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Just finishing a fork rebuild. I'm wondering what is the max i can adjust the oil level/air gap to stiffen the damping.

I the 10cc increment is the norm but whats max before I put seals in danger
 

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Discussion Starter #2
In case anyone ever thinks about this one - it works - just a tiny amount of fluid makes a huge difference and it's very easy to to do .
 

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Air Spring does not stiffen the damping, the valving does that. The Air Gap will not come into play until the very end of the stroke and is basically an extension of the coil spring rate although much more progressive.

If you are blowing through the stroke then you need more compression damping with the valving.

Additionally if you decrease your air gap by adding more oil then your rebound damping will suffer for it on larger bumps as you now have more spring force to counter as the forks extend
 

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As LDH mentions airgap works in conjunction with the main spring, not damping. As to the max you can put in, there really is no number. But again like LDH mentioned the higher you go, the more harsh it will feel. Generally for a street bike we'll stay somwhere around 170 to 190mm range. For racing it varies but we always go as low as possible, 190mm +.
 

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I know you didn't ask me, but I will throw this out there. It depends on the racer and the type of cartridge. When guys are "racing" at 15 seconds off the lap record they have completely different requirements from their suspension and geometry than those that are at or near the lap record. The faster they go the more unique their riding style and requirements are which means their set-up is more finely tuned.

Having said that, Generally YES less & less oil is used, but usually in conjunction with more coil spring rate and more damping. They want the most linear travel possible, but they also have to be able to support the front end to maintain geometry at all points on the track whether trailbraking to the limit or on the gas driving out at 100% throttle. Anyone ever notice how far Rea and Sykes front ends dive on braking on their current ZX-10RR? You have to really have your set-up nailed to pull that off without bottoming out which would be catastrophic.

With conventional carts at proper track pace 20-40mm less than spec is pretty routine, but with gas carts some of them have just enough oil in the actual fork tube to provide lubrication to the fork seals and that is about it.
 

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I know you didn't ask me, but I will throw this out there. It depends on the racer and the type of cartridge. When guys are "racing" at 15 seconds off the lap record they have completely different requirements from their suspension and geometry than those that are at or near the lap record. The faster they go the more unique their riding style and requirements are which means their set-up is more finely tuned.

Having said that, Generally YES less & less oil is used, but usually in conjunction with more coil spring rate and more damping. They want the most linear travel possible, but they also have to be able to support the front end to maintain geometry at all points on the track whether trailbraking to the limit or on the gas driving out at 100% throttle. Anyone ever notice how far Rea and Sykes front ends dive on braking on their current ZX-10RR? You have to really have your set-up nailed to pull that off without bottoming out which would be catastrophic.

With conventional carts at proper track pace 20-40mm less than spec is pretty routine, but with gas carts some of them have just enough oil in the actual fork tube to provide lubrication to the fork seals and that is about it.
Thank you for good input.

Yes have noticed how WSBK riders compress forks and they STAY compressed in bottom 1/4th stroke while transfering brake load to cornering lean load.
Guess tuning that zone is very important to them.

Just looked up that K-tech recommended level settings for RDS (conventional) and DDS (pro level) are 145mm and 185mm respectively. Rod diameters (defining airgap volume) are about same, but still 40mm difference!
 

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I know you didn't ask me, but I will throw this out there. It depends on the racer and the type of cartridge. When guys are "racing" at 15 seconds off the lap record they have completely different requirements from their suspension and geometry than those that are at or near the lap record. The faster they go the more unique their riding style and requirements are which means their set-up is more finely tuned.

Having said that, Generally YES less & less oil is used, but usually in conjunction with more coil spring rate and more damping. They want the most linear travel possible, but they also have to be able to support the front end to maintain geometry at all points on the track whether trailbraking to the limit or on the gas driving out at 100% throttle. Anyone ever notice how far Rea and Sykes front ends dive on braking on their current ZX-10RR? You have to really have your set-up nailed to pull that off without bottoming out which would be catastrophic.

With conventional carts at proper track pace 20-40mm less than spec is pretty routine, but with gas carts some of them have just enough oil in the actual fork tube to provide lubrication to the fork seals and that is about it.
Even for regular trackday riders who are just starting out we always run as low as possible. Like you mention we have to take spring into account but ultimately we run as low as we can go. We've done back to back testing and everyone can feel the difference. The one exception to the rule is street riders. It's not that they wont benefit from the lower oil level, it's just there are too many variables on the road to chance not having extra bottoming support.

While LDH and I have two different thought processes on this, neither one is wrong. It's just different ways to attack a problem.
 

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Thank you for good input.

Yes have noticed how WSBK riders compress forks and they STAY compressed in bottom 1/4th stroke while transfering brake load to cornering lean load.
Guess tuning that zone is very important to them.

Just looked up that K-tech recommended level settings for RDS (conventional) and DDS (pro level) are 145mm and 185mm respectively. Rod diameters (defining airgap volume) are about same, but still 40mm difference!
In this particular instance you are comparing apples to oranges, let me explain. The RDS is a open bath cartridge, so oil runs from inside the cartridge to the outside. In order for this to work the entire cartridge MUST be submerged in oil otherwise air will be sucked into cartridge and damping will be killed. In addition the oil level is setting air gap. So for an open cartridge (Ohlins 30mm, K-Tech RDS, GP suspension) the oil level serves two purposes, air gap, and making sure the cartridge is fully submerged.

