Islabike CNOC16 3 Speed Conversion

Background

Generally speaking these days you can easily buy suitable bikes that are ideal for kids, there are some companies like Islabike and Frog who sell kids bikes that are lightweight and designed with appropriate geometry in mind.

We all know that gears can make riding bikes easier (as long as you can choose the correct gear for the situation). My son is 6 years old and 101cm tall giving him an inside leg measurement of about 42cm making him just big enough for some bikes with 16" wheels (Islabike cnoc16 seemed to be about the smallest quality bike with 16" wheels). Moving to a bike with 16" wheels was a real step forward, the wheel size meant riding off-road on trails and pump tracks like those at Clayton Vale were really enjoyable for all.

Most of my son's friends who ride regularly have now moved onto bikes with 20" wheels and several gears; despite my son's boundless energy he simply can't spin the pedals fast enough to keep up. I looked at the growth charts and concluded that it would probably be about 18 months until we could try a bike with 20" wheels and gears so I made the decision to investigate a bike with 16" wheels and gears but could not find any on the market. My internet research showed that using a derailleur was not possible as this would not fit in the space available and would probably hit the ground on a 16" wheel. A friend mentioned Sturmey Archer bringing back memories of the Raliegh Chopper with it's 3 speed hub. More research showed that it was possible to buy a 3 speed wheel with an O.L.D. of 110mm which would fit in place of the original wheel without any modifications. The next concern was whether the selector cable would get hit by shoes whilst pedalling - I worried about this, but finally decided to take a risk and see what happened.

The Conversion

The biggest issue was that the islabike uses an 8-speed shimano chain which is not compatible with the Sturmey Archer sprocket. I lined the Sturmey Archer sprocket up against an old Shimano Cassette and decided that the hole diameter was identical, and that the Shimano Gear could be made to fit the Sturmey Archer hub.

 

Figure 1: Left - Sturmey Archer Sprocket, Right sprocket from a shimano 9-speed cassette (you must punch or drill the pins to get the gear off the cassette).

NOTE: The 14T Shimano gear that was actually used does not have as many holes and appears more suitable)

 



Figure 2: The 2 sprockets on top of each other, some careful work with the Dremel allows it to fit snug on the Sturmey Archer hub.

A little work with the Dremel and the correct sprocket was fitted to the hub. I changed the retaining ring for a more robust circlip as the ring seemed too weak.

I removed the chain guard and fitted the wheel (I think some minor modification would be needed to make the chain guard fit).

I decided to run the cable along the top tube then onto the seat stay clamping just above the vbrake using a fulcrum clip from a local bike shop (Sturmey Archer Fulcrum Clips can be sourced on ebay).

Figure 3: The wheel fitted showing the cable and fulcrum clip.

I initially chose to use a "Sturmey Archer Rapidfire Trigger" shifter which needed a rubber insert to allow it to grip on the smaller diameter Islabike handlebars. The shifter is ok, but not light enough for small kids to change gear easily - I intend to upgrade to a trigger shifter as this looks like a more natural way to push your thumb.

Figure 4: The "rapidfire trigger" shifter

Figure 5: The desired shifter

Conclusions

• The conversion works really well
• My son's UK kids size 9 shoes don't interfere with the gear selector.
• He can ride up hills he couldn't previously manage
• He is significantly faster on the flat
• Only having 3 gears is great at this age; my son usually chooses the correct gear using the following:
• Gear 1 for uphill
• Gear 2 for flat
• Gear 3 for downhill
• Sturmey Archer hub gears are great for kids as you can change gear whilst stationary.

Figure 6: The finished 3-speed conversion.