The next part of the upgrade for the Bestrider Pump Pro 16 is to install a 3 speed internal hub. I have previously used the Alfine 11 speed and also the Nexus 7 speed, as well as the Brompton wide ratio 3 speed hub.
Although I can build a wheel from scratch, having learnt it at Bike School Asia, I prefer to let others do it as I find it too troublesome. Not only it is a hassle to get the correct spoke lengths, I don't have the time and patience to do it well. Therefore, I bought a stock 16 inch 305 rear wheel with Nexus 3 speed internal hub SG-3R40 from Taobao. It is actually the rear wheel of a Xiaomi QiCycle E-bike, but it so happens to be exactly what I needed for this upgrade.
Exactly what I needed, with black spokes and rims, to match the front wheel.
Uses the Shimano Nexus 3 speed internal hub, SG-3R40.
This rear wheel with internal hub is heavy, at 1242 grams.
Based on my estimation, a 18 teeth rear sprocket with a front 32T chain ring should give a good gear ratio. Shown here is also the dust cap and the snap ring.
Dust cap goes onto the hub first...
...before placing the sprocket on top and securing it with the snap ring.
Weight of rear wheel + sprocket is 1298 grams. Getting heavier now.
Finally, axle nuts plus the yellow non-turn washer is needed to secure this rear wheel onto the bike frame.
Single speed freewheel on the stock rear wheel.
Stock rear wheel + freewheel is 657 grams.
Add the axle bolts and chain tensioner, the stock rear wheel setup is 691 grams.
A fair comparison would be to compare the rear wheel system weight. In this case, the stock rear wheel system weighs 691 grams, while the new rear wheel system weighs 1298 + 37 = 1335 grams. The weight increase at the rear wheel is thus 644 grams.
To digress a bit: If I add a rear derailleur + cassette drivetrain instead, my estimate is that the rear derailleur would weigh around 250 grams, with the cassette another 250 grams. This ~500 gram increase would be a bit less than the 644 grams seen here from the 3 speed internal hub change.
This still excludes the additional weight of other components needed for the 3 speed drivetrain, such as the shifter and the bell crank, plus extra outer casing and shifter inner cable.
New wheel with 28 spokes on the left, stock wheel with 20 spokes on the right. I am happy to find a 3 speed rear wheel that has a matching appearance.
For now, the stock MTB tires will be used. Since I have to remove the tire and inner tube from the stock rear wheel and move them over to the new rear wheel, I took the chance to weigh them.
Stock MTB tire (52-305) is 314 grams. Actually not heavy considering the width and knobs.
Stock inner tube is 119 grams.
Stock tire installed on the new 3 speed rear wheel!
With the rear wheel ready, the next step is to assemble everything onto the bike and test it out. I have not installed a 3 speed internal hub system on a kids bike before, so there will be something new to learn and surely there will be some problems to solve.