20mm versus 25mm diameter fork cartridges

[Pussy]

Poos, where are you?? Some time ago I recall you mentioned something about the merits etc of 25mm cartridges, and I can't be arsed searching way back to find it.
Surely a 25mm diameter piston is going to displace more fluid for any given movement, and with bigger diameter cartridge shims, this will be easier to control? Been thinking about this a bit, and would welcome feedback from KB land

[cowpoos]

Poos, where are you?? Some time ago I recall you mentioned something about the merits etc of 25mm cartridges, and I can't be arsed searching way back to find it.
Surely a 25mm diameter piston is going to displace more fluid for any given movement, and with bigger diameter cartridge shims, this will be easier to control? Been thinking about this a bit, and would welcome feedback from KB land
MY thoughts have been...shall we say modernised on my thoughts..

where my theory on the matter was in displacing fluid...a given piston size and rod size...comapared to a larger rod and piston size...in regards to displacing fluid...was that both were displacing fluid...and displacing that fluid is whats required to build damping...what I was not so much as arguing [debating] was that, relitive to capacity within the cartridge...and size of the rod...they were still both displacing a similar amount of fluid at a similar rate...But in actual fact I was incorrect in how it related to the action of building damping...Where infact the smaller diameter cartridge and rod built damping slower..there for letting more stroke occure before it start resisting the action...not good for brake dive control [whick could be corrected with different inernal valving no doubt...but at the expense of loosing other attributes] [and I'm sure robert or JDRacing will be along shortly to correct me if I'm wrong in this case? **prays that I'm not far off the ball park**]

[Pussy]

One of the reasons I ask, is that I now have a set of 25mm cartridges in my bike, and a characteristic I am noticing is a lot less travel being used in general day to day road riding, but not at the expense of harshness. For any given bump the forks are moving less, but the damping is doing it's thing just as if not more effectively than if more travel was being used. I really want to know how/why this is happening, and as mentioned in the first post, would be very receptive to inputs from the rest of KB

[Grub]

From all accounts of road tests on your bike, it is a minter. "...The best handling GSXR I've ever ridden..." I believe was the expression used. You're not worried about its handling are you?

The theory that bigger is better sounds right to me as the 25mm is going to have to work less hard than the 20mm - that just sound right. That's as far as I know because it must get into the Theory of Hydraulics which I bet your 'supplier' could explain pretty well.

[Pussy]

I'm thrilled with the way it handles, Grub. I'm just very interested to get to the bottom of WHY. I'd love to hear for/against ideas on the 25mm concept

[JD Racing]

The only displacement in a cartridge is that from the damper rod, a K1-K6 GSXR 1000 with a 12.5mm damper rod and 20mm cartridge will displace more fluid than a TL1000 25mm cartridge with a 12mm damper rod, the damper rod is bigger so more fluid is displaced.
The difference is in the swept volume....the amount of fluid the rebound piston passes through.
Pussy your forks have a compression stack on the back of the rebound piston which slows down the speed at which the piston moves through the cartridge thats why you use less travel, the velocity that the forks achieve for a given bump is less.
If Cowpoos did the same to his 20mm cartridges he could achieve the same thing it's just a lot, lot more difficult to pressure balance a 20mm cartridge.

[Pussy]

The only displacement in a cartridge is that from the damper rod, a K1-K6 GSXR 1000 with a 12.5mm damper rod and 20mm cartridge will displace more fluid than a TL1000 25mm cartridge with a 12mm damper rod, the damper rod is bigger so more fluid is displaced.
The difference is in the swept volume....the amount of fluid the rebound piston passes through.
Pussy your forks have a compression stack on the back of the rebound piston which slows down the speed at which the piston moves through the cartridge thats why you use less travel, the velocity that the forks achieve for a given bump is less.
If Cowpoos did the same to his 20mm cartridges he could achieve the same thing it's just a lot, lot more difficult to pressure balance a 20mm cartridge.

So, is it generally easier to control 25mm set ups?

[cowpoos]

One of the reasons I ask, is that I now have a set of 25mm cartridges in my bike, and a characteristic I am noticing is a lot less travel being used in general day to day road riding, but not at the expense of harshness. For any given bump the forks are moving less, but the damping is doing it's thing just as if not more effectively than if more travel was being used. I really want to know how/why this is happening, and as mentioned in the first post, would be very receptive to inputs from the rest of KB

Probally more a evolution of technology and valving spec has as much to do with it as size of the cartridge..and at a guess with more spirited riding you would use more travel as high G-force,bump loadings are applied!!

But I think Jdracing has probally summed it up from a technical aspect in his post quite well.

[Pussy]

..and at a guess with more spirited riding you would use more travel as high G-force,bump loadings are applied!!

But I think Jdracing has probally summed it up from a technical aspect in his post quite well.

