KDXRIDER.NET

Go with less.

There aren't really any long, shift, top out springs. They are pretty short and stiff.

Those screws are bras, so don't be to tough with them.

After the front wheel I'd up in the air, on a work stand, open the screws to let the air build up out of the forks. The air build up can make the forks a bit harsh.

ummmm ... nevermind.
Figured it out myself... continuing forward tomorrow

So I opened up my forks and found the factory 3.5" steel preload spacer. And as I understand it... this size spacer gave the stock KDX some 38mm of preload. Correct?

Bro, you got it open. Just measure it.

Don't try to do some math on the old one, then guess / cut the new one.

Since I am on the heavy end of the .40KG springs (210lb rider) I went with Jeff Fredette fork formula - meaning 7.5wt oil filled to 100mm from top. He uses the stock metal spacers which are a ton of preload, so I went with 12mm preload trying to split the difference between what I read here and the Fredette formula. It felt like a great fork action for aggressive hare scramble with some jumps. But in the technical tight rocky woods at my very basic riding skill, I thought it was a little too stiff. Tried 8 then 10 then 12 clicks out.

Finally changed to the spec 5 weight oil, same 100mm from top, and cut preload down to 8mm. Much better in that technical rocky riding. Wonderful, really. At this point, a couple compression clicks either way from 8 should woods riding at my skill level. Thanks all ~!!

Thanks for the report.

A little tuning can go a long way.

BamBam wrote:Finally changed to the spec 5 weight oil, same 100mm from top, and cut preload down to 8mm. Much better in that technical rocky riding. Wonderful, really. At this point, a couple compression clicks either way from 8 should woods riding at my skill level. Thanks all ~!!

I realize this is an old thread, but you cut off 30mm of preload??? Or did you cut 8mm off the preload spacer which was 38mm?

Cut the spacers so that one gets 4 mm or so of preload after reassembly.

I think stock preload is around 28 or 38 mm. If it was 38 mm, then he cut 30 mm off the spacers.

I wouldn't do it with the stock butter springs. (unless you are 125 in full riding gear maybe)

After installing new springs I recalculated lengths to set my forks up to have 8mm of preload. And to do that I replaced factory metal preload spacer thing with a piece of schedule 40 PVC so I could easily cut to length. The new PVC insert was around 1-5/8" in the end to achieve the 8mm preload I was looking for. A lot shorter than factory.

The distance from the top of the cartridge to the bottom of the fork cap is X mm long. The combination of spring length and spacer length (and washers) will equal the same length with no preload. If the spring is compressed any mm, then that is the amount of preload in the forks.

Thanks for clarifying. I have some RT springs on the way after having the bike for a year. Finally going to get these forks setup as they should be for me. I dont want to change too much initially, just springs and oil, but it may be wise to make a few PVC spacers to try out.

It would be VERY wise.

On top of the cartridge is normally stacked...

washer
spring
washer
spacer
washer
fork cap

Hold the chrome tube in your hand or in a special vise and then measure how many mm it will take to move the bottom of the fork cap from its stacked position to the assembled version.

With correct rate springs, around 4 mm or so of preload is about right. I think stock is 28 or 38 mm. I can't remember which I measured. That makes soft butter springs keep the front end from sagging too much. Your new stiffer springs with a modern amount of preload will be softer in the first inch or so than the stock setup.

Awesome! Really looking forward to the updating of the fork. I have some Maxima 5wt and some various spacers ready at 1.5" and 1.25" to try. Thanks for the great explanation too KDX Garage!

You're welcome.

I wouldn't worry about spacer length until after all the parts are stacked up and measured.

"Measure twice. Cut once." :-)