It might be worth trying your child on an adult model though. I was ready to splash out on a PNW kid's model but found the regular Brand X 27.2 was fine in terms of activation weight and he's pretty small for his age.

Until #2 grew big enough to fit a dropper in, I just cut down the cheapest post I could find. Much cheaper.

I was happy with the OneUp V1 as it could be shimmed down to 100 mm and be adjusted as she grew.

My daughter (9 yo and 28kg now) has the brand x ascend 70 mm and it is perfect. She tried a number of adult droppers prior to that and none worked. She actually enjoys using this one, really light action and it allows her to put the seat exactly where she wants it. I was worried 70mm wasn’t enough, but as it turns out, it is! Definitely worth it from her perspective, makes the hills a lot less effort as she always used to run her saddle really low and pedal standing up a lot 🙂

sophie (7) been using a ks lev internal for the last year without any issue.

I was ready to splash out on a PNW kid’s model but found the regular Brand X 27.2 was fine in terms of activation weight and he’s pretty small for his age.

this is the info I've been looking for. Do you mind if I ask how heavy your son is? My 11yo is 30kg now and getting a Nucleus 26 soon so I was looking at the Brand-X CX post as an option but unsure if he could move it.

I bought my lightweight 12 yr old a Brand X ascend II (100mm drop) and he loves it, no issues with getting it to move.  Externally routed, but I run it down the side of the seat tube, through the front mech band on then under the BB shell and up to the bars.   Works for now without having to trim the cable, when he grows a bit I'll have to re-route the cable as it will be too short.

My 26kg 10 year old lad just got a 70mm brand X dropper.

70mm slammed on his frame is perfect for his legs, max drop for the space. He drops it no problem. He had it worked out half way through the first ride.

The lever isn't great but the post works really well for him.

He can't drop a OneUp and if the pressure is reduced it comes back too slowly.

My 11yr old has a 100mm Brand X one, the normal type and he's fine on it, he is 40kg mind. Seems the threshold for for operation is around 37kg

Seems the threshold for for operation is around 37kg

What happens if you had less air in it? I need something for my 30kg kid, would prefer the 100mm post as it's externally routed (less faff than drilling a hole) and a touch more drop

What happens if you had less air in it? I need something for my 30kg kid

You can't on the new Brand X ones, sealed cartridges

My 35kg ish 11 year old can make a standard brand X on my bike move but it is marginal downwards and a little fast on the return stroke 😜.

@Rich_S, - my kids loved their Mini Tadpoles when they were 1 but they grew out of them pretty quickly and my daughter found the head angle really steep and twitchy the first time she shot off down the pump track start ramp. Lol. Dead cute though.

I've a 35kg 9 year old on a 125mm Brand X in a XS Trek Marlin and a 45kg 11 year old on a 150mm Trans X on a Poylgon T8. Both adult droppers with no changes. They don't need the full extension but just use their bums to stop at the right height.

... we can ride so much better now i'm not constantly having to stop with them and adjust their saddle heights for dh and climbs.

all good info thanks. I've taken a punt on a second hand BrandX post, which I'll put on my G'bike if it doesn't work out on my son's bike.