Adding schrader valves to the forks? to add pressure to the air spring?

[treecat]

just wondering if anyone has had a play with doing this yet? used to do it on mountain bikes and still have my shock pump.

[Alex]

Which air spring?

[choneofakind]

Ummmm ninjettee use metal coil springs in the forks, not air like MTB forks...

[alex.s]

obviously op is confusing types of shocks, but there is a volume of air above the damping oil and the size of the air volume does change damping characteristics... so, not completely off. but you don't need a valve to do it, you just open the top and remove some fluid or add some fluid

[treecat]

alex.s is on the money

the air inside works the same as an air spring and can be adjusted by the oil height. i just wanted to see if anyone had done it as it can offer an easier way of adjustment.

[choneofakind]

Not to be rude, but if you knew exactly what you were doing, why bother starting a thread? Oil height adjustment is a common change.
[/attitude]

FWIW, the forks off the '08-'12 250R are the same as those on the 300 but with different oil height, spring rate, etc. Feel free to read through the suspension threads for the '08-'12 bike for more ideas.

Welcome to the forum! Head over to the new members section and introduce yourself so we can get to know you a little bit and hook you up with other users who can best help you.

[alex.s]

Originally Posted by choneofakind

FWIW, the forks off the '08-'12 250R are the same as those on the 300 but with different oil height, spring rate, etc.

the bottoms are slightly different with the 300 not having the speedo gear. it's basically two right-side 250 forks for the 300.

[choneofakind]

I know, but my point was the internals are the same so everything about suspension adjustments written for the newgen is still valid for the 300. That should help with search queries to get help quickly. This stuff has already been done, no need to reinvent the wheel.

[alex.s]

Originally Posted by choneofakind

no need to reinvent the wheel.

DARPA disagrees with you

[Motofool]

Originally Posted by treecat

just wondering if anyone has had a play with doing this yet? used to do it on mountain bikes and still have my shock pump.

Welcome to our site, Tim !!!

You may need to improve the sealing of the caps against the tubes, in order to avoid compressed air leaks.

Copied from:
http://nc700-forum.com/forum/nc700-m...able-ride.html

"I got the idea from one of my Goldwings that had air valves on the forks.
If you add only 6 psi to 10 PSI of air into the forks it will make your ride that much more comfortable.
It also made all of my bikes I did this to, handle better as well.
All I did was remove the fork cap, then, drill and tap the fork cap to the threads on the standard Schrader valve, then blue Loctite it to the cap, then re-install the fork caps.
By adding air it will add a preload and get rid of sagging front suspension, and any/most front end dive also."

[EsrTek]

Curious, as this seems off to me...
Adding air seems like it would lessen the dampening from bumps, sending more jolt through bars and w/o the front squat under braking, make it harder to get traction for hard cornering??

What benefit comes from this that the person quoted felt it 'helped handling', would it be a street mod or track mod?

[old3]

Air spring is a common term among dirt guys in off road forks.

I doubt the seal at the cap will hold higher pressure. These are pretty crude forks.

You can't hurt it by trying, I did Emulators in mine. Pretty happy with the damping on both comp/reb but the tiny fork tubes aren't holding up, thus my CBR929 fork swap thread down the page. I'm torn about trying a brace first. The 929 parts are nutty $$$. I should have done a ZX6/7 or GSXR front end in hindsight.

[Snake]

Great info Herman!

[choneofakind]

Bottle of fork oil: $4

Fancy (but awesome) fork cap with valve to pump in air that may or may not work: $unknown

Just add oil to make your air volume the desired size. It's been done. It works. It's cheap. It's easy and adjustable. Why overthink this?

[alex.s]

the top chamber is sealed (poorly) and the gas acts like an air spring. on compression the gas does get compressed and should reach a few bar. the air pressure is weak though and effects oil flow rate mostly im told. its effectively like having a multi-rate spring setup; the air spring being much looser picks up the higher frequency jaunts while the stiffer metal spring does the lower frequency stuff. it works much better if you have multi-rate valving like emulators which are just normal valving with an extra high-flow valve that opens up when the pressure gets really high (so you can compress the forks quicker when you hit a bump, but normally when its smooth the forks are stiffer) i guess it really just depends on the application... if you're on smooth stuff, you want less air. rough stuff, more air. ..... i think? i donno. dean knows all about this ****.

