Statement #2 from JRitt@essex: “Air Gap- AP J Hooks have an open path for the air to flow through the vanes. If you look at the RB discs, their hat attachment points block a considerably portion of the disc. The flanges on the iron rings cross over the area where air enters the internal vanes, blocking airflow. The only places where the air isn't at least partially obstructed is in between hat attachment points, which is less than 50% of the disc (there are 9 gaps between the 10 hardware attachment points).”
To be more precise, this comparison of “air gap
” here is referring to the difference of how a disc is attached to the rotor hat and how it impacts the air flow.
There are two types:
Conventional/Competitions' Surface Mount:
RacingBrake Center Mount
- Air circulation is limited as this type of mount admits no cold air from outboard* (spoke side) while the inboard is usually blocked by dust shield. (inboard).
- Stress load is unbalanced as the load center is on the outer friction surface where the hardware connects.
- Heat load to hat is solely from outboard disc surface and is unbalanced.
- Heat transfer is directly from outer disc surface to rotor hat which heats up rotor hat more rapidly.
: (RacingBrake’s Patented design)
- More efficient air circulation – Center mount provides air inlets from both inboard and outboard sides.
- Heat load on rotor hat is balanced from both sides of friction surfaces.
- Heat transfer from disc surface to rotor hat is greatly reduced due to longer distance of mounting tab to travel.
- Stress load is balanced due to the mounting surface being at the center plane of the disc.
- RB disc can be assembled to either left or right by flipping the hat, without having to identify whether left or right like surface mount. This can save your inventory cost and head-ache and avoid mix-up in assembly. Uni-directional disc is a truly remarkable design that tuning shop and track enthusiasts appreciate.
- Change of disc thickness will not affect the offset (unlike surface mt which the offset will change according to disc thickness), so same hat can be used for different duty discs (eg. 34mm for track and 30mm for street).
* Stoptech has a directional hat design to improve the air flow. This design requires 4 P/N for a set of rotor (2 for disc, 2 for hat), while RB only needs 2 P/N (1 ea for disc and 1 ea for hat).
Other manufacturer also has the similar idea with unique hat design to achieve the same purpose (allowing more air to flow from outboard side of rotor):
But the problem is the air doesn't travel in angle so the ventilation effect is very limited.
The benefit of Center Mount design was observed by Brembo's when they started shipping this "Dual Cast" rotors
for CTS-V although their discs are not replaceable, and many other applications since (BMW, Corvette, MB, Porsche etc.)
RB’s Center mount two piece rotor is still the best design in the performance industry.