Damping Technology

[enigma51]

I think we need to test this in practice any one want to long term "borrow" me a set for the 750 I will give all my feedback exclusively to the internet

I am more than happy to test road and track usage and you will get the benefit of an average slowish rider

[Pancakes]

Most of this just flew over my head.

Where do you go to learn this jargon? Do you have to take an engineering course at uni or something?

They are building stuff that might not have been made in that configuration before so they get to make up the name too. I'm sending RT a case of Becks and have a feeling the "Pancake Valve" will be released in time for the 2009 European season!

[Shaun Harris]

I think we need to test this in practice any one want to long term "borrow" me a set for the 750 I will give all my feedback exclusively to the internet

I am more than happy to test road and track usage and you will get the benefit of an average slowish rider

DONE

I will lend you a set of forks all set up, totally built by RobT not ever touched since he last worked on them! ( If Rob wants them first for service reason's etc, A OK ) with full ohlin"s and Rob's Skill put into them for (a year ago give or take a month or 3 for these ones) for a week or so in January 08- OK ? They bolt in, no worries at all, In fact, I will fit FOC!

Then, swap them out for a set that I spoke about at the start of this thread, for you to try! And comment on.

Then, try the gear I will be working with next year, again FOC, and you have your say man, a bumps a bumps as you know I am sure

I do and have sold all 3, so, why not

[Robert Taylor]

Most of this just flew over my head.

Where do you go to learn this jargon? Do you have to take an engineering course at uni or something?

You first have to become a distributor of a leading suspension brand ( there are only 3 ) after years of learning the basics and proving yourself. You work at it for a decade or two. You spend literally tens of thousands of dollars in overseas travel to attend seminars. Such seminars are in depth distributor level, not something you can just buy into.You develop a very good relationship with the engineers. You must not be afraid to do very long hours and to test many things that wont work so well, but learn from it. You totally stay away from illegal substances that slowly destroy your brain.You invest 100k or so in test equipment and tooling to provide a full and proper service.

This doesnt happen overnight. Like Max said this is not black magic, but it is a lot of hard work.

A uni course in fluid dynamics would be a good start, but the real rewards are overseas.

[Robert Taylor]

Great thread.
Amateur side question: So shims have a service life? Presumably more so in MX applications & certain arrangements more than others (light shims mentioned). How would the punter know? How does the tech know to replace?, presumably they take a set like a worn set of reeds?

Yes they do develop a set and allow the forks to ''ride low'' and blow through their stroke too readily

[JD Racing]

You know Max I got to thinking in the middle of the night about the relative merits of bending shim stack type mid-valves as opposed to fixed / limited stroke mid valves.
Lets be clear that this is a tech discussion devoid of politics and if any ''third party'' posts trivialising or patronising what has been said then it abundantly proves a point.
As you well realise the conventional check plate type mid valve has a clearly definable area of ''dead stroke'', that being the check plate opening distance, because it is the first thing that moves when the fork is under compression. Most compression damping control is via the base compression pistons in the bottom of the cartridge.
In the bending shim stack type mid valve there isnt a sudden opening of a check plate but a modulated flow contolled by a shim stack. With a properly arranged / developed shim stack and port sizes it will modulate limited flow at small fork shaft velocities but with also lots of allowable deflection can move much greater volume of fluid ( than a checkplate type ) at higher fork velocities. Much less emphasis is therefore placed on the base compression pistons ( although they are by no means redundant ) and the fork damping action becomes much closer to a shock in action, albeit an emulsion shock.
I see that at least the basic principle ( not neccessarily the intended function and true benefits ) are appearing in more and more oem sportbike forks. In quoting my beloved viking cartridges the compression flow ports through what they now call the main piston ( also the rebound piston ) are huge in size with a very responsive shim stack with lots of allowable deflection. With the proper settings these forks ride the bumps quite well. I imagine K-Tech cartridges are similiar in principle.
Last season we were still using checkplate rebound pistons as we had no pre-testing time. These old pistons are now ''consigned to the bin'' !
I do agree that gas charged cartridges are the future, as with everything there is a ''gestation period'' for the market to accept it due to the extra cost. The set I purchased off you are still in circulation and will probably be raced with again this season and certainly when Craig Shirriffs used them he made very favourable comments.

