Brake tech is a very complex and nuanced topic, so we asked the experts at Alcon Brakes to help us clarify and expand on some frequently asked questions in the braking universe. Today, they’re discussing the pros and cons of aluminum vs. iron brake calipers.
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Regardless of the design, both opposed-piston (OPC) and single sided (AKA floating or sliding) brake calipers are available in either aluminum or cast iron.
So what’s the difference? Which one is better? And what applications will you find each one?
The Origin of Iron & Aluminum Calipers
For starters, most brake calipers you’ll find on cars and trucks nowadays are machined from cast iron. At first, opposed-piston brake calipers were made from grey iron, but many modern single sided and OPCs are now made from stronger SG iron.
Aluminum calipers showed up a litter later, primarily to shed weight, and are now quite common as well.
Weight vs. Strength
In short, aluminum is lighter, but iron is stronger.
For lightweight vehicles, an aluminum brake caliper housing will generally be strong and stiff enough for the application without too much deflection—which is a fancy word used to describe how much force a structural element can take before deforming.
But the heavier the vehicle, the higher the brake torque will be.
That means the extra loading seen by the caliper housing through the large piston area and high torque will cause higher levels or deflection. As a result, the brake system will require more fluid capacity and can cause fatigue issues.
For an aluminum caliper, more material is required to compensate and, eventually, you’ll get to a point where it all becomes difficult to package—in other words, the brake caliper gets too big to fit inside the wheel.
On the other hand, with iron, you can create a much stiffer caliper in a smaller package, which makes an iron caliper a good choice for higher brake torque applications like you’d see on a heavier vehicle.
Better still, the iron caliper may even enable you to reduce the axle weight and un-sprung mass, because a more compact caliper design lets you run smaller, lighter wheels on your car or truck.
With opposed-piston calipers, a monobloc (single piece) caliper will be lighter, but a two-piece caliper will be stiffer through the use of high tensile bolts across the bridge section.
Again, with lightweight applications, the effect of this will be lower.
The Effects of Corrosion
Although iron calipers can look rusty through a wheel, the working parts inside remain functional for longer. Truth is, aluminum will corrode more quickly.
That usually means that iron calipers have a better chance of being rebuilt, as remanufacturers often discover that aluminum calipers are usually too corroded to recondition.
Cost & Aesthetics
Generally speaking, iron is less expensive than aluminum.
…But a large painted aluminum opposed-piston caliper sure does look pretty when it’s peeking out behind a custom wheel. Then again, so can a painted iron OPC.
It might just boil down to the type of look you want for your vehicle.
So, What’s Better—Aluminum or Iron?
As a simple summary, for lightweight performance applications, aluminum is preferable in order to reduce overall weight and un-sprung mass.
But for heavier vehicles, iron will be much stiffer and easier to package. In some cases it may even give an overall weight reduction when compared to aluminum too. All told, if the vehicle is going to be used as a serious off-road vehicle, the brake experts at Alcon usually would recommend iron over aluminum.
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