Wednesday, July 17, 2019

Bike Friday HaD: Deore XT Di2 Rear Derailleur and 11-40T Cassette

The drivetrain of the Bike Friday Haul-A-Day cargo bike needs to be simple and robust, and be able to shift well even under load. Due to the heavier weight of a cargo bike (even when not loaded), it is better to have some lower gearing to make pedaling and climbing easier.

Although there is a front derailleur mount on the frame, I decided not to install a front derailleur, even though it will give me a really nice gear range with a front double drivetrain. This is to keep it simple, as I think a wide ratio cassette should give me sufficient gear range for the intended purpose.

I will not be going fast on a cargo bike, what I need is good low end gearing for climbing up slopes when carrying a heavy load. As such, a gear range similar to that of a mountain bike should be quite suitable.

My Polygon Cozmic CX3.0 MTB has a really wide gear range of about 18 to 80 gear inches, with a 11-50T 12 speed cassette. Adjusting the chain ring size will shift the whole range up or down, depending on your needs.

However, it is not possible to put such a large cassette on a 20" wheelset, as the rear derailleur cage will touch the tire or the ground. Therefore, I need a cassette that has a relatively wide range, but not too big that it cannot be used on this bike.

Testing a large 11-40T cassette on the 20" wheel (Dahon Kinetix Pro), used on the Dahon MuEX, to get a sense of how it looks.

Prior to looking for the suitable cassette size, I need to first decide the rear derailleur to use. This is not the usual sequence, as normally, the cassette is first chosen (based on your gearing needs), then a suitable rear derailleur will be selected to work with the cassette. However, one of my requirements is for electronic Di2 shifting, which greatly limits the choice of rear derailleurs.

For Di2 shifting, I have a choice of either road or MTB Di2 rear derailleurs. A road Di2 rear derailleur will definitely have enough ground clearance, but it also limits the size of the cassette I can use. For example, the Ultegra RD-R8050 rear derailleur can support up to 34T cassettes (GS spec), but I don't think the gear range (1x11 speed, 11-34T cassette) is low enough for this cargo bike.

In order to have a wider gear range with a front single setup, I need to use wider range MTB cassettes, which means a MTB Di2 rear derailleur is needed. There are not many choices, with XTR or Deore XT Di2 rear derailleurs as the only options.

For a cargo bike, using Deore XT is already quite extravagant, not to mention XTR. The choice is thus to use the Deore XT M8050 Di2 rear derailleur on this cargo bike. As this Deore XT Di2 rear derailleur is only 11 speed compatible, I will need to use an 11 speed MTB cassette. As for the exact choice of 11 speed MTB cassette, it will be confirmed later, let us take a look at the Deore XT Di2 M8050 rear derailleur first.

Deore XT RD-M8050 Di2 11 speed rear derailleur. Comes with a few little caps for unused Di2 ports and a rubber cover.

Rubber cover goes over the Di2 port on the RD, for improved sealing.

First and only generation of MTB Di2 RD, very similar to the top end XTR RD.

B tension screw on top, High and Low limit screws in black colour at the bottom.

Part of the Dynasys 11 drivetrain. The clutch is housed under this cover.

The grey lever turns the clutch On and Off. More details at a previous post here.

With the bottom cap opened, the clutch tension can be adjusted with an Allen key. Contrary to what some people think, it is NOT a grease port, do not inject grease inside!

Rear side of the RD, with the motor unit located at the back end of the RD.

Saver unit at the back of the RD, to prevent damage to the motor in case there is an impact.

Cage set of the RD

Cage length (pulley to pulley) is about 85 mm, which is a rather standard value. A shorter cage is better for more ground clearance, provided there is enough chain capacity.

Weighs 321 grams, which is rather heavy, but understandable due to the Di2 motor unit and the long cage. Claimed weight is 319 grams.

With the rear derailleur decided, the appropriate cassette can now be selected. An 11 speed cassette is needed, since this Deore XT Di2 rear derailleur is for 11 speed drivetrains.

As mentioned earlier, road 11 speed cassettes only have a maximum of 34T, which I feel is not low enough for a cargo bike. This means an 11 speed MTB cassette is needed. The choices are 11-40T, 11-42T, or 11-46T cassettes.

