The big squeeze

Drag, glazing, judder and squeal. Not only a great night out, but a sign your brakes aren't at their best. Here's why

Can the front brakes fitted to your bike lock the wheel, or life the back off the deck? If yes, then they have all the power you can use. Most modern bikes' brakes are phenomenally powerful - more powerful than their engines. A kawasaki ZX-6R's motor imparts enough energy to have the bike up to 70 mph in 75 metres, taking 4.3s; the brakes are powerful enough to remove all this energy in 3.1s, halting the bike in 52 metres.

If you want more braking power, the cheapest and easiest thing to do is build up your hand strength and squeeze the lever harder. You could fit a more powerful system (from another model, or specialist manufacturer), but this is expensive and changing single areas of a system - calipers or discs - can throw a whole expensive and extensively tested system out of balance.

Feel Factor

So, with very few exceptions, braking systems fitted to production bikes are more than capable of providing what's needed for even very serious use. It's differences in fell that affect how we, er, feel about our brakes. So what is the 'feel'?

Feel is the relationship between our brains, hands and brakes. Our brains are happier and have less work to do if the amount of stopping power delivered rises and falls incrementally in tandem with the amount of squeezing power we deliver at the bar. We want twice the pressure at the bar to deliver twice the stopping power, and we want the pressure needed to be comfortably attainable.

We also want 'bite'. We want the reassurance that something's happening the moment we stroke the lever. But we don't want 'grab', for the brakes to come on without progression, upsetting the road. And yet we want more. Operation must be smooth, free of fade, judder, squeal and sponginess. We want all of the above, whatever our speed and whatever the weather.

Easy squeezy

Twice the squeeze gives twice the force at the caliper, but other factors come into play. As heat in the pad increases, the coefficient of friction (grippyness) may change, requiring more or less pressure on the lever to retain a given rate of deceleration.

If heat goes beyond the pads' operation range they can fade, requiring more input to keep slowing. This condition is rear these days as sintered pads, with high metal content, are very efficient at removing heat from the pad surface. This can lead to another problem, 'fluid fade' where water vapour in the fluid boils, leading to total brake failure.

The chance of this happening is remote and it only occurs where the brakes are lightly applied, 'dragged', over distance. So when descending a mountain in the Alps, or picking your way down a Lake District B-road, use the gearbox to moderate your speed and only brake when you need to.

To complicate things yet further, wind resistance plays a part in feel. At the ton, just closing the throttle will decelerate you at around 0.5g. So if you're slowing at a linear 1g then, during the course of the stop, your brain is telling your hand to double its pressure. Unless, of course, the pads' friction increases as they heat...

Original and best

Changing pad material (make) can change the size of your squeeze, bite, progression and power. All the major pad-maker have a 'racing' or 'road performance' pad in their ranges. Often these will improve power (through changing the ‘friction’ bit of the overall equation) and feel, but the only way to be sure they’ll work with your bike is to try them out. More friction can also mean more wear to pad or disc, or both.

Everyone has a different idea of what good feel is. And every pad/disc combination will behave differently. There is one compound of pad that has been extensively tested with your bike, taking all factors into account, and that’s the standard one.

Down the tubes

Most braking inadequacies are due to poor maintenance, age, wear and bad riding. Sponginess – where the lever comes a long way back – can be caused by a several factors: air in the hydraulics, leaks at cylinder seals, bulging brake lines and flexing calipers. Even pivot wear can have the lever nearer the bar than you’d like.

The first thing to do if brakes are too spongy is bleed air from the system. If the brakes are still springy, fit braided or Kevlar-sheathed lines that resist bulging.

If brakes are only used lightly, a ‘glaze’ may build up. This can be removed with glass paper. Until then brakes will feel ‘wooden’, like the pads aren’t gripping properly – which they’re not.

Glazing, overheating and fade can also be caused by brakes binding (part-seizing) on and is often accompanied by blueing of discs. In this case, calipers must be stripped, cleaned and reassembled with new seals. If pads are anywhere near the wear-marks, change them.


extracts Bikes Nov 02