Knowing the actual rate of each spring is crucial. Whenever a manufacturer sets up to run several hundred springs of one particular rate, the end result is less than perfect. Even though the winding process using CNC automated equipment is consistent, the variances in the quality of spring wire is not as consistent. As a result, not every spring will come out exactly to specification. No one, including Landrum, can guarantee every spring to rate out exactly. Knowing this, Landrum Spring has elected to rate, dyno, print numerical as well as graphical data, and engrave each spring’s serial number and rate. Furthermore, Landrum Spring is recognized as the only company in the racing industry worldwide to do so.
However, some manufacturers feel and state that racers should monitor a spring’s free height instead of its rate. Landrum Performance Springs, as well as many top-level teams, have found this to be counterproductive when setting up a car and compiling consistent results. While it is important to monitor free height for spring set, it is more crucial to know the actual rate in its working range. For example, while testing at Charlotte, a car had a 375 lb. tagged spring in the rear, the driver felt that the car was loose on corner entry and the tire temperatures supported this. After stiffing the spring to a 400 lb. tagged spring the driver did not feel any changes. The tire temperatures still supported this. After the supposed spring change, the team then began to change shocks, sway-bars, and pan-hard bar heights. At the end of the day, the springs were rated. After viewing the data sheets, we found that the 375 lb. tagged spring was actually a 387 lb., and the 400 lb. tagged spring was a 385 lb. So, the actual change in spring rate was not an increase of 25 lb. as was intended but a decrease of 2 lb. This is why the driver felt no change and the tire temps showed no change. Furthermore, the crew made unnecessary changes, wasted valuable time, resulting in wear and tear on the engine, tires and other components.
The reasons are easy. For example, say the spring industry standard is 5%. Then a 2,000 lb. spring could be anywhere between 1,900 to 2,100 lb. Here is a typical situation found at any given track. Let’s say that a chassis engineer wanted to increase the right front spring rate by only 200 lb. The current spring is tagged 2,000 lb., however, the unknown actual rate is 1,900 lbs. If the new spring is tagged 2,200 lb. on the other hand, the unknown rate is 2,310 lbs. The actual total spring change instead of 200 lbs. is 410 lbs., over 100% more or twice the spring change desired.
CORRECT MARKING: Having a spring with the correct markings is crucial. Most companies incorporate a metal tag denoting the “theoretical rate” of each spring. These theoretical rates are just that, “Theoretical”. Knowing that every spring has its own characteristics, Landrum Spring, engraves the exact rate of each and every coil spring to one-tenth of a lb.