Have a ride of it sometime, Poos, and you'll see what I mean. I am running one step DOWN from standard spring weight as well (.95 installed, stock 1.0).
It's showing up how effective the mid-valving is... even giving it a good punt on the rougher stuff, you'll be surprised how little fork travel is used for very effective damping
Yep, JDRacing's explanation is a goodie

[cowpoos]

So, is it generally easier to control 25mm set ups?
I think what he's eluding to is...its easyier to set up/get a good comprimse on the cartridges you have because of the thicker damping rod [14mm ??] and the compression stack your rebound valve has on the back off it...but I dare say there is a lil more to it than that..because the cartridges and any suspension product are only as good as they are setup!!

But on a side note...using less travel may relate to alot of other things aswell...when the cartridges were initually valved and installed..the instal may have had the impression that you were a faster rider than you actualy are...and heavier braker..and they were valved to suit this impression..besides the fact they still work faultlessly in your impression..there still maybe alot more tuned into your setup than you have realised! and credit goes to the technision for make his product usable across a range of abilities and circumstances..sounds like a almost perfect compromise!! ;)

[Pussy]

No secret that Robert set the spec for me... he has been doing suspension stuff for me since 2000, and knows what I like.
What I REALLY want to know is the good oil on 20mm versus 25mm. Where are you, RT? TDC?
C'mon, there's more than one or two of you out there who can enlighten us

[cowpoos]

Have a ride of it sometime, Poos, and you'll see what I mean. I am running one step DOWN from standard spring weight as well (.95 installed, stock 1.0).
It's showing up how effective the mid-valving is... even giving it a good punt on the rougher stuff, you'll be surprised how little fork travel is used for very effective damping
Yep, JDRacing's explanation is a goodie
I don't think stock spring rate is 1.0...more like .80 I may be wrong...but 1.0 is very heavy for a stock front spring in any sportsbike...and I have ridden stock 750/600...and its a pretty cool bike stock..but seeing as I've been riding on superior suspension for a while I felt its faults easily..front had shit feel..and a odd odd feeling over multiple sharp edge bumps..not sure what sort of feel it was..but I remember it was enough of a odd feeling for me to back off!! other impressions were..bugger all ground clearence..and the rear felt like a typical modern suzuki..out in the dark [because I personally reckon the seats are to dam comfortable!!] with feel..harsh damping..lowly sprung...

And yer..I would love to take her for a spin sometime...I'd preffer on a track though [as I'm not partial to road riding these days]...I have never ridden a bike with the newer ohlins 25mm cartridges installed..and apparently they are good with brake dive control...which is a rea I would dear love some improvment in my front end!! [and feel!! lots more feel!!]

[cowpoos]

No secret that Robert set the spec for me... he has been doing suspension stuff for me since 2000, and knows what I like.
What I REALLY want to know is the good oil on 20mm versus 25mm. Where are you, RT? TDC?
C'mon, there's more than one or two of you out there who can enlighten us
lol...the good oil...that open to debate I suppose...hahaha...Maxima and ohilns oils are well rated in suspension circles...but It probally depends on what your used to working with to a degree!! [i know thats not what your meaning..lol]

[Pussy]

I don't think stock spring rate is 1.0...more like .80 I may be wrong...but 1.0 is very heavy for a stock front spring in any sportsbike...and I have ridden stock 750/600...and its a pretty cool bike stock..but seeing as I've been riding on superior suspension for a while I felt its faults easily..front had shit feel..and a odd odd feeling over multiple sharp edge bumps..not sure what sort of feel it was..but I remember it was enough of a odd feeling for me to back off!! other impressions were..bugger all ground clearence..and the rear felt like a typical modern suzuki..out in the dark [because I personally reckon the seats are to dam comfortable!!] with feel..harsh damping..lowly sprung...

And yer..I would love to take her for a spin sometime...I'd preffer on a track though [as I'm not partial to road riding these days]...I have never ridden a bike with the newer ohlins 25mm cartridges installed..and apparently they are good with brake dive control...which is a rea I would dear love some improvment in my front end!! [and feel!! lots more feel!!]

On the 750 the stock spring actually is 1.0, the 600 is .90. I'll lay money that odd feeling you mention was the weak high speed rebound. Robert has taken care of that in the other 750 that lives here.
I don't remember what the stock rear shock felt like, it was only on the bike for a few days after I bought it

[JD Racing]

What I REALLY want to know is the good oil on 20mm versus 25mm. Where are you, RT? TDC?
C'mon, there's more than one or two of you out there who can enlighten us

The size of the cartridge is just one of many factors involved in achieving a desirable rate of compression and extension.

Spring rate, air gap, oil viscosity, damper rod size, the size/ number/ position of the ports, the valving on the ports, the bleed size etc all contribute to the overall action of the forks. Taking all of that into account it's possible to have very bad 25mm cartridges as well as very good 20mm cartridges.

The fact that the new Ohlins cartridges provide instant solutions to the action of the previously popular manufacturers product is not solely down to it being 25mm.

[Robert Taylor]

The size of the cartridge is just one of many factors involved in achieving a desirable rate of compression and extension.

Spring rate, air gap, oil viscosity, damper rod size, the size/ number/ position of the ports, the valving on the ports, the bleed size etc all contribute to the overall action of the forks. Taking all of that into account it's possible to have very bad 25mm cartridges as well as very good 20mm cartridges.

