European car once heard a tale of an importer of extremely low-priced springs. To get a new application, it used a front spring from another vehicle from the same manufacturer and the rear spring from yet another. The springs fit in the seats and lowered the car about the amount the company's head salesman thought looked right, so it started selling the combination as a kit. That's frightening.
Striving always to be the best, earning TV approval for all one's products and ISO certification of one's entire business, requires a lot more work. The process of developing any H&R suspension system begins in the marketing department, with a proposed list of applications. After analyzing the business plan for each, prioritizing decisions are made. The engineers then take over.
Designing A System
When a car arrives at H&R for development, it is measured as an assembly, and its suspension parts are taken apart and measured. Spring curves are plotted, overload travel reserve is quantified and the dampers are dynoed, their forces plotted.
The W201-chassis Mercedes-Benz 190 had great lowering potential with its wheel and tire cl
Then the engineers consider the customer's requirements: How much lowering will he want? What will he desire in the balance between comfort and performance? There are distinctions between a Mercedes, a BMW and other, more sporty cars.
Joachim Frettlh, H&R's Manager of Spring Development and Motorsports, relayed that H&R never tunes the handling of street cars as precisely as a race car. A race car will often have spring rates five times greater, and all the rubber will be gone. The driver can then instantly feel all the details of the road and the car's movements. The driver is experienced and very demanding. A race car setup is much like a custom shoe in that respect.
In a street car, there is a wide range of design because the car is "never close to the edge." A normal street driver won't even feel a 10% change in spring rate. With H&R's suspension systems, it aims to make a 25-year-old as happy as a 50-year-old and a 1.6L engine work as well as a 3.0L. Often, on a refined chassis, there will be two spring sets for cars with very different engines, but it simply doesn't make sense to tune a street car as finely as a particular race car.
One might think this makes the job easy, but it presents its own, quite difficult challenges for an engineer. Rather than reducing the requirement to a lap time, spring design becomes a "soft science," requiring the engineer to rely on his experience, intuition, understanding of "normal" people, enthusiasts or not, and their desires and expectations. How is a Mercedes driver different from a BMW driver? How is a Golf GTI driver different from an Acura RSX Type-S driver? What makes one ecstatic may leave the other indifferent, or perhaps with buyer's remorse.
Once the desired characteristics are determined, the engineers design a spring that will fit in the spring seats, have the correct rate, loaded height, travel and progressivity. It must work with the intended damper, whether stock or performance-engineered. It must not have coil bind, where the spring runs into itself before the suspension runs into the bumpstop, and the metal must not be overstressed, which would cause the metal to yield and the spring to sag. The factory then builds a prototype set of springs, which are installed in a car and road tested.