New Ohlins front end review

[JD Racing]

So Gas forks with one rb and one comp, would be the best way to go? If one leg is trying to do 2 jobs, the chance of cavitation must be higher, than a fork only doing one thing at a time?

Not necessarily, this is where you have to look at the system as a whole and not get hooked up on one thing. If you have one leg doing only one operation then you have to increase the damping force as only one leg is doing the work, this leads to a larger pressure differential which has the potential for more cavitation, so you may need to increase the gas pressure which then adds to the extension force acting on the damper rod, the stiction on the seals...

[warewolf]

ummm...yeah on the cavitation issuse...why hasn't someone though of having a separate air canister away from the forks...

Infinity Subtanks

[Robert Taylor]

Not necessarily, this is where you have to look at the system as a whole and not get hooked up on one thing. If you have one leg doing only one operation then you have to increase the damping force as only one leg is doing the work, this leads to a larger pressure differential which has the potential for more cavitation, so you may need to increase the gas pressure which then adds to the extension force acting on the damper rod, the stiction on the seals...

All fair points. Ohlins get around that issue with their twin tube TTX gas cartridges used in AMA and World Supersport. Gas pressure is 5 bar, quite low. Gas pressure used is always of course indicative of how well pressure balanced the system is. They are a nice piece of kit and appear to work really well. I have no doubts also that WP have something pretty clever.
If they can eventually get these into volume production they should still be affordable as they only have half the number of pistons etc.

[cowpoos]

Infinity Subtanks

shit a brick...thats what I was thinking. turns out I'm a bit slow on the thinking though!!

anyone else care to make a educated comment?

[Shaun]

Not necessarily, this is where you have to look at the system as a whole and not get hooked up on one thing. If you have one leg doing only one operation then you have to increase the damping force as only one leg is doing the work, this leads to a larger pressure differential which has the potential for more cavitation, so you may need to increase the gas pressure which then adds to the extension force acting on the damper rod, the stiction on the seals...

Would not building a compilation of a lot more shims ( Smaller than the std big piston shims) take care of this?

so there are more shims doing the job as you say, but as there are more, and easier to pass by being small initially, help to control/elliminate the cavitation, as well as the fact the leg is only doing one thing, so this will also aid eliminating cavitation?

Stiction is not really an issue on NZ roads and tracks \i feel, as our conditions are so bumpy any way, that it would take a data loger for a lot of riders here to really notice that NEGATIVE


I am realy just filling in time at the airport weighting for my flight to the Isle of Man TT races, but thanks for the feed back

PS, gis a job MR as a tester for you

[JD Racing]

shit a brick...thats what I was thinking. turns out I'm a bit slow on the thinking though!!

anyone else care to make a educated comment?

they were invented by Ross Maede at Enzo, here is a copy of an email he sent to someone explaining their operation.

"The concept of my subtank system is to create a "speed sensitive spring characteristic". As you know, the two elements of suspension are SPRING and DAMPING. The SPRING element is load or position sensitive. If 10 lbs. is applied to a 10 lbs. per inch rated spring, it will compress one inch. 20 lbs. = 2 inches, etc. But it is not speed sensitive, because if 10 lbs. is dropped on the spring, it will compress more than 1 inch, but after bouncing up and down for a while, it will settle at 1 inch of compression. Adding speed to the situation changes the reaction. The second element is DAMPING, which is speed sensitive. It is like stroking your hand through water: the faster you stroke your hand, the more resistance the water provides. Speed determines the amount of resistant force. But DAMPING is not position sensitive or load sensitive. If a load is placed in the water, it will sink to the bottom. Nothing will hold it in place, only the speed sensitivity will control how fast it sinks.

So the two elements work together to give total suspension action. But my system creates an additional speed sensitive element within the spring characteristic. In a front fork, the TOTAL spring character is determined by the coil spring rate, and the AIR SPRING RATE combined. The AIR SPRING RATE is the compression of the air volume within the fork determined by the oil level. A low oil level provides a large air volume which compresses at a slower progressive rate. A high oil level provides a small air volume which compresses at a faster progressive rate.