The fact that the new Ohlins cartridges provide instant solutions to the action of the previously popular manufacturers product is not solely down to it being 25mm.

Well..... I think I can fairly say that in NZ I have personally had way more experience than anyone here re the whole cartridge thing. Years back we were simply respringing and reoiling, then we started fitting high flow preloading piston kits to the predominantly 20mm cartridges we still see in oem cartridges today. Sourced from a road race specific supplier in the States I was told I would never need to change the settings. It was in effect intimated that the settings were perfect, if I can be a little impolite that turned out to be a load of old bollocks and we laboriously improved the settings to match our tracks.

Bumps are indeed bumps, its just that we have a higher percentage of bumpy roads and tracks and therefore a lower percentage of smooth groomed roads and tracks.

Then we sourced from the same supplier full 20mm cartridge kits, sold quite a few and won a few national champs with them. Once the settings were optimised they worked pretty good but to be frank not night and day better than a rekitted and optimised oem cartridge. And we went through exactly the same grief of them blowing through their stroke as JD intimated in another thread.

Ohlins released their 25mm cartridge kits and all of a sudden the game has been lifted. I hear what JD is saying that the advantage is not solely down to it being both 25mm and sweeping more volume for any given distance of stroke. That is so. Its easier to better tolerance a cartridge when the size is 25mm and it is clear that the performance of the larger size shims is both more responsive and stable. Its no accident that in the world of MX the cartridge i.d size has grown over the years from 20 to 25mm and now beyond 30mm. In ordinary everyday road bikes the size has remained at 20mm because of 3 or more predominant reasons, cost, cost and cost. A few years back the TL1000 S / R and first GSXR1300s had 25mm cartridges, a much better base to improve from. But clearly making such stuff in low volumes when 90% of everything else remained at 20mm didnt rest well with the accountants who call the shots in these large factories. Less volume and more material cost....

JD mentioned pressure balance and how true it is that you cannot get too aggressive with the 20mm cartridges otherwise you end up with cavitation. That is one reason a checkplate mid valve system is largely employed in oem and aftermarket 20mm cartridges. Bending shim stack midvalves have appeared in some oem cartridges but the setting cannot be firmed up as much as desired for a road race application without introducing the very bad effects of cavitation.

The human mind is always afraid of change and I was no less than that when we started embracing the bending shim stack midvalve in Ohlins 25mm cartridges. (This has only largely occured this race season.) But having now intensively worked with it the advantages are very very obvious, 3 to 4 riders under the lap record at every round of the national champs this year in Superbike, in part because they can go in deeper on the brakes. More sidegrip, better feel. And in a roadbike installation ( albeit with a slightly softer setting ) the rider is over the moon with the performance and ride compliance. And this same guy has shared the journey that I have been through with respec kits, then 20mm aftermarket cartridge kits and now 25mm.

Apples for apples a well sorted 25mm cartridge kit with good components will outperform a well sorted 20mm cartridge kit with good components. That in essence is what the top riders in the National champs are telling me and proving on track. It is always possible for a good rider to win a national level road race with 20mm stuff but in doing so being right on the edge of his comfort zone.

In this application ( notwithstanding the overall mix of excellent well developed components ) bigger is better.

[JD Racing]

There are many racers, road riders and track day riders who just don't have the budget for a full cartridge kit, does that mean they are facing imminent death on the road or have the grim reaper riding pillion for every lap of a race, absolutely not, does it mean they can't set lap records or win races and championships absolutely not, 20mm cartridges still have their place and can still be made to offer awesome performance.

[Robert Taylor]

There are many racers, road riders and track day riders who just don't have the budget for a full cartridge kit, does that mean they are facing imminent death on the road or have the grim reaper riding pillion for every lap of a race, absolutely not, does it mean they can't set lap records or win races and championships absolutely not, 20mm cartridges still have their place and can still be made to offer awesome performance.

Granted, the post was about the relative technical and performance benefits which are very real. 20mm cartridges have their place because we are stuck with them but not struck with them. Improvement is a term of relativity and given the often abysmal components and settings in the oem 20mm stuff very real improvements can be effected. And to that end we personally do a lot of work with rekitting 20mm systems because as you say cartridge kits are unaffordable to many.
The Japanese manufacturers are geared up to produce 20mm in volume, that they have found even cheaper ways to produce 20mm cartridges eg 07 / 08 ZX6 is testament that accountants rather than engineers control their world.
We have a top level road race customer with a ZX6, the lad weighs in at over 100kg and is tall. He tried to get away with just fitting 11 newton springs in combo with his oem cartridges and heavier oil, it still blew through its stroke under braking. I have no doubt that we could have improved the stock cartridges ( once we figure a way we could stitch the cheap and nasty construction back together ) but only to a certain level. When we fitted appropriately valved 25mm Ohlins cartridges in combo with the same 11 newton springs the problem was fixed and he was instantly competitive.
I imagine that other manufacturers will soon follow suit with this very nasty and cheap cartridge construction. It may work okay on the road ( excepting square edge bump compliance! ) but it is a piece of shite on the track, no question.

