Fork oil weight/spring rate

[choneofakind]

FWIW, The spring rate calculator suggests I'm on a 0.64something also. I'm on EX500 springs and intiminators. It's not a bad setup. I have too much fork oil ATM and need to fix that so I get full travel again, but it's a comfortable street setup with decent feedback and decent front wheel tracking over bumps that holds up well at the track. Not as stiff as it COULD be for tracking, but a good overall setup for me. Happy with it.

[ieathonda]

Well anything is better than stock..

I took an overpass turn going about 60 and i felt like the suspension was extremely soft. Coupled with the stock tires I felt as if I were sliding through the turn.

What i ultimately am striving for is positive feedback from the front and rear. I will be taking this bike to the track sometime so I do have a racing setup in mind..

[Ghostt]

Once you've got the suspension dialed in, and better tires, it will feel like a different bike, trust me.

And then go attack some twisties and walk all over the bigger bike, at least til you get to the straightaways

[ieathonda]

After a few months of lurking and reading up, that definitely seems like the best route..

I will keep you guys updated on the suspension upgrades and pretty much anything else I plan to do with the bike.

[ieathonda]

Originally Posted by Ghostt

The PreGen Ninjette and 1st Gen EX springs are a direct replacement, with the exception of the overall length, below it a picture of when I did mine, showing the difference at OEM lengths, with the EX springs being longer, also not the springs themselves are slightly diameter material. I had a replacement set of forks for the EX laying around anyway.


As far as the adjustable preloads go, you could, but to be honest once they're set, you shouldn't need to be adjusting them again. They would add some flash to the top of the tubes, since your going with clip-ons anyway.

I personally just went ZX600C risers to lower mine.

https://www.ninjette.org/forums/blog.php?b=8344

So the forks I am getting will be the pregen Ex500. Since the springs are longer, what is the approximate spacer size so sag is set correctly? And since the ex500 spring is longer, wouldn't fitting it into the 250 essentially increase the effective spring rate since it would be compressed to the size of the 250 spring? Would the spacer be smaller to accommodate this longer spring?

I just ordered the fork seals, 5w fork oil and forks along with an ss brake line and some clip ons. going to wait for the new tires, intiminators and preload adjusters before i begin..

[Ghostt]

Originally Posted by ieathonda

So the forks I am getting will be the pregen Ex500. Since the springs are longer, what is the approximate spacer size so sag is set correctly? And since the ex500 spring is longer, wouldn't fitting it into the 250 essentially increase the effective spring rate since it would be compressed to the size of the 250 spring? Would the spacer be smaller to accommodate this longer spring?

I just ordered the fork seals, 5w fork oil and forks along with an ss brake line and some clip ons. going to wait for the new tires, intiminators and preload adjusters before i begin..

The springs will fit just fine, as the fork itself is identical length for both. Just less spacer length is needed.

You'll need to measure your spring with spacer total length, then just match the EX spring and make your own spacer to set the sag.

If I remember correctly, the EX spacer is just a few washers, the overall length of my Ninjette OEM spring and spacer was 20.5".

So if your not cutting the EX springs, just buy some thick washers that fit inside the upper fork tubes.

Don't worry it will all make sense when you have all the parts and compare.

SIDENOTE: as long as your doing the SS brake line, it would also be a good time to disassemble and clean the calipers, grease the caliper sliders, and flush and new brake fluid as well.

[ieathonda]

Originally Posted by Ghostt

The springs will fit just fine, as the fork itself is identical length for both. Just less spacer length is needed.

You'll need to measure your spring with spacer total length, then just match the EX spring and make your own spacer to set the sag.

If I remember correctly, the EX spacer is just a few washers, the overall length of my Ninjette OEM spring and spacer was 20.5".

So if your not cutting the EX springs, just buy some thick washers that fit inside the upper fork tubes.

Don't worry it will all make sense when you have all the parts and compare.

SIDENOTE: as long as your doing the SS brake line, it would also be a good time to disassemble and clean the calipers, grease the caliper sliders, and flush and new brake fluid as well.

Ok sounds like itll be fun.. I have some motul 600 waiting for me and I was going to check on the calipers as well as the brake pads.. New tires may be here about the same time so it will be a dramatic improvement over stock feel in the front end in the course of a day or two.. pretty excited

[Ghostt]

Very cool, here's my how-to guide on calipers just in case


For those of you whom are scratching their heads, here you go,*


Front Caliper Service (also rear as well)

Many folks have posted here with a Varity of front brake problems.*

*Many of which are attributable to the lack of proper maintenance.

*Here’s how you can always have a brake like when your bike was new.

A short list of the problems and the causes.

Soft lever or lever goes to the bar.

