Titanium Springs are the new performance standard in racing applications from downhill mountain bikes to Formula 1 racing. Here's why:
Titanium vs. Steel
|Renton Spring Grade Titanium||Chrome Silicon Spring|
Titanium possesses material properties that are superior to steel for making springs. For more material information, click here.
Okay, so titanium can produce a lighter spring with more travel. These are both desirable characteristics for performance springs, but there are still some questions to answer.
What is a spring rate?
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.
Do Titanium springs ride differently?
Yes. A titanium spring is more responsive then a steel spring and helps the suspension keep the tires on the ground for better traction and handling. Titanium springs have less mass and thus less inertia. As springs are rapidly compressed the material mass is displaced and generates momentum or inertia based on the product of the velocity and mass involved. In demanding applications this can cause spring surge where the spring coils are moving in the opposite direction of the shock travel. This can disrupt the performance of the suspension system and lower the ability of the suspension to follow the terrain and keep the wheel on the ground. The less mass in the spring, the better performing the suspension will be.
Lower mass systems generate less inertia and accelerate faster allowing better "responsiveness". This allows the suspension to keep the wheel in contact with the ground more resulting in better traction and handling. For more on suspension systems see Ti vs. Steel
What about spring memory?
Many people refer to spring "memory", in fact the proper terminology is "resistance to set." When springs are said to lose their memory or "sack out" the spring has taken a permanent set.
Deflecting a spring results in stresses within the material. The amount of stress is proportional to the deflection imposed. As long as the imposed stress is lower than the yield strength of the material the spring will fully recover its initial length when the load is removed. If the stresses imposed exceed the yield strength of the material the spring will "take set" and will not fully recover its original free length when the load is removed.
It is important to understand that the spring rate is never affected by use. Even when springs take set their rate does not change. To compensate for set, the spring perches must be adjusted or spacers added to replace this lost length. Additionally the available travel of the spring is reduced by any set that it takes.
Properly designed titanium springs utilize the superior material properties to minimize or eliminate set entirely.
What about fatigue life?
The life of the spring to failure, discounting set, is affected by the magnitude and number of deflections that the spring is subjected to in relation to the material properties of tensile strength, ductility and toughness. Remember that steel springs for performance applications are designed "at the limit" to keep weight and size down. With titanium, replacements can be designed where the stresses are "backed-off" just slightly so that typically we can design for twice the life of the steel spring we are replacing. Experience is required of the spring designer to know what levels of stress can be sustained for each type of material used in springs.
What about cost?
Titanium alloy suitable for spring manufacture is approximately 40 times more expensive than spring making steel alloys. Since the titanium spring is typically 60% as heavy as steel we can assume the material required costs about 25 times as much. At first glance this would appear prohibitive. In practice the retail price of the spring is rarely this high, though it is often 4 to 5 times as much. It is important to look at the actual cost of the weight savings and improved performance.
Ti valve springs for pro stock drag racing: Titanium springs are run 5-8 times as many times down the track. A set of steel springs cost $400 and a titanium set costs $1750. The per-use cost of Steel is $400. The per use cost of titanium is $1750/5 = $350. In addition time and labor is saved as the springs do not need to be changed in between each race. Titanium springs deliver higher performance (stable at higher RPM) for slightly less cost.
Titanium Motocross springs cost about $500 where the stock springs retail for $80. The average weight savings is 1.7 lbs, and the titanium spring will maintain optimal loads twice as long. Combining the added life and weight savings you spend about $240 for each pound saved and also enjoy improved performance. Compared to other costs for weight savings this is a bargain.
Titanium springs are the new standard of performance. Utilizing the best material available and computer design optimization. RCS Titanium springs are the best springs you can buy.