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Originally Posted by lutfy
Am trying to understand the rationale here. The reason people upgrade to BBK for the E9X platform is because the stock system cannot dissipate heat effectively. Folks go with 380mm or 378mm FROM stock 360mm. This is almost a step backwards in terms of total area (of rotor).
While it may work with a lighter Corvette, in my case my car weights 3800lbs (yes on the scale) and I go through set of Pagid Yellow or PF08 pads (front) each track weekend (on almost all the tracks I attend) with the stock brake system. Going with smaller rotor is counterintuitive in this case for me, hence asking the question.
Thanks,
Lutfy
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Hey Lutfy, I know you're not trying to be a smart@ss or anything...no worries at all. I actually addressed this topic in my very first post. That said, there was a lot to take in there...so I pasted the relevant section below. When evaluating discs, there is a lot more to the question than simply size! The design of our discs is a far cry from what comes stock on these cars. The demands on a system are also not strictly dictated by vehicle weight. Weight, speed, weight bias/weight shift, tire capacity, etc. all factor in.
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I'll try to head off a few more of the questions people will likely have about this kit with a brief Q & A:
Q: Why aren't the discs bigger?
A: Short answer: Because they don't need to be! Long answer: Our systems are built from a racing mentality. In the pro racing world, teams scrap and scream to remove ounces of weight from the cars. Anything that is larger than necessary to get the job done is simply dead weight to drag around. That is how we approach our design. If you want to go faster and a 14" disc will work, a 15" disc will simply add weight, increase the moment of inertia, and hinder wheel fitment. Sure it will look pretty behind 20" wheels, but that's not what this product line is about.
The 14" AP Racing CP5773 Heavy Duty J Hook discs we are using are the exact same discs that won the championship last year on the Action Express Corvette Daytona Prototypes. These discs are being tortured in endurance racing events every weekend at the hands of some of the top drivers in the world. Yes those cars are significantly lighter, but they're also significantly more powerful, and far faster. To give you an idea of the boundaries they're pushing, one recently hit 223 mph in testing! :O If you think you'll give these discs a harder workout in your 20 minute DE session than these guys will when running 24 Hours of Daytona...no offense, but you're probably wrong. Keep in mind that the amount of energy transfer (changing kinetic spinning energy from the disc into heat) in a braking event is most greatly impacted by speed....more so than by weight. I'm going to get a bit technical here, so feel free to skip ahead if you feel your eyes glazing over! The core formula for kinetic energy is:
kinetic energy = vehicle weight x vehicle speed2
Take note of that little superscript at the end. If you look at the equation above, you'll note that doubling the vehicle's weight would double the kinetic energy, but doubling the vehicle speed would increase the kinetic energy by a factor of four! So in plain English, that means a stop from 220mph on a lighter car is going to be tougher on the brakes than a stop from 140mph on a substantially heavier car.
When comparing discs, you can't simply look at the diameter and decide that one will be more effective than another. The number of vanes, air gap, wall thickness, vane shape, metallurgy, hat attachment design, etc. all have to be taken into account.
To give you another example, our small four piston C6 Corvette Kit has found its way onto quite a few C6 Z06's pushing 600hp at the track. That kit features a 325x32mm disc. The OEM front disc on a C6 Z06 is 355x32mm. With a disc that is 30mm smaller in diameter than stock, many of our customers are seeing huge increases in pad and fluid fade resistance, less disc cracking, longer disc life, pads that wear longer, etc. Again, it's not just disc size that matters. It's all about design and optimization.
Wheel fitment is also of critical importance in our design process. As mentioned above, most of our customers run the smallest, lightest wheels available for the platform. I won't go into all of the merits of doing so, but obviously unsprung weight, lower rotational mass, cheaper tires, etc. all factor in. Our systems are packaged tightly to allow for a wide range of wheel fitment. Using an extremely large diameter disc kills wheel fitment, and the utility of a track-optimized brake system.
Okay...I've beaten that one to death.
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