[alex.s]

Originally Posted by choneofakind

Bottle of fork oil: $4

Fancy (but awesome) fork cap with valve to pump in air that may or may not work: $unknown

Just add oil to make your air volume the desired size. It's been done. It works. It's cheap. It's easy and adjustable. Why overthink this?

if you want to increase the pressure provided by the air spring without losing your oil height, you would need to add "preload" by pressurizing the air spring higher than 1 bar

[choneofakind]

Originally Posted by EsrTek

Curious, as this seems off to me...
Adding air seems like it would lessen the dampening from bumps, sending more jolt through bars and w/o the front squat under braking, make it harder to get traction for hard cornering??

What benefit comes from this that the person quoted felt it 'helped handling', would it be a street mod or track mod?

So. As your forks compress, they move a certain displacement. Since oil doesn't compress much, there's air in the top of your fork. If the oil went to the top of the fork, the fork would never compress. It would be hydrolocked.

Now, this mass of air stays constant because your fork is a sealed system. As your fork compresses, the entire available volume of the fork decreases. Since oil doesn't compress readily, this reduction in volume all is taken up by the air in your fork. Constant mass of air + reduction in volume = increased pressure of air. Air pressure x area of fork = force. That's why OP is referring to it as an 'air spring' because as the fork compresses, the air does create a force resisting the compression of the fork.

Now, imagine we add more oil. This displaces air. Smaller mass of air + same compression = higher pressure than before. This gives more force from the 'air spring'.

Basically, the air in the top of the fork acts as an 'anti-bottoming' spring. It gets progressively stiffer as the fork compresses more. More oil = less air = faster rate of change of the air spring rate through the compression of the fork. So heavier riders (or more aggressive brakers at track) will benefit from more oil as assurance that they won't bottom out if they hit bumps while braking (a situation that already has the fork compressed a lot). However, it's important to remember that the force generated from compressing the air is also exerted on your fork seals; so if you add too much oil, you're likely to beat up your fork seals. They can only handle so much pressure. It's a balance.

I'm no expert, but that's the basics of what changing oil height does. Like alex.s mentioned, there's other things, but that's the basics.


EDIT: If I'm totally wrong here, call me out please. I'll edit/delete as needed.

[choneofakind]

Originally Posted by alex.s

if you want to increase the pressure provided by the air spring without losing your oil height, you would need to add "preload" by pressurizing the air spring higher than 1 bar

Right, but for a street rider or moderate track rider, is it really necessary? seems like you'll get 99% of the benefit with 1% of the hassle by just adjusting the oil height with a $4 bottle of fork oil.

[old3]

I think on these forks you could just add a few cc of anything oil related, vegetable oil, human sweat, Brylcreem...

Seriously, a few cc from any ATF or even motor oil would do it. You could spend a buck on the shatty oil at a grocery store. The stock oil isn't anything special, nor are the fork guts.

IIRC the KLR has/had the last of the 1970s style air valve adjustable air chamber forks. Give it some time, KTM's WP suspension company was running a air spring fork on Dungy's 450 last year. No steel fork springs at all. When they work that out forks will get lighter and have a fully adjustable spring rate with a pump or push of a button.

[alex.s]

after talking to chode about this for too long we came to a consensus.

air compresses on a P V curve so its progressive compared to the fixed rate spring. so in order to make the air spring "more progressive", you would want less air volume, which means the air compression ratio is higher, meaning at the end of the compression stroke the pressure on the air is higher, providing a greater resistance. a less progressive spring is achieved with a lower compression ratio, IE- more air volume. a schrader valve would let you set the starting pressure but it still follows the curve. since the pressure is a curve and not linear, adding more starting pressure means that the ending pressure will be that much higher. just remember that if your air volume can't compress the entire volume of fork change, you will essentially "top out" on the fork oil and it will be forced past the air seals in the top of the fork.

[choneofakind]

Originally Posted by old3

KTM's WP suspension company was running a air spring fork on Dungy's 450 last year. No steel fork springs at all. When they work that out forks will get lighter and have a fully adjustable spring rate with a pump or push of a button.

Cool that you brought that up, that's exactly how decent mtb forks work (not the huge DH forks though). No coil springs, your spring rates/progressiveness is controlled by a positive and negative air chamber. You adjust pressures on the positive to set the sag, then adjust the negative to change your spring rate. You can make it either very linear or very progressive, depending on your riding needs and trails. Then you have damping for both compression and rebound to play with also. The end result is you can get great small bump compliance, use full travel, and not bottom out. It takes some time to setup, but it's so much more adjustable.

