Following on from my initial post…
It’s few and far between when one comes into contact with a product in the bike world that is 100% truly fresh. The PCB or ‘Pancake Brake’ by Ashima is one such product. Yes, it’s a disc brake but it’s unlike most others on the market not by what it does but in the way it does it.
And now for a bit of drivel…
Traditionally a disc brake applies force via a piston, housed within the body of the caliper. The piston is pushed out by the ‘brake fluid’ in the system, exerting a force on the rotor via the brake pads. This is the principle that pretty much all disc brakes use, from cars to motorcycles and mountain bikes, and a disc brake for the most part is a fairly simple hydraulic mechanism. A well designed system allows for a progressive application of force, so the more you apply pressure (by pulling in the lever), the greater the force applied, much like a vice. This is commonly known as ‘modulation’.
But in any hydraulic system the fluid within is prone to expansion when exposed to extended periods of heat and for a brake system, that can be exposed to prolonged heat (via the metal pistons) through things like heavy and constant application, this can cause issues as the expanding fluid pushes the pistons out into the rotor, radically reducing ‘modulation’ as well as power. One could also say that this problem is not helped by the fact that disc brake systems on a mountain bike are teeny weeny when compared to their bigger brothers, so the problems are amplified.
The Ashima PCB though is quite a radical departure from this in that they do away with the pistons and instead apply the force via a membrane that effectively replaces what would otherwise be 20mm traditional pistons. Pretty neat. To keep things really short, advantages of the PCB are claimed as:
– With no pistons, you loose the main mechanism to transfer heat to the fluid.
– Being a membrane that’s expanded under pressure, the membrane elasticity has an inherent memory, so the pads will always retract to .7mm.
– The fluid flow has been designed to be single path, meaning that from start to end, it flows in one direction, on a single path; most brake calipers use pathways within the body to channel the fluid to the pistons. It also allows for a thin body as well as the ability to locate the hose on the left or right of the body.
– One way flow means bleeding is dead simple too and with the Ashima bleed kit, will change the way you think about bleeding a brake.
– The fluid transfer tube, that red tube that passes the fluid from one side of the caliper body to the other, also helps cool the fluid.
I could go on about the technicality of it all but the most important thing is how do they actually work in every day use?
I strapped my test units to my 6″ dually that I use for pretty much everything at the moment and they replaced my Hope Moto M4 and Moto Mini, running 180 and 160mm rotors respectively; I fitted a 160mm Hope rotor to the front and crappy 160mm Shimano Deore to the rear, though the PCB will ship with the Ashima AiRotors (180mm front/160mm rear) which I feel will only add to the overall performance. For the records I weigh in at 97kg (213lbs) in full ride gear.
Accustomed to 4 generations of Hope brakes, the first thing that struck me with the PCB was the way the master cylinders sat away from the bars. There’s nothing new or strange here, Hayes, Formula and others use similar designs but for a first timer to this, it seemed odd. I do have to chuckle when I hear people comment how such designs are prone to tree damage as to me, if you are hitting a tree hard enough and front on like that, your brakes surviving are the least of your problems.
Once fitted, lever reach was easy to adjust and with the new blade design fitted, I could dial the reach to just the way I like it. During a ride the brake levers were comfortable and I think I am actually a bit of a convert to this style of design as it gave me a little more hand clearance than more compact units. In terms of the master cylinder and lever design, what did I like?
– Easy reach adjustment.
– The nice rubber lined clamp.
– The all aluminium piston shaft (the shaft from the blade to the body) body housing with internal ball to allow smooth action.
– Considered anodised bolts.
On my first ride I realised the new sintered pads needed bedding in but once done, over a period of weeks I have been riding the brakes through a range of different conditions but mostly the sort of riding I would do on a typical ride – a selection of XC single track, ranging from fast and flowing to tight and rough as well as hard steep braking on the road, where the tyres grip hard and tax brakes. It should also be noted that we have had a second pair tested on a 8.5″ DH bike in DH use.
Once bedded in I have found that the brakes offer plenty of power, even through a 160mm front rotor. Admittedly ‘brute’ pull up power was not as firm as running through a 180mm but I put this down directly to the rotor size, not the power of the brake itself. In tight singletrack, where one can often find the need to brake hard to snap a corner, the PCB worked very well providing ample power which is evident by the fork dive under application. Certainly when I needed to stop, I stopped and did so without thought. I should note that on a lighter XC rig, running pure XC use, the 160mm rotor would actually be a perfect blend of weight, power and feel.
Modulation has been good from the start and I am not sure if it’s me becoming more accustomed to the brake or if under more use it’s hitting its strides but I feel that modulation has been improving with each ride. Generally the more you pull the lever in, the more bite you get as it firms up so it’s easy to gauge the amount of power you’re putting into the units – the PCB system does not suffer from the on/off feel of some brakes on the market.
Perhaps the best way to describe the overall performance is that I feel one should not have to ‘think’ about the brakes working – they should transfer what you are thinking to the motion of the bike seamlessly. In my view, the PCB did this perfectly and the only time they didn’t was when I expected the grab of a 180mm rotor failing to remember they were grabbing a 160mm. Even then, I feel that they easily out performed my previous brakes both in terms of modulation and lever feel.
[original version was posted on G’s blog https://www.mag100.com]
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