The DDS cartridge is a fully enclosed pressurized system. What this means is the oil never leaves the cartridge and always stays full. This allows you to run extremely low oil levels without introducing air into the cartridge. So in this case when your setting the oil level you are ONLY using it for air gap unlike open bath cartridges.

You mentioned rod displacement, in this conversation rod displacement does not have an effect like you would think. In a pressurized system the rod displacement will not change the oil level height in the cartridge. In open bath like the RDS it would be minimal level, not enough to even worry about.

EXAMPLE - Anthony West this weekend at PittRace was on K-Tech DDS and Dave Anthony was on K-Tech RDS. We wanted to run 210mm on Anthonys forks but could not because we were too close to the top of the cartridge, so we ran 190mm. On Anthony's bike we have no issues so we can run 210 to 220mm all day long without any issues.
 

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When guys are "racing" at 15 seconds off the lap record they have completely different requirements from their suspension and geometry than those that are at or near the lap record.
Interesting, what are the biggest differences between pro rider fork setup and "15s racer"?
Or are requirements that much personal, that one pro has more and other less damping compared to Ohlins factory recommended settings for for example FGRT201 forks?
I had chance to make 3 laps on IDM rider gen4 with FGRT201 forks and that had much less compression damping making front dive quickly.
 

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EXAMPLE - Anthony West this weekend at PittRace was on K-Tech DDS and Dave Anthony was on K-Tech RDS. We wanted to run 210mm on Anthonys forks but could not because we were too close to the top of the cartridge, so we ran 190mm. On Anthony's bike we have no issues so we can run 210 to 220mm all day long without any issues.
Valuable information, this and like you wrote before: low level for regular riders too. Will try going down from 145mm to some 185mm with RDS.
 

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Interesting, what are the biggest differences between pro rider fork setup and "15s racer"?
Or are requirements that much personal, that one pro has more and other less damping compared to Ohlins factory recommended settings for for example FGRT201 forks?
I had chance to make 3 laps on IDM rider gen4 with FGRT201 forks and that had much less compression damping making front dive quickly.

First & most obvious the physics working against a bike chassis at or near the lap record are exponentially higher than the guy riding around at 15 seconds off the lap record. The bike near the lap record is moving around, compressing the suspension, flexing the frame and drifting all the time and that all has to be controlled predictably. To get a rider to that level takes a lot more technically correct suspension set-up focused to those needs. Those riders, as awesome and skilled as they are, do not get to that level on their own. It's a team effort and a lot of it.

If you take a newbie ham-fisted rider and just arbitrarily remove most of the oil from his fork tubes like you would end up doing for a pro racer then you are risking the event of bottoming out which is catastrophic. When a rider actually touches the inner stanchion to the fork cap while in a turn it almost always results in exceeding the tires grip and a front end wash. That is why we have higher oil levels and hydraulic stops for street bikes and the like. It's a safeguard.

When you work with faster riders you can read their data and know how much fork travel they are actually using and where on the track that is happening and you can tune the suspension for it. This always includes custom oil level and spring rates which varies even more when you have gas kits where you have additional pressure inside the forks to factor in. Gas kits are even more reliant on the riders specific style and requirements. Additionally we almost always use a higher spec valving to compensate for those additional forces on the bike regardless of whether it is conventional or gas kits. There is way more to it, but to try to explain it in detail would take a novel and way more time than I can spend here talking about it.

In my experience there is a line around 8 seconds off the lap record where things start to happen and custom attention is needed for suspension bits. That's where the FGRT201 forks for example "as delivered" aren't going to be quite up to the task and need some help to get them to that next level. That being said most riders are not at 8 seconds or less off the lap record. Most trackday guys are easily 20+ seconds off the lap record at any major circuit so those forks work wonders for both the physical requirements of making their bike handle properly as well as their own mental confidence. They are riding faster with less drama so it is money well spent. If they want to go faster and are capable of it there are better options with gas or spring charged cartridge kits to get them there, but like always speed is a question of money. How fast do you want to go equals how much do you want to spend?

The bottom line is riders at or near the track record are getting a focused level of support where intimate knowledge of the trade is applied in a manner that would be mostly if not completely irrelevant for riders 15 seconds off that pace. In my years I have ridden one World Level Unobtanium Superbike and several AMA Level racebikes and all of them were basically un-rideable at 20 seconds off the lap record. One AMA Factory 600SS bike in particular felt like I was riding on wooden shocks on a warm up lap and the bike would protest the input into every turn, but get it down to 10 seconds off the lap record and it started to feel almost normal, 7 seconds off the lap record even better and almost instinctual entering every turn. Now I couldn't go any faster than that because I am just not a good enough rider to do it so I don't know how much better it was going to get, but there was no denying that the faster I went the better the bike handled which is the exact opposite for a bone stock bike off the showroom floor. From a streetbike having to safely carry a rider & passenger to Hooters on Bike Night to a racebike designed to carry a solo rider to a championship at the lap record. It's all in how the set-up knowledge is applied and it is very specific for the task.
 

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As far as the FGRT201 forks you experienced. It's hard to say whether you were over-riding the existing valving or if they had been set-up incorrectly... I cannot count how many times I have seen Ohlins forks and cartridges incorrectly backed way off on Compression. Usually because some clueless tuner starts pushing up and down on the forks and visually tries to ascertain how the valving is set and that CANNOT BE DONE. Nobody can push up & down on an Ohlins suspended bike and gauge what is happening inside the suspension as you cannot emulate what is happening dynamically at speed on the track just by pushing on it with your hands. When I see tuners doing that shit to Ohlins products I warn others to stay the hell away from them.
 
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