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Shop floor science: I cut my Corvair’s coil springs, should you?
Lowering the ride height of a classic car is an always-popular modification, particularly because of how much it changes visual character, stance, and ride/handling behavior. Of course, there are right and wrong ways to go about the procedure. When it comes to cutting coil springs, opinions vary considerably. Some swear it’s totally fine, while others promise that cutting springs ends with you crashing into a bus full of nuns. Let’s look at this common suspension modification scientifically, and hopefully we can suss out whether it’s the right call for your vintage ride.
With a slice of the angle grinder, cutting coil springs accomplishes two things: it lowers the vehicle and stiffens up the ride. How? It comes down to spring rate, measured by the amount of force required to compress the spring one inch. The gauge (diameter) and length of the wire used to construct the spring determine the rate. Comparing two springs with the same gauge wire, one with a longer length will have a lower spring rate, meaning it will compress more with the same amount of weight placed on it.
That means by shortening the spring, the spring rate goes up, and there’s less compression with the same weight. Put simply, by removing part of the spring to make it shorter, you’re also making it stiffer.
Engineers tune production cars for the broad car buying public, which means balancing ride quality with handling capability. It should come as no surprise then that most cars from the factory have a softer spring rate than us performance enthusiasts would like—because we have a higher tolerance for a stiff ride in exchange for better handling.
Case in point: my 1965 Chevrolet Corvair. It came from the factory with the ride quality of a well-balanced economy car. With minimal tuning, the Corvair can take on the character of a road-hugging sports car. After all, Don Yenko played with Corvairs before Camaros.
The front end of a Corvair is delightfully unburdened from the weight of an engine, because the flat-six is rear-mounted as in a Porsche 911 or Volkswagen Beetle. The result is a sizable frunk (front trunk), allowing Chevy to use tall springs for the front suspension to soften the ride. Load the frunk with luggage, and there’s still enough ground clearance for practical use.
To infuse some sportiness, many Corvair owners swap the standard suspension to the optional F41 Heavy Duty Suspension springs, which have a higher spring rate. They still give the car’s nose a relatively high stance, though, and could stand to be stiffer if sharp handling is the desired goal. As a result many owners choose to cut one coil off each of the front springs in an effort to reduce the ride height and improve handling.
Of course, one could order custom coil springs that have both the correct spring height and a desired spring rate. But that solution is typically pricey—the less popular Corvair isn’t catered to by big aftermarket companies who sell standard Mustang or Camaro parts for cheap. This means Corvair owners are often thrifty, and the cheap path is the one most often traveled.
So what are the downsides? For one, cutting suspension coils can be dicey. It’s possible to clip too much out of the spring, creating a situation where the spring compresses as the car travels over a bump in the road, but the spring is too short to stay seated properly. A spring not seated properly can jam the suspension or fall out completely, causing the driver to lose control of the vehicle. Not to mention that brake lines and suspension pivots were engineered to operate within a certain window of suspension travel, and lowering a car by cutting springs can put undue stress on these components and potentially damage them.
Plus, not every coil can be cut and still function properly. Coil springs come in several shapes— tangential, square, and pigtail. They can be identified by appearance; in tangential-style springs the last coil just ends, with no shape formed. A tangential spring won’t stand on its own either, as the end is too uneven for the spring to stand straight. Square styles have an end coil that touches the second coil, creating a smooth seat for the spring to sit on. Pigtail coils have a beehive-type shape that fits a specific spring perch. Given that pigtail and square springs have a specific shape to them, they can’t safely be modified by simply cutting them—the end shape needs to be replicated on the shortened spring in order for it to seat properly. Home mechanics cannot do that.
Is cutting coils the right move for your car? It was for me, and it might be for you. My Corvair had tangential springs front and rear, which allowed me to carefully trim half a coil off before reinstalling them. Now the ride height of my Corvair is right where I’d like it to be, and the suspension is sporty stiff. I do, however, still need to take the car to the alignment shop to ensure that the steering geometry is correct and won’t wear through tires at a rapid rate.
As with any project that involves working on a car, be sure you take into account the full scope of the modifications you’re performing, and don’t do anything you don’t feel comfortable with or that you can’t undo if it goes south. Performance at the cost of safety is a bad idea.