Inside KW Suspensions Solid Piston Shock Technology

We were recently at KW Suspensions North American headquarters for some new product training and we got to take apart some of their latest technology, the innovative solid piston damper. The solid piston damper is a radical departure from conventional shock technology and is for sure worth a close look at how the insides work.

We had a quick look at the prototype solid piston damper at last years SEMA show. The concept was very fascinating to us and we were eager to see actual working shocks.

We got to see the insides of a 4-way adjustable solid piston shock from a Porsche 911 cup car.  The shock is standard equipment on them. Here are the shocks guts minus the outer tube.  Compared to other shocks, the solid piston is quite simple.  That is one of the beautiful parts about it.

The solid piston shock is technically a twin tube.  It has an inner and outer tube with the shock rod and piston contained in the inner tube.  This is where the similarity to a conventional twin tube ends.  In the KW solid piston shock the outer tube serves as a fluid transfer passage.  The piston is connected to the shock rod.  Unlike a conventional shock, the piston itself is solid with no valves!  The piston serves to move fluid back and forth inside the shock and serves no function to control damping at all! Here is the shock rod, piston and inner tube, the outer tube has been removed.

On compression the piston moves the fluid and it flows through the black manifold pictured on the right.  It then goes through a one way check valve and the compression valves. The fluid then flows out of the manifold and through the space between the inner and outer tube, through holes into the inner tube and to the other side of the piston.  On rebound the fluid flows through the inner tube through the holes, through the space in between the inner and outer tube, then into the manifold through a one way check valve, then the rebound damping valves, then out the manifold and to the inner tube on the other side of the piston.

So the piston acts like a push me pull you for the fluid.  This has many advantages. The first one is that there is a lot of fluid flow volume available to generate damping control force. Normally a lot of the compression damping is done by the small amount of fluid displaced by the shock shaft that flows out to the remote reservoir through the high and low speed compression valves.  With this small volume of fluid generating the control force, the orifices must be very small and the valves tightly shimmed to develop hundreds or thousands of pounds of control force.  This causes a big drop in pressure across the valve system.  With the pressure drop you have the possibility of cavitation with localized boiling and aeration of the fluid. To combat this the shock must be pressurized to a high pressure which has issues with potential leaks, high seal sticksion and high gas reaction force which gives the suspension a potential rising rate.

With the solid piston shock the fluid volume of entire body of the shock is flowing through the valves giving the valves many times more fluid flow to develop the control force.  With more fluid, the orifices and shims do not have to be as small or tightly preloaded to develop the force. More fluid flow, the more sensitive the valves are with less hysteresis. With greater fluid flow, the solid piston shocks run a lot cooler as well leading to more constant damping and more fade resistance.

With the solid piston doing the push me and pull you, there is very little pressure differential across the valves so there is less potential for cavitation! With less potential for cavitation the shock can run at a lower pressure.  In fact, the remote reservoir can be a lot smaller because its only function now, is to hold enough gas to make up for the displacement for the shock shaft.

14 comments

    1. It’s a good question! Motion Control shocks are completely different in operation and function. They have a neat turret type valve that makes the damping response to the adjuster click very consistent through the entire adjustment range. Moton was the first to have this type of valve and KW 3-Way club sports have something similar as well. However the way Motion Control shocks are and how the fluid flows is very conventional, not that there is anything wrong with that.

    1. The KW solid piston shocks are not through shaft shocks. Not all TTX shocks are either, only the ILX series. The TTX is also a solid piston design but the valve design and function is very different. I think only one Penske shock is a thru shaft, the 8781 which is a cool twin piston design that I haven’t seen the insides of yet. The TTX has cartridge valves so revalving can be done very quickly, even while the shock is on the car which is a great feature while the KW has fast responding short travel valves which is an advantage. I don’t know much about Penske because they got me really mad a few years ago so I don’t support their company.

      1. Dynamic does solid piston shocks “like” this too but they do their spool valves, of course. Koni 2822 Mk2 also but not sure what their shims look like. I remember seeing an interview with Quantum on why everyone moved to stuff like this and they commented that it’s the only practical way to do some of the adjustments.

        1. Wow Koni came out with something new in 30 years! I think the applications are very limited to some or even one Formula car sizes. In fact I can’t even find them for sale! I think spool valves allow freer movement in high frequency square edged type bumps. The disadvantage is they have higher hysteresis. Working with spool valved shocks I like how they work. Not many people know but the older KW Motorsports valves are spool valves and have been for years before they became cool kid stuff. I hope to work on something with Dynamic shocks one day but they are not widely available here.

          1. Dynamic seems very much to be a “call us and we’ll arrange a project consultation, oh and here’s the shipping address so we can put your car on the shaker rig” sort of deal – I know KW operates in that realm too, but it seems like Dynamic only operates in that realm these days. I’ve seen their modern stuff in SCCA paddocks on Atlantic cars here and there but not commonly on anything “lesser”. Can’t argue with some of the pro-level results though. Weirdly I think they used to do lower price point stuff too – I know a handful of guys who have them on E Production 1st gen RX-7s, though from the build sheets I think those are just conventional monotubes.

            One of the things I think is interesting about KW as a company is that they don’t seem tied to just one way of doing things – their consumer stuff is modified classic twin tube, they do various motorsports monotubes with different adjuster concepts, and now these. Most other big shock makers seem to innovate within more limited areas if you get what I mean, and the smaller ones seem to innovate less but focus on tailoring to application.

          2. There are interesting things in the KW Consumer twin tubes as well, they have something that works like a spool valve called a Phifer valve. They also have an internal offset adjuster so they can be blueprinted on the dyno. In fact all KW’s have that. I think before, Dynamic was a smaller boutique sort of damper maker and anyone could buy some made to order shocks. Then they were bought out by Multimatic and things are not so simple, sort of like Sachs. Interesting product, huge facilities but man how do you even go about buying them!

  1. Idk if you are aware, but they DO have shock dynos with software that can evaluate frequency response.

    “Road (random) – We can upload road profiles into our machine to simulate the roughness (or smoothness) of any road.

    The video below shows our MTS 852 Damper Test System testing one of our custom-built dampers. It is tested with a sine profile of 5 inches at 1 HZ and 5 Hz, then a sine on sine profile with a major displacement of 5 inches at 1 Hz, minor displacement of 0.5 inches at 10 Hz (watch the video, it makes more sense!) then a major displacement of 5 inches at 1 Hz, and minor displacement of 0.5 inches at 20 Hz. ”

    https://youtu.be/EmFseuQZ7sc

    1. That’s an awesome shock dyno! None of the manufacturer’s I work with has one with that sort of capability. Roehrig seems to be the industry standard.

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