11-46T will give the greatest range, but I am quite sure there will not be enough ground or tire clearance with the rear derailleur cage.

11-42T and 11-40T are very similar, with only a 2 teeth difference. Gear ratio wise, they are almost the same, but the 11-40T cassette will give slightly more clearance between the rear derailleur cage and the ground/tire.

The final choice is thus the 11-40T cassette, chosen for the wide gear range, and hopefully also sufficient clearance between rear derailleur cage and ground/tire. At this point, I am hoping I can strike a balance between these two conflicting requirements.

Deore XT CS-M8000 11 speed cassette, 11-40T combination.

Gears look to be evenly spaced out, with the largest 40T sprocket made of aluminium instead of steel. This is unlike the 11-46T cassette with a large jump between the largest two sprockets.

Unusual 7 sided aluminium cassette spider at the rear, which is used to improve the rigidity of the larger sprockets and also reduce overall weight.

Largest 3 gears are riveted together, and the next 3 gears as well. There are 2 cassette spiders in this cassette. The other 5 gears are made up of individual sprockets.

Closer look at the 7 sided spider. Usually, cassette spiders are 6 sided.

Gear combination of the larger sprockets. 24-27-31-35-40 teeth sprockets.

Claimed weight is 411 grams, while the actual weight is almost the same at 413 grams.

Gear combination and the gear ratios, when used on a 20" wheel with a 44T front chain ring.

As planned, the gear ratios are similar to that of a MTB. The top gear of 80 gear inches is the same as on the MTB, which should be enough, from my experience riding the MTB. The low gear of 22 gear inches is the lowest that is feasible, given the constraints of the small wheel size and the 11-40T cassette. Even if a 42T low gear is used, the lowest gear is 21 gear inches, which is practically the same. This gearing should be low enough for climbing on this cargo bike.

Dura-Ace/XTR CN-HG901 chains are used. Note that the newer pack (right side) comes with the Quick Link instead of the chain pin.

Since the chain stay is super long, at 690 mm instead of the usual 400+ mm, 2 chains are needed. I expect to use about 1.5 chains. The Dura-Ace/XTR HG901 11 speed chain is used for good corrosion resistance and best shifting performance with the Deore XT cassette.

Later on, during the actual bike testing, I noticed that there was a clinking sound whenever I shifted inwards to the low gear. Upon closer inspection, I found that this was due to the chain touching the frame during shifting, when the chain bounces around a bit.

This was totally unexpected, as I did not consider or check this at all. Luckily, the chain just manages to clear the frame with about 2 mm of margin when riding in the low gear. The touching only occurs during shifting, but not during riding.

Small clearance between the chain and the frame, when in the lowest gear (44T chain ring, 40T sprocket).

View of the overall area, where this issue occurs.

Although the clearance is small, it is lucky that there is still a bit of clearance during riding. What I did was to just paste some clear tape over the frame at the touching area, to protect the paint. Not a big issue at all, but interesting to note this limitation.

In other words, if a larger rear sprocket (>40T) and/or a larger front chain ring (>44T) is used, the chain might rub the frame in the low gear. If that is the case, either the chain ring or the sprocket will need to be reduced in size. Alternatively, the chain line of the front chain ring can be shifted outwards slightly to create more clearance.

Tuesday, July 9, 2019

Bike Friday HaD: Deore XT 4 Piston Brake Components

On a cargo bike, the effective choice of brakes would be hydraulic disc brakes. This is for safety, as it is necessary to have sufficient stopping power when hauling heavy items or people. Especially when traveling downhill, it is critical to be able to stop properly, since the whole bike is dependent on the 2 small brake levers to apply sufficient brake power.

Mechanical disc brakes are less powerful, but they are easier to set up as it just needs a brake inner cable and brake outer casing, with no need for bleeding of the hydraulic hoses. Rim brakes are even less effective, and I don't recommend using it on a cargo bike, since disc brakes are easily available.

Brake power depends on a few factors, which are mainly the size of the wheels, the size of the brake rotors, and the type of brake caliper. Brake levers are not so critical as even the entry level hydraulic brake levers can work well and effectively.