[JD Racing]

Its easier to better tolerance a cartridge when the size is 25mm and it is clear that the performance of the larger size shims is both more responsive and stable.

So those FGR700 forks I've just been servicing with a 20mm cartridge, I need to call the guy up and tell him sorry mate, you've just wasted a whole bunch of dollars on a poorly toleranced product. Applying the same logic that small parts are badly toleranced I would then have to question the angles on all Ohlins 1.5mm, 2mm etc bleed needles, the 20mm piston kit that Ohlins supply for R6's, should I also question the tolerances on the TTX body-that's a lot smaller than the PRX????

[Shaun]

The ballance of thought and communication that you 2 are sharing here, is fantastic for people to read:calm:
Very funny ( Normall I guess) How 2 obvious experts can differ on opinions of a product so much! But that is another good thing about having you both on here, I don't think any thing is perfect, Just different:spanking:


Ya man Cowpoos, is loving it, I have even see some big cleaver words from him:lol:

Cheers guy's keep it up

[Robert Taylor]

Its easier to better tolerance a cartridge when the size is 25mm and it is clear that the performance of the larger size shims is both more responsive and stable.

So those FGR700 forks I've just been servicing with a 20mm cartridge, I need to call the guy up and tell him sorry mate, you've just wasted a whole bunch of dollars on a poorly toleranced product. Applying the same logic that small parts are badly toleranced I would then have to question the angles on all Ohlins 1.5mm, 2mm etc bleed needles, the 20mm piston kit that Ohlins supply for R6's, should I also question the tolerances on the TTX body-that's a lot smaller than the PRX????

As you well know the FGR is based on TTX principle and is not so dependent on shaft displacement to build damping. As we also both well know mass volume 20mm oem cartridges and the small bit part aftermarket manufacturers of same struggle to build to the exacting tolerances and quality that companies such as Ohlins and WP achieve. Albeit front fork components or shock absorber components. I have seen the Ohlins quality control department a number of times, the investment they have in this alone would blow many companies out of the water, and I would guess WP is very similiar.
In the end event I think that you know exactly what I am saying without any need to split hairs.

[Robert Taylor]

As a further adjunct to the whole cartridge deal. JD has quite correctly pointed out that not everyone can afford a 25mm cartridge kit....or indeed an aftermarket 20mm cartridge kit.
Race tech have recently released a 20mm two port preloading type piston. The basic function of a preloading type piston is that when it is combined with ample port flow area it delivers good ride height control combined with excellent abrupt bump compliance. There is always a compromise though with huge port area as there can be a tendency to blow through stroke too readily, especially under brakes.

The Race Tech G2R valve is designed and machined in such a way that it in effect introduces another 2 tuning parameters. Where a preload packing shim is normally installed if it is made of large enough diameter that it can tune the size of the ports. Therefore you can enjoy the benefit of good brake dive control that you get with a small port piston. BUT ALSO, if that ''shadowing shim'' is made thin enough it too will deflect at higher velocities exposing more port flow area when riding over abrupt bumps.
Maybe someone has done this before, I really dont know. For those familiar with damping curves such a set up will give a first ''knee'' in the curve as the bleed bypass chokes off and the shim stack opens. The size of the shadowing shim will determine the steepness of the slope. And then dependent on the thickness of that shadowing shim there will be a second more subtle knee further up the curve. I.e ''abrupt bump valve lift''
Over the winter we will be developing base settings for both road and road race application, using both our dyno and then road and track tests. The result I confidently expect will perform better than aftermarket 20mm cartridge kits at a fraction of the cost. While it wont approach the very real advantages of a top level 25mm kit the bang for buck will be very very good.

[Tony.OK]

Any chance of showing the cost differences?Including the Race Tech?

[johnsv650]

great reading and we can all learn alot from this,
thanks for your knowledge sharing...

[JD Racing]

As we also both well know mass volume 20mm oem cartridges and the small bit part aftermarket manufacturers of same struggle to build to the exacting tolerances and quality that companies such as Ohlins and WP achieve. Albeit front fork components or shock absorber components. I have seen the Ohlins quality control department a number of times, the investment they have in this alone would blow many companies out of the water, and I would guess WP is very similiar.
In the end event I think that you know exactly what I am saying without any need to split hairs.

Sorry I don't understand what you are saying, I suspect your suggesting that the tolerances accepted by other aftermarket manufacturers other than Ohlins and WP are of a dubious standard, you would have to have some serious measuring equipment to come to that conclusion.

There is some inconsistency in your argument when you then go on to state that your soon to offer mass produced brass pistons from another bit part manufacturer.

Good luck with those, I read a statement by Jim Lindeman that he hated working with the 2 port, now there's a guy who's been around longer than all of us, so if he's struggling I'll steer clear. Ohlins did have a 2 port rebound piston in 2000, it didn't last long.

[Robert Taylor]

Sorry I don't understand what you are saying, I suspect your suggesting that the tolerances accepted by other aftermarket manufacturers other than Ohlins and WP are of a dubious standard, you would have to have some serious measuring equipment to come to that conclusion.

