[todd_fuller]

How are the seat post and bras for weight on the Room bikes? Are they pretty light or is there room for improvement by going to carbon? Looking at this for my daughter and would like to make it a light as possible. she is tall but very petite so low bike weight is important.

To address this specifically, get some carbon bars. Seat post is weight weenie light already.
I did some weighing of components and they have a pretty good build. Bars, cassette, saddle are areas to improve. Seat post is 199g, saddle is 224g.
Unless you go Ti Bb, not much to get out of that. I'm keep my eye out for old XTR brakes.

 

[mfacey]

Has anyone any experience of BMC Blast 24"? The specs looks decent and the weight is below 10kg.

BMC BLAST 24" Kids Bike - 2021 - orange

I cannot find any reviews of the bike.

Looks pretty decent although specs are a little less than on the equivalent Woom 5. Actually, outside of the dedicated lightweight kids bikes manufacturer's its one of the better alternatives to Woom I've seen so far. And its available immediately!

 

[mfacey]

Update: the woom Off 5 I ordered direct from Woom back in March finally got delivered this week. Can't believe it took 4 months! Apparently the forks, both rigid and air, were on back order.

 

[gramr]

Early Rider and Commençal make some ridiculously nice kid's trail bikes, too - but they ain't exactly cheap. It seems like Woom's Off series is basically impossible to beat in terms of how good of a bike you get for the money.

 

[mfacey]

I haven’t checked the specs on those bikes but the problem is often that they still use a lot of adult size components like cranks that are too long or an adult dimension q-factor. Even high end adult suspension components aren’t built or tuned to kids needs. It just makes a lot of kids bikes XXS sized adult bikes. That’s fine if your in your teens but doesn’t work if you’re 8 or 9 years old.

I guess it’s just too small of a niche for most manufacturers to take seriously.

 

[gramr]

@mfacey
Check them out then, because every single point you mentioned and then some are considered in the design and specification of the Woom, Early Rider and Commençal bikes.

Crankarm length, bottom bracket width, brake lever reach, pedals, handlebar, grips, saddle, geometry, spring and damping rates are all proportionate to rider size in their smaller bikes. They're not cheap, but you do get what you pay for.

 

[rton20s]

What @gramr said!

Cranks
Early Rider: 150mm (Narrow Q-Factor)
Commencal: 145mm (165.8mm Q-Factor)
Woom: 130mm (Narrow Q-Factor)

Forks
Early Rider: RST F1RST (Kid Specific Fork)
Commencal: Manitou Machete JUNIT Pro (Premium Kid Specific Fork)
Woom: Woom / RST F1RST? (Kid Specific Fork)

Other
Early Rider: SDG Fly Jr Saddle
Commencal: Pro Taper JUNIT Bars & Grips, SDG Fly Jr Saddle
Woom: Woom Kid Specific Bars, Grips, Brake Levers and Saddle

 

[TimTucker]

Crankarm length, bottom bracket width, brake lever reach, pedals, handlebar, grips, saddle, geometry, spring and damping rates are all proportionate to rider size in their smaller bikes. They're not cheap, but you do get what you pay for.

IMO, based on my own experiences dropping down from 175mm to 152mm cranks on my own bike, I'm still convinced that crankarm lengths are too long on pretty much all kids bikes.

Huge benefits to having better ground clearance and far more downsides to going "too long" than "too short"

The progression we've followed so far has been:

• 14 & 16": 89mm
• 20+: 102mm
• 24+: 120mm

Most kids bike companies are shipping anywhere from 140mm to 155mm for 24" bikes -- we're not likely to go up to 140mm until at they get to at least 26".

 

[rton20s]

@TimTucker I've had similar observations, but haven't made the drastic changes you have.

We changed out heavy stock cranks with non-swappable chaingrings on our 16" bike to a 102mm, and the 20" bike to a 127mm Spawn cranks. This has reduced weight and allowed us to swap chainrings as we desire. The 24" bike has 140mm aluminum cranks with a 32T 104bcd chainring. So far this has worked well for us. I could see going 5-10mm shorter on the 24" as being advantageous, but haven't really felt the need to make a change.

