Why Is Double-Wishbone Suspension the Best?

There are a lot of accepted truths in the automotive world. One is that where performance is concerned, double-wishbone suspension is superior. Most race cars use double wishbones and a lot of the best road cars do too. Yet, if you were to draw up a list of the best-handling cars of all time, you'd find that many use MacPherson struts. All 911s but the newest GT3 and GT3 RS; every Boxster and Cayman; all BMW M3s; the new Honda Civic Type R; Cadillac's Blackwing siblings; the Toyota GR86/Subaru BRZ; the list goes on.

It was our recent comparison test between the Mazda Miata and the new GR86 that got me thinking about this. While a car is so much more than its spec sheet, I do like taking a good look at the mechanical makeup of a car to try and explain why it feels the way it does. In my mind, the double wishbones at the front of the Miata make it a more "pure" sports car than the GR86, with its MacPherson strut front (a consequence of its distant mass-market-car roots). Yet, the GR86 has excellent handling and proved to be a very worthy adversary to the Miata. Some digging was required.

To understand why a double-wishbone setup is held up as some kind of platonic ideal, let's start with the basics of independent suspension. Terry Satchell, a former engineer for both Penske racing and GM, defines it well in Race Car Vehicle Dynamics, one of the best books on the subject. "For an independent suspension, be it front or rear, the assemblage of control arms is intended to control the wheel motion relative to the car body in a single prescribed path," he wrote. The job of an independent suspension is to control—or as Satchell puts it, "severely" limit—five directions of tire motion: Bump/jounce, rebound/droop, lateral, longitudinal, and camber. To control each, you need a link of some sort, and a suspension wishbone is essentially just two connected links. Two wishbones plus a tie rod is five links.

In the early days of independent suspension, auto engineers employed control arms of equal length, but soon discovered this led to excessive tire scrub across the road surface, as the track width changes as the body of the car rolls in cornering. Also in cornering, the outside tire gains camber and the inside tire loses camber….which is the exact opposite of what you want. All of this results in less grip, and using a longer lower arm and a shorter upper arm solves both of these problems. With this so-called short-long arm suspension an (SLA) suspension, the track width remains stable in cornering, while the outside tire gains negative camber and the inside tire either stays neutral—tread parallel to road surface—or gains some positive camber. This is why you often see race cars running a lot of negative camber. When the car rolls onto the outside tire, you get a wider contact patch, resulting in more grip.

The problem with a double wishbone layout is that while it’s a dream for a driver, it’s a nightmare for a major car company. There are so many parts to manufacture, and they take up a great deal of room. They are hard to package on any car that prioritizes cabin space, double hard on a compact car, triple hard on a compact car with front-wheel drive. A double-wishbone might be ideal, but it comes at a cost.

If I've learned anything in my near 10 years of writing about cars, it's that making cars is expensive. Automakers are always looking to save a bit of money wherever possible, and thus, a simple, cheaper solution is almost always preferable. Earle S. MacPherson's simple, cheap strut suspension—which used a spring-damper unit to locate the front wheels, doing away with the need for an upper arm—proved to be revolutionary. While working at GM in the Forties, he developed a version of what became the MacPherson strut for the Chevrolet Cadet, a small car that was canceled after a feared post-War recession never materialized. MacPherson took his talents to Ford in the Fifties, and soon, the automaker started using MacPherson struts on many of its European models. Getting rid of upper arms helps automakers cut costs, and brings packaging advantages. The use of a strut makes the suspension package taller than a double-wishbone setup, but much narrower above the lower arm.

By the Sixties, many European cars adopted MacPherson strut front suspension while American cars followed in the decades to come. (MacPherson struts don't really work for body-on-frame cars, so it wasn't until the Seventies, with gas crises forcing American automakers to build smaller, unibody cars that they began to ditch double-wishbone suspension.) For many automakers, the choice to go with MacPherson struts over double wishbones was obvious. It does the same basic job, for less money. Additionally in front-wheel drive cars, the space above the lower arm also makes packaging driveshafts much easier.