There's even forks that have multiple options for platforms and adjustment for the amount of travel, all with the flick of a lever. Imagine if we could get that kind of adjustment on a motorcycle, but make it controlled by an ECU. They've kinda done this with some Ohlins shocks, but not like what they could do.

[EsrTek]

[Motofool]

Originally Posted by alex.s

...........air compresses on a P V curve so its progressive compared to the fixed rate spring.............since the pressure is a curve and not linear, adding more starting pressure means that the ending pressure will be that much higher............

For the same volume of air chamber, the difference between initial and final pressures gets bigger as the initial pressure gets higher (disregard the arrows in the schematic and see process 1-2 and 4-3 as spring effect at different initial pressures (P1 and P4)):



As compressed air precipitates part of the humidity that it contains, although relatively small, condensation of water contaminating the oil is a problem to consider after several refills.

[alex.s]

yeah i said it wrong. "that much higher" as in, it follows the same curve, so moving the starting pressure moves the ending pressure up the curve that much (that much being the pressure increase from the compression ratio) so if you have a (example) 2:1 compression ratio, and start at 1 bar, compressed the air will be at (roughly) 2 bar. but if you start at 2 bar, compressed the pressure will be (something like) 4 bar. it follows the p v curve.

[treecat]

Originally Posted by choneofakind

Not to be rude, but if you knew exactly what you were doing, why bother starting a thread? Oil height adjustment is a common change.
[/attitude]

To see if someone has bothered trying it with the baby ninja to any success?(why figure it out myself if someone else has already tried it) Its nothings new and has been done on motorbike forks for the last 40 years

FWIW, the forks off the '08-'12 250R are the same as those on the 300 but with different oil height, spring rate, etc. Feel free to read through the suspension threads for the '08-'12 bike for more ideas.

They are not that different from basic mountain bike forks I played with over 10 years ago. Doesn't mean I cant ask the question and create a discussion (what forums are all about) as I haven't seen anything relating to doing this with a baby ninja in my searches

Im trying to fix an issue a friend is having with her 300 that she didnt feel on her 250, wavy/bouncing up and down feeling.

I have made improvements by adding 16mm of preload to the forks and upping the rear to the 2nd highest preload adjustment

pretty sure she will be getting new springs(the bike used to sag 30mm under is own weight) and maybe emulators but money is tight right now.

how much oil should i be adding to the forks to test it in stages? (this is where adding an valve makes things easy as i can lower it a dam lot easier)

[Somchai]

Maybe before changing many things and going for many tests you could give this a try (sorry it's german only, so I'd use Google for translation):
"Through the use of HKS GGV the so-called telescopic fork breakaway torque is completely eliminated. The smallest bumps and the like are no longer transferred from the unsprung part of the telescopic fork on the bike. The result is silky, smooth ride and the safest ground. A noticeable benefit! In combination with a HKS extremely lubricated chain results in a "smoothest driving"! A breakaway torque no longer exists!"

Here's the link: http://www.hks-czech.de/hks-ggv.html
In Germany many riders are having a big improvement with using this.

[jkv45]

Originally Posted by treecat

Im trying to fix an issue a friend is having with her 300 that she didnt feel on her 250, wavy/bouncing up and down feeling.

I have made improvements by adding 16mm of preload to the forks and upping the rear to the 2nd highest preload adjustment

pretty sure she will be getting new springs(the bike used to sag 30mm under is own weight) and maybe emulators but money is tight right now.

how much oil should i be adding to the forks to test it in stages? (this is where adding an valve makes things easy as i can lower it a dam lot easier)

I think that would be a damping issue, not related to preload, and would be corrected with a heavier viscosity fork oil.

Air caps on forks were popular in the 80s, but faded. By increasing pressure in the fork you are making the rate more progressive as it compresses. Reducing the amount of air in the fork by raising the oil level will accomplish the same thing, but there has to be enough air-space to ensure there is still space when the fork is fully compressed.

[old3]

Originally Posted by treecat

Im trying to fix an issue a friend is having with her 300 that she didnt feel on her 250, wavy/bouncing up and down feeling.

