Differences in forks

[kdxdazz]

I have a 97 kdx220sr the previous owner has messed about with the internals of the forks and I need to get it sorted as they are terribly harsh, he also gave me a spare set of disassembled forks, first thing is to change the oil and make sure he is using 5w. Could anybody tell me how to tell what kind of forks I have as I heard there are a couple if different types depending on model and year.

[KDXGarage]

Any chance to post a picture?

[kdxdazz]

i have no idea how to post photos on this website and have asked how to a couple of times with no replies

[KDXGarage]

Host the pictures somewhere else, then link to the URL using the IMG tag. It is the ninth button to click on in the "Full Editor & Preview" Box.

Below the text box there is "Full Editor & Preview" and "Submit". Click on the "Full Editor & Preview" to get to the box and the IMG tags.

The site is free of ads and runs on donations from members to keep it going. It is not going to be as fancy as a site that has ads all over it and makes the money to host pictures for everyone, super easy to load pics, etc. Thanks.

Supporting members can use the Attachment function to have the site host the picture and upload it within the thread.

Thank you.

[kdxdazz]

cheers.i've never hosted pictures in another place but i am the most useless guy when it comes to technology. finally got my forks apart today,they are not upside down forks just the standard conventionals. i am trying to work out why they feel so harsh. i worked out the fork oil thats in there is a 5w just by making up a simple viscosity tester. the fork springs that are in it are stamped .38 at the top and measure 480mm long, i do recall the previous owner saying it has fredette springs in them,does this sound right? i weigh only 62kg and the single track i ride i barely get out of second gear. the bike came with a spare set of springs which i assume they are standard,they measure 460mm long. does anybody know what weight the factory springs are
my plan is to put the factory springs back in and maybe drop down to a 2.5w oil. any thoughts would be appreciated

[KDXGarage]

how much preload is there?

[kdxdazz]

The preload is just what the factory spacer is. Looks like 100mm.

[KDXGarage]

You may want to read up on how to measure how many millimeters of preload is in use. I would really hope there is not 100 mm of preload.

I am not talking about preload spacer length. Basically, how much are the springs compressed when assembled.

If you have a 20 mm longer spring in there and used the stock spacer, you went from (I THINK) 38 mm of preload to 58 mm. Race Tech recommends 4 mm.

THIS is why I want to know how much preload the forks have.

[bufftester]

The factory springs are .35 kg/mm and measure 35.8 dia x 472 length and the stock preload spacer is 90mm. As KDXGarage said, 4 mm is Racetechs suggested preload. You can make your own spacers out of PVC pipe (25.4mm dia). Quick math would suggest the stock .35kg springs for your weight. I would suggest going with the stock 5w oil at the standard height and then making a set of spacers for each spring that gives you the same amount of preload, then try both sets to get a feel for the changes. If they are truly .38kg springs in there it would feel harsh. Spring changes are very easy and fairly quick.

[KDXGarage]

Are you 62 Kg with full riding gear, extra parts, extra tools, water backpack, etc.?

[KDXGarage]

Damn! 136.4 pounds?!

Forget the bike, buy some food!

[kdxdazz]

cheers guys,i am using the stock 90mm preload spacer, just took a few measurements. the .38kg stamped springs measure 479mm and the wire gauge is 4.45mm, what i thought are a spare set of standard springs measure 457mm long which is what the service manual lists them as but the wire gauge measures 4.7mm just me manually pushing down on both springs it seems like the 0.38 springs are lighter. can anybody confirm the standard spring gauge diameter. will take some preload measurements today,i have some nylon rod around here somewhere so will get my machinist to knock me up a few spacers

[kdxdazz]

i'm 62kg with out riding gear, 5'6 , 8 percent bodyfat and eat like a pig

[KDXGarage]

I was in ninth grade once.

The different thickness is not going to be a good indicator since the lengths are not the same.

Get a brromstick and some bricks with holes or SOME kind of weight. Whichever one sags less is the softer one. Measure from 25 - 50mm and then again at 50 mm - 75 mm. Don't go by 0 mm - 25 mm. That is not consistent enough.

[kdxdazz]

I was unable to view racetechs calculator to see the recommend preload. With 4mm preload my bike now has 45mm of static sag and 55mm of race sag. This seems like quite a lot. Is that 4mm of preload definitely for conventional forks and not upside forks, an upside down spring is about twice as wide

[KDXGarage]

It is not related to USD or conventional.

www.racetech.com

I have read comments from some tuners who get paid to work on suspension, and they were recommended around the same.

A British guy who I trust and helped me out a bunch over a decade ago said this in a post about 5 years ago:

as low as 45mm but no more than 65mm

His comment was with the rider aboard.

It sounds to me like it is spot on.

Which springs are in there? What did you on the spacer?

[kdxdazz]

I put in the fredette o.38kg spring and cut the spacer down to 61mm. Just measured my rear spring and looks like it has a lot of preload on it, measures 125mm as per the service manual, that and I am running a rear trails tyre which is quite tall so I guess that could make the rear of the bike quite high which transfers weight to the front. In my spares I found another set of springs which are 500mm long and the guage is 4.3mm thick, they seem extremely light, also found a weird set of springs that are about an inch long. No idea what they suit

[bufftester]

Rule of thumb for most dirt bikes is that race sag should be 30% of suspension travel and static 7-10%.

Generally you should shoot for 30 mm static and 100mm(rear)/80 (front) race. Getting both right involves getting the right shock for your weight (race) and the right amount of preload (static) So in general you have too little preload on a too stiff spring in the front to end up with the numbers you have.

This makes sense as the stock KDX front end was designed with a 140lb (65kg) rider while the rear was geared towards a 185 lb (85 kg) rider...unbalanced. Which is why setting proper suspension is such an important part of tuning the bike. Sag also applies to the front forks and is set and measured the same way, with slightly less race sag than the rear (for reference I usually use 20/80 static/race in front and 30/100 static/race in rear)

At 125mm of preload on the rear you have enough preload for like a 110 kg rider. Manual specifies standard position (w/ stock spring) at 116.5mm (for 82kg of preload) and each additional turn of preload increases it by 7.5kg per turn. I bet the rear feels pretty harsh as well.

All of this is based on stock springs of course.

Inch long ones sound like clutch springs if they are around 20-30 mm in diameter.

[KDXGarage]

Put the rear sag at 100 mm with you on it in full riding gear. After that, measure the static sag.

I think there is an article posted on here, maybe I the reference section of suspension.

We all need to remember that stock springs with 38 mm of preload is not the same as 5 or 10 mm of preload and the same rate springs.

[kdxdazz]

Cheers guys, will make some adjustments, the short springs are not clutch springs, they are fork springs of some sort, they are the same diameter and winding pitch, they are not cut down from anything either as they are neatly flat on the ends. I have a theory that the kdx was set harder in the rear so it could support the weight of a pillion passenger given it has foot pegs for the pillion unlike true enduro bikes