Friday, February 7, 2020

Fnhon DB11: Brake Levers and Brake Calipers

On the new Fnhon DB11 folding bike, I will be using hydraulic disc brakes, which is a big performance upgrade over the V-brakes used on the previous Dahon MuEX. Not only are hydraulic disc brakes more powerful, they work better in the rain, and does not dirty the rims with brake residue. I am a firm supporter of hydraulic disc brakes as they just work better.

However, there are also downsides to using hydraulic disc brakes. The initial set up is more troublesome, as you need to use brake fluid to bleed the brakes, instead of just installing the outer casing and inner cable. Also, the hydraulic brake system weighs more than a traditional cable operated brake system, mainly due to the addition of the disc brake rotors and stronger hubs, frame and fork.

I want to minimize the weight increase when I change from V-brakes to hydraulic disc brakes, which is why I decided to utilize high end, lightweight brake components.

As I am setting up a completely new brake system, I can choose freely between the different brands and types of brakes available on the market. In reality, there is only Magura or Shimano for me to choose from, as these two big brands use mineral oil, which I much prefer over other systems that use DOT fluid. For a detailed comparison between mineral oil and DOT fluid, you can check out this link.

The weight of the Magura MT8 SL is about the same as the XTR M9120, both weigh about 200 grams (brake lever + brake caliper). However, the Magura MT8 SL brake system costs over $100 more than the XTR, which itself is already expensive. Therefore, the XTR system was chosen, with the added benefit of being similar (setup, brake fluid, tools) to the brake systems on my other bikes.

XTR BL-M9120, which is the Trail spec instead of Race spec. Note the new I-Spec EV clamp design, which is supposed to stiffen up the brake lever due to multiple contact points with the handlebar.

The Trail spec has tool-less brake lever reach adjustment, which is something that I like. It also has Free Stroke adjustment, which the Race spec also lacks.

High brake lever stiffness is possible, due to the additional bracing point between the brake lever and the handlebar.

Servo Wave technology to increase the leverage ratio after pad contact, for increased brake power deeper into the stroke.

One side of the Trail spec brake lever weighs just 100 grams! The Race spec would have been even lighter.

Product specifications that I found online, showing the differences between BL-M9100 and BL-M9120. Note that the Clamp Bolt, Brake Lever and Master Cylinder use different materials.

With a pair of XTR BL-M9120 brake levers weighing just 200 grams, this setup will turn out to be very lightweight. If I had used the Race spec BL-M9100, the weight would be even lower, as the master cylinder would be made of magnesium instead of aluminium. 

I did more research and found that the actual weight (online information) of BL-M9100 is just 68 grams each! This will give a total weight of just 136 grams per pair of BL-M9100, 64 grams (32%) lighter than a pair of BL-M9120. Now I kind of regret my decision to get the Trail spec instead of the super lightweight Race spec.

Moving on, let's take a look at the brake calipers. Normally the Race type brake lever will be paired with lighter 2 piston brake calipers, while the Trail type brake lever is paired with powerful 4 piston brake calipers.

Depending on the purpose and usage, we can increase the brake power by using 4 piston brake calipers, or reduce some weight by using 2 piston brake calipers.

Previously, when I first tried hydraulic disc brakes on small wheeled bikes, I found that the brake power was a bit too high. That was on the Ascent Bolt mini velo which I tested, which were using basic MT200 brakes with 2 piston brake calipers. Therefore, for a similar type of bike (small wheel, similar purpose) such as this Fnhon DB11, a 2 piston brake caliper is more than enough, as the smaller wheels naturally increases the brake power compared to a bike with larger wheels.

On the other hand, the Bike Friday Haul-A-Day is a heavy cargo bike, which will need to have sufficient stopping power to slow down safely when rolling downhill with extra weight. Although it also has smaller 20" wheels that naturally increases the stopping power, I chose the more powerful Deore XT 4 piston brake calipers on that bike to further improve the stopping performance.

XTR BR-M9100 2 piston brake calipers

Looks very high quality, with the polished metal and anodized surface treatment.

Note that the hydraulic hose connects directly to the brake caliper with a connecting bolt, instead of using a banjo bolt like on most other MTB brake calipers.

The exit angle of the direct hose connection (at the back) seems to be ideal, which means that it should line up neatly along the frame. 

