Cool calipers take the heat out of the hardest braking

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YOU can expect to see them on the front forks of a bike in a pub car park near you very soon: Radially-mounted brake calipers.

If you have eagle eyes and an anorak attention to detail, you’ll have noticed them on WSB bikes already. And when WSB riders start feeling the benefits we can’t be far behind.

The imposing-looking parts are now on the works Ducatis, Kawasakis, Suzukis and Aprilias. Only Honda has resisted the temptation to follow suit.

Italian firm Brembo pioneered the new mounting method, and Japanese rival Nissin has followed with its own version for Noriyuki Haga’s Yamaha.

So what’s the big idea? Traditionally, front brake calipers are mounted to the bottom of the fork leg by two bolts near one end of the caliper casting. The bolts screw in at right angles to the brake discs, pointing towards the caliper on the other side of the front wheel. This has been the way it’s been done for decades. No-one saw the need to change it until Aprilia asked Brembo to make the brakes better on Valentino Rossi’s works RSV250 in 1998.

The radially-mounted caliper system they devised was, they claimed, better at resisting flex under heavy braking. The design also reduced heat build-up and so made them better at resisting fade under hard use.

Rossi won the 250 title that year, and it wasn’t long before the gold-coloured alloy mounts appeared on Carl Fogarty’s works Ducati 996.

When brakes are applied, traditionally bolted calipers are wrenched with a force of hundreds of kilos not only in the direction of the turning disc, but also, minutely, to one side. The end of the caliper which is not bolted to the bike moves fractionally. The flex would be barely visible to the human eye, a tiny oscillation from side to side as the disc spins through the slit in the caliper.

Over time, and particularly with the soft compound pads used in racing, the pads can wear unevenly, with the pad material at the bolted end of the caliper taking the brunt of the burden. This in turn causes uneven heating in the pad surface, with a build-up of heat in that burdened area – and that can reduce braking performance.

Brembo redesigned the caliper so that there is a mounting bolt at both ends of the casting, with the bolts themselves directed in the line the bike travels in, not across it like the old method.

Because the two mounting points are in a line parallel with the direction of the disc’s rotation, the more rigidly mounted caliper is only pulled in one direction. That immediately reduces the flex found with the old method. There can be little oscillation of the caliper because both ends are secured.

Pad wear becomes much more uniform, hot-spots are prevented and there is a second benefit. A traditional mounting can suffer from uneven heat dispersal, with the attached end of the caliper cooling faster than the unattached end, as heat sinks into the old-style alloy bracket.

The radial mount draws heat away from the caliper more evenly – along the entire length of the casting.

And because the new bracket is more substantial than the older ones, it can soak up more heat.

Getting rid of heat helps sustain brake performance for longer – and that is vital in long races where each lap could see well over a dozen heavy braking points. The man who has the best brakes at the end of the race could have a winning advantage.

Foggy, the first in WSB to use the radial mounting system when they were fitted to his works Ducati last year, says the feel at the lever is better and the bite more immediate.

So how long do we have to wait to see one on a road-going 996? At present, Brembo says it has no plans to make them for road bikes, but if pressure mounts from buyers that decision might be made for them. The bracket is made easily from relatively cheap alloy. The brackets only weigh around 50 grams more than the old-style ones.

Brembo won’t say if the new system actually lets you brake harder, but in tests with bench-mounted brake dynamometers we’ve heard the outright pressure exerted on the disc is fractionally higher, attributed to the more even pad pressure.

Would you notice that tiny difference in day-to-day use? Who cares? If it’s good enough for Foggy…

HOW CHANGING THE MOUNTING GIVES PADS A LONGER-LASTING BITE

The traditional way of securing brake calipers to the fork legs (left) sees one end of the caliper casting bolted firmly in place, while the other is unsecured. This can lead to tiny amounts of flex in the caliper itself, and to uneven pad wear and a build-up of heat in the pad material. The caliper both heats up and cools down unevenly.

The new radial mounts secure the caliper at both ends, virtually eliminating flex. The pad wears far more evenly, leading to better braking. Less flex and movement means less heat build-up in the pad material, too. The fact that the mounting has more metal in it means it can usefully soak up excess heat from the caliper.

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MCN Staff

By MCN Staff