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Discussion Starter · #1 ·
I have a 2007 1098S. Doing track days, I ride mid pack A group.

I had my dealership change out the compression and rebound valves in the OEM Ohlins forks for the Superbike spec kit.

We stuck with the springs that were in it and these are correct for my weight. I use all but the last inch of travel under heavy braking.

But since doing the fork valves, I get a lot of front end chatter while cornering.

I've only ridden my 1098 as COTA since doing this mod, so this is happening on a relatively smooth track.

I'm not sure which direction to go, rebound/compression, to try and resolve this.

Thanks
 

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As Bob says - chatter is usually a function of too much grip, that the tyre and suspension cannot absorb.

Try softening things off a little - tyre pressure and compression damping. One thing at a time of course.

I prefer to start with little or no compression damping on the adjuster, and increase it as needed, rather than the other way around.

But - as you are probably aware - chatter can be a very difficult problem to cure. The best team engineers in the world struggle to fix it.

It's an issue that usually comes up when you start riding faster..
 

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Discussion Starter · #6 ·
Thanks for the replies.

I did not get the hot tire pressures as we only got three dry sessions and the track was cool as it was cloudy most of the day when it wasn't raining.

I had used these tires (GP211's) for two days at COTA last September, which was when the problem first appeared.

On the OEM Ohlins rear shock, the rear tire cold tore quite badly. We had Dunlop techs on hand and we tried different pressures to try and cure this.

Since that first pair of track days, when the chatter first showed itself, I have installed a TTX-GP rear shock along with a Kyle Linear link. That worked great and cleaned up the cold tear quite considerably.

On the front, I installed a Nichols 30mm Offset triple and while the front wheel was off, I checked the balance of the tire and wheel.

The tech who installed the WSB valves is going to talk to Ohlins and we are going to double check the bikes settings and oil height in the forks.

I don't ride the bike on the street, so I'm going to have to wait for my next track day before I can start to mess and try and fix the problem.
 

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Your issues may stem from the stiffer sidewall of the Dunlops, although you don't say what you ran before.

I much prefer the softer sidewall of the Pirellis.

But I did notice when I fitted the SBK cartridges to mine that the compression damping was more progressive as the forks compressed.

But on the information given, I would be trying lower tyre pressures on the front, or a different make of tyre.
 

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I ran the Dunlop's for 3 years with the SBK kit in my forks with no problems. The 211's are a good tire, with excellent grip. Suggested hot (170f) pressures are 31 front and 26 rear. Some of my Ducati compatriots complain about the Dunlop's and chatter however. Some of them gave up and switched brands. However, none of them had the proper tools for measuring actual tire temp's, which I feel is important. If you really wish to nail down the problems, you need to know how hot your tires are getting so a pyrometer is a critical diagnosing tool.

I'd do some more testing with the proper diagnostic tools, in better conditions and see how it goes.

Also, if your forks don't already have a travel measuring device like a zip tie, I'd throw on one. It's important to determine how much travel you are using up. Bikes that don't go into the stroke enough under breaking, could chatter because they're over-damped.
 

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From the Ducati RS Manual... in case it's helpful:

TROUBLESHOOTING
This section details some of the
problems encountered and how to
solve them.
1) Front wheel chatters when
starting a turn; chattering stops
when the brakes are released and
the throttle is opened.
In most cases this is caused by an
overload of the front tyre as the front
fork travel setting is too low and the
hard part at the end of the stroke is
reached.
Solutions:
a ) Increase the preload setting so
that the fork works in the higher,
softer part of the stroke.
If necessary, put on a lot of preload
maybe you have to:
- lower the front end of the bike to
get the handlebars and balance of
the bike back to normal.
b) If a lot of stroke remains (10 mm),
reduce the oil level.
c) Ensure that the front fork is
operating smoothly.
d) Rear height is too high or rear
spring preload is too high. Lower the
rear end or decrease preload.
e) It might be a good idea to check
the condition of brake discs, calipers
and pads, as well the tightening
torque of corresponding retaining
screws.

I would add that make sure you go through the proper sequence for tightening the axle and pinch bolts to make sure there isn't a lateral load on the forks.

