KLX250 Sag and Pre-Load, Part 1

As I approach the one year anniversary of the purchase of my 2019 KLX250, and after another bumpy rally (Wild Bear Safari), I finally started working on the suspension. I haven't had any issues with the forks. The rear shock has been a significant weakness, perhaps the only weakness the KLX has in it's design.

The rear shock is an oil dampened, coil-spring, mono-shock with a nitrogen reservoir. The spring rate is reported to be 5.6 kg/mm. Race Tech's spring calculators show a spring for my weight and riding of 8.0 kg/mm, so I'm already in the hole.

However, there's a process that needs to be followed and it starts with the pre-load which I hadn't touched until today because it required me to remove the whole shock.

There are so many sites to take you through the process of measuring sag that I won't go through the why of it all. What I will say is that before you can justify any changes, including clickers for compression and rebound, you need to set the rider sag using the following guidance.

Optimal rider sag 33%* of travel
Optimal static sag 10%* of travel

* Optimal percentages are those that we generally attribute to dirt-bike and motocross suspensions. Other type of motorcycles and riding may be less or more.

Below is a screen shot of my data and calculations. The measurements are from the rear axle to a random point consistently used. The meaningful numbers are the differences that calculate the sag numbers:

In summary, my stock Rider Sag was nearly 60% (optimum being 33%) at the stock pre-load of 107 mm. In short, what that means is that the shock in its stock configuration was giving up 60% of the available travel (9.01 inches) to my own weight plus the static weight of the motorcycle before I even got on the bumpy trails.

Is it any wonder why I was so whipped on the very technical Perry Mountain Tower Run last year?

Onward...

In advance, these actions and calculations are preliminary. They need to be tested, tuned in or abandoned.

To compensate, I adjusted the pre-load to near-max at 120 mm (max is 123 mm). That adjustment brought the Rider Sag percentage down from 57.8% to 38.6%; closer to the optimal sag, but not quite there. Plus, I wound up with an unwanted additional full inch of seat height that I need to look into.

I plan to do some testing next month on the Croom single track, where I can tinker with the compression and rebound. However, I'm probably heading for a new spring with a rate more in line with my needs.

Stay tuned.

I've now completed the purchase of a Cogent Spring with a 7.0 kg/mm spring rate. Installation coming soon...

See KLX250 Sag and Preload, Part 2 for completion of my suspension project.