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[big_t]

Has anyone ever stiffened up their front by using PVC pipe spacers at the top of your springs?  If you have, how much it it work out for you?

[Knightslugger]

Done to increse preload?

[FOG]

This not only has been done before , It's almost essential.  Unless you weight only 120 lbs. you need stiffer springs.
I wrote an article in the old list about Setting Sag  Anybody have it?

Generally speaking you need to shorten the spring a couple of inches and replace that amout + some more for correct sag  with 1" PVC or metal tube.
Best sag is about 1 1/4".

FOG

[jms]

I need to do this mod. Anyone have the documentation ?

[maverick9611]

ok who's gonna do a pix/article on this?

[McBiggity]

i'll get some pics when I take my forks apart to replace the fluid/seals/bushing.

[maverick9611]

right on mr. big!!the pix really help out

[HotRod]

Adding some pipe to increase the preload on a fork WILL NOT increase the forks spring rate. It will only raise the front of the bike and will lower the spring rate of the fork. It has no effect on the metal spring in the fork but it lowers the forks spring rate because there is now more air in the fork and the air spring rate in the fork is now lower.

Removing 2" from the metal spring WILL increase the metal spring's rate. However you can also change the air spring's rate by the amount of fork fluid you put into your fork. More fluid means a higher spring rate and less fluid means a lower spring rate.

The air spring in a fork is progressive and gets stiffer the more the fork is compressed. This means you can still have a light spring rate at small fork movement and a high spring rate at larger fork compression to help prevent bottoming.

You can check out my motorcycle web page at
http://www.members.cox.net/rodneyj123/motorcycles/motorcycles.htm
and choose "Front Forks" to see some crummy pictures and get an explanation of how a fork works.

You can actually put so much fluid into a fork that you stiffen it up too much. It's too bad most people don't know about the air spring that's in every fork made and how easy it is to change the spring rate with the AMOUNT of fluid put into the forks.

[Knightslugger]

I had talked this over with FOG a while back, and he schooled me a little about spring rates.  as far as i can recall, a .55kg/mm spring is still a .55kg/mm spring regardless of how much fluid you jam in there.  The Damping effect, however, is changed, which has nothing to do with spring rate whatsoever.  Now if you cut some coils, the amount of free coils is lessoned and the spring becomes stiffer.

that's about all i remember.  FOG, if you could chime in and give me (Read: us) a refresher, that'd be great.

[maverick9611]

how many ounces does fork leg hold?i'm interested in trying this mod. cuz my front forks are way to soft. hot rod, how much extra fluid would you add on top of the standard amount?

[FOG]

how many ounces does fork leg hold?I'm interested in trying this mod. cuz my front forks are way to soft. hot rod, how much extra fluid would you add on top of the standard amount?

You don't want to think about ounces but the level of oil in the forks. Your dealing with a Compression Ratio. and changing the oil level is like Milling the head. Check the level with the forks open and fully extended then add oil in small increments changing the level an inch is a huge change so be carefull.  Since your dealing with air, which is totally compressable, you probably won't notice much effect till you near hydraulic lock.

Truthfully since your in there anyway you might as well cut the springs and add a spacer. This will be a much more effective way of improving you front end.
More in another How too .

FOG

[HotRod]

I don't know how many ounces to use, I've never taken my EX500R apart and measured anything on the bike. You do like FOG says, measure the inches down from the top that the oil level is. Either use the top of the fork spring or the top of the fork or anything else that won't be changing it's position. I actually use a hollow brass tube attached to the end of a brake vacuum pump to set my oil level. I mark the distance from the bottom end of the tube with a magic marker. I then fill the fork with a little bit too much oil and then just drop the tube into the fork until the magic marker mark lines up with the top of the spring and suck out the excess oil. Do this on both forks and your set.




Be carefull though because unless you know how much fluid is in the forks to begin with, you don't know if you have the right amount specified by Kawasaki. What I do with a new bike is take the fork caps off and measure each fork for it's oil level. Write those numbers down. Then I drain all of the fluid out of the forks and refill them with the amount of ounces specified by the manufacturer. Then I measure the fork oil level again and write that number down. If the new fork oil level is different than what it was I just try it to see if I like it. If the fork dives too much while braking, I will add oil, about 1" at a time, until they work better. If I've got too much oil in the forks they will become much too stiff and I remove about 1" at a time until they are better.

Changing the fork oil level is more for street driving, it's not the answer for road racing where you are driving on a smooth road and don't need a soft ride and are trying to prevent the bike from bottoming due to G forces around corners. No road course is as rough as the street is, with it's potholes, tree parts, car parts and a few parts from old Harleys and Triumphs, etc., etc., etc.. When you drive on a road race course or speed through your favorite canyon road, you put up with a harsher ride than when you're just putting around town. So you increase the metal spring rate. But I just drive around town and there don't seem to be many places here in North Las Vegas to go around fast corners (also, the roads are very, very sandy out here and are very slippery), so I prefere a soft ride and I'm not going to change the metal spring rate.

