The Titanium Advantage
Titanium possesses material properties that are superior to steel for making springs. As the table below shows: Titanium is approximately twice as "springy" (lower modulus); weighs 40% less than steel per volume; and has 75% of the strength of steel.
| Renton Spring Grade Titanium | Chrome Silicon Spring | |
|---|---|---|
| Tensile Strength | 200,000 psi (1.27 GPa) | 250,000 psi (1.72 GPa) |
| Density | .174 lbs/in³ (4.82 g/mm³) | .285 lbs/in³ (7.90 g/mm³) |
| Elastic Modulus | 5,350,000 psi (36.9 GPa) | 11,500,000 psi (79.3 GPa) |
These properties combine to allow a spring designer to utilize a larger wire diameter and many fewer coils to provide a spring rate that is equivalent to the steel spring being replaced. The resulting Titanium spring is both significantly lighter (typically by 40%) and will provide more travel due to having fewer coils. This gives the titanium springs the characteristic "open spaced coil" look. Additionally titanium is essentially impervious to corrosion so the springs need not be coated.
Spring Rate is defined as the amount of force required to deflect a spring a certain distance. It is typically expressed in lbs/inch. Thus a spring rate of 320 lbs/inch describes a spring that will deflect one inch when 320 lbs of force is applied. Other common units are N/mm and Kg/mm. N(ewton) being the proper metric representation of force and Kg the common but technically incorrect metric units. Rates are converted as 1Kg/mm = 56 lb/in. and 1Kg/mm = 9.86 N/mm.
Case Study: Motocross Rear Suspension Springs
In the picture above is a tianium spring (left) which is a direct replacement for the steel spring on the right. Both springs have a spring rate of 5.4 Kg/mm.
Comparison Data
| Titanium Spring | Steel Spring | Difference | |
|---|---|---|---|
| Weight | 2.33 lbs. (w/spacer) | 4.27 lbs. | 45% less weight |
| Free Length | 10.0 in. | 10.0 in. | |
| Travel | 6.4 in. | 5.2 in. | 1.2 in more travel |
| Natural Frequency* | 127 Hz. | 88 Hz. | 44% Higher |
The result is a 1.94 lb. weight savings. The lower weight improves suspension dynamics and response.
Aftermarket steel springs typically retail for $80. The titanium springs retail for about $500. This is $216 per pound of weight saved. Compare this cost with other methods of saving weight. Combined with the improved performance, titanium springs are a must have for the performance minded enthusiast.