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Speed, heat and money

Kevin Cameron

On Saturday evening at Laguna Seca, I had dinner with Eugenic Gan-dolfi, a Brembo engineer, and learned many fascinating things. First, I was told that even in this time of restricted spending, all teams in MotoGP buy rather than receive as sponsorship Brembo brake systems and Marchesini forged magnesium wheels (Brembo now owns Marchesini).

MotoGP managers Dorna, in trying to reduce costs to the teams, have cut practice by 25 percent and now require that engines be run longer between replacements (this means extending useful life by cutting stress through reduced rev limits). Also proposed has been the banning of carbon-carbon brakes and magnesium wheels. Gandolfi revealed that the annual budget of the team of French rider Randy de Puniet-one of the smallest squads in the series-is 6 million L euros, or about S8.4 million, but that brake parts make up only Vioths of 1 percent ($25,000) of that. Brake life in MotoGP is stated to be 2200 miles per wheel set. As you would expect, the largest expenses for racing teams arc salaries, hotels, food and air travel. To achieve truly significant savings, we must have all the GPs in one place.

As to cost savings from proposed elimination of mag wheels, Dorna officials were asked if they would prefer to tackle regulation of the aerospace lithium-aluminum alloys that would surely take the place of magnesium (Li is third-lightest among the elements, just after hydrogen and helium).

With much fanfare, Formula One has banned use of "high sliffness-to-mass metals" from its cars, which is a nonspecific way of saying "no beryllium" (Be is the fourth-lightest element). This wonderfully stiff material, if used to make brake calipers of stiffness equal to present aluminum versions, would offer a 45 percent weight reduction. Gandolfi said that Be has a fierce 0.9 coefficient of friction, as compared with the 0.5 of carbon-carbon and 0.3 of 1970s-gcncra-tion organic friction materials. But the dust generated by Be friction is poisonous, requiring special manufacturing precautions. The attraction of Be as a disc material was mainly its exceptional heat capacity.

I asked Gandolfi about the touchiness of early carbon-carbon motorcycle brakes. He replied that the first 270mm-

diameter c-c discs of 1988-89 were sawn from thick "logs" of finished material, which required eight months of residence in high-temperature ovens for its production. The strange size resulted from buying from the maker, Hitco, parts originally sized for aircraft applications. He said the process of impregnating a preform of carbon-fiber with amorphous (unstructured) carbon was most complete at each face of the log, and least so at its center, resulting in discs with varying physical properties.

I asked about the surface "hard spots" that continually formed on the iron discs of Honda's RS500 "selling bike" GP racer of the mid-1980s. Factory instructions called for these bumps to be hand-sanded away after each use. Gandolfi replied that successful manufacture of high-performance iron brake discs (as mandated in World Superbike) is a very demanding business.

Then I asked about the problem of pad retraction, which is accomplished solely through the elasticity of the rcc-tangular-section elastomer piston seal. They call this "piston roll-back."

"We can have a symposium on this," replied Gandolfi, clearly warming to a subject of great interest to him. "Chamfers, rubber compound and hardness, surfacc finish-all arc important."

At first, it would seem that the seal would stick to the piston through several applications of the brake, each time pulling it back to its starting position. Then, as pad wear required the piston to be advanced even farther, it would seem the seal would finally slip and the piston would take up a new retracted position. This would imply that the lever would get lower and lower for a few laps, and would then jump up again when the seals slipped.

"No, it does not do this," Gandolfi countered, though he could not explain in detail at risk of revealing valued trade sccrcts. "This is the heart of the caliper," is all he would divulge. But you can imagine how varying the chamfers at the edges of the seal groove would vary the seal's exposure to and deflection by hydraulic actuating pressure, thereby modifying the above simple picture in useful ways. Ditto for piston-surface finish and seal-compound hardness.

Now think about the latest Brembo forged Monoblocco calipers, whose piston bores and seal grooves are machined by a device that acts from within the pad gap; these calipers are not bolted together from two pieces, and neither arc they bored from one side which is then plugged. How do they solve this modern ship-in-a-bottle manufacturing problem? Outsiders have seen the production machine but have not been permitted to photograph it.

Gandolfi described the friction process as the continual formation, straining and breakage of micro-welds between pad and disc surfaces. The straining of the welds is the classic force x distance = work equation, and its repetition over the whole swept braking surface consumes the kinetic energy of a bike during braking. As the micro-welds break, strained atomic bonds snap back, setting all nearby atoms into violent vibration. Our simple word for this vibration is "heat."

Carbon-carbon itself is on a list of technologies whose international trade is controlled by Cold War-era prohibitions. This is because the nose cones of ICBM reentry vehicles, leading edges of the Space Shuttle Orbitcr's wings and exposed parts of hypersonic research vehicles are made of it. Although MotoGP competition is intense, it is not a war, so its use of c-c is accepted. □


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