I have made improvements by adding 16mm of preload to the forks and upping the rear to the 2nd highest preload adjustment

pretty sure she will be getting new springs(the bike used to sag 30mm under is own weight) and maybe emulators but money is tight right now.

how much oil should i be adding to the forks to test it in stages? (this is where adding an valve makes things easy as i can lower it a dam lot easier)

Is it something like the fork locking up, not moving on very high speed compressions? Hammering? The stock forks were super soft and harsh for me on repetitive, square edged, sharp hits. (high speed compression is not bike speed, but the speed the suspension is moving towards bottoming). Low speed comp would bottom them, like heavy braking. High speeds would lock them up and send the shock to the bars, jarring hits went right thru the grips.

I ended up with Emulators. My guess is the stock dampers can't flow enough to deal with a second, third, etc... hit and they basically stop compressing. The dampers can't move the amount of oil it needs to after the first compression. The emulator slows it down enough that it can. Against all common theory, I left my damper rods alone (no drilling) and just dropped the emulators on the springs. I just cut the preload spacers. My thought was I could still drill the holes later. Nearly a year later I haven't opened them up to change anything.

In upright use, they are pretty good now. In NJ/NY I get severely busted up roads, lots of nasty tar. Cracks, holes, lumps into turns, ripples etc. Compared to stock, they are great. I rarely bottom them now and they can deal with as many hits as I can feed them.

http://www.ninjette.org/forums/showthread.php?t=125693

I'm told it can't work without drilling out the damper rod holes to flow more oil, but it does!

[choneofakind]

This might sound stupid, but describe this wavy/bouncy feeling? Only after bumps? Is it constant but varying with speed? Is your friend a featherweight or a clyde?

If it's a constant bouncy feeling, have you checked the tires for flat spots?

Do you know what end it feels like it's coming from? Can you (heavier rider I'm assuming) replicate this feeling while riding it?

There was one lady a while back who has the same issue. She was a featherweight on her 300 and insisted it was the shock. But she got mad at us and left after about 3 days. No resolution unfortunately.

[choneofakind]

Originally Posted by jkv45

By increasing pressure in the fork you are making the rate more progressive as it compresses.

This is false. Raising the pressure is analogous to adding preload to a coil spring while altering the change in volume as the fork compresses (changing oil height) is analogous to changing the spring's linearity.

See attached proof using ideal gas law. Yes, we can assume that air behaves as an ideal gas for this situation.

Rotate and zoom to read it. I'm on my cell phone.

[Somchai]

Originally Posted by choneofakind

Do you know what end it feels like it's coming from?

THIS is a good question, since I also thought that my front end is to stiff and now after a real professional riding my Ninjette with after that making minor adjustments at the REAR shock (only preload and rebound softer) I can say WOW what a difference...

[treecat]

Originally Posted by choneofakind

This might sound stupid, but describe this wavy/bouncy feeling? Only after bumps? Is it constant but varying with speed? Is your friend a featherweight or a clyde?
I cant get it to reproduce what she describes in a short test ride, but then I am lighter then her(im a lightweight) and probably center my weight further to the rear then her.

If it's a constant bouncy feeling, have you checked the tires for flat spots?
yes constant bouncy feeling, but tyres were replaced with something stickier less then 300km ago, could be out of balance but were fitted by a trusted tech

Do you know what end it feels like it's coming from? Can you (heavier rider I'm assuming) replicate this feeling while riding it? front, but uping the preload on the rear may of worsened the issue, will test with a heavier rider this weekend
.

[treecat]

Originally Posted by old3

.

the way she describes it, its like its rebounding too quickly toping out compressing and topping out again and again and again even on smoothish roads.
she was bottoming it out and getting the harshness you described but with the preload spacers I cut her she hasnt bottomed it since

[jkv45]

Originally Posted by choneofakind

This is false. Raising the pressure is analogous to adding preload to a coil spring while altering the change in volume as the fork compresses (changing oil height) is analogous to changing the spring's linearity.

See attached proof using ideal gas law. Yes, we can assume that air behaves as an ideal gas for this situation.

Rotate and zoom to read it. I'm on my cell phone.

I'll have to trust you on that, because I can't get anything out of that photo...

So you are saying that decreasing the volume of air in the fork (raising the oil level) does not have the same effect as increasing the air pressure, and that you will only get more progressive suspension action with less air volume - not more pressure? Is that right?

