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Originele artikel [hier...]How we test hydraulic disc brakes
By Guy Kesteven, What Mountain Bike/MBUKThe latest reviews of hydraulic disc brakes on BikeRadar are the result of our most comprehensive grouptest ever.
We’ve run brakes on a dyno before, but never as accurately as we have this time round. We’ve never tested so many brakes – 33 to be exact – in one hit either.
Before we go into details, we need to be clear that the test was split into two halves: real-life trail testing all over the world and mechanical dyno testing at Fibrax.
For the real-life work we’ve been running long-term sets of every brake since they first became available. For some new sets like SRAM’s XX and Hope’s Race X2 that isn’t long, but most of the units here have well over a year of continual all-weather use in the log. We’ve deliberately recruited the most relentless high mileage riders in Britain's most unforgiving areas (Peak District, Dales, Lakes and Pennines) to put each brake through as much evil as possible.
It’s not just in the UK either. We’ve got Simon at http://www.freeridespain.com" onclick="window.open(this.href);return false; keeping a close eye on what visiting brakes survive on the long, hot, super-technical descents of southern Spain. Over in Canada, BikeRadar and Mountain Biking UK gravity slave Cal Jelley has put over one million vertical feet of Whistler descending into several sets from Hope, Shimano, Formula and Avid this season.
This gave us an unparalleled breadth and depth of feedback to work with before we even went to the dyno. In many cases it’s these real-life aspects of the brakes that make the biggest difference to whether we’d recommend them or not.
However experienced our test team are and how sure they are of their own rankings, this time we wanted to underline the subjective with real science, which is where Fibrax came in. They've have been making brake parts and pads for the motor and bike industry for over a century, and do a lot of their development work on a purpose-built bike brake dyno.
However as they don’t make any brakes themselves, just spare pads for them, they’re totally independent in testing terms. Massive thanks to them for not only letting us use the facilities for our testing but also making us endless cups of tea and even buying us fish and chips while we worked our way through a massive pile of brake boxes.
The rig itself uses a full bike chassis with the front wheel on a powered rolling road. Hydraulic arms at wheel axle level push the front tyre down to replicate 100kg of rider weight being thrown forward as the brake is applied.
A hydraulic ram with articulated lever blade cradle is bolted onto the dummy handlebar to provide totally accurate, repeatable load brake pulls. Water sprinklers can also be sprayed onto the calliper and rotor to simulate brake use in wet conditions. The braking power on the ‘road’ drum is then cross referenced with the lever pull (in newtons) to give the performance graphs.
For total consistency and to remove any risk of contamination we ran a totally fresh sample of every family of brake, using a 180mm (or nearest equivalent) six-bolt rotor. To ensure the brakes we tested were exactly what you’d get if you bought them, we also ran the original pads whether they were sintered or organic.
With the advice of Mark from Fibrax we ran a cycle of 10 four-second pulls at 50newtons with a 30-second rest between to bed each brake in. We then moved onto the dry test cycle. Each brake did three 'four seconds on, 30 seconds off' pulls at 50N, three at 100N and then three at 150N. This gave us averaged power ratings simulating gentle, reasonably firm and proper panic lever pull.
We then switched the sprinklers on and ran the same test cycle with wet rotor and pads. A lot of the sintered pad brakes developed more power when wet and cold than when dry and hot. This is why many of the brake readings on the wet test stop at 100N or even 50N as that’s when the wheel just seized on the drum.
To keep things totally comparable we ran each brake with a 180mm rotor or the nearest equivalent. However we ran one brake with 160, 180 and 200mm rotors to check what difference they made to the power output.
The results were pretty clear, with a roughly 20 percent increase in power for every 20mm extra diameter. You’re looking at around 50g extra in weight for each step too though.
The comparison overlays below let you see how each model compares. For individual results, see the brake reviews here on BikeRadar. (At time of writing, tests of 13 high-power brakes from Mountain Biking UK have been published – see the Related Articles on the right. Watch out for 19 trail brake reviews from What Mountain Bike over the coming weeks – or check out issue 106 of the mag).
The vertical axis is calibrated in terms of decelaration in metres per second squared (m/s2). The higher the brake is on the graph, the more power it produces.
The horizontal axis shows the average output of the 50, 100 and 150N pulls. This lets you spot which brakes put out a lot of power at low lever forces, and which need a good squeeze to get the best results.
The straighter the line between the three pulls, the more consistent the relationship is between how hard you pull the lever and how hard the brake stops.
You’ll notice that the lines for a lot of brakes droop slightly between 100 and 150N. This is a result of increased heat build-up across the three hard pulls and a resulting reduction in pad ‘grip’ that simulates intensive mountain use.
It’s worth noting that fine control levels of each brake at the moment the pad contacts the rotor are hard to assess except by very careful studying of individual pull spikes. This means it’s a lot easier to feel that through your fingertips.
Met video van de test.