For the Bike Friday Haul-A-Day cargo bike, it uses custom built 20" wheels, and can accept hydraulic disc brakes as there are disc brake caliper mounting points on the frame and fork.

I want to have as much brake power as reasonably feasible, as it is important to be able to brake effectively when rolling down a hill, with an additional load on the bike. A rough estimate of total bike + rider + cargo weight would be 20 kg (bike) + rider (70 kg) + additional rider (70 kg), giving a total of 160 kg. This is quite a lot and as explained earlier, there are only 2 small brake levers to operate the brakes, so the brake system had better be effective!

My plan is to use a 4 piston brake caliper, as compared to the usual 2 piston brake caliper. 4 piston brake calipers are usually only used for downhill bikes, such as on the Saint or Zee series of components. Recently, 4 piston hydraulic brake calipers were added to Deore XT, but they are actually just rebranded Saint brake calipers, since the shape of the brake calipers look exactly the same. These 4 piston brake calipers are meant for e-MTB, which are heavier due to the additional motor and battery pack.

The good thing is, these Deore XT 4 piston brake calipers are compatible with standard hydraulic brake levers, which are usually used with 2 piston brake calipers. For best performance and best compatibility, the same Deore XT series brake lever should be used. The only trade off of using a 4 piston instead of 2 piston brake caliper is that the brake lever stroke is now slightly longer, as slightly more hydraulic fluid needs to be pushed at the lever side, in order to activate 4 pistons instead of 2.

Deore XT M8000 brake levers!

Tool-free lever reach adjustment, with free stroke adjustment on top.

Clamp band area, with Servo-Wave design.

Bleed port at the top of the master cylinder (right side).

Dimpled aluminium brake lever for extra grip. Not carbon fibre like the top level XTR brake levers.

One side weighs just 106 grams, which is really nice.

As for the brake calipers, I decided to get the powerful Deore XT 4 piston brake calipers. It is claimed that these offer a 20% increase in brake power over the standard 2 piston type.

Deore XT M8020 4 piston brake calipers. Essentially rebranded Saint brake calipers.

It has 4 pistons (2 pairs), of diameter 15 mm and 17 mm. A standard 2 piston (1 pair) type has diameter 22 mm pistons.

The white pistons (ceramic?) can be seen on the inside of the brake caliper.

If you calculate the surface area of the pistons (2 vs 4), you will find that the total area is actually quite similar.

Area of diameter 22 mm piston = PI * (22/2)^2 = 380 mm^2
Area of diameter 15 mm + 17 mm pistons = PI * (15/2)^2 + PI * (17/2)^2 = 404 mm^2

The main contributor to the higher brake power is not extra piston area, it is actually the larger area of the brake pad used in the 4 piston brake caliper. As the 4 piston brake pad is longer and thus has a bigger area than the 2 piston brake pad, it can contact the rotor with a larger surface area for higher braking power.

2 piston brake pad on the left, 4 piston brake pad on the right. The difference in area is very obvious.

Bleeding block for the 4 piston brake caliper.

Brake pads and associated hardware.

Weight of 1 brake caliper plus the brake pads, which is the actual weight when installed.

Brake mount adapters, for the front and rear.

Left side adapter is to convert the front fork IS mount to Post Mount. The right side adapter is to convert 160 mm to 180 mm brake caliper mounting, for the rear.

Front brake adapter weighs 33 grams.

Rear brake adapter weighs 35 grams.

The biggest headache for installing a hydraulic brake system on this cargo bike is the extra long brake hose needed for the rear brake. When you buy a standard brake kit, it comes with a 1000 mm hose for the front brake, and a 1700 mm hose for the rear brake. This is sufficient for standard bikes, but not for the Haul-A-Day with an extra long chain stay length.

If the hose joins to the brake caliper with a normal bolt, it will be easy, as I just need to measure the correct length from the bulk packaging of the brake hose, and cut to the length I need. It does not matter even if the hose is long as the bulk packaging hose length can cover any bike requirements.

Bulk packaging of hydraulic brake hose. Can be cut to any length you need.

However, as the brake hose is mounted to the 4 piston brake caliper using a banjo bolt, I cannot use the hydraulic hose from the bulk packaging box. The banjo bolt is crimped to one end of the hose at the factory, and it is not possible to install it myself on the desired hose length.