There is some inconsistency in your argument when you then go on to state that your soon to offer mass produced brass pistons from another bit part manufacturer.
Good luck with those, I read a statement by Jim Lindeman that he hated working with the 2 port, now there's a guy who's been around longer than all of us, so if he's struggling I'll steer clear. Ohlins did have a 2 port rebound piston in 2000, it didn't last long.

You never fail to dissappoint!
Frankly I think Im being realistic and ''sharing'' of my own experience. Improvement is relative and what I am intimating at is a cost effective mod, if people are on the other hand able and willing to pay the big bucks for the ultimate then they have the choice. Bit part kits that offer a sizable improvement at a cost that more can afford....but at the very same time being very candid that these will not offer the same level of outright improvement as my beloved Swedish product.

Lindemann is a respected name but I would wonder if there is a slight whiff of politics? Anybodies guess. Traxxion rubbished the Ohlins cartridges in the US ( look at US forums ) but service there can be patchy. Here in NZ the Ohlins stuff is working so well it has contributed significantly to lap records being smashed.
I will keep all that are interested posted on our progress with these pistons, perhaps Jim Lindemann is now too advanced in years and too ''tired and blase'' to spend the time to work with new stuff ( or variations on a theme) ?
BTW, a year ago I adapted a TTX40 to fit into a GSXR600, Mats Larsson from Ohlins said it wouldnt work so well in a bike. Well we got it working really well and that bike won races, a couple emphatically so on a tight, technical track. NOT afraid of hard work!

[JD Racing]

I'm 3 years ahead of you on the stack within a stack design and still working on it, to stop it collapsing in a 20mm cartridge your going to need smaller ports, by a huge margin.

[Sensei]

Bugger & here I was thinking that now I have Ohlins forks that ya didn't need to do anything to them . :gob:

[Pussy]

My first GSX-R to be modded in the front was my K1 1000. The pistons in the stock cartridges had extremely small transfer holes, which led to a "lock" situation on me one day on a rough corner. With only an average riding ability I found a front end slide a bit too character building. RT suggested to me to give the Traxxion piston/valving mod a go, and I had them fitted with a road-bias setting. The flavour of the day was also a short top out spring... which I bloody hated!(I will elaborate on this some time).This valving was transfered over to my K3 GSX-R1000. One problem that showed up pretty early in the piece was stiction, so RT finally got sick of me bitching about it, stripped the forks, and we put a dial guage on them. The damper rod wasn't concentric with the cartridge body. Good old KYB! Robert then designed and had made some floating top bushings for the KYB cartridge. Worked a treat! When the cartridges were to bits I had the stock LONGER top out springs refitted. Again, better for my preference.
I sold my K3 and got a K4 GSX-R1000, and RT had removed the modded cartridges, they were sold to a mate with a K3.
In May 2005 I had a set of AK-20s fitted to the K4, with a road-bias compression valving... we left the rebound "as delivered". The AK-20s had VERY weak higher speed rebound, so had to come out to get beefed up a bit in the valving. These cartridges were smooth in action, but we seemed to have quite a few issues getting them to perform.. RT suspected some leakage at the top of the cartridge. Quite honestly, I found the modded stock cartridges with the floating top bush a better bet, and wished I hadn't bloody sold them, especially after riding the bike they went in.
After several decent earning months, I decided to bite the bullet and get myself a set of the recently released Ohlins cartridges. With 20/20 hindsight, this is what I would have done in the first place. After an initial bit of pissing about with the clickers I found "My" settings, and left them alone after that. I have only ridden one bike with full Ohlins forks (an Aprilia) since, and reckon, IMHO, that the gixxer forks with Ohlins guts are about as close as you will get to them. Thankfully, the cartridges were a straight drop in for my K6 GSX-R 1000 when I got it. No worries
Then I buy a K6 GSX-R750... the cartridges WON'T fit that. Never mind, RT takes them off my hands, and I end up trading them for a set of FGK 132 cartridges for the 750. These have the bending shim mid-valve that the 1000 ones didn't.
And this now takes me to the present... and my questions on the theory behind why these things work so very nicely. Keep up the input, peoples....

[Robert Taylor]

I'm 3 years ahead of you on the stack within a stack design and still working on it, to stop it collapsing in a 20mm cartridge your going to need smaller ports, by a huge margin.

Thats what I figured and I keep going back to the Ohlins 20mm road race pistons ( small ports ) as they do work very well. But this whole checkplate mid valve thing sets everything in motion, ''the horse bolts'' and then the damping has to play catch up. I know I described that not very well but it seems to make more sense that there is instant control on the midvalve rather than instant oil dump?...........
With the 2 port piston the shadowing shim for road race application will I imagine leave a thin ''sliver'' of port on each side.

[Robert Taylor]

Bugger & here I was thinking that now I have Ohlins forks that ya didn't need to do anything to them . :gob:

If you are happy with them fine but even good gear can be better.

[JD Racing]

Thats what I figured and I keep going back to the Ohlins 20mm road race pistons ( small ports ) as they do work very well. But this whole checkplate mid valve thing sets everything in motion, ''the horse bolts'' and then the damping has to play catch up. I know I described that not very well but it seems to make more sense that there is instant control on the midvalve rather than instant oil dump?...........
With the 2 port piston the shadowing shim for road race application will I imagine leave a thin ''sliver'' of port on each side.

