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Yes, the rotor ring is 390mm in diameter. But the first, call it half of the radius for easy calc is the hat. Total area is = pi *r^2. To find the braking surface area you need to subtract the hat area. So a 30mm total diameter increase should give you a massive % increase in braking surface area.
So the total 360mm rotor area is = 101,788 sq mm
A hat area of 180mm is = 25,447 sq mm
For a braking surface area of = 76,341 sq mm
Doing the same math for a 390mm rotor you get a braking surface area of = 94,013
Doing more math (I know it’s hard)....
The 390mm rotor has almost 25% greater braking surface area than the 360mm rotor
And that was using a very rough calc. The hat assembly is more like 3/5 of the total radius. I bet the true increase is something like 30%.
So the guy is just incorrect in every way possible.
It is clear too me, that you don't know the physics behind brake calculations.
Brake torque is influenced by 3 things.
1. Effective brake diameter on the rotor, which is from the center og the rotor, to mid brake pad.
2. Force applied to brake pads on rotor, by the pistons in the caliper.
3. Friction coeff.. between brake pads and rotor.
If you change only #1, and go from 360 to 390 mm. rotors, the increase in brake torque will be 8.3 % The cal looks as follows. (((390/2) - (360/2))*100) / (360/2) = 8.3%
Rotor area has only minor influence on brake torque,
2012 P31 C63 Coupe Trackrat, 2019 GLE63S Coupe Beast
Originally Posted by SLcharge
Guy's I don't want to take away your impression that you got way better brakes, but the physics can't be defied.
The placebo effect can be big, since common sense tells us that what we see do look a LOT bigger, therefore the brake torque MUST be a lot bigger.
Be happy with your big brakes
I don’t want to take away your impression that your math isn’t wrong and your classroom analysis of the brakes is far from reality. But it’s wrong. All of it. The big brakes are a night and day improvement, backed up by hundreds of hours on a track. Like, in real life. Not in your make believe land.
It is clear too me, that you don't know the physics behind brake calculations.
Brake torque is influenced by 3 things.
1. Effective brake diameter on the rotor, which is from the center og the rotor, to mid brake pad.
2. Force applied to brake pads on rotor, by the pistons in the caliper.
3. Friction coeff.. between brake pads and rotor.
If you change only #1, and go from 360 to 390 mm. rotors, the increase in brake torque will be 8.3 % The cal looks as follows. (((390/2) - (360/2))*100) / (360/2) = 8.3%
Rotor area has only minor influence on brake torque,
I missed out on the rotor being 390 mm.
I think your delivery got off on the wrong foot. 3 is what the larger rotor helps the most with.
For the street it's a complete waste of cheese, I agree. But for track, hands down completely worth it.
I think your delivery got off on the wrong foot. 3 is what the larger rotor helps the most with.
For the street it's a complete waste of cheese, I agree. But for track, hands down completely worth it.
Sorry to say, but you are completely missing the point I made.
The only thing I relate to is the statement that RB Brakes made that changing rotor size from 360 to 380 ( turned our to be 390 ) mm. would improve brake performance significantly.
The change in size do contribute approx 8% in brake torque, not more.
That you and others do feel that the performance of the brakes are increased beyond these 8%, is very much possible due to other factors, like increased friction coeff., better pads, higher thermal capacity, less or no fading, etc.
So, I do not question the performance of the rotors, as I don't know the remaining variables, but only stating that the change in size only contribute with approx 8%.more braking torque.
What really contributes is piston area, second, hydraulic pressure, and third, friction coeff.
That is why you often see bigger calipers than bigger rotors.
also factor in the leverage arm for braking related to the hub has been lengthened...... on my RS6 the 390mm Mov'it kit utterly changed the car on the track.
2012 P31 C63 Coupe Trackrat, 2019 GLE63S Coupe Beast
Originally Posted by SLcharge
Sorry to say, but you are completely missing the point I made.
The only thing I relate to is the statement that RB Brakes made that changing rotor size from 360 to 380 ( turned our to be 390 ) mm. would improve brake performance significantly.
The change in size do contribute approx 8% in brake torque, not more.
That you and others do feel that the performance of the brakes are increased beyond these 8%, is very much possible due to other factors, like increased friction coeff., better pads, higher thermal capacity, less or no fading, etc.
So, I do not question the performance of the rotors, as I don't know the remaining variables, but only stating that the change in size only contribute with approx 8%.more braking torque.
What really contributes is piston area, second, hydraulic pressure, and third, friction coeff.
That is why you often see bigger calipers than bigger rotors.
You. Are. Wrong.
Like, completely. Your math is incorrect. Take your head out of your math book and go look at a rotor sometime. Round metal thing. Not the wheel but behind it.
What really contributes is piston area, second, hydraulic pressure, and third, friction coeff.
That is why you often see bigger calipers than bigger rotors.
Right, and friction coefficient is variable with heat. The ability to keep brakes cool helps prevent the decrease of friction coefficient during repeated usage which is extremely important at the track.
This car has absolutely zero issue with piston area, or hydraulic pressure. If the rotors are too fkn hot you'll just destroy the pads even faster with larger calipers.
How do you keep rotors cool? Increase the diameter, add cooling vents, or both...
For most Mercedes owners' spirited driving style, a larger rotor can certainly extend the life of consumable such as pad & rotor, lower maintenance in brake fluid replacement and caliper rebuilt etc. due to lower service factor (run at cooler temperature in all braking conditions).
So overall they all add up to saving you time and money in the long run, although most people tend to neglect those long term benefit when making their replacement purchase.
RacingBrake is proud to serve Mercedes community with the finest brake products in the performance industry regardless you are just looking for OE replacement, or performance upgrade we have them all. https://www.racingbrake.com/MERCEDES...com-s/6217.htm
Last edited by RacingBrake; 10-10-2019 at 01:20 PM.
For the rear brake rotor, we make the rotor hat drum size to C63 so it's fully compatible with OE brake shoes, yet the disc is oversized to Black Series. The only rear BBK that's fully compatible to the original C63.
100% bolt on installation for the lasting performance and durability.
Feature & kit content:
Front kit - Reuse your OE caliper with exclusively designed caliper adaptor supplied by RB to instantly increase your rotor size from 360 to 390mm
Rear kit - Rotor is over-sized from 330 to 360mm - A pair of brand new OE "black series" rear Red caliper is included in the kit..
Car set of SS brake line - Included.
Car set of low dust, no squeaky street performance brake pads (XT910) is included.
10-09-2019, 11:36 PM