The usual cause is the pistons are pushed too far back into the caliper by a flexing a warped, coned, disc.*

*Using up too much piston travel before the disc is pinched.

Juddering in sync with wheel rotation.

The disc is worn, and its thickness varies. *This causes the caliper to “sink” into the thin part and when the thick part comes around, it gets wedged into a smaller space causing a tightening of the brake. Then the tight spot passes through and it like the brake is released. Then repeat, repeat.

Cupped, coned, or warped disc.

Unfortunately this is a common problem with EX’s the cause is the disc is stretched in the center due to being rigidly bolted to the wheel. *The huge force of braking is transmitted to the wheel through the webbed center of the disc which gets stretched and becomes larger than the space it occupies in the center of the disc. This causes the center to push to the side trying to find room for itself.*

*Resulting is a cone shaped disc.

Soft lever 2

The caliper has pistons only on one side, so as the pads wear the caliper must shift sideways apply even pressure on both sides of the disc.*

*To allow this the caliper floats on two pins. *If these pins get dry (no grease) dirty or bent. The caliper won’t center itself and bends the disc to wherever it is.

*This take up lever travel and when released pushes the pistons further back than necessary.

**If not fixed will eventually destroy the disc (warp it).


Ok how to prevent all of the above.

When new pad time comes around, resist the temptation to just pop in new one and go.

*Every time you must do these things.

Remove caliper disassemble and clean it.

Clean and re grease the sliding pins.

Polish the caliper pistons to remove dirt. If you just push the pistons back into the caliper leaks will result. Or binding.

Tools required:*
12 mm socket
8mm open end wrench
3” or bigger C clamp
a supply of new bake fluid.*
wire brush and or steel wool.

Remove the caliper from the fork leg but leave the brake line on.

Remove the old pads and the mounting frame (the sliding pins)

Remove the cover from the Master Cylinder on the Handel bar.

Attach the C clamp to one of the pistons but don’t squeeze it. *Pump the lever on the bar slowly to push out the other piston almost all the way. *Put the C clamp on that piston and push out the other one.

Remove both pistons by hand.

Remove all the rubber part from the caliper, the seals are in the grooves in the caliper and dull pointed thingy will get them out easy.

Disconnect the caliper from the brake line.

Soak all the rubber parts in new clean brake fluid * ONLY!!!!! * Rub them with you fingers till as clean as new.

The caliper can be cleaned with a wire brush or even a Moto tool for the internal grooves, NOW’s the time to paint it if you wish.

Polish the pistons till they are smooth and shinny. They are chrome plated. If any of the plating is chipped or damaged below the dust cap groove. *Replace it.

The master cylinder is the subject of another write up and we’ll assume it in good working order here.

If you suspect your disc is bad, your bets bet is to replace it with an after market one fro EBC or Galpher.

*Don’t remove the disc unless you intend to replace it. *It will assume a new shape if it is * stressed and will not be flat again. You can try to check its condition by placing a straight edge across the face of the pad swept area looking for any distortion.

Re assembly

Take the nice clean rubber seals and install them into the caliper then the Dust covers.
Wet all the rubber with new clean brake fluid and partially fill the caliper with new fluid.

Push the pistons though the dust seals and into the caliper body until the dust covers snap into the grooves.

Fill the MC with new fluid and pump the lever while holding the Line above the MC till clean fluid flows.

Connect the line to the caliper while holding it above the MC.

Pump the lever with the bleeder valve open till fluid flow from the bleeder.

**Hold the caliper so that the bleeder is the highest point.

Close the bleeder and pump more fluid into the caliper but don’t push the pistons all the way out.

Then squeeze the pistons all the way back in and install the new pads.

Re grease the slider pins and assemble the dust seals and re mount the caliper on the forks but leave the bolts loose.

Now clamp the caliper to the disc with the brake lever.

Look at the space between the fork lugs and the caliper, clamp and release a few times as you tighten the bolts by hand. It one lug touches much before the other the odds are you mounting bracket is bent. You can straighten it.*

*After you get it the best you can. Some shim washers made from alum can stock can be fitted to the loose side.*

** *What we are doing here is trying to minimize the bedd in time and gets the best pad life.


Ok with everything tight you should be through, Notice we don’t need to bleed the brakes, but if you screwed up in any of the above steps, you might do that here.

Be careful to Bedd in the new pads gently.

**Too much pressure too soon will burn the pad material as only a small area will be gripping at first. You also won’t have full braking power till the pads are fully familiar with the disc

[InvisiBill]

Originally Posted by ieathonda

So the forks I am getting will be the pregen Ex500. Since the springs are longer, what is the approximate spacer size so sag is set correctly? And since the ex500 spring is longer, wouldn't fitting it into the 250 essentially increase the effective spring rate since it would be compressed to the size of the 250 spring? Would the spacer be smaller to accommodate this longer spring?

