FORK SPRING PRELOAD
LONG SOFT TOP-OUT SPRINGS - RELAXED PRELOAD 

INTERNAL TOP-OUT SPRING

OPEN CARTRIDGE

If you have been directed here from the Product Search these should be the correct instructions. If not please call.

These instructions use a Right-Side-Up fork. It is the same for Upside-down.

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 Long Soft Top-Out Springs

BEFORE YOU BEGIN you must confirm that you have Long Soft Top-Out Springs

Remove the cap and spring and pull on the rod. It should feel very springy. If the rod extends more than 5mm these are the correct instructions. 

Long Soft Top-Out Pull Test

 

Tool Required - Street Bikes Only

One of the following Spring Compressors is required:

  Fork Spring Compressor - Portable TFSC 01 – Add to cart

  Fork Spring Compressor - Wall Mount TFSC 02 – Add to cart

  Radial Pin Spanner - TFPS R5701 - Add to cart

 
 FORK PRELOAD
Conventional Stiff Top-Out Springs
  

 

This section is for explaination only - not for Long Soft Top-Out Springs
 
 

 

Back-in-the-day when Top-Out Springs were pretty stiff life was easy. Measuring preload was simple. All you did was measure the Free Length of the spring and subtract the Set Length to calculate Preload.

  • Preload - the length the spring is compressed from its Free Length when it is installed (with the suspension fully extended.)
  • Free Length - uninstalled relaxed length
  • Set Length - installed length

Preload = Free Length - Set Length
 
 
 FORK PRELOAD - Relaxed
Long Soft Top-Out Springs

Life is harder now (tell mom and dad). Towards the end of the 1900s some street bikes started using Long Soft Top-Out Springs.

The Problem: A Long Soft Top-Out Spring Fork actually grows when the main Fork Spring is installed.

OOPS! This means that the Actual Preload is less than calculated with the previous method because the Set Length grows.

In the old days the Top-out Spring was so stiff the fork barely grew when the main spring was installed so we didn't have to account for this.

What to do, what to do?

Let's define some new terms:

  • Relaxed Set Length - the measured installed length without the spring installed
  • Relaxed Preload - the calculated Preload using the Relaxed Set Length

Using a similar method as with Stiff Top-Outs...

Relaxed Preload = Free Length - Relaxed Set Length
To set the proper Preload we need to adjust the Spring Spacer length. The amount the Set Length grows depends on the stiffness of the Top-Out Spring as well as the desired main Fork Spring Rate and Actual Preload.

Don't worry read on...
The difference between Long Soft Top-Out Springs and Conventional Stiff ones can be as much as 40mm. 
  • Actual Installed Set Length - the length of the spring installed 
  • Actual Preload - the amount the spring compresses from its Free Length when installed

Actual Preload = Free Length - Actual Installed Set Length

  (Note - With a Stiff Top-Out Spring the Actual Installed Set Length is pretty much the same as the Relaxed Set Length)

 

Actual and Relaxed Preload Recommendations

In most cases both Actual and Relaxed Preload recommendations are available on the Product Search and DVS Setup Sheet.
 
 
 
METHOD 1
This method can be used when the cartridge is out of the fork.

You will use both the Relaxed Preload and the Actual Preload from the Product Search.
 
1- Install the spring spacer hardware and the cap fully onto the rod.

2- Extend the cartridge. Do your best to extend the cartridge to the point where the Top-Out Spring just comes in contact.

Measure from the top of the Cartridge to the bottom of the Spring Washer. This is the Relaxed Set Length.

3- Measure the Spring. This is the Free Length
 

Free Length minus Relaxed Set Length is the Relaxed Preload.

4- Set the Preload using the Relaxed Preload recommendation from the Product Search or your DVS Setup Sheet.
 
Adjust the preload by adding or subtracting washers or adjusting the Preload Spacer Length.
 
NOTE: RT Springs are often a different length than stock. This is how they are designed. You will have to make your own custom spacers.
 
The spring should always rest on a steel or plastic washer. It should NEVER rest on the aluminum fork cap. Be sure to take washer thickness into consideration.
 
On many Open-chamber forks washers are added at the bottom of the spring.
 
The Preload Washers must be retained so they cannot shift off center. If it shifts off-center on an Upside-down fork it will damage the fork tube.
 
5- Double check the Actual Preload.

6- Tighten the jam nut to the fork cap on the damping rod. Install the fork cap. Set the adjusters.
METHOD 2
This method measures Actual Preload. It is perfect for final checking the Preload. It is a little hard to use while sizing the Spacer as the amount the Actual Set Length grows changes with Actual Preload.
 
1-  Back out any damping and preload adjusters on the fork cap all the way.

2- Remove the fork cap and spring.

3- Insert the new spring and bottom the fork tube fully.
 
Measure from the top of the Fork Tube to the top of the Spring. This is the Free Length Reference
 
4- Install the cap fully onto the rod.

Measure from the top of the Fork Tube to the top of the Spring. This is the Set Length Reference.

The difference between the two measurements is the Preload.
 

Free Length minus Set Length is the Preload.

5- Set the Preload as the previous method.
 
NOTE: RT Springs are often a different length than stock. This is how they are designed. You will have to make your own custom spacers.
 

In some cases we recommend replacing the stock Long Soft Top-Out Springs with our Reactive Spring Series. They are not as stiff as the old days but are not nearly as soft as some. The proper top-out spring can drastically affect traction particularly when leaned over in the turns.
CALCULATE RELAXED PRELOAD
Feel free to download our â–ºRelaxed Preload Worksheet