BXT 20" build

[tamerlano]

Hi,

So my son (5 going on 6) is fast outgrowing his first bike (14" wheels, single speed, coaster brake) and as he really enjoys bicycling, I've decided to get him a proper one. Final price tag will be around 900 euros, but I hope to be able to sell once he outgrows it; lots of bike loving households in our neighbourhood. Expected weight: ~7.5 kg

Frame: BXT Carbon Frame for 20" wheels. Ticks all the boxes (BSA, tapered steerer, 12/142 through axle, postmount).

Front fork: Meinier 20" rigid Carbon fork, PM/15x100. I want to keep the bike as light as possible, there are also no "serious" suspension forks for kids' bikes to the best of my knowledge.

Wheels: Pasak 20" ("406"). Alu, 6-bolt, HG body, through axles. Price difference is negligible compared to other QR options.

Tires: Maxxis Minion 20" DHR (2.30") and DHF (2.40"). Perhaps a bit too aggressive, any 20" alternatives with XC treads?

Derailleur: Ltwoo T3 (short cage) with shifter, 8-speed, bundle with chain and 11-36 cassette. I preferred the 8-speed Microshift Acolyte (short cage), but those seem to be out of stock everywhere.

Crankset: Goldix Children's crankset, probably 30T chainring/127 mm cranks

Pedals: Cruzbike Ultralight Children's Pedals

Disc brakes: Zrace x2 or similar 2-pot. 2x 160 mm brake rotors

Integrated bar+stem: AE Syncros/Roval "inspired", I'll just cut off the ends to suit his size.

Grips: West Biking kids grips, 92 mm

Everything else (seatpost, TPU tubes etc) will be what's usually preferred and considered safe on this forum. Any obvious flaws in my line of thinking?

[Ludo]

I would go 28T chainring with that cassette.
7.5kg is super ambitious, my son 24 is 9.4 with about that set up.

[jefflinde]

If you go to the woom bikes website you can order the rocket Ron 20". They are super light and are basically a 20" version of the top spec 29er tire with the same casing and addix tread compound.  Great grip and crazy fast rolling.

[Ludo]

Yes that’s what i put on my son 20”, worked well but wears fast. I found them cheap on trailcraft website IIRC.

[Zachdds]

I built my son’s bike last week. Used almost all the same components you have listed and got the bike to come in at 17.2 pounds or just under 8kg. I did go with the Microshift 9 speed and Meiner frame and fork. But otherwise pretty much what was listed.

The wheelset is heavy and I could not get it to seal up tubeless. The frame and fork and matching paint job were very nice. I did use a 10 speed cassette that I had and locked out highest gear. Shifting was easy to set up.

Pictures included. One of them is an ai rendering of the bike. It is slightly off, but gives a good idea of what it looks like.

[Ludo]

Great looking bike!!

[jefflinde]

Love these builds.  Any idea on total cost for these?  I went with a woom 4 a few years back and have been happy with it but I wish I would have gone this route.  Too late now but once my youngest moves to 24" wheels I will be building another Chinese frame up.  Love to see the 20" options expanding.

[Ludo]

650 for a 24 with front sus, 21lbs.

[tamerlano]

Thanks for your comments! I will switch to a standard stem+bar combo, such as the Shikra 35 mm Al stem and a 600 mm carbon flat bar, as the stem length in an integrated handlebar for adults seems too long (> 60 mm) for a child.

I would go 28T chainring with that cassette.
7.5kg is super ambitious, my son 24 is 9.4 with about that set up.

You're absolutely right. After revising weights, total will be around 8 kg. It's rather flat where we live (think the Scandinavian equivalent of the Great Plains) so perhaps a 30T is the better choice for the gravel roads in our vicinity where we'll do most of the riding?

I built my son’s bike last week. Used almost all the same components you have listed and got the bike to come in at 17.2 pounds or just under 8kg. I did go with the Microshift 9 speed and Meiner frame and fork. But otherwise pretty much what was listed.

The wheelset is heavy and I could not get it to seal up tubeless. The frame and fork and matching paint job were very nice. I did use a 10 speed cassette that I had and locked out highest gear. Shifting was easy to set up.

Pictures included. One of them is an ai rendering of the bike. It is slightly off, but gives a good idea of what it looks like.

What's the required length (unthreaded+threaded) and pitch for the front/rear through axles? I can't find this information on the BXT/Meinier web sites.

[tamerlano]

Finally done! Most items were delivered after 2-3 weeks, but the wheels required 5 weeks. This was partly my fault as I didn't pay attention to the different AE freight alternatives. Spent around 1000-1100€ in total, including freight to central Sweden. No issues at all with customs. Total weight is around 8 kg.

- Chain was cleaned in mineral spirits, degreaser, boiling water and ethanol/isopropanol before applying KMC drip-on chain wax. Admittedly, there are better waxes out there, but I went with KMC as I will use a prewaxed KMC chain for my own XC build in the future.
- Saddle (the only item not sourced from AE) is an older Bontrager road model with Ti rails; so far, my son finds it rather comfortable.
- Could not find a suitable integrated CF bar+stem, so I went with a Toseek 600 mm carbon bar (no need to cut, suits my son's anatomy) and a 35 mm Al stem.
- I was planning to use TPU tubes with sealant, but I accidentally bought tubes with Schraeder valves instead of Presta with removable valve cores.
- Frame and fork included through-axles for Allen keys after discussing with both vendors.

Good:
BXT 20" frame:  no complaints whatsoever - beautiful orange paint job, no excess resin/paint near BB threads/headset/brake bosses. Frame was delivered with plastic hoses inside the frame, which facilitated internal routing of derailleur cable/rear brake hose.

Pasak 20" wheelset: bearings feel smooth; rims are drilled for Schrader tubes.

Ltwoo T3 8-speed derailleur bundle: works great, although plenty of effort (for a child) is required to push the shifter, but it could also be because he's never shifted gears previously. Derailleur cage (short version) clears everything, including spokes and tire sidewall.

Zrace X2 brakes: very powerful, lever reach can be adjusted for small hands

20" Maxxis Minnion DHF/DHR tires: exceptional traction and suspension, increased rolling resistance compared to XC treads is not an issue for an energetic 6-year old ...

Cruzbike pedals: built-in reflexes, bearings rotate freely, look great.

Goldix crankset: the built-in metallic chainring protector is a neat feature which protects the shin/ankle.

Bad (but in the greater scheme of things, these are minor quibbles:
Zrace X2 brakes: only 1 loose barb/olive included for the rear brake. Will have to shorten the preassembled front brake in the future and also route the hose inside the left fork leg.

Goldix kid's crankset: axle is a few mm too long for the 68 mm bottom bracket shell. I could not preload the BB even with all three washers installed, so I used a spare metal washer to preload before tightening the left crankarm bolt. Also, the chainring is not completely round, it "wobbles" sideways around +/- 0.5-1.0 mm when rotating.

11-36 8-speed HG cassette: locking was damaged and would not thread unto freehub. LBS provided me with a spare one, free of charge.

Stem: way out of specification; could not slide it down the steerer tube at all, so I inserted a nail inside the slit and forced both ends apart by screwing in the bolts.

Meinier 20" fork: was delivered in a plastic bag without any protective cardboard, albeit wrapped in plenty of bubble plastic/foam.  No obvious damage though after visual inspection.

Pasak wheelset: freehub is very noisy, might have to grease the pawls.

Conclusion:
I am very happy with the bike - a fun and reasonably smooth build process. What matters most however, is that my son loves it!  After only a week, he's already tackling more technical trails.