When kids reach 140 to 150cm they usually can ride small adult bikes when enough care is given to details. Besides modifying a used bike, doing a budget build over a certain time frame might result in a light and reasonably priced alternative to buying new.
This story started in 2018 when I was looking for an Orbea MX 24 for my seven year old son to replace the too small Orbea MX 20. Since no dealer in our area could supply the bike, I searched Ebay. After buying the kids bike, I stumbled upon a frame without decals that seemed to be a 2013 oder 2014 GT Avalanche: Built for 26″ wheels, disc brake only and with the classical triple triangle design. The 16″ frame size seemed right for 150cm up, so I decided to build the bike over the course of two years.
Simple, light, not too expensive
Although many kids bikes come factory equipped with V brakes, I decided to go for slightly heavier disc brakes for a single reason: Flexibility. Do the math: Adding twice the tire width to the rim diameter roughly calculates the outer diameter of the tire. So the ETRTO/ISO dimensions 559-57 (26×2.2, about 673mm), 584-42 (27.5×1.5, about 668mm) und 622-25 (700x23C, about 672mm) all result in similar wheel diameters and thus are interchangeable. Since the then seven year old kid had plenty of fun riding his bike, I wanted to add the possibility to suit the bike for different conditions by just changing the wheelset. For start I chose the intermediate size: 584mm. Light and good rolling Schwalbe G One should provide a good combination of light rolling resistance and proper grip.
For weight reasons I decided to go with a carbon fork. There are lots of chinese manufacturers selling well made, albeit not extremely light forks. Since the fork is safety crucial, shedding the last 50g and buying a fork from a not certified manufacturer is not recommended. Expect to spend between 55 and 75€ for a proper fork that weights a bit less than 600g. Abandoning suspension forks is the easiest way to lose one kilogram.
When buying the carbon stem, seat post and handlebar, I chose to go for the auctions some chinese suppliers use as a cheap method of creating interest. Auctioned parts are sometimes cheaper than regularily sold, but sometimes it takes a few tries.
Is it possible to build without Shimano or SRAM?
When starting in 2018 drivetrain choice was either Shimano or SRAM. Only SRAM was providing proper One-by-drivetrains at this time with their 1×11 offerings already known for being finicky to adjust. This resulted in the choice of a Microshift XLE derailleur and push pull shifter with gear indicater – well suited for smaller hands. Both are Shimano ten speed compatible so getting spares in case of crashes are no problem. Pricing for Microshift parts is really decent with the derailleur currently costing 25€ and the shifter 15€ at Decathlon. As cassette I choose Sunrace 11-13-15-18-21-24-28-32-36-40 with aluminum spider. Today I’d probably use 11-13-15-18-21-24-28-32-36-42 because the XLE derailleur copes with 42 teeth if the chain length is properly set.
For the wheels I went for XLC Evo hubs with DT swiss 466 rims. Today I’d probably go for hubs with industrial bearings and lighter rims, a good possibility to save another 100g without spending much more money.
More modern drivetrain choices
In the meantime there are more One-by offerings with clutch. One that is notable is Microshifts 1×9 Advent that I use on my everyday bike. Since the gear indicator is missing and spring loads are rather high, it is more suited for teenagers. Then Microshift offers the 1×8 Acolyte that is specifically designed for 24″ and 26″ kids bikes, with push pull shifter and gear indicator. Acolyte should be available by the end of 2021 in retail channels. If a clutch is not necessary, there are some chinese offerings that are compatible to Shimano 10 speed. I’ll do some separate blog posts on LTWOO and Sensah later.
Please note the cranks: When building a bike for a 150cm large kid, you might go with “short” adult cranks of 170mm length. For 140cm kids you should chose 152 or 160mm. The large folding bike scene in Asia offers these cranks. Just check Aliexpress or Ebay for offerings.
No frills brakes
Since I went Shimano free, I opted for Clarks Clout brakes. Shimanos MT-200/201 offer a great value and should be readily avaivable, so there is no technical reason to skip Shimano here. Good alternatives are also available from Tektro or Nutt.
After finishing the bike we did some changes: The carbon seat was too hard, so it was replaced by a kids saddle from Decathlon. The platform pedals were replaced by Shimano PD-T421 with light springs – great for kids.
The result was just below 10kgs, including pedals. I prepared a comprehensive list of all parts used and their sources available.
Without happy end
After seven months of use the bike was stolen from our balcony, I offer 100€ for any hint that helps returning the bike!