I have a clear picture in my mind's eye - with a loud whistling sound as background noise. When test rider Toni (105 kg) is caught by gravity on the steep section of tarmac, I can't help but think of a loudly bubbling kettle already dancing on the hob. It's the first ride with the Brake Force One. The sensational brake at Eurobike, which uses water as a braking medium instead of mineral oil or DOT. Why not, some of you may be thinking. After all, compared to the other two fluids, water is easy to obtain, environmentally and skin-friendly and therefore very practical to use. If it weren't for the boiling point. With water, the boiler whistles at 100 degrees Celsius. By comparison, DOT 5.1 only boils at 260 degrees. As soon as a liquid boils in the brake line, gas bubbles form and the brake lever falls through to the handlebar grip. I hope for the best as Toni picks up speed and disappears from my field of vision.
In addition to the Brake Force One H²0 we have six more new disc brakes to test. Formula R0 Racing, Hope Tech 3 E4, Magura MT5, Shimano's new XT, Sram Guide Ultimate and Trickstuff Direttissima. Prices range from 151 euros for the Magura MT5 to a whopping 399 euros for the brand new Trickstuff Direttissima from Freiburg. Mind you, we are talking about a brake for the front wheel including 180 mm disc and adapter. As big as the differences are in price, they are all very close in weight. A manageable 85 grams separate the heaviest from the lightest model. At 364 grams, the water brake from Brake Force One weighs the least, even if the brake is the last component on the bike that you should save weight on.
On our brake test track in Bolzano, the going gets tough. 700 metres of downhill per descent - 300 metres of downhill trail with rough ground, garnished with hairpin bends and then 400 metres of downhill on a very steep tarred road with good grip. Anyone who knows the route knows that a brake that stops in Bolzano usually doesn't cause problems anywhere else. In both the practical and laboratory tests, we deliberately tested extremes in order to cover the broad spectrum that an MTB brake may face. After all, not every biker weighs less than 75 kilos and only rides in the low mountain ranges.
Collecting at the first break point. It stinks of hot brake pad. Some discs are already rubbing slightly. In order to load each brake equally, the brakes are applied on tarmac according to a fixed procedure. There are defined cooling phases in between. The outgassing of the pads is usually accompanied by a rapid loss of braking force. Initial fading is the name of this treacherous phenomenon and usually occurs on brakes with new organic pads that are braked really hot for the first time.
With the exception of Formula, all brakes in the test are equipped with organic pads. Depending on the composition of the pad, anything is possible, from slightly reduced braking effect to total failure. This is a real risk that still occurs even if you have already braked the pads according to the manufacturer's instructions and think that the braking effect is fully and, above all, reliably available. This is one reason why the stability of a brake can only be conclusively assessed after the second test ride.
The defects that occur with Shimano and Sram when a very high load is reached in practice and in the laboratory are now well known. The weak point of both is the brake disc. While both brakes held up for a 75-kilo rider even on extreme downhill gradients, the Icetech discs of the Shimano brakes melted on the 85-kilo man, while the Sram centreline discs deformed. However, the problem of a wandering pressure point on the new Shimano XT brakes is new (BIKE 2/16). On various test bikes, the pressure point on the lever varied regardless of the temperature of the brake. The rougher the surface, the more frequently. However, our test brakes in this comparison worked perfectly. Only Toni was able to uncover further weak points with full physical effort. On both the Formula and the Brake Force One, the backing plates of the brake pads bent slightly.
And the tea kettle effect? Apart from the initial fading on the first ride, the Brake Force One showed its ability to take a beating. There were no problems whatsoever with the 85-kilo man. Although the boiling point of water is significantly lower, the heat capacity is higher. So you have to put in more energy to heat the water.
Conclusion Peter Nilges, BIKE test editor:
As in last year's test, Magura scored the most points overall and was able to set itself apart from the rest of the field. The powerful MT5 is also the cheapest brake in the test. The rest of the field is also at a very high level. Alongside Magura, Trickstuff and Hope also show no weaknesses in terms of durability, even with heavy riders, although Hope is a little less powerful. Despite being downgraded in terms of stability, the new Sram Guide Ultimate made a very good impression thanks to its great ergonomics.
BRAKING POWER
Thanks to the integrated brake booster, the BFO is able to apply a decent amount of force even with a medium amount of manual force. The Magura also decelerates powerfully and can even increase with more leverage. The Hope, on the other hand, is a little dull and powerless.
WEIGHT
The filigree BFO also comes out on top in terms of weight. With only 187 grams for caliper and master, it extends its lead. Shimano XT and Hope weigh a good 80 grams more per brake and thus bring up the rear.
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HOW BIKE TESTS
PRACTICAL TEST
Traditionally, we put all new brakes through their paces on our infamous test track from Jenesien down to Bolzano. Here we simulate the extreme case. Brakes that remain stable on this gradient generally don't reach their limit anywhere else.