Dave
 

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Yes. Dave raises a good point. A surprising number of people get this wrong (not saying you have)!

The last steps in refitting the wheel should be to 'work' the forks up and down with the RH axle pinch bolt loose, to centre the RH fork on the axle where it best aligns.

Then tighten the pinch bolt.

You can use that pinch to tighten the axle nut, but it needs to be loosened, and the above step carried out, before the final tighten.
 

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Discussion Starter · #11 ·
I've run several sets of Dunlop GP211's and GP212's and never had this issue previously.

I think the forks may be bottoming, I do have a zip tie on the forks and it's pushed very low, lower than where I've previously seen it.

The tech may have installed a softer spring. I'm going to check that and also check the oil level at the same time.

I have another track day lined up in a couple of weeks, so I'll give it another try.
 

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Measure how far the zip tie is from the bottom of the fork travel. If it's 10mm or less, then it's a problem.

Like the Ducati RS manual states, if it's too low, simply try adding some preload or damping to compensate.

If your concerned about the spring rate, simply re-check your rider sag and make sure you're in range.
 

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Like the Ducati RS manual states, if it's too low, simply try adding some preload or damping to compensate.
No, if the sag is correct (or let's say generally at or below 20mm static and 40mm w/rider with the stiction averaged in), add a little bit more fork oil, just a few cc's at a time. Don't compromise by screwing up the suspension settings.

The quick way to do this is to raise the bike in a way that takes load off of the forks, loosen the top triple pinch bolts to the fork (they will prevent loosening), remove the caps using the pronged socket (available cheap on e-bay), lower the front slowly to raise the caps, add perhaps a tablespoon of Ohlins fork oil in each one, and reverse the process. It takes maybe 5 minutes once you get good at it.

I've had to learn how to do this as many places like to put less than ideal amount of fluid in the forks, including Ducati from the factory. Actually, just did this for the track bike on Monday.

Dan Kyle also did a writeup about NOT trying to screw with springs or preload for bottoming out, but to do it properly with fluid level adjustment.
 

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No, if the sag is correct
Which is why in the 3rd sentence, I mentioned re-checking sag to determine if the right springs are in there.

There are three tools which are used to keep the fork up in it's travel.

- Spring rate (determined by riders weight)
- Damping (determined by riders skill)
- Oil height (added or subtracted to prevent full bottoming)

Spring rate is the critical one and adding preload is generally not what you wanna do as a permanent fix, but it will tell you if the spring is wrong, which is why it's highly recommended as a first "DIAGNOSITC" step.

Damping circuits are designed to have a certain amount of bleed (clicker) and if the bleed is too far open, the stacks won't be functional enough to hold the fork up in it's stroke. So the second "DIAGNOSTIC" step is to adjust damping to figure out if you can keep the fork up in the stroke, AFTER you've determined the springs are right.

Finally, if the springs are right, if the damping is perfect (especially at the initial part of the stroke) and the fork doesn't dive, but simply bottoms under VERY heavy hits, then you can add oil to prevent complete bottoming. Fork oil height is part of the bottoming circuit because outside of being the active fluid for damping and lubrication of the tubes, bushings and spring, it also fills up the chamber so when the fork compresses, the remaining air inside will compress. This air compression helps stop the fork from traveling too far into the stroke. However, it can be used as a crutch when the fork doesn't have the proper spring rates or damping curves. This is why it's generally a final/last resort for tuners.
 

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No, if the sag is correct (or let's say generally at or below 20mm static and 40mm w/rider with the stiction averaged in), add a little bit more fork oil, just a few cc's at a time. Don't compromise by screwing up the suspension settings.

The quick way to do this is to raise the bike in a way that takes load off of the forks, loosen the top triple pinch bolts to the fork (they will prevent loosening), remove the caps using the pronged socket (available cheap on e-bay), lower the front slowly to raise the caps, add perhaps a tablespoon of Ohlins fork oil in each one, and reverse the process. It takes maybe 5 minutes once you get good at it.

I've had to learn how to do this as many places like to put less than ideal amount of fluid in the forks, including Ducati from the factory. Actually, just did this for the track bike on Monday.