I prefer to connect the hose directly to the brake caliper, instead of using the banjo bolt. As previously explained, the banjo joint requires the hose to be factory prepared at the banjo end. Therefore, it is a bit more tricky to shorten the hose as it can only be done at the brake lever side. This is another reason for choosing this XTR brake caliper, as it is one of the few brake calipers to actually use a direct connection without a banjo. The next brake caliper with a direct connection is all the way down at Deore level, where the weight will be quite a bit heavier than this XTR brake caliper.

Brake pads with no fins for a bit of weight savings.

Brake caliper (inclusive of brake pads, 2x caliper fixing bolts, connecting bolt) weighs just 101 grams.

Titanium caliper fixing bolts, with an aluminium washer.

This pair of titanium bolts weigh just 5 grams. Every little bit counts when it is XTR grade.

Even the brake pads have a titanium backing to save a bit of weight, I certainly was not expecting this.

A pair of titanium brake pads plus spring weighs 13 grams. I don't have a chance yet to weigh standard non-finned brake pads so I am not sure how much lighter this is.

4 of the standard steel connecting bolts weigh 10 grams, which means about 2.5 grams each.

4x olives and 4x connecting pins don't register at all on my weighing scale. At low weights such as this, the weighing scale is not precise enough to give proper readings.

4950 mm of BH90 hydraulic brake hose weighs 99 grams, which works out nicely to be 1 gram per 50 mm of hose length.

In order to make it possible to bleed the brakes off the bike, I decided to measure the length of the hose required, by mounting the brake levers and brake calipers on the frame, and routing the hydraulic hose externally. This means not threading the hose through the cable guide holes on the frame. By doing so, once the brake lever + hose + brake caliper has been joined together with the correct hose length, I can remove the whole set from the bike for easy bleeding, away from the bike. This concept is the same as what I did on the Bike Friday Haul-A-Day. By doing so, it is possible to bleed the brakes more easily and also more thoroughly as compared to bleeding the brakes when on the bike.

Front brake kit with hose length 740 mm (without hydraulic fluid) weighs 217 grams.

Once filled with hydraulic fluid, the weight increases by 8 grams to 225 grams for the front brake kit (740 mm length).

Rear brake kit with hose length 1430 mm (without hydraulic fluid) weighs 230 grams.

Rear brake kit weight is 241 grams, once filled with hydraulic fluid.

As shown below, here are the standard disc brake mount dimensions for IS type of frame mount. Note that the distance is different for the front and rear mounts, as the rear mount is closer to the hub axle by about 10 mm. This 10 mm difference in radius corresponds to a rotor diameter difference of 20 mm (Eg. between 180 mm and 160 mm rotor), when the same adapter is used.

Standard specifications for front IS mount


Standard specifications for rear IS mount

We need a IS type to PM type adapter, so that the PM type brake caliper can be mounted to the IS mounts of the frame. Different adapters are used to match different rotor sizes.

In other words, a 180 mm adapter for the front would become a 160 mm adapter when it is mounted onto the rear mount.

Front 180 mm adapter = Rear 160 mm adapter
Front 160 mm adapter = Rear 140 mm adapter

On this bike, I will be using the smallest disc brake rotor that is possible, as the smaller wheels already mean a higher-than-normal brake power. Also, I want to minimize the weight of the bike, and smaller rotors will help.

At the front, I will use the smallest rotor and adapter, which will be 160 mm. There is no lightweight IS to PM adapter that will allow a smaller 140 mm diameter rotor to be used at the front, due to physical frame limitations. I have seen third party IS to PM adapter for 140 mm rotors, but it is very bulky and will defeat the purpose of running the smaller rotor to save weight.

This is when I would have preferred the non-standard disc brake mount used on the Bike Friday Haul-A-Day, where the front fork actually used the specifications for rear brake mounting. The result is that a smaller-than-usual rotor can be used at the front.

As for the rear brakes, using a front 160 mm adapter would mean that it becomes a rear 140 mm adapter. This would prove to be critical and absolutely necessary for clearance later on, as I will find out later during assembly. If I want to use a 160 mm rotor at the rear, then I will need to get a front 180 mm adapter or a rear 160 mm adapter, both of which are the same things.

To save a bit of weight from the adapter, I got the lightweight version of the IS to PM adapter, which is less bulky than the OEM version.

Lightweight XTR grade IS to PM adapter at the top, usual OEM version at the bottom.

This adapter with the 2 adapter fixing bolts weigh just 21 grams.

I will be using the same adapter type for both the front and rear brakes, and the result is a 160 mm front rotor and a 140 mm rear rotor. With the brakes settled, we can move on to the other parts of the bike, such as the wheelset and rotors.

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