[Motofool]

Originally Posted by treecat

the way she describes it, its like its rebounding too quickly toping out compressing and topping out again and again and again even on smoothish roads...........

If she bought the bike used, it is possible that the previous owner changed the viscosity or level of the fork oil or drilled the damping rod.

If she feels a bump per each turn of the wheel, the wheel itself could be deformed due to hitting something hard or simply because the new tire was improperly installed and one (or both) bead is not seating all the way around.

Copied from here:
http://faq.ninja250.org/wiki/Where_c...oad_spacers%3F

"One of the 'cheap-out' Band Aids that has been done by some people in the past is putting long spacers in their forks in lieu of stiffer springs. This is positively not recommended, and here's why: By adding more preload (the spacer), you make the bike stiffer/harsher for everyday commuting/riding, and it'll still be all mushy and wallowy when you push hard. That's kinda the opposite of what most riders really want. So, you're really much better off putting in new, correct-rate springs than using the Band-Aid formula.
Good, Cheap, Fast... pick any 2."

[choneofakind]

Originally Posted by jkv45

So you are saying that decreasing the volume of air in the fork (raising the oil level) does not have the same effect as increasing the air pressure, and that you will only get more progressive suspension action with less air volume - not more pressure? Is that right?

Yes.



The progressiveness is determined by the percentage difference between the compressed volume and the uncompressed volume. In the case if a fork, you will get more linear suspension with a larger uncompressed air volume. It's all about the uncompressed volume relative to the compressed volume. If the two volumes are very close, it will be very linear. If the two volumes are very different, it will be very progressive. Just remember than in terms of a fork, we will always have the same amount of compression distance at the bottom of the stroke, so like Alex said, your air pocket has to be 'taller' than that or else you'll lock the fork with oil (or it will just blast out the top).

The starting pressure is nothing more than a coefficient (as shown in my sideways proof). It does not change the ratio of volumes, it only changes the ending pressure by a constant ie if you raise P1 by 4 psi, P2 (and every prrssure measured along the way) will also be 4 psi higher.

I used ideal gas law for a closed system. What I showed was that the relationship between beginning and ending pressures does not change just by starting with a higher pressure. You'd have to change the volumes for that. And since we have a fork with a set amount of distance change, that means changing the starting volume. Dont forget when you add pressure, you're really just forcing more stuff into the same space. You aren't adding volume by adding air.


Edit: I guess my whole point in doing this was to show that adding a valve was never the right thing to do here. That would just make the fork stiffer, which is silly because we get get different rate springs. it would also test the seals more. Since I've had leaky seals, I'm all for not adding more pressure than necessary. Like hernan's link says, preload is a bandaid and isn't the right way of doing it. Well if preload is analogous to pressure... yes pressurizing it is a great tool for tuning. But it shouldn't be the only thing done.

[jkv45]

Got it - thanks.

[choneofakind]

Hold the phone. Did the PO forget to put all the preload spacers back in the forks when they were apart?!? You said it sagged 30mm under it's own weight and when you added preload it stopped topping out (nice MTB trick ) how far did it sag with her on it before you added spacers? How far now? Front end is 5" of travel right? So that makes 30mm with rider about 25%.

Did the PO forget to put all the parts in the forks? Can you confirm that the springs are the actual OEM parts? Are you sure it's the correct viscosity oil at the suggested oil height?

[old3]

I'd start with lifting the bike and feeling for harsh metallic top out of the forks. Just grab the bars and yank it upwards. Might need two people to get it up enough. Is there noise? In the forks or in the steering head...

Second, jack it up in front by the engine. Grab those fork legs and shake fore/aft while another feels the gap at the upper triple and the head tube of the frame. Expect a click or clunk. Replace the loose ball bearings with tapered rollers from All Balls. Another test is to release the bars at about 55 MPH ad let it decal to 35MPH. If it starts shaking the head (and be ready to grab the bars!) into a violent head shake, replace bearings.

3rd, put a small, thin zip tie on the tube at the dust wiper. Have her ride over a spot you can use over & over where it happens. Inspect location of zip tie to see how much travel she is using.

I'm going to bet the steering bearings are clapped out and she is getting feedback from them. Known issue on the 300. The races gall and scar within 1000 miles on many bikes.

Let the bearing jokes fly boys!

[alex.s]

im going to make a bet that the bike was used and the PO put new springs in but didn't cut new spacers..... or put any oil in.