I've put together some pretty extensive comparison spreadsheets and found that the average crank length of a quality 20" bike is 135mm with the longest being 152mm. On the 24" side the average was 145mm with the longest being the same 152mm. I never even took anything with a crank length longer than 152mm into consideration.

 

[mfacey]

What @gramr said!

Cranks
Early Rider: 150mm (Narrow Q-Factor)
Commencal: 145mm (165.8mm Q-Factor)
Woom: 130mm (Narrow Q-Factor)

Forks
Early Rider: RST F1RST (Kid Specific Fork)
Commencal: Manitou Machete JUNIT Pro (Premium Kid Specific Fork)
Woom: Woom / RST F1RST? (Kid Specific Fork)

Other
Early Rider: SDG Fly Jr Saddle
Commencal: Pro Taper JUNIT Bars & Grips, SDG Fly Jr Saddle
Woom: Woom Kid Specific Bars, Grips, Brake Levers and Saddle

OK good examples in this case!
I recently saw the announcement of a new chromag kids bike which is just not a kids bike: https://www.pinkbike.com/news/video...om/news/video-chromag-announces-full-suspension-kids-bike-the-minor-threat.html

Another example, the pricey YT Jeffsy Primus 24" which has 165mm cranks... YT Industries

I've looked at building my own kids hardtail but did notice distinct lack of options when it comes to cranks suitable for kids. Maybe its just an availabity thing?

 

[rton20s]

I've looked at building my own kids hardtail but did notice distinct lack of options when it comes to cranks suitable for kids. Maybe its just an availabity thing?

Look to the brands that already have kid specific bikes. Some offer various components (cranks specifically) sized for kids (Trailcraft, Prevelo, Spawn, etc). Other will list what brand and model the cranks are and you can use that information to try to source your own. Finally, take a look at offerings from BMX brands. Cranks are actually one of the easier problems to tackle, if you know where to look. Just don't expect to find adult brands (Shimano, SRAM, Race Face, etc.) readily available in kid sizes.

 

[mfacey]

Assembled my son's Off 5 yesterday evening and there is a distinct wobble on rear disc. It touches the pads on the left and right alternately. I removed the disc to see if it was warped/bent but it seems perfectly flat. That leaves the hub not being 100% flat. I couldn't detect any visible dirt or other damage that would cause the wobble. I've emailed to Woom to see what they say. Anyone else face similar issues?

Luckily I could get it to wear it only lightly touches each pad so its definitely rideable without dragging too much, but too bad nonetheless...

 

[mfacey]

Has anyone successfully converted the stock rims with the Schwalbe tires to tubeless? I’ve seen a video and article of someone stating that it was fairly straightforward but they used presta valves. I’m going to give it a shot in the coming days. I don’t have a compressor only a pump with a booster. Served me well on all my other tubeless setups so let’s see what happens!

 

[mfacey]

Decided to go for a test of tubeless on the front first. So far so good. Removed the rim liner and used gorilla tape around 26mm wide to tape up the rim bed. Went around once, overlapping the valve hole to double up. Getting the tire bead to seat required the use of my booster. Second shot got it to seat nicely. No pops like i get on my 29 rims.

I'm using muc off sealant and I've spotted a little bit of sealant coming though where the rim was welded together. See pic. Going to leave it overnight to see how well it holds.

I'm using el cheapo Ali-express tubeless schrader valves which are ok. I don't like the tapered shape of the rubber seal that sits inside the rim. Doubles up too easily. Looks like there's a tiny amount of sealant seeping through. Might get some Stan's to see if they work better.

One week update:
Tire isn't holding pressure great. To be fair it hasn't been ridden besides a few mins up and down the street so perhaps the sealant hasn't distributed great. I'll do a leak test with some soapy water to see where its coming from. Wouldn't surprise me if its the valves....

a few weeks later update:
Yeah the valves suck. I tightened down the cheap valve further but struggled to keep the tires inflated. Installed Stan's valves which have a noticeably more solid rubber seal to connect to the inside of the rim. Rear tire also needed the booster to seat after some persuasion. The rear rim also was seeping some sealant around the weld. That sealed up quickly though. Good to go!