Custom 24"Kids Bike

[Kuys]

After a long search end of last year for a proper 24"bike for my daughter, I ended up with the following:

 

Frame: Semi custom Mercer frame (short reach, low BB, slack head angle)

Fork: Suntour XCR AIR LO 24, 68mm travel

Headset: Cane Creek 10 series

Stem: Rapidé ControlColumn Stem 45mm

Handlebars: Rapidé ControlStick 760-9 Flat Bars

Grips: ESI foam grips

Brakes: TRP Slate with 160mm rotors

Rear Derailleur: Shimano Saint M820 10 spd

Shift levers: Shimano Saint M820 10 spd

Cassette: Shimano XT 11-36t 10 spd

Chain: Shimano 10 spd

Crankset: Aerozine XEON-A1 mini, 135mm

Chainring: 28t, direct mount

BB: Aerozine

Pedals: TBD

Rims: Stans Crest, 24"

Hubs: Hope RS4, QR axles

Tires: Maxxis Recon 2.2 / Schwalbe Rocket Ron 2.35

Saddle: SDG Fly JR

Seat post: Rapide inline

Seat binder: Mercer integrated

 

Over the next couple of days I'll post some more detail about the what, why and how of each

 

To be continued...

[Shebeen]

E

P

I

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[DJuice]

Following this!

[Kuys]

Frame is currently getting powder coated

[Kuys]

This is how geo compares with the "competition" 

 

Reach: 340mm

BB drop: 60mm

HA: 68 deg

[Kuys]

This is the fork I'll be ordering directly from Suntour

 

https://www.srsuntour.us/products/xcr-air-lo-25?variant=5469981933599

• 63mm travel
• Internally adjustable to 80mm travel
• Lockout with factory preset rebound 
• Air adjustable preload
• Forged aluminum crown 
• 28mm stanchion tubes
• 9x100mm drop out
• Lower magnesium casting
• Disc brake only
• Direct mount 160mm
• 1 1/8" aluminum steering column
• 255mm long
• Fully serviceable
• 2 year limited manufacturing warranty
• 415mm axle to crown measurement set at 63mm travel
• 54mm maximum tire width
• 1950g

Edited February 11, 2021 by Kuys

[Kuys]

https://thebikedads.com/kids-forks/

 

There's quite a few options available abroad, and most you can order, but shipping cost becomes very expensive. Prevelo Heir charges $300 for shipping only! Making it a $700 fork!

 

The Suntour seemed like the best option price vs performance balance. 

[Kuys]

Crank options: 

 

If following the 10% rule (crank should be 10% of overall length) she should be riding 120mm cranks...

 

I could have gone either the route of getting hold of old cranks and have it shortened by machine shop or buy it off the shelve. 

 

To shorten it, it could not be a hollow crank like Shimano, or have any cut-outs at the back like most modern aluminium cranks have (Rapide, SRAM etc). Then you are stuck with really old cranks that have large 5 bolt BCD's which is difficult to get small 1x chainrings for. 

 

Off the shelve there are quite a few options (but shipping is expensive):

1. SR Suntour Zeron (shortest length is 152, so still a bit too long, uses proprietary chain ring mount

https://www.srsuntour.us/collections/cranks/products/zeron-1-x?variant=45338041742

 

2. Jet Racing BMX cranks. Uses square taper BB (no problem for a 6-8 year old), shortest length is 140, uses 104BCD chainrings, 

https://row.sourcebmx.com/products/jet-bmx-square-taper-race-cranks?variant=31876233429110&currency=zar

 

3. Hope Kids Cranks - 135 or 150mm length. Expensive!

https://www.bike-components.de/en/Hope/Kids-No-Spider-Cranks-p74887/

 

4. Prevelo Heir cranks - these go really short at 120 or 140 options, but was not able to ship to SA

https://prevelo.com/products/heir-direct-mount-crank

 

5. I eventually settled on the Aerozine cranks - 135mm length with 28t direct mount chainring. Compatible with SRAM chainrings so easy to source alternatives. 

https://www.aerozinebike.com/product/transmission/crankset/for-kidbike-crankset/aerozinexeon-a1-mini-crankset-kidbike/

 

Shipping was quick and I received it after about a week via Fedex

 

I was able to source an Aerozine BB locally through my LBS and Paragontech. 

Edited February 15, 2021 by Kuys

[l4y3rcake]

Crank options: 

 

If following the 10% rule (crank should be 10% of overall length) she should be riding 120mm cranks...

 

I could have gone either the route of getting hold of old cranks and have it shortened by machine shop or buy it off the shelve. 

 

To shorten it, it could not be a hollow crank like Shimano, or have any cut-outs at the back like most modern aluminium cranks have (Rapide, SRAM etc). Then you are stuck with really old cranks that have large 5 bolt BCD's which is difficult to get small 1x chainrings for. 

 

Off the shelve there are quite a few options (but shipping is expensive):

1. SR Suntour Zeron (shortest length is 152, so still a bit too long, uses proprietary chain ring mount

https://www.srsuntour.us/collections/cranks/products/zeron-1-x?variant=45338041742

 

2. Jet Racing BMX cranks. Uses square taper BB (no problem for a 6-8 year old), shortest length is 140, uses 104BCD chainrings, 

https://row.sourcebmx.com/products/jet-bmx-square-taper-race-cranks?variant=31876233429110&currency=zar

 

3. Hope Kids Cranks - 135 or 150mm length. Expensive!

https://www.bike-components.de/en/Hope/Kids-No-Spider-Cranks-p74887/

 

4. Prevelo Heir cranks - these go really short at 120 or 140 options, but was not able to ship to SA

https://prevelo.com/products/heir-direct-mount-crank

 

5. I eventually settled on the Aerozine cranks - 135mm length with 28t direct mount chainring. Compatible with SRAM chainrings so easy to source alternatives. 

https://www.aerozinebike.com/product/transmission/crankset/for-kidbike-crankset/aerozinexeon-a1-mini-crankset-kidbike/

 

Shipping was quick and I received it after about a week via Fedex

 

I was able to source an Aerozine BB locally through my LBS and Paragontech. 

