I have a 2006 KLX250S. I just replaced the stock fork springs and rear shock spring with Cogent .44kg/mm fork springs and a 6.2 kg/mm rear shock spring.

I used Maxima 7 wt fork oil, which is heavier (more viscosity) than the stock oil KHL15-10 or Kayaba 01. I am running an air space of 100 mm.

With the addition of stronger fork springs will I see an increase in the rebound of the front fork over stock? With the stronger springs will it "push" the fork back to its extended position faster then the stock .38kg/mm springs?

The Kawasaki shop here in town recommended I go to a slightly heavier oil then stock to compensate for that and slow the rebound down a bit by using the thicker oil.

Thx for any input.

 

I think historically that is a strange recommendation. I and others who have/had '06/'07 KLX's found the rebound to be too slow. This is pretty much accepted as fact on the forum and elsewhere. I have an '06, and I've modded it with springs almost exactly like you did with 44 fork springs but a 6.0 Eibach in the back instead. I also installed Gold Valves front and rear.

The rear shock is a very good KYB unit in OEM trim...usually just a spring tweak depending on use and rider weight. The fork, however, has pretty lousy compression and rebound damping. Springs are usually a necessity except for super flyweight riders. The compression damping in the fork is fixed with valving, but unfortunately the rebound circuit is sealed and I'm not aware if anyone has come with a solution.

So...with the rebound damping too slow and not tunable, going with heavier oil generally aggravates an already problematic issue. Even with the heavier springs, the rebound is too slow for just about everyone. IMO the fork needs revalving to at least address the compression damping...remove the nasty compression spike...and it brings it to a point where the compression adjusters actually do something. I think you'll find the rebound to perform better with the standard 5wt. I've even toyed with the idea of mixing a 2.5wt with 5wt and perhaps using my compression adjusters to compensate. I've got my fork performing quite well for trail riding, so I just haven't gotten energized to putz with that oil experiment.

Something you'll often hear from people who haven't fiddled with suspension tuning very much is how they feel they fixed a problem like the KLX fork has with heavier oil. Generally what you're feeling is less travel where the heavier oil is masking the nasty part of the compression range and slowing down the spike you get further into the travel. This usually becomes apparent when you get the bike into some actual trail riding where the suspension and rider get challenged and the fork moves deeper into the travel range. Then the compression spike hits harder, and everything is made worse because the rebound has slowed waaaaay down.

 

Thank you for your detailed answer.

I will run the Maxima 7wt for a bit to see what I think. It's easy enough to do an oil change to a lower weight/viscosity oil.

Mike