Problem is the thin sliver is still a large area relative to the flow volume so it's hard to control, as one old sage once told me, "it's like trying to let 2psi out of your back tyre with a bead breaker".
With such a huge port acting on opposite sides of the piston the bending dynamics of the shim are in one plane so you need a thick shim to stop it folding real easy, so you need thick shims to control the area and the folding and end up with something that when you hit the brakes feels like you hit a corrugated dirt road at 200k's.

[Robert Taylor]

Problem is the thin sliver is still a large area relative to the flow volume so it's hard to control, as one old sage once told me, "it's like trying to let 2psi out of your back tyre with a bead breaker".
With such a huge port acting on opposite sides of the piston the bending dynamics of the shim are in one plane so you need a thick shim to stop it folding real easy, so you need thick shims to control the area and the folding and end up with something that when you hit the brakes feels like you hit a corrugated dirt road at 200k's.

Thanks for that and I guess we will draw our own conclusions when we get to test in varying combinations. You know, that Ohlins 20mm piston has stood the test of time very well and is an ''old faithful''.

[Shaun]

Bigger or smaller holes in the piston, does it really matter?

Is it not possible to control the extra quick dump of the fluid with the bigger port piston with a more fuller comp stack of shims, ie 10 of the chosen size, versus 6 of a chosen size for the smaller piston?

As the holes in the piston only determine the amount of fluid flowing, and the way that fluid flows due to design of the holes in the piston, surely this is all finally controlled by the stack?

Kind of like changing just the bleed jet in a shock, ie a smaller or bigger bleed jet= MORE OR LESS OIL FLOW-

To me, I would choose as much fluid flow as possible, and then turn around and design the shim stack to work with this controlled flow, by directing it to control the area in the fork stroke, that I was not happy with, ie, mid stroke, top stroke etc

[Robert Taylor]

Bigger or smaller holes in the piston, does it really matter?

Is it not possible to control the extra quick dump of the fluid with the bigger port piston with a more fuller comp stack of shims, ie 10 of the chosen size, versus 6 of a chosen size for the smaller piston?

As the holes in the piston only determine the amount of fluid flowing, and the way that fluid flows due to design of the holes in the piston, surely this is all finally controlled by the stack?

Kind of like changing just the bleed jet in a shock, ie a smaller or bigger bleed jet= MORE OR LESS OIL FLOW-

To me, I would choose as much fluid flow as possible, and then turn around and design the shim stack to work with this controlled flow, by directing it to control the area in the fork stroke, that I was not happy with, ie, mid stroke, top stroke etc

Actually yes it does matter, a whole lot.

To once again recite the phrase ''the best youve ridden is the best you know'' Well, you havent ridden on the very latest generation of Ohlins FGK cartridges with bending shim stack mid valves and enjoyed set up specific to you. Time and progress doesnt stand still and if anyone anywhere says they have the perfect set up and it doesnt need changing then they are in denial.

Being thankfully blessed with a very sturdy memory I can well recall that on a number of occassions right through until last years nationals that you said a set of forks you had in a GSXR750 ( around 2000 ) were the best youd ever ridden on. I remember putting those forks together with Ohlins small port pistons, the ''old faithfuls '' that I eluded to in another post.

I will try and explain the whole big port thing to you in terms that you as a rider will understand, without launching into too much technical jargon. Big port pistons will dump a lot of oil when the shim stack opens, but therein lies the first issue of control. Someone said to me ''youll never have to revalve these, ever'' Fine if you want a pleasant afternoon ride on a bumpy road as opposed to braking as late as you can get away with on a racetrack. To stop the forks blowing through the stroke with such pistons you do indeed need stiff stacks, but then the initial opening pressure becomes so high ( knee on a dyno curve ) the forks become harsh and sidegrip etc is compromised.
I also recall a set of forks that Chris Perris was sent out from the US with as I had to fix them for you, the opening pressure of the shim stack was so high that they were impossibly harsh. Bumps are bumps, everywhere.
During Sam Smiths 600 season last year we changed the compression pistons 4 times and each time the front end got better. We started with Traxxion 20mm pistons, followed by Yoshimura pistons, better ( a rip off of the Ohlins 20mm preloading pistons but with bigger ports ) Then the Ohlins preloading pistons, small port and better again. Finally the ''old faithful'' linear face Ohlins 20mm pistons, best of all. Just ask Sam... This was all with old style checkplate midvalve but we have now moved on to something clearly better.
JD Racing has in fact broadly answered your questions anyway when it comes to controlling big port pistons. He has also correctly stated the limitations of 20mm cartridges in trying to get them to work with bending shim stack midvalves, there are pressure balance issues which means the forks will drop their lunch with cavitation.
Have a look at rebound pistons in Traxxion stuff, they are big port and need a preloading shim to give some control. Not only that the big black anodised back up washer immediately next to the clamping shim acts as a shim stack travel restrictor to stop the shim stack opening too far and letting the forks ''drop their lunch'' on rebound.

