Article by Andrew Halonen
Back in January of 2016, I was curious if the fuel economy push was going to incentivize the growth of lightweight brake discs (see prior article). I received a fair amount of feedback; most stating that there is “low hanging fruit” in lightweighting, at far lower risk than radical changes to the brake disc. The insight that was most actionable for me was when one person stated, “if the auto companies have not changed the brake calipers to aluminum yet, they sure are not going to move to a novel lightweight brake disc.”
Taking action, we set out to investigate the brake caliper materials on light duty vehicles from small car to crossovers to pick ups and work vans. We combed dealerships, armed with a magnet, a camera, and a spacer as a gage to evaluate the gap between the caliper bridge and the inner wheel diameter. At the same time, we investigated the wheels, steering knuckles and control arms. In all, we studied 89 models across 16 brands, and we provide the evaluation across 6 vehicle segments.
As a lightweighting consultancy, we keep abreast of the industry, and we hear many engineers and managers say “every gram counts.” Certainly lightweighting is happening, however, if you get down on your knees and look underneath most of these vehicles, the push for lightweighting is what I will call “a mixed bag.” There is considerable opportunity for weight reduction in suspension and braking.
For brake calipers, the hurdles to reduce the weight are primarily cost, stiffness, and packaging. The modulus of aluminum is lower than in iron, and to compensate, the bridge section of the caliper needs to be made thicker. With most of the braking load taken by the front brakes, the brake discs may be larger than in the rear, making it more difficult to package a thicker aluminum caliper. Anticipating this thickness increase, we used a 9.5mm scratch-free spacer as a quick means to know if there was space for bridge thickness growth on an iron-to-aluminum conversion. Only 10 vehicles did not meet the criteria for fitting the spacer on the front axles, yet the far majority of the front brake calipers are iron on 2017 models. On the rear where there is a larger gap, there are more aluminum calipers, yet still less than 50%.
Is the reluctance to use lightweight aluminum calipers one of technical risk? On the rear, looking at competing SUV’s, pick-ups and sedans – some use iron, some use aluminum.
What is the cost delta of aluminum calipers? If the weight reduction opportunity on the front axle is 5 pounds, or 2,267 grams, what is the cost premium, and how does this compare to cost to reduce the weight elsewhere in the vehicle?
Photos taken by Mayflower Consulting LLC (Top Photo: Premium Aluminum Caliper)
About the Author:
Andrew Halonen is President of Mayflower Consulting, LLC, a lightweighting consultancy that provides strategic marketing and business development for high tech clients. Andrew works with castings, composites and new alloy development programs. The market study referred above is available at www.lightweighting.co/market-research.