Quick Tech With Mar­lan Davis

Hot Rod - - Contents - hHOTROD. COM/ Mar­lan-Davis

Cross-drilling brake ro­tors sup­pos­edly helps vent gases cre­ated when the resin bond­ing agents within the brake-pad ma­te­rial be­gin to break down at ex­treme tem­per­a­tures. When this hap­pens, the pedal still re­mains firm while the fric­tion co­ef­fi­cient de­creases, caus­ing a loss of brake ef­fec­tive­ness. Rac­ers of­ten re­fer to this con­di­tion as “green pad fade” or “out­gassing.” With newtech, pre­bur­nished car­bon fiber or ce­ramic rac­ing brake pads, this gas buildup is no longer a ma­jor con­cern. Less ex­otic street-pad com­po­nents are still sub­ject to out­gassing, but only when used on a race­track at ex­treme tem­per­a­tures rarely, if ever, seen on the street.

An­other the­ory was that drilling mul­ti­ple small holes in the ro­tor sur­face in­creased the co­ef­fi­cient of fric­tion be­tween the pads and the ro­tor be­cause all the ad­di­tional small edges let the pads bite more ef­fec­tively. But to­day’s mod­ern car­bon-fiber pads are de­signed to op­er­ate at higher heat lev­els where the fric­tion co­ef­fi­cient is in­her­ently higher, so any ad­di­tional hard-edge bite is su­per­flu­ous. And all those added small edges eat into the pad ma­te­rial, short­en­ing its life.

That leaves only po­ten­tial weight sav­ings and (if you are into pro­filin’) vis­ual en­hance­ment as the pri­mary rea­sons why any­one would drill ro­tors to­day. Nev­er­the­less, there’s a big po­ten­tial downside to drilled ro­tors: mi­cro­c­racks that prop­a­gate out from the holes. This can be a par­tic­u­lar prob­lem for street-driven cars. We’ll get into more de­tails on this prob­lem next time.

[ Drilled disc brake ro­tors look cool on a high-end street car, but do they re­ally work ef­fec­tively with to­day’s mod­ern brake pads?

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