The most common car parts replaced in the name of performance are exhaust, suspension and wheels. All three of these parts can also make a car turn quicker, grip harder and accelerate faster. While each of the three components fulfills its own task, a common benefit shared between all three is generally reduced weight when compared to the factory counterpart. The lighter the vehicle, the less power it takes to accelerate, braking can be performed in less distance, and the car should pull more G’s through a corner.
Now what if I told you that replacing brake rotors could have a similar impact on performance?
Before we talk about lightweight brake rotors it’s important to understand that replacing safety equipment all willy-nilly is not something to take lightly. In fact, I don’t suggest it at all. Lightweight components may compromise integrity and may not be able to handle as much abuse as the factory parts. Weight reduction in any capacity generally means sacrificing something. In a street car that something is typically measurable by noise, vibration, or harshness. And if it doesn’t affect those, it is probably very expensive.
We strapped the car down and did a pull with the stock rotors: 327 HP / 313 TQ. Then, actually jacked the car up ON THE DYNO and changed the rotors and ended up at 339 HP / 319 TQ.
Enter lightweight brake rotors. Any company can manufacturer brake rotor that weighs less than stock. It’s rather simple. Non-performance brake rotors are usually cast in a single piece. Aftermarket manufacturers may choose to use metal alloys of less mass, save material by designing rotors to be thinner in critical areas, use different shaped cooling veins, or even add “performance” features such as slots and cross drilled patterns.
But wait! Real race cars use slotted and cross drilled rotors! Yeah, sure some do, but those rotors you speak of are likely carbon ceramic and properly designed to take the abuse. Plus a pair of carbon ceramic for a street car will easily cost you five figures. Realistically, this isn’t an option you’re going to pursue while at the local repair shop.
Lightweight Rotor Design
A more performance oriented method of reducing weight in brake applications is by utilizing a 2-piece design. In a 2-piece rotor, the center of the rotor, called the ‘hat’, is bolted to the ‘ring’, the surface which contacts the brake pads. The sole job of the hat is simply to keep the ring in place, so this piece can be as light as possible so long as it keeps the hat aligned and in position. The hats in a 2-piece brake rotor are typically made of aluminum and that alone can save multiple pounds over a single piece cast brake rotor. Additionally, 2-piece rotors may be connected via pins that allows the ring to float freely and places less stress on the hat during heat expansion and contraction from cooling. This helps minimize the chances of warping rotors in off-road and race conditions. Another benefit in race applications is that the rings can be replaced instead of tossing away the entire rotor.
The largest percentage of weight in a traditional rotor comes from the ring itself. A manufacturer can find the right alloy, the perfect combination of slots or cross drilled sections and internal veining but there’s only so much weight that can realistically be shed. If you want to save the most weight in a the actual rotor, you’ve got to look at carbon ceramic options. Carbon ceramic brake rotors weigh roughly half of a traditional rotor and more or less kick-ass when it comes to motorsport due to their heat resistance and better friction properties. Carbon ceramic rotors are also advertised to last four times longer than standard cast iron rotors. So why doesn’t everyone run out to buy a set of carbon ceramic rotors? Currently, it’s the price. A set of carbon ceramic rotors, if they’re even available for your car, may run several thousand dollars for just a pair compared to a hundred dollars for a set of cast rotors.
Real World Performance
Now let’s talk horsepower. Simply changing your brake rotors will not magically increase your engine’s power output. But it will free up power that was once lost in transfer to the ground. If you’ve ever replaced a 25 lb cast wheel with a 18 lb forged wheel you’ll know just how much of a difference unsprung weight can make. The same goes for brake rotors. Reducing rotational mass can yield great improvements in braking, turning and overall driving feel. How much horsepower? A small percentage likely comparable to under drive pulleys. Want hard numbers? Well, STM Tuned dyno’d a Mitsubishi Evolution before and after installing a set of lightweight rotors. Emery at STM Tuned claimed the Evolution pulled 327 HP and 313 TQ and then jacked the car up while still on the dyno, replaced the rotors with Baer 2-piece rotors, and performed another dyno pull to the tune of 339 HP and 319 TQ. That’s a gain of over 10 horsepower to the ground.
We were instantly curious to hear the weight difference between the two sets. We know you are too so here ya go:
|Rotor Type||Weight (lbs)|
|Baer Front 2-Piece Rotor||15.8 lb|
|Stock Front Cast Rotor||17.75 lb|
|Baer Rear 2-Piece Rotor||11.75 lb|
|Stock Rear Cast Rotor||14.45 lb|
What we see is this particular 2-piece rotor saved roughly two pounds of rotational mass on each side up front and about three pounds per side on the rear for a total of ten pounds. Ten pounds doesn’t sound like a good deal when factoring in the cost. Depending on the vehicle, a complete set of lightweight rotors may easily cost several thousand dollars. But consider the fact that a set of forged wheels could easily double that price and may just equal the weight savings.
For a weight-weeny, I’d be all in for a set of lightweight rotors. Would love to see a back-to-back dyno comparison when swapping to carbon ceramic rotors.