How to Install Motorcycle Fork Springs

DIY FORK SPRING INSTALL - WHAT YOU NEED TO KNOW 1, 2, 3.

#1 DO NOT INSTALL SPRINGS WITH TOO LARGE AN OD!

Spring Outside Diameters (OD) example sizes:

WP 48mm 43.5mm OD

KYB 48mm 44mm OD

SHOWA 49mm 45mm OD

If the springs are 1/2mm smaller OD no big deal.

#2 YOU MAY HAVE TO TRIM SPRING GUIDES!

Spring inside diameters:

Spring inside diameters will vary depending on the wire size. Stiffer spring rates need thicker wire and the ID will be smaller.

Many times heavier rate springs will not fit over your spring guides, or the spring guide in WP fork caps.

This is more often the case on adventure bikes that need a lot of spring rate, but some dirt bikes too.

Spring Guides

Spring Guide

We turn spring guides on the lathe so the springs fit over the plastic. DIY we see folks using a grinder or a file to get the job done.

Suspension101 long travel WP 890R spring guides shown above have a smaller ID to omit this step for most springs.

#3 DO NOT INSTALL TOO LONG OF SPRINGS!

Length of springs:

Seems simple but hold on.

The factory fork springs are often too long and it hurts performance. Not all of them but most.

It is because the factories have to make the bike work for 135lb to 265lb riders but this definitely makes the forks harsher and less plush for all of us.

Most of the aftermarket sells stock oem spring lengths. Yes, correct spring rate for your weight but still too long of a spring. So you're half way correct?

Example: WP Xplor dirt bike forks have oem 8mm of spring preload. Optimal is 3mm for most but you can’t shorten a spring!

The KTM 890, 990, 1090, 1190, 1290 have about 15 to 17mm of spring preload. Ouch.

Spring preload is a big issue and only the more advanced tuners address it.

Suspension101, to address this issue, makes shorter springs, shorter spring perches, or sometimes slice the oem spring perches to make them shorter. We absolutely address the issue on every bike we do.

FYI Adventure bikes with spring preload adjusters can use just 6mm of initial preload, with no adjusters we use 8 to 10mm of preload.

How to measure your preload:

Open Chamber forks: 1. Pull the cartridge out of your forks and set the cartridge on your bench.

2. Install the fork cap until it bottoms on the damper rod.

3. Extend the damper rod till it stops.

4. Measure from where the fork spring sits on both ends. The spring perch at the bottom and the inside of the fork cap where the spring sits.

   
   

This measurement is your spring cavity.

5. Now measure the spring. If the spring is too short you can cut a piece of PVC or Aluminum to get the wanted preload (even the factories use this method).

   
   
   
   

Closed Chamber forks:

1. Install the spring, then the cartridge and screw the cap into the upper fork tube. DO NOT put the bottom of fork rebound adjuster on yet.

2. Push the upper fork tube in until the cartridge meets the spring and measure how much lower chrome is showing and note it.

3. Compress the forks, install your rebound adjuster on the damper rod and screw it into the lug as it will be when you fully assemble the fork.

4. Then measure the chrome showing. A little subtraction and you’re off to the races. (Chrome uncompressed - chrome compressed = spring pre-load)

Fact: Stiffer springs with light spring preload are plusher than softer springs with heavy preload.