TL;DR
This is physics and physics I have an affinity for. So I researched the math a bit.
Thanks btw. these are the kind of fun math problems I enjoy.
The math is straightforward, larger brake disc creates a stronger lever for torque which directly translates into a mechanical advantage. The relative increase in stopping torque is 17.08%% for the power brake big brake kit vs stock Ineos brakes. You'll have to do the math for other vendors system (That is straight up math on facts I know using just physics and known simple math.
So at the same brake pressure you get 17% increase in counter torque. But this compounds as you brake, this math compounds as the car dissipates energy from motion into energy as heat while at the same time stopping faster at the same time faster through increased counter torque and controlled thermal management.
It's really lovely, the counter torque is really what the people report as pedal feel. Eg 17% more counter torque at the same press on the pedal.
net 17% increase in counter torque against the wheel just on the disc itself. A meaningful and significant increase. And probably better since the product of counter torque is energy, which has to be dissipated through heat and I didn't even include that in the math yet.
The more I'm looking at that math the more sold I am on the benefit for cars with weight on them. It looks meaningful, particularly as you're out in the edge of heat management and counter torque performance envelope.
Long version;
Here is a simplified text book definition of the underlying math. I didn't work in all aspects of it, piston size and pad calculations and thermal energy management, but that math works out and I'll probably do it at some point when I have the kit for my own enjoyment.
Braking is the process of converting the kinetic energy of a moving vehicle into thermal energy (heat) through friction.
Improved braking performance generally means two things:
Greater Stopping Power (Mechanical): The ability to generate more braking torque to decelerate the wheel faster.
Better Heat Management (Thermal): The ability to absorb and dissipate the immense heat generated without "fading" (losing effectiveness).
Larger discs and pads address both of these aspects, but in different ways.
Part 1: The Mechanical Advantage (Torque)
The primary mechanical benefit of a larger brake system comes specifically from a larger diameter brake disc (rotor).
When you press the brake pedal, hydraulic pressure forces the brake pads to clamp onto the spinning disc. This creates friction. However, friction alone doesn't stop the car; torque stops the car.
Torque is a twisting force. To stop a spinning wheel, you need to apply a counter-torque.
The Physics of Braking Torque
Imagine trying to stop a spinning bicycle wheel with your hand. If you grab the hub (the center), it is very difficult to stop. If you grab the tire (the outer edge), it is much easier. This is the principle of leverage.
The brake caliper applies a clamping force at a certain distance from the center of the wheel hub. This distance is the "effective radius."
The Formula for Braking Torque (T):
T = F_friction * r_eff
T = Braking Torque (The twisting force that stops the wheel rotation).
F = The total friction force generated between the pads and disc.
r_eff = The effective radius (the distance from the center of the wheel hub to the center point where the pads contact the disc).
We can break down F further:
Where:
mu * F_clamp
(mu) = Coefficient of friction between the pad material and the disc material.
F_clamp = The normal force (clamping force) exerted by the caliper pistons onto the pads.
Combining these, we get the complete braking torque formula:
T = mu * F_clamp * r_eff
How a Larger Disc Improves Performance
Looking at the formula above, if we keep the brake pedal pressure constant (meaning F_clamp is unchanged) and use the same pad material (mu is unchanged), the only way to increase torque (T) is to increase the effective radius r_eff.
A larger diameter disc moves the caliper further away from the wheel hub, increasing r_eff.
Conclusion 1: A larger disc provides a longer lever arm, generating more stopping torque for the same amount of pedal effort. This is the most direct mechanical advantage.
Part 2: The Thermal Advantage (Heat Management)
This is where both larger discs and larger pads play a crucial role.
The amount of energy a braking system must handle is enormous. The kinetic energy (KE) of a moving vehicle is defined by:
KE = 1/2 *(mv(pov 2))
Where m is vehicle mass and v is velocity. Because velocity is squared, slowing down from 100 mph takes four times as much energy as slowing down from 50 mph.
All of this energy must be turned into heat instantly. If brake components get too hot, three bad things happen (known as "brake fade"):
The coefficient of friction (\mu) drops significantly (pad fade).
The brake fluid boils, introducing compressible air bubbles into the lines (fluid fade).
The metal rotors warp or crack.
Larger components combat this through Heat Capacity and Heat Dissipation.
A. Thermal Mass (Heat Capacity)
Think of the brake disc as a heat sink or a "thermal battery." It needs to absorb the initial intense burst of heat generated during a panic stop.
The relationship between heat absorbed (Q) and temperature rise (Delta T) is:
Q = m_disc * c * Delta T
Where:
Q = Heat energy absorbed (equal to the KE lost by the car).
m_disc = The mass (weight) of the brake disc.
c = Specific heat capacity of the disc material (usually cast iron or carbon ceramic).
Delta T = The change in temperature of the disc.
If we rearrange to solve for temperature rise:
Delta T = Q / (m_disc * c)
How Larger Components Help:
A larger diameter disc is physically heavier; it has more mass (m_disc). According to the formula, if you increase the mass in the denominator, the temperature rise (Delta T) becomes smaller for the same amount of braking energy (Q).
Conclusion 2: Larger, heavier discs act as larger heat reservoirs, keeping peak temperatures lower during a single hard stop.
B. Heat Dissipation (Surface Area)
Once the heat is absorbed into the disc, it must be shed into the surrounding air to prepare for the next stop. The rate at which a surface cools is roughly proportional to its surface area exposed to the air.
The formula for convective heat transfer (Newton's Law of Cooling) is complex, but simplified it is proportional to:
Heat Transfer Rate proportionalTo A_surface * (T_disc - T_air)
Where A_surface is the surface area of the disc and pads.
How Larger Components Help:
Larger Discs: Have more surface area exposed to the air, allowing them to radiate and convect heat away faster.
Larger Pads: Have a larger backing plate surface area to transfer heat into the caliper and surrounding air.
Conclusion 3: Larger surface areas allow the braking system to cool down faster between stops, preventing heat buildup over multiple braking events (e.g., driving down a mountain or racing on a track).
Part 3: The "Larger Pad" Misconception
It is a very common misconception that larger brake pads create more friction simply because they are bigger. This is false based on standard friction models.
As shown in Part 1, the friction formula is F_friction = mu * F_clamp.
Notice that surface area (A) is not in this formula.
If you apply 1000 lbs of clamping force to a small pad, you get the same friction force as applying 1000 lbs to a giant pad.
So, why use larger pads?
Larger pads are necessary to support the increased capabilities of a larger disc system for two reasons relating to pressure and wear:
Pressure (P) is Force (F) divided by Area (A):
P = F_clamp / A_pad
Lower Operating Pressure: By spreading the clamping force over a larger area, the pressure per square inch on the pad material is reduced. Lower pressure means less mechanical stress on the pad material.
Thermal Distribution: A larger pad spreads the intense heat generation over a wider area of the disc surface, preventing localized "hot spots" that can lead to disc warping and uneven friction material deposits.
Longevity: A larger pad simply has more physical material available to wear down, meaning it lasts longer under heavy use.