Dan Kyle also did a writeup about NOT trying to screw with springs or preload for bottoming out, but to do it properly with fluid level adjustment.
^^+ 1, also there is a very good set-up spec sheet by Dan Kyle, Kyle Racing, that has been posted on this Forum a few times. You should be able to do a search "suspension set-up to access the article.. if you cannot locate, let me know and I will re-post.....
 

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Been following along with this thread. My thoughts...:
Too much oil - not a big enough air spring.
Apples and oranges, I know... My 1098 with stock Showa front has less than one inch left (tie wrap) after spirited street riding and still doesn't feel like bottomed/chattering. Suck 10 cc out of each leg
 

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No, if the sag is correct (or let's say generally at or below 20mm static and 40mm w/rider with the stiction averaged in), add a little bit more fork oil, just a few cc's at a time. Don't compromise by screwing up the suspension settings.

The quick way to do this is to raise the bike in a way that takes load off of the forks, loosen the top triple pinch bolts to the fork (they will prevent loosening), remove the caps using the pronged socket (available cheap on e-bay), lower the front slowly to raise the caps, add perhaps a tablespoon of Ohlins fork oil in each one, and reverse the process. It takes maybe 5 minutes once you get good at it.

I've had to learn how to do this as many places like to put less than ideal amount of fluid in the forks, including Ducati from the factory. Actually, just did this for the track bike on Monday.

Dan Kyle also did a writeup about NOT trying to screw with springs or preload for bottoming out, but to do it properly with fluid level adjustment.
What's the proper amount of oil for the forks, and what's an easy way to check the level?

Also what happens if you have too much oil in the forks?
 

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What's the proper amount of oil for the forks, and what's an easy way to check the level?

Also what happens if you have too much oil in the forks?
Just saw this... I have the same Ohlins forks with the 25mm kit that i noticed you wrote about in another thread.... and bottomed out without dust seals the oil level measured from the top of the tubes at the midpoint center line side view is set to 120mm's... springs in. I would probably lower it a bit to 122-125mm's after running it on the track this weekend, as the tie-wrap was a good 1.25" off of the bottom. Very happy with the forks and the braking. Here's my front end setting (200lb rider with gear)... bike weighs 368lbs topped off with fuel (front 188 rear 180).

1. 40mm average total sag (average to take out stiction)
2. 20mm average static sag (right on the money)
3. 28mm offset
4. Ride height at the top of the fork tubes with the Attack triple clamps
5. Preload is one full turn in on 9.5 springs
6. 12 turns out rebound
7. 12 turns out compression
8. Bridgestone V02 slicks

If the oil level is a little too high, it creates a stiffer air spring right in the area where you need the best suspension action in the sweet spot of the forks. If it's a lot too high, the front will be way too harsh, air is a progressive helper spring, and fluid does not compress.

The Ohlins spec for oil level is 165mm "without" the spring and the cartridges pumped up very well with fluid as to not throw the numbers off. Trouble is, too many times there is air remaining, and the actual oil level ends up being too low, bottoming out the forks (using up all the mechanical travel)
 

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Discussion Starter · #19 ·
On Saturday, per Ohlins, N.A. suggestion, I pulled the forks and changed the air gap to 135mm.

Sunday, I got to do a private Ducati track day at Cresson Mototsports ranch, TX. The video below was primarily a test of a new Gyro system for GoPro cameras, that I received about a week ago. MotoGyroVision GoPro
The track is quite bumpy, but the main problem, with the quality of the video is my bike.

The Gyro worked very well and really highlighted the chatter issue.

The video starts off slowly as I didn't have my tire warmers, so I am super slow for the first couple of laps and then progress up to being not quite so slow.

I did find through the day, that backing off the comp and rebound clickers did seem to help, or maybe I was getting accepting of the chatter.


Next step, I'm swapping out the GP211's with a set of Pirelli's, so we'll see if that helps.
 

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I don't know what my oil level is...and I'm not sure how to even measure the level accurately to be honest. But based on feel I expect I need more oil in there. I weigh about 20-25 lbs more than you Harsay and I'm running 10.5 springs in the forks with quite a bit more preload on them. My sag was set at 36 mm originally, but I've added 1/2 turn of preload since then. Comp and rebound are set at 10 clicks out for both.
 
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