Saturday, May 21, 2022

Bestrider Pump Pro 16: Nexus Inter-3 Rear Hub

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.

Bestrider Pump Pro 16: Handlebar Area Modification

For the modification to the Bestrider Pump Pro 16, I will start from the handlebar area. The objective is to install a 3 speed internal hub drivetrain onto this bike. Why 3 speed? Because the shifting force for the 3 speed shifter is very light, which makes it well suited for kids.

First of all, I need to change out the stock handlebar which is ridiculously tall. From what I see, the stem position is OK, just that I need to change to a handlebar without such a big rise. At the same time, the handlebar should be narrower to match the narrower shoulders of a kid.

I have used Toseek flat handlebars on quite a few bikes. Namely, the Fnhon Gust, the Bike Friday Haul-A-Day, United Trifold, and the Fnhon DB11. These carbon handlebars are cheap and good, and available in a wide variety of widths. You can even choose between glossy or matte finishing.

This time, I got the same 480 mm width as what I used for the rear passenger of the Haul-A-Day cargo bike. I found that this handlebar width seems to be well suited for my kid.

I was not sure whether the flat type or the riser type would be more suitable, so I decided to get both and let him choose. The clamp diameter on the stem is 25.4 mm, not the larger 31.8 mm diameter.

Flat vs riser type Toseek carbon flat handlebar, 480 mm width.

Actual width is slightly longer than spec, but not an issue.

Flat bar is 85 grams.

Riser bar is slightly heavier at 92 grams.

Stock aluminium handlebar is a lot heavier at 223 grams, as it is also wider and taller.

The riser bar was chosen, here is how it looks on the bike.

Adjusting the handlebar rotation angle for the optimum rise and sweep.

The tricky part of using the 3 speed Revoshifter is that it takes up valuable space on the handlebar, and requires a shorter grip to match. This means some trial and error before finding the optimum solution.

3 speed Revoshifter for Nexus 3 speed internal hub, SL-3S41. Weighs 75 grams.

It uses a steel clamp band, which may cut into the carbon handlebar. Got to make sure I don't overtighten the Clamp Bolt.

Backtracking a bit, let's take a look at the stock rubber grips of the bike. A smaller grip diameter is better for kids as they have smaller hands. The easiest way to have a smaller grip diameter on a standard 22.2 mm diameter handlebar, is to use thinner rubber grips.

Stock grip outer diameter is less than 28 mm. This is smaller than the usual adult grips which is around 32 mm in diameter.

Stock grips are 64 grams for a pair.

Due to the relatively narrow handlebar (480 mm width), there is limited space on the handlebar to fit the grips, shifter and brake levers. Therefore, I need to make sure that the rubber grip length is not excessively long.

Stock grip length at the bottom, new short grip + Revoshifter grip at the top. Based on my kid's hand size, this length is sufficient.

I bought many different rubber grips of various brands and lengths, and tried to mix and match them to get a suitable set for the left and right side. This is the final set I used, at 58 grams.

On the left side with no shifter, I used an 85 mm grip, which is still shorter than an adult full length grip of 130 mm. Outer diameter is larger than stock at 31.2 mm.

On the right side with shifter, I used a super short 65 mm grip to match the Revoshifter grip. Diameter on the grip is 29.5 mm.

Diameter around the Revoshifter grip is large at 38.9 mm diameter. Hopefully it is not too big!

Here is how it looks with the rubber grip beside the Revoshifter grip. Just managed to fit the brake lever beside, without the lever bottoming out.

Just enough space to fit the grip, Revoshifter and brake lever.

On the left side, in order to ensure the same position relationship between the grip and the brake lever, a gap between the grip and brake lever is necessary.

On the left side, although I could have used a longer grip to close up the gap between the grip and the brake lever, I decided to maintain a short grip. This is to ensure that the hand position is resting correctly at the intended position for 1 or 2 finger braking, instead of sliding inwards towards the centre.

With this setup, it is necessary to use 1 or 2 finger braking, as the brake lever is too far away to put all 4 fingers on it. Hopefully this is OK as kids' hands are not as strong and I am not sure if the fingers are strong enough to apply the brakes effectively.

Bestrider Pump Pro 16: Comparison with Early Rider Seeker 14

Before I dismantled the stock bike for upgrading, I checked out the stock condition in the Part 1 and Part 2 of the bike introduction. Now, I will compare the stock Bestrider Pump Pro 16 to the Early Rider Seeker 14.

Side by side comparison, with the bottom bracket aligned to each other.

The handlebar on the new red bike is much higher, which I find really weird.

View from the back, showing the ridiculous difference in handlebar height.

A big difference in handlebar height, giving very different riding postures.

For the Early Rider Seeker 14, handlebar is 560 mm from the ground.

On the Bestrider Pump Pro 16, stock handlebar height is 680 mm from the ground, a full 120 mm higher!

Slightly longer reach on the red bike, and also wider handlebars.

Handlebar width on the Early Rider Seeker 14 is 450 mm, much more appropriate than the 560 mm on the Bestrider Pump Pro 16.

I love the red paint with glitter on the frame, looks awesome in the light.

Standover height of the Early Rider Seeker 14 is about 400 mm, shorter than the 450 mm on the Bestrider.

Both bikes come stock with the suitable Tektro short reach brake levers. Best for kids' small hands.

Actual tire width on the Early Rider Seeker 14 is 56 mm, a full 10 mm wider than the tires on the Bestrider.

Chain stay length on the Seeker 14 is 261 mm, quite close to the 273 mm on the Bestrider.

Wheelbase is 655 mm, shorter than the 700 mm on the Bestrider.

Tire outer diameter on the 14 inch Early Rider Seeker 14 is 360 mm.

Tire outer diameter on the 16 inch 305 Bestrider Pump Pro 16 is 400 mm.

Stock saddle width on the Seeker 14 is 105 mm

Stock saddle width on the Bestrider is 125 mm. Wider for a growing butt.

More comparison pictures

The tires on the 14 inch Seeker 14 is really large.

The belt drive on the Seeker 14 is good, but it is hard to upgrade that drivetrain.

The Bestrider Pump Pro 16 is larger than the Early Rider Seeker 14 in almost every way, as it is a step up in size for a growing kid. Check out the following posts for the multi-speed drivetrain upgrade!