The dynamic of rebound from fully closed to fully extended is that you initially have a lot of spring force to control requiring a lot of ( high speed ) rebound damping. As the fork ( or shock ) re-extends the spring force progressively lessens so the damping needs to be progressively weaker to be in unison. That function is best served by a small port piston ( i.e Ohlins, WP, Race Tech and a lot of oem stuff ) In combination with a less agressive shim stack. A stiff stack on a big port piston will give too much low speed damping, if you are searching for grip rebound is often where its at.

Same for compression, within sensible limits and varied applications ( road compliance, road race control ) the ports need to be smaller with a less aggressive stack. The opening pressure is less so you are not risking hurting side grip / tyre edge grip so much and the slope of the curve ( which often is used to catch too sudden movement ) is not too determined by the shim stack!

The bending shim stack midvalves that our riders are so delighted with are a whole new area. Much less emphasis is placed on the traditional base valve main compression pistons to ''catch the runaway train'' because the checkplate system provides a whole lot less initial control, the door is opened right away. The mid valve becomes the main piston and beleive me playing with the shimming on that piston yields great results once you understand it.

[JD Racing]

Thanks for that and I guess we will draw our own conclusions when we get to test in varying combinations. You know, that Ohlins 20mm piston has stood the test of time very well and is an ''old faithful''.

Ha haa, absolutely, you can spend a whole lot of time playing around but if there's one thing you can always fall back on it's those.

Don't rule out the bending shim midvalve in a 20mm cartridge it can be done with great results and no cavitation, checkplates can also be successfull, Honda HMAS pistons share the same dimensions as an Ohlins kit but with a significant difference, use that with a good checkplate build and it really adds dive control, some KYB rebound pistons can be used to achieve the same thing.


Shaun, get a piece of paper, lay a rule across the middle and hold the rule down, pick up the outside edge of the paper, the paper will fold at the edge of the rule, stack up 50 sheets and try the same thing, the paper no longer folds at the outside edge of the rule, apply this to shims and it means that what started out as a small increase of seat pressure becomes something very stiff once the shims start deflecting.

[JD Racing]

Bigger or smaller holes in the piston, does it really matter?
To me, I would choose as much fluid flow as possible, and then turn around and design the shim stack to work with this controlled flow, by directing it to control the area in the fork stroke, that I was not happy with, ie, mid stroke, top stroke etc

Unfortunatley damping is speed sensitive not position sensitive.

[Shaun]

Unfortunatley damping is speed sensitive not position sensitive.




Understand but, if I wanted my mid stroke to be furmer, surely we would consider altering the shim stack at that stage, ( To change any other parts, would have a big effect over the entire range) that is assuming all other of the fork is fine?

[Robert Taylor]

Understand but, if I wanted my mid stroke to be furmer, surely we would consider altering the shim stack at that stage, ( To change any other parts, would have a big effect over the entire range) that is assuming all other of the fork is fine?

Midstroke is a contradiction in terms because it is all about velocity as has been correctly stated. Changing it as you understand it will invariably affect low speed as well, that is not always desirable. That is exactly why a big port piston which places too much emphasis on the shim stack for control is so hard to get right.

And digressive curves are not the holy grail as invariably there is not enough slope on the curve to ''catch'' a sudden stroke movement.

No fork or shock will work perfectly for every scenario with just a spring and clicker change, FACT.

[Shaun]

Midstroke is a contradiction in terms because it is all about velocity as has been correctly stated. Changing it as you understand it will invariably affect low speed as well, that is not always desirable. That is exactly why a big port piston which places too much emphasis on the shim stack for control is so hard to get right.

And digressive curves are not the holy grail as invariably there is not enough slope on the curve to ''catch'' a sudden stroke movement.

No fork or shock will work perfectly for every scenario with just a spring and clicker change, FACT.



Cheers, so then, if Midstroke is a contradiction in terms then, and it is all about velocity, how do you go about determing in what area to make the change then?

Because with all the years we worked together on suspension Robert, WE always refered to area on the fork that a change was required in, not the Velocity range?



Midstroke is a contradiction in terms because it is all about velocity as has been correctly stated. Changing it as you understand it will invariably affect low speed as well, that is not always desirable. That is exactly why a big port piston which places too much emphasis on the shim stack for control is so hard to get right.




Yes it will , but then you can re adjust externall settings on the dampner clicker, or fit a softer spring, or lighter oil, to work on the low speed issue

[cowpoos]

Ya man Cowpoos, is loving it, I have even see some big cleaver words from him:lol:

Cheers guy's keep it up

Lol...yeah your right...I do have alot of interest in this subject.

But...the problem with learning in depth about suspension dynamics is how it relates to feedback on a race track/road... understanding what is been discussed and how the best comprimises are found..why changes in piston design,differnt valving,mid piston stacks,check plates,etc are done..are all good..but it would be nice to know the difference's in how a bike reacts..