The only choice is to buy the extra long hose kit, which is actually the Saint type. Luckily there is an option for a 2000 mm long hose, which should be enough from my estimate. If not, I also have no idea how to make it work.

Extra long hydraulic hose kit, that comes in 2000 mm length for this cargo bike. I can trim off excess length (if any) from the end without the banjo bolt.

The 2000 mm hydraulic hose kit, with all the parts shown here weighs 52 grams.

As you can already tell from the choice of brake adapters shown earlier, I plan to use 180 mm rotors for extra stopping power. Some people prefer to use a smaller rotor at the rear to balance out the braking force, but I prefer to use the same size for simplicity sake.

XTR SM-RT99 brake rotors, in 180 mm diameter.

Each rotor plus lock ring weighs 138 grams, about 15 grams more than the XTR RT99 160 mm brake rotor.

From the choice of all the brake components, you might infer that I want to achieve as much brake power as possible. However, my objective is not to achieve super high brake power, but to enable sufficient braking force, with as little input at the brake lever as possible. In other words, to achieve good (sufficient brake power), while only pulling lightly on the brake lever.

For my set up, brake power will be determined by 3 factors. Wheel size, brake rotor size, and type of brake caliper (2 or 4 piston). This is assuming that all other factors are the same (such as brake lever, rotor and brake pad grade, brake hose grade, tire friction, etc).

Wheel Size:
A smaller wheel will have greater brake power than a bigger wheel, with all other factors being constant.
Comparing a 20" wheel to a 700C (28") wheel, the 20" wheel will have 28/20 = 1.4 times more brake power. This is exactly the phenomenon that I experienced on the Ascent Bolt mini velo, with hydraulic disc brakes on the 20" wheels.

Brake Rotor Size:
A 180 mm diameter brake rotor will be more powerful than a 160 mm brake rotor.
180/160 = 1.125 times more brake power.

Brake Caliper Type (2 or 4 piston):
The 4 piston brake caliper is claimed to be 20% more powerful than the standard 2 piston type, which means it will be 1.2 times more powerful.

Let's set the brake power of the standard bike (700C wheels, 160 mm rotor, 2 piston) as 100%. An example would be the Canyon Endurace with these specifications.

If all these brake enhancing factors are multiplied together, the total comparative brake power will be 1.4 x 1.125 x 1.2 = 1.89 times, or 89% more powerful!

This is a big difference, and I am not too sure if it is too powerful or not. In any case, there are some interference issues which forced me to downsize the brake rotor to 160 mm. The details will be shared during the other blog post on the wheelset and brake caliper installation.

In summary, the final brake rotor used will be 160 mm in diameter. Total brake power is thus 1.4 x 1.2 = 1.68 times, or 68% more, which is still plenty of brake power!

The 160 mm diameter brake rotor that I chose is the new Ultegra RT800 brake rotor, which looks exactly the same as the Dura-Ace RT900 brake rotor, except for no black paint on the cooling fins.

Ultegra RT800 Ice-Tech brake rotor, 160 mm diameter, with Centerlock mounting.

Weighs 133 grams with the lock ring, just 5 grams lesser than the XTR 180 mm rotor.

Size and appearance comparison. Very different design used for these brake rotors.

Final choice of brake components:
Brake Lever: Deore XT BL-M8000
Brake Caliper: Deore XT BR-M8020 4 Piston
Brake Rotor: Ultegra SM-RT800 160 mm
Brake Hose: SM-BH90 High Power brake hose

This collection of brake components should result in really nice brake performance for this cargo bike! Installation of the wheelset and these brake components will be in another blog post.

Sunday, June 30, 2019

Bike Friday HaD: Ascent Bikes Custom Wheelset and Schwalbe Marathon Tires

As you may already know, I am starting to build a cargo bike. One of the special requirements for a cargo bike is a set of wheels that can endure higher loads, since that is the purpose of having a cargo bike. The bike frame and the wheels have to carry an additional passenger or items, and so will need to be rated for the extra weight.