The sub tank system provides additional air volume to manipulate. By dividing the total air volume into two "chambers", and separating them with a "restrictive barrier", it is possible to control the compression of the air volume by metering restriction between the two "chambers". The compressing "charge" is created by the inner fork tube entering the outer fork tube. This charge compresses the oil level chamber in the fork. With the sub tank system installed, a high oil level can be set within the fork. The sub tank provides additional air volume, which when combined with the oil level volume is actually providing a large total air chamber volume. When the fork is compressed slowly or uses shorter amounts of stroke, the total air volume of both chambers is compressed equally, giving the sensation of a very low oil level, and the action is soft. But as the fork compression speed increases, or longer amounts of stroke are used, the restrictive barrier prevents equal compression between the two chambers, so the oil level air chamber compresses at a higher rate than the sub tank chamber volume. This gives the sensation of a high oil level in the fork, and the action is firmer. In other words, when the fork is compressed slowly or uses short stroke, it feels like it h as a low oil level. But when the fork is compressed faster, or uses longer stroke, it feels like it has a high oil level. The tuning elements of the system are the volumes of each chamber (oil level and sub tank volume) and restrictive barrier (flow adjustment on sub tank). My system is installed on the stock cap through the air bleed hole, which is drilled out larger and tapped to accept a larger flow fitting. The hoses attach to the cap fittings, and then to the sub tanks. The adjustment flow is the point of greatest restriction.

I hope that this clears up any confusion about the system. The difference between the KAYABA bladder system and my sub tank system is that the restrictive barrier between the two chambers is HYDRAULIC in the bladder system, and PNUEMATIC in the sub tank system. WHich is better? I believe that PNUEMATIC, air restriction is better because air can compress and will not spike. HYDRAULIC, oil restriction is not compressible, so sometimes it spikes. Also, the bladder system is not adjustable, and the sub tank system is. "

[Shaun]

you read to much JD, back to work now snap snap[

[Robert Taylor]

Would not building a compilation of a lot more shims ( Smaller than the std big piston shims) take care of this?

so there are more shims doing the job as you say, but as there are more, and easier to pass by being small initially, help to control/elliminate the cavitation, as well as the fact the leg is only doing one thing, so this will also aid eliminating cavitation?

Stiction is not really an issue on NZ roads and tracks \i feel, as our conditions are so bumpy any way, that it would take a data loger for a lot of riders here to really notice that NEGATIVE


I am realy just filling in time at the airport weighting for my flight to the Isle of Man TT races, but thanks for the feed back

PS, gis a job MR as a tester for you

Thin''scrubbing'' shims. In regular ''single tube'' systems the more agressive the stack ( especially on midvalve ) the greater the chance of cavitation. I need to describe and show you this one on one. JD may want to elaborate in writing.
I disagree with you about stiction.
Night.

[cowpoos]

they were invented by Ross Maede at Enzo, here is a copy of an email he sent to someone explaining their operation.

"The concept of my subtank system is to create a "speed sensitive spring characteristic". As you know, the two elements of suspension are SPRING and DAMPING. The SPRING element is load or position sensitive. If 10 lbs. is applied to a 10 lbs. per inch rated spring, it will compress one inch. 20 lbs. = 2 inches, etc. But it is not speed sensitive, because if 10 lbs. is dropped on the spring, it will compress more than 1 inch, but after bouncing up and down for a while, it will settle at 1 inch of compression. Adding speed to the situation changes the reaction. The second element is DAMPING, which is speed sensitive. It is like stroking your hand through water: the faster you stroke your hand, the more resistance the water provides. Speed determines the amount of resistant force. But DAMPING is not position sensitive or load sensitive. If a load is placed in the water, it will sink to the bottom. Nothing will hold it in place, only the speed sensitivity will control how fast it sinks.

So the two elements work together to give total suspension action. But my system creates an additional speed sensitive element within the spring characteristic. In a front fork, the TOTAL spring character is determined by the coil spring rate, and the AIR SPRING RATE combined. The AIR SPRING RATE is the compression of the air volume within the fork determined by the oil level. A low oil level provides a large air volume which compresses at a slower progressive rate. A high oil level provides a small air volume which compresses at a faster progressive rate.