Max is in a position where he pretty much has to use a check plate, using a 20mm cartridge and a 12.5mm damper rod the pressure drop across the rebound piston is far greater than with a 25mm cartridge and a 12mm rod, this pressure drop makes the piston more susceptible to cavitation if a mid valve shim stack is used.
The oem manufacturers can get away with a light stack as they use a 10mm rod and add bleeds to the piston so cavitation doesn't become an issue.
The 25mm cartridge has a much larger area and swept volume, the larger area means that to achieve the same damping force less pressure has to build in the cartridge so there is less pressure differential across the piston so a shim stack could be used without the risk of cavitation. The much larger swept volume means that the ports need to be much larger to achieve the desired flow rate and that the shims will have to deflect further to give the desired increase in valve open area. Shims are only effective at low lifts beyond this their bending characteristics change, so here a check plate can also be desirable.
Adding a shim stack to the midvalve increases the overall damping coefficient of the forks, to prevent the forks becoming too hard often the base valve then needs to be softened to compensate. Softening the base valve can lead to having a less powerfull compression adjuster.
You can't soften the base valve too much or add too much stiffness to the midvalve as it then becomes difficult to build pressure in the cartridge, this can lead to a pulsing in the cartridge at the top of the stroke. As the forks start to compress there is insufficient air pressure within the forks so the rebound piston instead of flowing through the oil pushes a slug of oil in front of it, the base valve faced with 4 times the volumetric flow rate it's designed for generates 16 times the resistance, the forks stop for a fraction of a second then the midvalve opens, the pressure drops and the above is repeated, if your hard on the brakes the forks will continue to dive the internal air pressure will rise and the forks will start to work efficiently. If you'd just brushed the brakes to check your speed you'd feel this pulsing through the bars, this was very common when Ohlins were using a massive stack of wave washers or a real heavy duty check plate spring.
The strong point about a 25mm cartridge tends to be they offer more support on the brakes, at these shaft velocities the overall damping coefficient of the 2 stacks really kicks in, providing of course that's what you want. How riders like the forks to compress on the brakes varies as much as braking styles, some riders like to brake progressively others like to wait till the very last second then grab a huge handfull of brake. Some riders like the forks to compress quickly and load the front tyre so they can get maximum feel and turn in real easy, others like a slower dive with the forks operating higher in the stroke through the turn. A lot of riders don't know what the hell they want they just use what the guy is winning uses, sometimes this is a backward step as often the guy who is winning usually has the talent to ride around on anything.

Phew, I somehow managed to write all that without being an importer of the top 3's products, how the hell did that happen.

[Ixion]

Y..

A uni course in fluid dynamics would be a good start, but the real rewards are overseas.

I did that, and this is still over my head. Is there an ABC anywher eon the web? I *think* I sort of understand what you are saying (without of course having the faintest notion who is right - two of a trade never agree!) But a little basic cramming would be good. Bear in mind that I have still not fully recovered from the abandonment of girder forks. I understood those.

[Sensei]

I have been lucky enough to try Roberts handy work on a friends bike which was used as a test bed for the AK20 kits & the Traxtion gear as well as the Ohlins internals & I can say that all of these products are such aleap ahead of the standard stuff that come in the Jap bikes that it tranforms them to where they meet their motor performance . The ins & outs of making it work tho is a skill in its self & take my hat off to Robert & others that can do this . Even better when they live in my home town .

[JD Racing]

I did that, and this is still over my head. Is there an ABC anywher eon the web? I *think* I sort of understand what you are saying (without of course having the faintest notion who is right - two of a trade never agree!) But a little basic cramming would be good. Bear in mind that I have still not fully recovered from the abandonment of girder forks. I understood those.

I don't think there is any such thing as being right, most in the trade have their own agenda and argue from that stand point, all your doing is controlling the dynamic behaviour of a sprung mass, if you spend enough time looking at something, testing, doing something for the hell of it you can make pretty much anything work and work well.

[Robert Taylor]