The spring's rate is set by its length and how it's made. Compressing it more or less doesn't change the spring's rate at all. If the fork was exactly the length of the OEM spring, and you replaced it with a longer spring, it would inherently be preloaded some. But as stated above, preload does not affect the spring's rate, only how it behaves within its range of travel.

Generally speaking, you want the new spring & spacer to be the same length as the old spring & spacer. So if the new spring is 2" longer, you'd want to make the new spacer 2" shorter to compensate for that.

However, changing the spring rate inherently changes the length of spacer needed to maintain the same amount of preload. If your spacer is compressing your .44kg/mm spring down 10mm, that's 4.4kg of preload. 4.4kg of preload on a .585kg/mm spring only requires the spacer to compress it by 7.5mm.

But if you don't currently have the spacer length set to give you proper preload/sag, then trying to get the new parts to match the current (incorrect) settings is pointless. http://www.ex-500.com/wiki/index.php...ension_Preload has a lot of info to help you understand preload/sag, and how to properly set it. This is where preload adjusters would come in handy, as you can simply turn them up or down instead of tweaking the length of your spacer. But once you get them set, you don't really change them much (perhaps between street and track riding, or between a really rough track and a really smooth track).


As Ghostt said above, the Gen1 springs should be the same .585kg/mm rate as the Gen2 springs, just longer. This gives you a little room to play with the rate if you want. Think of a spring as a long, coiled lever. Making it shorter makes it harder to bend; cutting a spring shorter will actually increase its rate. Based on Ghostt's pic above, it looks like the 500 spring is 20-3/8". You can find a new length or rate with the formula Length1 * Rate1 = Length2 * Rate2. 20.375*.585 is 11.919375, so divide that number by a desired length or rate to find the corresponding rate or length. Cutting it down to an even 19" would give you a .627kg/mm rate, for example. That might be an easy way to bump the spring up a little closer to what it "should be" for your weight.

[ieathonda]

Very informative post invisibill. I will more than likely cut the ex500 spring down to 19" flat because my calculated spring weight sits about .641. I know that spring rate/fork oil setting are probably the most important aspect of the front suspension. I'm just waiting to get my intiminators, springs and preload adjusters in before I can start eyeing everything out and modifying parts to my specifications.

I will read up more via the links you provided.

[Somchai]

@ieathonda, when your calculated springrate is .641 why don't you just take the springs from the new-gen (2008-2012) then since the new-gen has a .65 springrate?
Or don't they fit your bike?

[choneofakind]

Where are you getting that 0.65 number, Rowland? That disagrees with everything I've seen.

[Somchai]

Originally Posted by choneofakind

Where are you getting that 0.65 number, Rowland? That disagrees with everything I've seen.

Hi Chris,
thank you for your question, since this is a good chance to correct the wrong talk about the springrate of the new-gen (2008-2012).
The first I've got it from the following thread here in Ninjette started by @rojoracing53 - https://www.ninjette.org/forums/showthread.php?t=136453 - who calculated .629 as springrate.
After that I've made my own calculation which gave by the given parameters from the spring a result from .64 to .65 and to be sure I'd ask the 'Masters of Springrates' and in the attached jpg you'll see the email-answer which states a springrate of .65 for the new-gen.

[choneofakind]

Huh. Would have been nice to know thatt a long time ago.

[InvisiBill]

Related posts about RT's NewGen numbers: https://www.ninjette.org/forums/show...239#post909239

[Ghostt]

Originally Posted by InvisiBill

Related posts about RT's NewGen numbers: https://www.ninjette.org/forums/show...239#post909239

So @InvisiBill Will the NewGen springs fit PreGen?

[sharky nrk]

Originally Posted by Ghostt

So @InvisiBill Will the NewGen springs fit PreGen?

RT shows replacement springs are the same P/N so yes, they should swap and fit. If you buy a spring from them for a Pre or New Gen you get the same spring for a specific rate.

[ieathonda]

interesting... found the new gen springs for about 30 each from skagit motorsports

[Ghostt]

Good to know, makes sense that the fork springs are stiffer, just like the rear, so they match.

So one could inexpensively upgrade the PreGen suspension springs to NewGen.

NICE!!

[ieathonda]

We learn something new everyday... heh.

so... pre gen frame upgrade to new gen frame?

[choneofakind]

Actually... Almost, yes

[InvisiBill]

Originally Posted by sharky nrk

RT shows replacement springs are the same P/N so yes, they should swap and fit. If you buy a spring from them for a Pre or New Gen you get the same spring for a specific rate.

