How do I avoid springs which exhibit rate overlap?

'Rate Overlap' occurs when the manufacturer’s manufacturing tolerance(s) is more than one half the rate change desired. For example, assume you are considering a rate change from 475 to 500 lbs., which is a change of 5.3%. Further assume that the spring manufacturer’s tolerance is plus or minus 3%, a tolerance level, which is very common among manufacturers today. It is possible, therefore, that the rate for your 475 lb. Spring could range from 460 lbs. (475 X 97%) on the low end to 489 lbs. (475 X 103%) on the high end. The rate for your 500 lbs. spring could range from 485 lbs. (500 X 97%) to 515 lbs. (500 X 103%). In the worst case, you could be going from a 460 lb. Spring rate to a 515 lb. Spring rate, a 12% variation (remember you were looking for a 5.3% change!) that would dramatically affect your car’s handling, and leave you scratching your head, wondering what to do next!
 
At Hyperco, we have invested in material and manufacturing technologies to ensure that our spring rates are accurate and consistent. While we guarantee plus or minus 2 percent tolerances, in actual experience, Hypercoils generally run within 1 percent tolerances, and we do not offer rates that overlap. Consistent rates and manufac-turing tolerances allow our customers to develop “set ups” that repeat race to race, year to year, and coil to coil. This is one of the reasons the many of the top teams in all forms of motor racing use Hypercoils.