2-Piece Racing Rotor Floating Pin Design Vs. 2-Piece "Euro-Rotor" Floating Design
by Matt WeissThe Euro-Rotor has an aluminum center section with pins imbedded in a radial pattern, that is, the pins are parallel with the rotor friction surface (Figure 1). We have not cut one of these rotors apart yet, but it would appear the rotor outer ring is cast and semi machined, including drilling a series of holes around the inside of the rotor that the pins are inserted into (Figure 2) . An anti-seize compound is applied to the pins and they are inserted into the rotor. It then appears a casting mold for the aluminum center section is placed in the center of the rotor with the pre-installed pins protruding into the aluminum center. When the center is poured, the pins are captured, thus attaching the hat and rotor (Figure 3) . The aluminum center is then machined, and in all likelihood, the final step is grinding the rotor surfaces parallel using the inside face of the center hat as the reference point. The anti-seize compound lubricates the pins as the rotor expands and contracts in a radial direction, minimizing distortion. If anyone on the board has first hand knowledge of how these rotors are made, we would appreciate your constructive input.
The system employed by StopTech and others is dramatically different. The pins are perpendicular to the rotor face and held in place with a bolt and washer set-up (Figuress 4 , 5, 6 & 7 ) . There are precision round holes in the aluminum hat that the pins fit into. In the rotor, there are milled slots the pins rides in. The width of the slot is machined to match the OD of the pin. The bolt circle of the pins in the hat positions the pins so they are to the outside end of the slot (Figure 8) . As the rotor expands and contracts in a radial direction, the slots slide along the pins, which are held in place by the hat.
The length of the pins is slightly longer than the stack up of the hat and rotor flanges, so even if the bolt is tightened all the way, the pin will not bind (Figure 9) . Because there is the slight amount of free play in the pins, if nothing is done to control that movement, the rotors will rattle on the hats. This is not an issue on a racecar in terms of noise, although excessive movement can cause the pads to get kicked back into the calipers and make the first pedal stroke longer than desired. On a street application, the rattling is unacceptable.
Brembo® developed a really trick spring clip when they adapted their racing rotors to the McLaren F1 Supercar. They utilize this same setup with their current street kits, hence the reference to an F1, or McLaren anti-rattle clip (Figure 9). StopTech came up with a simpler more economical solution that has proven just as effective in controlling the rattling (Figure 9). The Brembo® set-up uses the spring clip on every other pin. StopTech utilizes a Bellville high-temperature spring washer made from Inconel ® Stainless Steel. The washers are used on every pin, and when tightened, maintain spring tension evenly spread around the rotor/hat interface.
One of literally thousands of examples of this system used in racing is illustrated (Figure 10) . This particular hat and rotor are from the PTG BMW M3 (6 cyl) raced in the 2000 and part of the 2001 seasons. The rotor is the same 355 X 32mm Brembo® rotor supplied in their big brake kits. The hat was manufactured by the team (or at least to their specifications). Standard floating drive pins and hardware are used, the only changes being slightly more play between the rotor and hat (hat flange is slightly thinner) and no anti-rattle clips are used. Though the exact history of this part is unknown (what race, how many miles), it is showing signs of stress cracking common on virtually all racing rotors when they have gone through excessive heat cycles. Also of interest is the area on the rotor face adjacent to each slot. Close inspection reveals the even transfer layer of pad material deposited onto the rotor face (Figure 11) . This is an excellent example of even pad material buildup on the rotor face from a pad utilizing an adherent type of material technology. Though severely used, there is not much rotor face wear as the pad material is constantly being consumed and re-deposited on the rotor face. An abrasive pad type would show much more rotor wear. We take every opportunity to tell our customers (and even other manufacturer's customers if they ask) how important proper rotor and pad bed-in procedures, and proper pad selection (especially for the track) are to the performance and life of the rotors.
In conclusion, the Euro-Rotor is a very clever and unique design in terms of reducing weight and being able to be produced in large quantities at a somewhat reasonable cost for an OE manufacturer. It would appear the biggest benefit would be a reduction of weight, and the ability to expand and contract in a radial direction with less distortion. Drawbacks are severely reduced airflow through the rotor vanes due to the aluminum hat section the pins are imbedded in blocking the vanes, limitations of the system in aggressive track like conditions, and a higher cost of replacement verses a one-piece design, as both hat and rotor must be discarded.
The 2-piece racing rotor will cool more effectively due to less restrictive airflow and will be much less prone to distortion under even the severest driving conditions. Though more expensive initially, long term operating costs in an aggressive driving environment may actually be less as the rotors will typically outlast other designs and the aluminum hat may be reused.
In other words, you get what you pay for…
If there are any questions about the material presented
here, please feel free to contact
us.