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14 Jun, 2016

Honest Truth about Braking

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After many years and many events, our resident bike guruThe Gentleman Racer can share a few tips and tricks that could help smooth your ride. For the next few editions we will cover the basics of trailside maintenance, including the most common mechanical foibles and real-world repairs. We start off with something that is easy to do but has flummoxed many a rider: Fitting new brake pads.

As a rule of thumb, it’s a good idea to replace your pads when the pad material thickness reaches less than a third of what it was originally. Look at a new pad, the thickness of that pad is your reference for what the thickness should be, if it’s substantially less, or worse, ground down to the backing plate, then bomb some new one’s in!

Many think that pad wear can be gauged by time or mileage only – They’ve only done 700km!” – but how quickly pads wear depends more on the conditions they’re used in and how the rider uses them. A wet, muddy Sani2C Umko drop can easily destroy a brand new set of pads in one stage, especially when a nervous rider is on the brakes a lot during the descents. This is the reality, I’m afraid! Conversely, I have riders who routinely get well over 2000km out of a set of resin pads, while racing XC provincials, stage races, etc. The point is that there is no set rule for when to replace brake pads – it will differ for each rider.

Take note of exactly what make and model of brakes you have, as the pads required are specific to each respective brake type, for example Avid Elixir or Shimano XT 8000. You’ll note as well that there are different types of pad for each model, so shops will ask “Resin or metal?” What they’re asking is whether you want an organic, resin-based pad (a ‘softer’ pad with great initial bite and feel, but not particularly great life in harsh, muddy conditions) or a metal, sintered pad (capable of handling long, high-speed descents without fading as easily, and much harder-wearing, but needing a bit more work to bite). Metal is the safer bet for multi-day events with potentially harsh weather.

 

Let’s Get to Work

Fitting pads is actually straightforward, but there are a few extenuating circumstances that make things difficult when out on the trail. Regardless of brake make or type, there is the fact that as pads wear down, the brake compensates for this wear and the pistons move ever closer to the brake disc. What this means is that new, thick brake pads might not fit between the pistons when you do the swap, which is why it’s always a good idea to wedge apart the calliper pistons and push the pads back to a ‘baseline,’ with the old pads still in, before installing new pads (see pics).

Almost all brake pad sets, barring magnetic-backed types like early Hayes and current Maguras, will have a spreader spring between each pad, which is there to stop the pads from continually dragging against the disc when not in use. Take heed to correctly locate the spring’s ‘legs’ between the pads (see pic). Modern Shimano fin types will also have a right and left side to both the spring and pads, clearly marked on both. (Note: In the cycling world, right hand side refers to your right, when seated on the bike.)

Once I’ve prised the old pads as far apart as they’ll go, I unscrew the locating pin that secures the pads and calliper together (see pic) and slide the old pads out. Carefully squeeze the assembled new pads/spring into the hollow between the calliper pistons, taking care not to snag the spreader spring at any stage. Re-screw the locator pin and voila, almost back in business!

 

Final Fit

Once the wheel is back in and there’s now a disc between the freshly-installed pads, give the brake lever a few good, sharp tugs to help ‘retrain’ the calliper pistons into correct position. You’ll note that there will be no real pressure initially, but after a few sharp pumps of the lever, the amount of lever travel before the pads bite decreases dramatically, eventually finding it’s new ‘baseline.’ Then spin the wheel to make sure that the discs don’t drag against the pads, and check that everything has been assembled and tightened correctly. Now you’re good to go.