You've the full-blown Ferrari Challenge equipment there, nice. The rear rotors are actually too large on this application (front and rear are the same rotor), but they look great and have huge heat capacity. Rob
Technically, radially drilled (or 'grown')rotors (as opposed to axially, which is the original topic. And they're specified by the rules now to reduce (attempt to) cost. Mr. Shatten, you're up on your issues of Racecar Engineering or other fine F1 technical publication. Rob
been a subscriber and a sponge for years. =D ever since PVV came out with his book a decade ago I've been hooked. I appreciate the clarifications from the more experienced.
There seems to be a fair amount of folklore concerning slotted versus cross-drilled versus solid rotors. Let's take a critical approach. 1) How much do those holes weigh? Not much. The weight saving would seem to be minimal, and not worth the effort or potential that discontinuities in the metallurgy will produce (read propensity to crack). Slots, like holes, offer minimal weight savings. 2) Cooling? Surface area is what provides heat dissipation. Mass provides thermal "inertia". The greater the mass, the longer it takes to heat an object, and the longer it takes to cool. The surface area is increased in both slotted and cross-drilled rotors. Simple calculations, which I have not undertaken, could tell you which provides greater surface area, but I suspect they are comparable. In the limit, if the entire rotor where cross-drilled with only radial "spokes" holding the outer rim, the rotor would heat and cool very quickly. 3) Braking efficiency - translated to mean, which form provides the greatest braking potential? The answer is solid rotors. The contact surface area of pad against rotor is the critical issue. Why do manufacturers provide for larger rotors on high-performance cars? When drilling or slotting, one defeats this approach. The weight saved versus the surface area lost is simply not of value. 4) Wet braking. Now here is the most important issue, and I echo Elmaistro. When applying brakes on wet rotors, the pad will hydroplane like a tire on asphalt. The slots or rotors provide an escape route for water. Notice the pattern of slots or holes - they are in a pattern that supports radial flow on a turning surface. In summary - I believe folklore is at work here. The only reason to consider rotors with defects (holes or slots) is for wet braking and cosmetics. Weight, heat, and "out gassing" simply don't cut it. My thoughts. Jim S.
Jim - the weight might be ounces but it does add up. and not to forget, it's on rotating mass in the unsprung weight of the car as a whole. this adds up to considerably more than just losing a few ounces and translates to much better performance overall.
Agreed. Drilling is only worth it, as I stated, for light-weight, low-powered race cars who's rotors are large, too large, and a performance gain can be made by removing mass (MOI and unsprung weight, at a cost of component life). Agreed. Along with mean diameter and mass, agreed. On a motorcycle, sure, car, not an issue. Weight, yes, but only in certain, specific, limited applications. Otherwise, no way, one needs the mass. Cosmetics, yes, marketing drives this decision (because it adds cost, does not improve performance (so the engineers are not lobbying for drilled rotors, the marketing department is.) Out gassing is taken care of during pad bedding (break-in of the brake pads). Slots are there, and a performance benefit, to reduce the build up of aggressive pad dust, which scores the rotor surface, to the detriment of friction and rotor life. In race applications. Otherwise, this too is marketing on a road car. Best regards, Rob Schermerhorn
Rob and Schatten - thank you for your comments and insight. I was at Crystal Cove this morning (regular Saturday congregation of exotics in Southern California) and spoke to a few knowledgeable folks about this issue. Most agree that cosmetics are the driving issue. Mass and thermal characteristics are cited, but when pressed, the consensus is that these issues are not significant. Out-gassing was raised, but I have to believe that if this was the driving issue, that the holes could be much small and still allow gas to escape. If cooling were the issue, more holes with smaller diameter would provide greater surface area for cooling, and provide for out-gassing. Your thought concerning dust elimination (to reduce abrasive affects) is a good one. All in all, I am contributing to the folklore. Would be nice to hear from a mechanical engineer working in the brake business. Jim S.
I am a mechanical engineer, working in the auto racing industry for 14 years, including nine managing the race department for a Midwest US Ferrari authorized dealer. I have designed brake systems. I currently have my own business, Delta Vee Motorsports, consulting on full-vehicle dynamics, shock absorber development (I rebuild and modify Ferrari/Bilstein dampers, including the computer-controlled system, too), and provide race transmissions, including internal components to convert all Ferrari gearboxes. My web site is in development. Until then, you can read some of my Ferrari technical articles here. Best regards, Rob Schermerhon
Anyway to reduce unsprung weight will make a significant difference in handling.Each 1 lb of unsprung weight equals 10lbs of sprung weight. My experience with cross drilled rotors comes from street bikes, the bikes with the cross drilled rotors required much less brake effort since the gas escapes out the holes thru the brake vents, the brakes where also significantly superior in stopping ability especially in the wet, I would not say they are cosmestic at all.
Agreed, However, before you start drilling the rotor, you put an Aluminum hat on the rotor to get rid of the first 4 pounds, then you can drill a bunch of little holes to save another 1 pound (if you so choose).
I did this, and shaved off 4.5#'s per side - while increasing the surface area/diameter of my brakes. 9 #'s off of the front... fantastic!
From my research you are better off using two piece rotors with an aluminum hub than slotted or cross-drilled ones. They cool better, do not warp as easily and provide more brake surface area. I use euro-spec two piece ones on my M5 and have been well pleased on the street and track.