According to the manufacturer's recommended Braking process 700 metres of depth per descent are on the programme. 300 metres of depth Trail with hairpin bends and rough terrain and a further 400 metres downhill on Asphalt with an average gradient of 20 per cent. While the first part is used to assess modulation, lever ergonomics and braking force, the second part focusses on stability (fading, pressure point stability). Each of the three testers (75, 85 and 105 kilos) rides a complete descent for each brake model and disc size. To assess stability, we only brake with the front brake on the tarmac section. This ensures that each brake is equally loaded and that the rear brake is still available as an emergency anchor in an emergency. The stability test is carried out according to a set mode with defined cool-down phases. Grinding braking, interval braking and deceleration from 40 km/h.
LABORTEST
Every brake has to be tested twice in the BIKE test. After the road tests in Bolzano, we also test them on our in-house drum test bench. During all measurements, we record braking and manual forces (hysteresis curve) and the brake pad temperature. A fan simulates the airstream and ensures constant cooling.
Slow down: To allow the brake pads and disc to adapt to each other, the brakes are first applied at a moderate speed. At least 60 brake applications are on the programme until the braking effect has reached a constant level.
Braking force: The braking force and hysteresis curve are then determined for dry (red) and wet (blue) braking at room temperature. The curve in the test letters applies to a brake with a 180 mm disc at a drum speed of 45 km/h and a manual force limited to 120 N. The braking force assessed in the test letter is the result of averaged dry and wet braking at 80 N manual force and the test rider's assessment from the practical test.
Stability: The fading test on the test bench is based on data obtained in practice. The test is carried out in three increasing stages and, together with the practical values, is included in the stability rating. If a brake passes all three stages without defects, it is awarded the maximum number of points. Deductions are made for early onset or pronounced initial fading at temperatures below 300 °C.
As an additional recommendation based on the practical tests, we indicate the rider weight up to which the brake can withstand extreme slopes. Weight and installation/adjustment are also included in the final score.
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WHAT IS WHAT?
A disc brake is sometimes exposed to immense loads. Compared to this, the weight and size are very small. BIKE explains the compact technology and gives tips on adjustment:
1 Leverage width
The lever width adjustment is used to adjust the distance between the lever and the handlebar and thus adapt it to the respective hand size (adjustment range in the test letter). Some brakes require an Allen key for this.
2 Pressure point
This is used to set the free travel of the lever. In other words, how far you can pull the lever until the pads are in contact with the disc. The adjustment only changes the idle position of the master piston, not the gap between pad and disc.
3 Handlebar clamp
A two-piece clamp for easy installation is now standard. Many brake manufacturers offer their own combination clamps for better positioning of the shift and remote levers. Also Trickstuff.
4 brake pistons
Brake calipers with two or four so-called slave pistons are common. A four-piston brake does not necessarily have to be more powerful than a two-piston model. The advantage lies in the usually larger pad surface and the more even surface pressure over the entire pad.
5 Venting
The master cylinder and calliper can be filled and bled via this access, which is advisable after the line has been shortened. With only 15-20 ml of brake fluid in the entire system, just one air bubble can make a big difference.
6 Expansion tank
This brake fluid reservoir has two functions. Firstly, fluid can flow into the high-pressure area during automatic pad adjustment, and secondly, the heated fluid in the brake calliper can expand without the brake applying.
TREACHEROUS FADING
Organic brake pads in particular are affected by initial fading when new. This rapidly reduces the braking effect at high temperatures.
Fading is a reduction in the braking effect at high operating temperatures. Brakes with organic pads are particularly affected by initial fading. The diagram shows that the braking force suddenly decreases from a certain temperature, although the manual force on the lever continues to increase. The effect occurs because the uncured components of the pad compound evaporate above a certain temperature. Despite a hard pressure point and high manual force, there is hardly any braking effect left, which can lead to critical situations. This condition persists until all the components have evaporated. The pads are then stable and efficient until the temperature is reached. If the brake pads are braked even hotter due to heavy loads, outgassing and fading can occur again. Moderate braking with 20-30 repetitions from a medium speed, as required in most operating instructions, is therefore only half the battle. The practical test confirms that although the new brakes/pads work well on the trail after this braking-in procedure, they consistently suffer from fading as soon as very high temperatures are reached on the tarmac section. If you don't want to experience a nasty surprise, you must therefore provoke a degassing (alternating with a brake). Thermal pre-treatment by the manufacturer could solve the problem, but it is very complex and costly (see interview below).
INTERVIEW WITH MICHAEL RUOPP, MAGURA: Heat treatment is very complex
The initial fading problem with organic brake pads with a sudden drop in braking performance is well known. What determines how pronounced this effect is?
This depends primarily on the pad material. Due to their composition, some rubbers are hardly prone to initial fading, while it can be really dangerous with other rubbers.
How do you ensure that your coverings are not among the critical ones?
We carry out internal fading tests. All brake pads that exceed a defined limit in terms of initial fading do not go into series production. This requirement is directly taken into account when developing new brake pads.
Why don't you simply pre-treat the pads thermally so that they outgas before the first use and there is no loss of braking power?
This process is used in the automotive industry. However, a good coating can quickly lose its performance through heat treatment. It is a very complex process. We have already had heat-treated linings in the past, but the wear was too high. Heat treatment alone does not solve all problems. The aim is to ensure that the pad and the brake always remain controllable.
It would be ideal if the pads were already run in with the respective disc by the manufacturer and thus had more reserves in extreme situations.
That would of course be the ideal situation. For logistical reasons, however, this effort cannot be realised.
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