Product Review: Merge's Rising Rate Springs - Part 1

Merge Racing Technologies first made ripples in the racing community with its release of their adjustable leak jet. While the product hasn't revolutionized motorcycles, it has greatly improved in an area lacking with the modern surge in four stroke motorcycle sales. The dreaded “bog”. The ripples slowly built into waves, as many of the top 20 riders in the country started using the product and having great success with it during the 2008 Supercross and now Motocross season.

But a company can't exist merely on one product, and that brings us today.
The one mythical area on most rider's bikes has always been its suspension. Most riders never even venture into touching their suspension, let alone adjusting its internals or oil levels. Instead, they rely on various companies to rebuild, perform seal replacements, and ultimately re-valve their stock components to obtain their desired ride.

Merge Racing Technologies' offers a truly unique product in their Rising Rate Springs, or RRS for short.

[Ed Note: This is a very simplified technical explanation - techies: take it easy!]. The modern forks on race bikes are a “twin chamber” design, with an internal damping system that resembles a typical rear shock in design. While there are some differences your fork's design vs. your shock, one major difference is the lack of a nitrogen reservoir. Instead, to make up for the lack of a nitrogen reservoir, modern twin chamber forks use a spring. This spring is commonly referred to the ICS spring.

Why do ICS springs and Nitrogen

reservoirs exist?

When the shock shaft enters the shock body, it displaces a volume of fluid equal to its own volume. This fluid has to go somewhere, and thus a pressurized chamber is provided. The fluid is allowed to enter a chamber as the shaft compresses, but as the shaft rebounds the fluid returns.

The nitrogen and ICS springs maintain a positive pressure on the fluid at all times to prevent tiny air bubbles from forming in the oil while also providing an additional spring action. The farther the shaft enters the stiffer it gets. The nitrogen reservoir and ICS spring are purely position sensitive.

Many people feel that the ICS springs act only in combination with your main fork spring and the air spring adjusted by your oil height.

However, depending on velocity conditions, the ICS springs also effect what part of the valving gets used: if the fluid velocities are high enough, it can't find its way through the low speed part of your valving fast enough. It then transitions to the "mid valve" or rebound side of your piston.

To quote Hooligan, one of the partners at Merge, from thumpertalk.com,

"Here is a quick explanation on how they work - When you run a really light pressure spring the piston below it moves easily and the inwards (compression) damping force is controlled by the oil going through the upper piston holes, the shim stack that covers these holes and bypass holes in the piston (not covered by shims and inc the compression adjuster). The stiffer the pressure spring the more resistance on the floating piston, this in turn forces the oil through the shims on the bottom of the rebound piston (attached to the damper rod AKA “Mid Speed Valve”). You need to enough mid speed to slow the fork down over big hits so it doesn’t bottom but, too much mid speed is one of the most common causes of harshness."

Yeah, what he said.

Since their inception, tuners have been exchanging these ICS springs in favor for ones with lighter spring rates claiming much better small bump compliance and better overall performance. However, they are a compromise. By allowing better small bump compliance, bottoming resistance is lessened to some extent, and the risk of cavitation (tiny air bubbles in the oil) increases. While a good tuner can circumvent the bottoming issue and possible poor high speed damping performance by using other elements of the fork's systems, merely swapping your current ICS springs for lighter ones may not be the end all be all answer, and the risk of worse performance lingers.

Instead of merely offering a lighter spring, Merge Racing has brought a new concept to the table with their progressive ICS spring. According to Merge, this is the “linkage for your forks”, and by using a little engineering, the springs are wound and tapered in such a manner that they have a progressive spring rate.

What's a progressive spring rate?

Most springs are categorized in a manner such as kg/mm, or something similar in different units of measure.

For example, a spring with a 1kg/mm rate means as follows.

To compress the spring 1mm, and it requires

1kg of force, to compress it 2 mm it requires 2kg of force, and for 3mm it requires 3kg of force.

But the RRS spring is different.

To compress it 1mm and it may require .5 kg, but to compress is 2 mm it may then require 2kg of force, and then on 3mm and it may require 3.6kg and so on.

As you can see, the progressive spring is not linear, as opposed to normal springs.

Installation

Installation seemed difficult to say the least. Not only would it require removal of the fork inner parts, but it required removal of the important fork internals. At this point, the intimidation factor was at a 10. But after referring to supplied instructions, and taking a leap of faith, installation was actually a cinch.

Watch the video to see it Installed...kinda

Installation difficulty (1-10): 5

Its smack dab in the middle between: Installing an exhaust and changing a tire.
Make sure you use the correct tools.

Stay tuned on EternaltwoStroke.com for part two and find these, and many more, answers out:

Does it work?

Is it worth the money?

Can its design be improved?

A Linkage you say....

What adjustments must one make to best optimize its installation?