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Stop and think about your brakes

Published: 21 January 2000

THE biking moments most likely to stick in your mind more vividly than any other probably don’t involve hundreds of horsepower, or blue lights in the mirror. The ones that really stay with you are the times when you ended up in a situation where your brakes didn’t seem enough.

Horsepower can produce a rush, but a front brake lever squishing ineffectively back to the bar when you are hurtling towards a corner is far more memorable.

Yet brakes are among the last things people change on their bikes. Look at the bikes lined up for a track day and you’ll see any number of aftermarket race-spec exhaust pipes, tyres and suspension parts. But brakes...well, maybe the lines are changed for braided hose, but that's about it.

But improving your bike’s brakes has as much effect on its performance as any full race system.

One of Britain’s leading brake experts is AP Racing’s Ray Bailey. He honed his skills working on the brakes on Kevin Schwantz’s works Suzuki RGV500 for years.

He said: " People tell me the brakes are the most disappointing thing about their bikes on a track day. They build up to a pace they are happy with and then the bike doesn’t want to stop any more. It’s pretty frustrating, and not at all safe.

" The standard fitment on bikes like the R1 or the FireBlade are great under normal road conditions. Even when they are used repeatedly on a hard road ride, there is generally enough time for them to recover their performance. They are designed to be used by the average rider, in varied conditions and be durable and cost-effective. Their weaknesses are shown when you use them for something they are not designed for. And with the increase in people who regularly use their bike on tracks, we are supplying more and more ‘average’ riders with new systems. "

One of AP’s best-sellers is their six-piston caliper and cast-iron disc set, often allied to a fully-adjustable master cylinder which can be " programmed " to make the bike stop the way you want it to. It’s not cheap at around £1250 (although some people pay that for a full race exhaust).

To understand how they end up costing that much, consider what they must cope with. They don’t have lubricating systems, they don’t have coolant, there’s no filter to keep dust out and they need to work in the freezing-wet nearly as well as the bone-dry. A panic stop from high speed can yank at a caliper with hundreds of kilos of force, heat it to 400 degrees Centigrade and pressurise it from within by nearly 300psi. There’s no rev-limiter to stop them being used too hard and, if they do fail, it’s more likely an ambulance, not an AA patrol truck, will need calling. In comparison, your engine has it easy.

The real enemy of brakes is temperature, and Bailey says this is what causes the problems for standard systems when used on a track. He said: " Even in tough road conditions, a brake system will only heat up to around 175-200°C. A standard set-up of stainless steel disc and normal calipers, pads and lines copes with that. Under track use, temperatures can quickly get up to 400°C... and then you are in trouble. "

When a stainless steel disc hits that kind of temperature, it can’t get rid of the heat fast enough, so it transfers much of it to the pad, the caliper and then the fluid within.

" At really high temperatures, the pads can lose their ability to grip. If the hydraulic fluid boils it creates air bubbles which cushion the braking force made by the hand squeezing on the lever. "

Swopping the steel disc for a cast-iron item immediately helps solve the heat dispersal problem – the " old-fashioned " metal is one of the best at dealing with heat. As a bonus, the surface of an iron disc has more friction than steel, which means it is rubbed harder by a pad and will stop faster.

With a better disc in place, it is worth thinking about changing the calipers. Most standard calipers are made from an aluminium alloy of some kind, machined in two halves and bolted together along a join which runs lengthways along the line of the disc (Yamaha’s R1/R6 and Fazer brakes are one-piece). This join is an enemy of good braking. Under hard use, the force of the pads being pushed on to the disc tries to bulge the caliper outwards. So some of the lever pressure exerted by your right hand is wasted in overcoming this.

Most aftermarket suppliers retain the two-piece design but make the overall unit much more rigid and so less inclined to bulge outwards.

Making a lighter caliper saves unsprung weight, which helps the suspension work better. Weight savings and handling benefits are the real reason behind six-piston calipers. By having two more pistons than a normal four-pot set-up, you can have the same amount of braking force on a far narrower and lighter disc. That’s great for the suspension and brilliant for the handling because it reduces the gyroscopic effect that a disc spinning at high speed has on the handling.

The combination of two discs and two calipers can save around 0.75kg off the front end of a bike. Like tyres, pads come in different compounds, with the softer ones being the best for track use. They don't last as long as standard pads, but will stand up to hard use much better and stop you quicker.

It takes a few miles of hard and light use to get the pad and disc faces perfectly matched and until they are matched braking performance will be reduced.

The real hard-core track day abusers among you might consider ditching the stock master cylinder for a tiny, weight-saving one.

You can even programme adjustable systems like the AP Racing one pictured here, to go from all-four-fingers-in-a-death-grip stoppies, to single-finger-gently-brushing-the-lever stoppies.

There’s a dial on the beautifully-crafted lever which can be turned to change the gearing inside. With it you can adjust the amount of pressure any given pull on the lever will transfer to the pads, raising or dropping the stopping power to suit your taste.

It’s all about being in control.