The Titanium Advantage
Titanium Springs are the new performance standard in racing
applications from downhill mountain bikes to Formual 1 racing.
Here's why :
Titanium possesses material properties that are superior to
steel for making springs.
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.
Examples
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.
It started with one rider on one team, and in less than two
years grew into a national downhill championship and a world cup
downhill championship. Titanium springs have now become standard
equipment on several of the most advanced full suspension bicycles.
The suspension spring is one of the highest stressed components.
In an industry skilled at taking durability to the ragged edge
in the pursuit of light weight and improved performance, titanium
springs reduce weight, improve dynamic response, and give a level
of durability not found in most steel springs.
It's hard to beat the feel of "coil and oil" shocks.
They are also more bulletproof and reliable than air shocks. They
don't leak down, or blow seals as often. The drawback to coil
and oil technology is the weight. The strength required to support
the rider with the leverage ratios used in contemporary designs
dictate substantial springs. These springs get quite heavy, especially
as the travel increases in downhill or freeride style suspension
frames. Titanium springs can go a long way to reducing the weight.
Titanium springs are often 30 to 50% lighter than steel springs.
Additionally, they are designed within the material stress limits
to resist set. This means that once the suspension preload is
"dialed" it will stay that way, not sag, as overstressed
steel spring are prone to do. RCS titanium springs, are simply
a superior product utilizing high-grade materials and sophisticated
design techniques.
Titanium springs are the new standard of performance. Utilizing
the best material available and computer design optimization