 

135mm on a 24" bike sounds a bit short. My 8 yr old son has the 152mm Suntour on his stock Momsen JSL 40 and on his custom BMX he rides 150mm SD(Super Duper BMX components) Junior cranks(104bcd). He is also around 120-130cm tall.

 

Next time you need specific length cranks, get hold of someone in the BMX community. You will find all the sizes in 5mm increments and the cranks are mostly 104BCD.

 

Awesome project this. Would love to see the finished product.

[Kuys]

135mm on a 24" bike sounds a bit short. My 8 yr old son has the 152mm Suntour on his stock Momsen JSL 40 and on his custom BMX he rides 150mm SD(Super Duper BMX components) Junior cranks(104bcd). He is also around 120-130cm tall.

 

Next time you need specific length cranks, get hold of someone in the BMX community. You will find all the sizes in 5mm increments and the cranks are mostly 104BCD.

 

Awesome project this. Would love to see the finished product.

 

Cool thanks for the feedback. 

 

Yeah about the length, one gets influenced by many people, articles, experience etc. For example see this link:

 

http://www.bikesmithdesign.com/Short_Cranks/cranks4kids.html

 

I do know the 160's she's currently riding on a borrow 24" is definitely too long. 

 

I'll give some feedback once the bike is built up on how the crank length works out for her

[Pure Savage]

 

This is the fork I'll be ordering directly from Suntour

 

https://www.srsuntour.us/products/xcr-air-lo-25?variant=5469981933599

• 63mm travel
• Internally adjustable to 80mm travel
• Lockout with factory preset rebound 
• Air adjustable preload
• Forged aluminum crown 
• 28mm stanchion tubes
• 9x100mm drop out
• Lower magnesium casting
• Disc brake only
• Direct mount 160mm
• 1 1/8" aluminum steering column
• 255mm long
• Fully serviceable
• 2 year limited manufacturing warranty
• 415mm axle to crown measurement set at 63mm travel
• 54mm maximum tire width
• 1950g

 

is the 1950g worth it vs 400g solid? the 1,5kg as a % of the bike in the small bikes is rather large. 

[Jewbacca]

I would guess the 135mm will be perfect.

 

To be fair, most people riding 175mm would be better off with 170mm, so being a 1.2m tot I would suggest the 135mm would be spot on.

[Kuys]

is the 1950g worth it vs 400g solid? the 1,5kg as a % of the bike in the small bikes is rather large. 

 

Fair question. 

 

The reasoning is to give her a bit more confidence over roots and rocks. They are not so strong in upper body to man handle 'n rigid front end through technical terrain. With a rigid fork they get deflected off line easier. 

 

That's the reasoning, lets see how it pans out in real life. If it feels too heavy , I can always get David to make a rigid fork and only later move over to the suspension fork. 

 

What's making the project fun is the unknowns and to make a decision and then see how it pans out. I want to see for myself and not just make decisions based on some else's opinion.

 

The intention is to give feedback once the bike is running to see how these decisions panned out. Thus closing the loop.  

[Pure Savage]

Fair question. 

 

The reasoning is to give her a bit more confidence over roots and rocks. They are not so strong in upper body to man handle 'n rigid front end through technical terrain. With a rigid fork they get deflected off line easier. 

 

That's the reasoning, lets see how it pans out in real life. If it feels too heavy , I can always get David to make a rigid fork and only later move over to the suspension fork. 

 

What's making the project fun is the unknowns and to make a decision and then see how it pans out. I want to see for myself and not just make decisions based on some else's opinion.

 

The intention is to give feedback once the bike is running to see how these decisions panned out. Thus closing the loop.  

Agreed, the suspension is tricky as the smaller forks are not as plush or adjustable as the adult forks. Also as kids are so much lighter they tend to not get the full use of the fork. 

 

Its really down to the fork, I have seen kids sending it on real proper 24" forks and getting it dialed in, but also seen so many Spez/Scotts where its not setup and just running tubeless would have helped for the roots etc. 

 

Setting it up will probably be the key

[Kuys]

Agreed, the suspension is tricky as the smaller forks are not as plush or adjustable as the adult forks. Also as kids are so much lighter they tend to not get the full use of the fork. 

 

Its really down to the fork, I have seen kids sending it on real proper 24" forks and getting it dialed in, but also seen so many Spez/Scotts where its not setup and just running tubeless would have helped for the roots etc. 

 

Setting it up will probably be the key

 

Exactly. Will be critical to get at least some sag at static, and have as little friction as possible. It will probably require regular servicing to really keep it smooth as any friction will be amplified by the expected low pressure and small mass of the rider. 

 

Rebound is not adjustable, so I'll keep an eye out on that as well. If its really bad I''ll check and see if any of the local suspension experts can tune it a bit

[Pure Savage]

Exactly. Will be critical to get at least some sag at static, and have as little friction as possible. It will probably require regular servicing to really keep it smooth as any friction will be amplified by the expected low pressure and small mass of the rider. 

 

Rebound is not adjustable, so I'll keep an eye out on that as well. If its really bad I''ll check and see if any of the local suspension experts can tune it a bit

Sounds like extra 1.5kg will be worth it.