The sub tank system provides additional air volume to manipulate. By dividing the total air volume into two "chambers", and separating them with a "restrictive barrier", it is possible to control the compression of the air volume by metering restriction between the two "chambers". The compressing "charge" is created by the inner fork tube entering the outer fork tube. This charge compresses the oil level chamber in the fork. With the sub tank system installed, a high oil level can be set within the fork. The sub tank provides additional air volume, which when combined with the oil level volume is actually providing a large total air chamber volume. When the fork is compressed slowly or uses shorter amounts of stroke, the total air volume of both chambers is compressed equally, giving the sensation of a very low oil level, and the action is soft. But as the fork compression speed increases, or longer amounts of stroke are used, the restrictive barrier prevents equal compression between the two chambers, so the oil level air chamber compresses at a higher rate than the sub tank chamber volume. This gives the sensation of a high oil level in the fork, and the action is firmer. In other words, when the fork is compressed slowly or uses short stroke, it feels like it h as a low oil level. But when the fork is compressed faster, or uses longer stroke, it feels like it has a high oil level. The tuning elements of the system are the volumes of each chamber (oil level and sub tank volume) and restrictive barrier (flow adjustment on sub tank). My system is installed on the stock cap through the air bleed hole, which is drilled out larger and tapped to accept a larger flow fitting. The hoses attach to the cap fittings, and then to the sub tanks. The adjustment flow is the point of greatest restriction.

I hope that this clears up any confusion about the system. The difference between the KAYABA bladder system and my sub tank system is that the restrictive barrier between the two chambers is HYDRAULIC in the bladder system, and PNUEMATIC in the sub tank system. WHich is better? I believe that PNUEMATIC, air restriction is better because air can compress and will not spike. HYDRAULIC, oil restriction is not compressible, so sometimes it spikes. Also, the bladder system is not adjustable, and the sub tank system is. "

Thanks for that...I'm guessing that because thee is a production example already...and its not really seen in racing circles that it has limitations or its not that greater concept in the scheme of things???

[JD Racing]

The more pressure you have within the system, the more pressure you have acting on the seal, the more pressure you have on the seal the more force it applies to the shaft so the more stiction you have.

[Shaun]

Cheers JD and Rob. Hey Doc, i will be back to school after the 21st of June.

[Robert Taylor]

Thanks for that...I'm guessing that because thee is a production example already...and its not really seen in racing circles that it has limitations or its not that greater concept in the scheme of things???

Its more useful and used in MX because of terrain variation and the tracks change / cut up during a long moto. They also have 300mm of fork travel, we have 120 odd mm.
MX suspension dynamics are by implication more extreme. We see ''kerb strike'' velocities in road race of up to around 800mm / second ( turn 1 at Pukekohe ) Puddle jumpers 4 to 5 metres per second.
Also the more effective the damping response is the more you ''catch the horse before it bolts from the stable door'', so to speak. Forks that have less effective damping over-rely on high fork oil level to arrest the relatively uncontrolled movement.
MX forks tend to have much softer midvalve calibration so arguably they rely moreso on oil level / trapped air compression ratio for final control. Damn puddle jumpers!

[Robert Taylor]

The more pressure you have within the system, the more pressure you have acting on the seal, the more pressure you have on the seal the more force it applies to the shaft so the more stiction you have.

Have you seen those dodgy red coloured 3 lip fork seals peddled around the world and here in NZ? Theyve got the temerity to say they are very low friction. The results are;

1) Very high friction

2) If fitted to forks with titanium nitrate or DLC coatings it wears it off a lot faster

When I see these pieces of cr.p I just shake my head that people are so gullible.

[JD Racing]

I've not seen the red ones but I have worked on a couple of sets of forks where the owners have proudly boasted of having fitted "no leak seals", those things don't leak because they grip the shaft in a vice like fashion, unbelievable amounts of stiction, it's like having to overcome an extra 20mm of preload.

The coatings wearing off is down to the shocking quality of Japanese coatings, not only is it poor, it's inconsistent, no two fork legs are the same, it shouldn't wear at all that's the whole idea of it, you should be able to attack it with abrasive paper and it just laugh in your face, try that with an oem tube and it will surrender faster than a northern hemisphere front row.

[Robert Taylor]

I've not seen the red ones but I have worked on a couple of sets of forks where the owners have proudly boasted of having fitted "no leak seals", those things don't leak because they grip the shaft in a vice like fashion, unbelievable amounts of stiction, it's like having to overcome an extra 20mm of preload.

The coatings wearing off is down to the shocking quality of Japanese coatings, not only is it poor, it's inconsistent, no two fork legs are the same, it shouldn't wear at all that's the whole idea of it, you should be able to attack it with abrasive paper and it just laugh in your face, try that with an oem tube and it will surrender faster than a northern hemisphere front row.

Exactly and I agree with you about the microscopically thin DLC coatings etc, a marketing exercise more than anything, ''race replicas'' etc. Yeah right. The proper race ones have something like a 15 step process. Coat, polish, recoat, repolish etc.
But fitting low quality and especially these ''no leak'' / ''vice grip'' seals just invites disaster a whole lot sooner.