One note about cutting a spring that has a flat top on it. That flat top is to give the spacer lots of area to press against and just cutting the spring will leave a pointed end in contact with the spacer. If you can, you should heat the end of the spring till it's red hot and flatten it out so that the spacer will get more area to push on. I know that nobodies going to do this, I just though I might as well tell you the right way to finish the end of a spring, just so you'd know. Cutting the spring is just the cheep way to stiffen it up, saves you the money of buying new springs. I've done it many times on cars and bikes over the last 40 years.




When you cut a spring the new spring rate will be the old spring's length divided by the new spring's length times the old spring rate. So if your old spring was 20" long and you cut off 2" and it's old spring rate was 30 lb/inch (about .55 kg/mm) it's new spring rate will be:

20 / 18 x 30 = 33.3 lb/inch (about .6 kg/mm)

If you go to Racetech and buy springs for an EX500R it will have about 47 lbs/inch spring rate (which is about .85 kg/mm). Probably good for racing and canyon carving.

If you go to Provressive Suspension you'll get a 30/45 lbs/inch (.54 to .80 kg/mm) progressive spring rate. Sounds good for the street to me.


A note about changing the oil level being like milling the head - it's not. Cutting the spring is like milling the head because once you've done it, you're done. You can never go back, you can't add metal back onto the cut part. Changing the oil level is no big deal, if you don't like it you just put the oil level back to where it was and everything is the same. It's simple, cheep, repeatable, AND UNDUABLE.

[dad]

The stock fork oil level recommendation is 4 5/8". That is pretty high as fork oil levels go and is probably what is behind the factory's choice of grossly soft springs but relatively high fork oil to assist with bottoming. The attempt is to make it fit the lightest, smallest rider as well as the larger heavier riders, all in one package. A 20cc measured amount makes a 1" level change. Handy but not too important if you use the measured tube/extraction method described. Measuring oil when changing it is only good if you've dismantled the front end. Dry, it takes 352cc to fill to the 4 5/8" (117mm) level. Without dismantling them, it's approximately 300cc. The reason that's approximate is because the inner tube tends to retain some oil. Pumping it will get more out but virtually never completely dry, hence the approximate volume.

In my opinion, it's best to change the springs to a specific recommendation and rate from one of the folks like Racetech. They are available in every .5kg increment through 1.0kg. I would err to the soft side of their recommendations for track or street use but their's is still OK. That's within the range of rider preference, not right or wrong.

Cut springs can work but the cut end is potentially troublesome and it better be right. Tubing for spacers must be bought, too. If you're comfortable with the whole concept, go for it, but be sure you're right. About $100 will get an exact spring rate, made for the application, with the spacer tubing for cutting spacers furnished, and not require any special expertise in that regard.

With the proper springs the recommended fork oil level is lower because you no longer need the spring effect that the oil's displaced volume affords. They recommend a fork oil level of 5 7/8" with the proper springs. I've not bottomed mine out using those levels and their spring recommendations. That is both street and track riding. (BTW, I'm not necessarily the fastest on the track but I'm far from slow. Better to let others tell those stories.)

[HotRod]

That's good info, dad. Thanks.

[MrSciTrek]

Wow. I've messed w/ cars for years but never modded a motorcycle.  I'm an 8th grade science teacher & this type of forum is a practical-physics course.

I don't have a 500 yet, just looking into it to see what the veterans say and do w/ their bikes.  It's been 20 years since my previous 3 motorcycles & am considering a return.  I'm 54, 5'10+, 185 pounds, and am no crotch-rocket racer-type... Omaha, NE.   

Thanks for sharing your experience.

[pcdarks]

The 1" PVC I have will not fit into the fork tube. Are you using 3/4"? It is a little small but it's the next size down.

[Nick D]

I think I used thick 3/4" pipe (it wasn't PVC, just something thicker than sch40 that I found at work). 

Whatever fits somewhat snugly should be fine.  I'd just recommend throwing a washer in between the spring and the pipe.

[pcdarks]

I rebuilt the fork and cut spacers to give 1 1/2" preload. I put 415cc of 10w-30 oil to bring the level to 7" below the top of the fork fully extended. The fork feels good. Does this sound like it sound be right? 155lb rider, newbie,94 genII.

[bitzz]

I rebuilt the fork and cut spacers to give 1 1/2" preload. I put 415cc of 10w-30 oil to bring the level to 7" below the top of the fork fully extended. The fork feels good. Does this sound like it sound be right? 155lb rider, newbie,94 genII.

You used a MULTI GRADE oil in your forks?
Are you trying to get progressive dampening? Nice and cush when you start out but stiffens up quickly?
How is that working out for you?

[pcdarks]

Just put it in Haven't ridden far. The manual calls for a multi grade 10w20. I just went a little thicker. I think a change in viscosity would not be as noticeable if the temps aren't too extreme, like in an engine or transmission.