Standard bike wheels will not do the job, as they are not designed for heavier loads, therefore we need to look for a set of durable wheels. BMX wheels have stronger rims and many more spokes, due to the high loads exerted on the wheels when jumping off ledges or doing tricks. However, standard BMX wheels cannot support an 11 speed cassette as the hub is usually limited to single speed gears.

Since I want to run an 11 speed cassette on the cargo bike, I have to get a custom built wheelset that can support an 11 speed cassette, with strong rims and more spokes.

Ascent Bikes allow lots of customization of their bikes and wheels, and you can pretty much specify any component you want on the bike, down to the colour of the bolts or the type of stickers on the wheels. Still, this request for a custom built, extra strong wheelset is not common, but they are willing to help me out with this.

My request is quite straightforward. To have a 20" wheelset with 32 or 36 spokes, using a hub with 100/135 mm OLD, and compatible with Centerlock brake rotors. It should be all black in colour (rims, hubs, spokes, spoke nipples) for a clean appearance.

For the rims, 20" BMX rims were used, as they are strong and wide enough, and comes in 36 hole variants. Straight gauge 2.0 mm spokes and brass nipples were used for strength, no lightweight aluminium spoke nipples here. Finally, the request for a Centerlock brake rotor compatible hub pretty much limits the choice of hubs, and the dependable Deore XT M8000 hubs were chosen.

All black wheelset! Lots of spokes for extra strength and rigidity.

Deore XT M8000 hubs with Centerlock brake rotor mounting.

Extra wide BMX rims

Black brass spoke nipples

2.0 mm straight gauge spokes used for extra strength.

Rim height is about 17 mm, with no rim brake track.

Internal rim width is 24 mm, which is really wide.

External rim width is 29 mm. This also means that any tire that I install on these rims will end up being wider than the nominal claimed width.

Includes high quality, wide Schwalbe rim tape.

Front wheel weighs 703 grams (including rim tape).

Rear wheel weighs 866 grams (including rim tape).

The total wheelset weight, inclusive of rim tape, is 1569 grams. This is actually lighter than I expected (1.7 - 1.8 kg), which is awesome. In fact, it is lighter than the stock Dahon D7 wheelset that comes with the Dahon Boardwalk, but is much stronger.

Deore XT QR axles, which are heavy but strong. Not a place to compromise on strength for a cargo bike.

With the custom built, heavy duty wheelset ready, the next important choice is the type of tires. The tires also have to be strong enough to withstand the additional weight of a cargo bike, so lightweight, narrow tires are out of the question. Which leaves us with tougher, wider but also heavier touring tires. There are quite a few different types of touring tires, which makes it difficult to choose.

In the end, I chose the narrowest, lightest touring tire that I think I can get away with, and that is the Schwalbe Marathon. Taking into account the permissible load on each tire, the type of tread pattern (smoother for lower rolling resistance), and the puncture resistance, this was the choice. The standard Marathon does not have very high puncture resistance (like the Marathon Plus), but it is much lighter and rolls better, and it is a risk that I am willing to trade off. No matter what, it will be more puncture resistant than the tires on my other bikes.

Pair of Schwalbe Marathon tires! Equipped with reflective strips for additional visibility at night.

Closer look at the logo and model name.

This is the narrower variant, at just 1.5 inches wide. It would prove to be the correct choice, as shown later when installing the rear derailleur and cassette. The E-Bike ready label doesn't mean much here.

Rather deep treads, for extra grip over rough and loose terrain. The centre line has a continuous unbroken surface, which should mean lower rolling resistance and lower noise.

Recommended tire pressure is a wide range, from 55-100 PSI. For heavier loads, it is recommended to set the pressure at the higher end of the range for less chance of a pinch flat.

Each tire weighs 557 grams, a far cry from the 239 grams for Schwalbe Kojak tires. The heavier duty Schwalbe Marathon Plus tires are even heavier!

As for inner tubes, the 40-406 tire size is in-between inner tube sizes. Either SV6 or SV7 tubes can be used.

In the end, I chose the wider but heavier SV7 inner tubes, as the wider rims mean that the tire would end up being wider than 40-406.

Tires and inner tubes installed on the wheelset!

This wheelset looks strong and durable, ready to be installed on the cargo bike! At that time, I was still waiting for the frameset, and started gathering all the necessary components for the bike.