Max is in a position where he pretty much has to use a check plate, using a 20mm cartridge and a 12.5mm damper rod the pressure drop across the rebound piston is far greater than with a 25mm cartridge and a 12mm rod, this pressure drop makes the piston more susceptible to cavitation if a mid valve shim stack is used.
The oem manufacturers can get away with a light stack as they use a 10mm rod and add bleeds to the piston so cavitation doesn't become an issue.
The 25mm cartridge has a much larger area and swept volume, the larger area means that to achieve the same damping force less pressure has to build in the cartridge so there is less pressure differential across the piston so a shim stack could be used without the risk of cavitation. The much larger swept volume means that the ports need to be much larger to achieve the desired flow rate and that the shims will have to deflect further to give the desired increase in valve open area. Shims are only effective at low lifts beyond this their bending characteristics change, so here a check plate can also be desirable.
Adding a shim stack to the midvalve increases the overall damping coefficient of the forks, to prevent the forks becoming too hard often the base valve then needs to be softened to compensate. Softening the base valve can lead to having a less powerfull compression adjuster.
You can't soften the base valve too much or add too much stiffness to the midvalve as it then becomes difficult to build pressure in the cartridge, this can lead to a pulsing in the cartridge at the top of the stroke. As the forks start to compress there is insufficient air pressure within the forks so the rebound piston instead of flowing through the oil pushes a slug of oil in front of it, the base valve faced with 4 times the volumetric flow rate it's designed for generates 16 times the resistance, the forks stop for a fraction of a second then the midvalve opens, the pressure drops and the above is repeated, if your hard on the brakes the forks will continue to dive the internal air pressure will rise and the forks will start to work efficiently. If you'd just brushed the brakes to check your speed you'd feel this pulsing through the bars, this was very common when Ohlins were using a massive stack of wave washers or a real heavy duty check plate spring.
The strong point about a 25mm cartridge tends to be they offer more support on the brakes, at these shaft velocities the overall damping coefficient of the 2 stacks really kicks in, providing of course that's what you want. How riders like the forks to compress on the brakes varies as much as braking styles, some riders like to brake progressively others like to wait till the very last second then grab a huge handfull of brake. Some riders like the forks to compress quickly and load the front tyre so they can get maximum feel and turn in real easy, others like a slower dive with the forks operating higher in the stroke through the turn. A lot of riders don't know what the hell they want they just use what the guy is winning uses, sometimes this is a backward step as often the guy who is winning usually has the talent to ride around on anything.

Phew, I somehow managed to write all that without being an importer of the top 3's products, how the hell did that happen.

Actually Id like to see Max answer that one as it is the best description I have seen yet re the 20mm versus 25mm schools of thought, especially with respect to pressure balance.

My description of how you become conversant with suspension to a high level ( that you have clearly demonstrated ) cited clear examples of one route to do so. Add to that time overseas ( for example ) with top level race teams, not as a ''parts fitter'' but clearly involved in the deep end of working with suspension internals. This takes considerable time and years of hands on experience plus a ''touch'' that is focused towards very pedantic assembly precision. Not a job for those with a sledgehammer and ''she'll be right'' mentality. Doing a course or two does not make one an instant suspension guru.

As Ohlins has very large prescence and respect in the racing world I am assuming that you have worked with it overseas?

[Robert Taylor]

DONE

I will lend you a set of forks all set up, totally built by RobT not ever touched since he last worked on them! ( If Rob wants them first for service reason's etc, A OK ) with full ohlin"s and Rob's Skill put into them for (a year ago give or take a month or 3 for these ones) for a week or so in January 08- OK ? They bolt in, no worries at all, In fact, I will fit FOC!

Then, swap them out for a set that I spoke about at the start of this thread, for you to try! And comment on.

Then, try the gear I will be working with next year, again FOC, and you have your say man, a bumps a bumps as you know I am sure

I do and have sold all 3, so, why not

Bear in mind though that the pistons in these forks are for the old check plate mid valve system. And the top caps are oem which are a pain to work with compared to the Ohlins caps. All Ohlins cartridges for sportbikes are now delivered with ''bending shim stack'' mid valve type pistons, and base valves to match. So unless the very latest stuff is tested such a test would not be totally subjective. Time and technology is relentless.

[Robert Taylor]

I don't think there is any such thing as being right, most in the trade have their own agenda and argue from that stand point, all your doing is controlling the dynamic behaviour of a sprung mass, if you spend enough time looking at something, testing, doing something for the hell of it you can make pretty much anything work and work well.