From a bike setup point of view I have learned alot from Robert and JD...by picking bits of imformation out of the various threads...more so when a circumsatance has been explained and as a rider relating it to something I have felt or close to what I think I may have felt...as in my mind it helps greatly between distinguishing what maybe a rider input fault and a bike suspension adjustment thats needed..and having these guys here on KB is easily I feel cutting years of trial and error learning..which In my personal situation is fanfuckingtastic...as I know I have a very sensitive feel to changes on a motorbike..be it road,race track or dirtbike..and pre these guys and TDC making a appearence here I was rather indecisive about making changes as I didn't know the extent of the pro's and con's..

And because of...my perception on testing has changed...and what is required...and has made me far more egar to getting a new machine [once I decide what class to run in] and starting it all from scratch..and learning the development more as I believe its a key to running up near the front..as much as riding ability helps aswell of course.

[JD Racing]

You can't tune for midstroke with damping, if your hard on the brakes loading the forks at maximum velocity you want lots of highspeed damping. If your mid turn the forks loaded by g force you want lots of low speed for feel and little highspeed to soak up the ripples.

[Robert Taylor]

Cheers, so then, if Midstroke is a contradiction in terms then, and it is all about velocity, how do you go about determing in what area to make the change then?

Because with all the years we worked together on suspension Robert, WE always refered to area on the fork that a change was required in, not the Velocity range?



Midstroke is a contradiction in terms because it is all about velocity as has been correctly stated. Changing it as you understand it will invariably affect low speed as well, that is not always desirable. That is exactly why a big port piston which places too much emphasis on the shim stack for control is so hard to get right.




Yes it will , but then you can re adjust externall settings on the dampner clicker, or fit a softer spring, or lighter oil, to work on the low speed issue

Lots of riders use lots of different ways of describing things and as you well realise I work with lots of riders at all levels. Midstroke clearly is an unfortunate term that should be expunged from your own vocabulary and frankly my understanding of the whole suspension thing has gone ahead in leaps and bounds since the time I was valving suspension units for you.

JD racing has answered your question perfectly. Also lighter oil is only a tuning option I would use in an old damper rod fork to tune rebound speed! You really must get up to speed Shaun!

[Shaun]

Lots of riders use lots of different ways of describing things and as you well realise I work with lots of riders at all levels. Midstroke clearly is an unfortunate term that should be expunged from your own vocabulary and frankly my understanding of the whole suspension thing has gone ahead in leaps and bounds since the time I was valving suspension units for you.

JD racing has answered your question perfectly. Also lighter oil is only a tuning option I would use in an old damper rod fork to tune rebound speed! You really must get up to speed Shaun!


Thanks for the reply Robert.

I know your knoledge has grown in the last few years yet again Robert, that is the best part about having you around here these days. ( Midstroke has been expunged mate,Don't let me here you use that term again) Nah, don't want to get up to speed to quickly mate, it all takes time to learn

[Shaun]

Lol...yeah your right...I do have alot of interest in this subject.

But...the problem with learning in depth about suspension dynamics is how it relates to feedback on a race track/road... understanding what is been discussed and how the best comprimises are found..why changes in piston design,differnt valving,mid piston stacks,check plates,etc are done..are all good..but it would be nice to know the difference's in how a bike reacts..

From a bike setup point of view I have learned alot from Robert and JD...by picking bits of imformation out of the various threads...more so when a circumsatance has been explained and as a rider relating it to something I have felt or close to what I think I may have felt...as in my mind it helps greatly between distinguishing what maybe a rider input fault and a bike suspension adjustment thats needed..and having these guys here on KB is easily I feel cutting years of trial and error learning..which In my personal situation is fanfuckingtastic...as I know I have a very sensitive feel to changes on a motorbike..be it road,race track or dirtbike..and pre these guys and TDC making a appearence here I was rather indecisive about making changes as I didn't know the extent of the pro's and con's..

And because of...my perception on testing has changed...and what is required...and has made me far more egar to getting a new machine [once I decide what class to run in] and starting it all from scratch..and learning the development more as I believe its a key to running up near the front..as much as riding ability helps aswell of course.




You are obviously learning a lot mate, my post about you using big words, was actually meant as a compliment! you have learned a lot since I first met you a couple of years ago:niceone:

[Robert Taylor]

Thanks for the reply Robert.

I know your knoledge has grown in the last few years yet again Robert, that is the best part about having you around here these days. ( Midstroke has been expunged mate,Don't let me here you use that term again) Nah, don't want to get up to speed to quickly mate, it all takes time to learn

I wish you and Cowdung would learn to spell, your spelling on a good day is far worse than one of my hurried slip ups....

[cowpoos]

You are obviously learning a lot mate, my post about you using big words, was actually meant as a compliment! you have learned a lot since I first met you a couple of years ago:niceone:

Thanks Shaun...and I did take it as a compliment.


I wish you and Cowdung would learn to spell, your spelling on a good day is far worse than one of my hurried slip ups....

Cowdung?? lol you feeling abit raw after I woof whistled you in some humourous jest at being the uglyiest bolly dolly?? craig looked like he appreciated you being there though!! lol

But more to the point about the spelling...not everyone is good with english or precision engineering..suspension tuning..etc..some of us are better at riding the bikes and drinking the beer!! which are very important skills in there own right ;)