Yes, the PreGen, NewGen, and Gen2 all use the same RT part numbers for springs and emulators. The Gen1 (which Ghostt said is a direct spring swap into the PreGen) uses a different emulator part number and has no spring part number listed.

I assume that the 1mm difference is small enough, and the available space in the fork is large enough, that either spring would work in either fork. Just keep in mind that not everything matches up perfectly between these four models, and there doesn't seem to be a pattern as to what's different or the same.

[InvisiBill]

Originally Posted by Ghostt

Good to know, makes sense that the fork springs are stiffer, just like the rear, so they match.

For loose definitions of "match".

According to RT's calc (which may or may not be perfectly accurate), the NewGen's fork springs are good for 95lb while the rear is good for 220lb. Assuming the PreGen's rear suspension is pretty similar to the 500's, its rear spring is good for ~180lb and the fork springs are good for <30lb according to RT. Likewise, the EX500 has fork springs for <30lb and a rear spring for 130lb. The '06-'11 EX650 is the opposite, with 320lb fork springs and a 140lb rear spring.

I understand that they can only sell a bike with one spring rate, probably aimed at an average rider. The springs may be too heavy or too light for your particular weight. But I cannot fathom why the front and rear would be so far off from each other. Rather than the spring rate just not matching the rider's weight all that well, they're causing "rocking horse effect" and other issues with the wildly mismatched spring rates. I had some interference with the SV650 shock on my bike at first, so I can personally attest that a too-stiff rear can make even a good front end feel really bad.


But yeah, according to the RT calc, the NewGen's fork springs should be good for a ~150lb rider on a PreGen. The EX500 springs are good for ~110lb. That's still way better (33% stiffer) than stock, but the NewGen springs are probably better for a lot of people. It would be nice to have someone verify 100% that the NewGen springs will work in the PreGen forks. The Gen1 springs are longer than Gen2, so they could also be cut down to raise the rate to around .70kg/mm (180lb PreGen rider) at 17" long. If you don't mind doing the mod work, the Gen1 springs' higher rate and length give you a pretty wide weight range that could be covered.

[ieathonda]

Ok, so my new gen springs arrived with spacers but I do havea question.

I havent got the intiminators yet, would it be ok to overhaul the forks and use 5w oil in the stock damper rod configuration? Im not exactly sure what the stock fork oil is on the 250's. Some people are saying 10w and others 5w. It would be great to know if i can run the 5w so i can change out that leaky seal asap and throw in the springs.

[Ghostt]

Got for it.

[choneofakind]

Stock is 10W. You're more than welcome to use 5W, you'll just have less damping until your Intiminators show up. It's not like one type of oil is incompatible just because it's a different viscosity...

[ieathonda]

Yeah I was asking moreso in the effectiveness of 5w for a 145lb rider as opposed to the stock fork oil. I was a tad worried it wouldn't be sufficient damping with 5w

[choneofakind]

Damping is all about the system speed with a given spring rate. Your weight doesn't really have much to do with it directly.

Spring rate for weight and force needed in the travel.
Preload for sag height.
Damping to control the speed with which the forks compress and rebound.

You might notice the nose dives more easily with lighter fluid. Or that it rebounds quicker, and then goes too far and pogo's a bit. This is an under-damped system. Or you may not notice anything different at all, all depends on how sensitive you are to such things.

[InvisiBill]

Just to update this thread concerning the installation of NewGen springs into PreGen forks, ieathonda posted in another thread that he did it.

Originally Posted by ieathonda

I also upgraded to new gen fork springs, new maxima 10wt fork oil and new fork seals which dramatically improved front end handling

Btw, the forks never bottom out. Plenty of travel left. I am 145lbs if that helps

[ieathonda]

Yeah I used the stock spacers, I think 1/2"-3/4" with a new spacer would help a bit, I noticed the front sits a tad lower than usual and has a "dead spot. I can see that I can manually pull up the front and the forks still have some travel. I may or may not end up doing this as I have someone buying the bike in two weeks. That being said, I don't think ill ever find a forum with members as helpful as you guys for my new bike.

[choneofakind]

That's called sag. You need sag. Don't get rid of sag with excessive preload!

[ieathonda]

BTW I also did a fork oil height of 115 mm. Rode it for a few hours today and it felt great. Front end no longer dips under hard turns and doing 75-80mph turns on the overpasses feels tons more solid than before. When I changed out the fluid, it was a dark grey. Very nasty stuff.

[MountainMedic]

I bought my '04 250 as a fixer upper first bike project. One of the first things I noticed was that the fork and shock were very, very soft. I replaced my fork oil with 15w at 180mm just this week. The difference is amazing. I would recommend it to anyone complaining of a soft fork.

Now on to finding a replacement shock... maybe an adjustable new generation.