Have you looked at the cartridges in the 07 ZX6? Pretty much we cant do anything with this, the cost cutting is unbeleivable and I would reasonably guess that the other manufacturers will follow suit. The market for quality aftermarket cartridges looks pretty good

[Robert Taylor]

Max is in a position where he pretty much has to use a check plate, using a 20mm cartridge and a 12.5mm damper rod the pressure drop across the rebound piston is far greater than with a 25mm cartridge and a 12mm rod, this pressure drop makes the piston more susceptible to cavitation if a mid valve shim stack is used.
The oem manufacturers can get away with a light stack as they use a 10mm rod and add bleeds to the piston so cavitation doesn't become an issue.
The 25mm cartridge has a much larger area and swept volume, the larger area means that to achieve the same damping force less pressure has to build in the cartridge so there is less pressure differential across the piston so a shim stack could be used without the risk of cavitation. The much larger swept volume means that the ports need to be much larger to achieve the desired flow rate and that the shims will have to deflect further to give the desired increase in valve open area. Shims are only effective at low lifts beyond this their bending characteristics change, so here a check plate can also be desirable.
Adding a shim stack to the midvalve increases the overall damping coefficient of the forks, to prevent the forks becoming too hard often the base valve then needs to be softened to compensate. Softening the base valve can lead to having a less powerfull compression adjuster.
You can't soften the base valve too much or add too much stiffness to the midvalve as it then becomes difficult to build pressure in the cartridge, this can lead to a pulsing in the cartridge at the top of the stroke. As the forks start to compress there is insufficient air pressure within the forks so the rebound piston instead of flowing through the oil pushes a slug of oil in front of it, the base valve faced with 4 times the volumetric flow rate it's designed for generates 16 times the resistance, the forks stop for a fraction of a second then the midvalve opens, the pressure drops and the above is repeated, if your hard on the brakes the forks will continue to dive the internal air pressure will rise and the forks will start to work efficiently. If you'd just brushed the brakes to check your speed you'd feel this pulsing through the bars, this was very common when Ohlins were using a massive stack of wave washers or a real heavy duty check plate spring.
The strong point about a 25mm cartridge tends to be they offer more support on the brakes, at these shaft velocities the overall damping coefficient of the 2 stacks really kicks in, providing of course that's what you want. How riders like the forks to compress on the brakes varies as much as braking styles, some riders like to brake progressively others like to wait till the very last second then grab a huge handfull of brake. Some riders like the forks to compress quickly and load the front tyre so they can get maximum feel and turn in real easy, others like a slower dive with the forks operating higher in the stroke through the turn. A lot of riders don't know what the hell they want they just use what the guy is winning uses, sometimes this is a backward step as often the guy who is winning usually has the talent to ride around on anything.

Phew, I somehow managed to write all that without being an importer of the top 3's products, how the hell did that happen.

Further to my first reply to your excellent description

1) I would add that it is easier to make 25mm components with more exacting tolerances and therefore less unintentional bleed ( Max is sure to disagree! )

2) Funnily enough in recent testing we have gone to progressively softer compression specs to aid corner entry / turn in. There was an initial reluctance on my part to do this because experience with the 20mm cartridges is that they tended to ( in comparison ) ''drop their lunch'' and we would ultimately perhaps have worked in the direction of stroke restrictors. So many combinations, so little time.... The better inherent brake dive control in the 25mm cartridges appears to allow more latitude to go to softer setting specs

3)The TTX cartridge stuff when it becomes available for volume commercial resale is going to be interesting. On sale very soon for MX but the road race and road guys are going to have to wait a little longer.

Sincere thanks for the stimulation!

[White trash]

Although I can offer no technical expertise to this thread, it's gotta be one of the most enjoyable and interesting articles KB has to offer.

God bless Rob, JD Racing, Max and of course our resident protaganist Shaun for joining KB.

It's an interesting website again.

[JD Racing]

Further to my first reply to your excellent description

1) I would add that it is easier to make 25mm components with more exacting tolerances and therefore less unintentional bleed ( Max is sure to disagree! )

2) Funnily enough in recent testing we have gone to progressively softer compression specs to aid corner entry / turn in. There was an initial reluctance on my part to do this because experience with the 20mm cartridges is that they tended to ( in comparison ) ''drop their lunch'' and we would ultimately perhaps have worked in the direction of stroke restrictors. So many combinations, so little time.... The better inherent brake dive control in the 25mm cartridges appears to allow more latitude to go to softer setting specs

3)The TTX cartridge stuff when it becomes available for volume commercial resale is going to be interesting. On sale very soon for MX but the road race and road guys are going to have to wait a little longer.

Sincere thanks for the stimulation!

The 20mm cartridge certainly takes a lot of work to get right, port dimensions and shimming are extremely critical, I never understood how WP had so much success with their 21mm set up and the new closed cartridge although bigger is not a lot better, now that is one set up that sits up on the brakes.

I'd heard tha Broc Parkes was testing the TTX cartridges at Losail, I'd like to see how that's packaged.