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      Bump Stops

      BUMP STOPS
      Bump Stops: Also known as bump rubbers, play a vital role in suspension design and are essentially an additional spring made of an elastomeric material. They help prevent the damper and/or spring from bottoming out. More about bump stops below...

      BUMP STOPS
      As the suspension compresses two things will occur if there is not enough bump travel. The spring can "coil bind" or the damper can "bottom out", both leading to a situation where the effective spring rate becomes infinite (in other words a solid rod). When this occurs bad things can happen such as an abrupt loss of traction and/or possible damage to suspension components. This is why it is crucial to have the damper stroke position set correctly. However, even with the stroke position set correctly, large bumps can still cause the spring to coil bind or the damper to bottom out. Fortunately bump stops can help this situation. As the suspension nears bottoming out or coil bind, the addition of a bump stop creates a highly progressive spring rate, helping solve the problem of instantaneous infinite spring rate. This a great solution for smoothly controlling the wheel delivering a significant positive impact on ride comfort and cornering grip.

      Bump stops can be used for more than just protection from coil bind or bottoming, they also can be used for tuning the suspension as well. We will go over this briefly here and in more detail in a future article. One thing we can do is set our stroke position where we are roughly 1 inch away from the bump stop. This will allow the suspension to soak up minor bumps using only the coil spring, allowing for a more comfortable ride quality. Then as the car goes into a corner and the suspension compresses, the upper spring perch will hit the bump stop reducing body roll from the increased spring rate. It is important to know that there are special bump stops for this where the first inch of travel of the bump stop can be made soft, and at a certain point the bump stop becomes much more stiff to combat coil bind or bottoming out. This a great solution for smoothly controlling the wheel delivering a significant positive impact on ride comfort and cornering grip.

      Damper Valving

      DAMPER VALVING 


      Suspensions are VERY complex. Please note this guide is intended to be a BASIC damper valving guide and covers information at a relatively high level. Just like there are several ways to brew coffee, there are several ways to setup suspensions.


      UNDERSTANDING DAMPERS

      It is important to understand WHAT the shocks (dampers) are doing in order to understand how to make changes to the handling characteristics of your car.

      Dampers create force to control the springs and the dynamics of the suspension/chassis. When the suspension moves we measure it by velocity. When the suspension compresses it is called “Bump” and when the suspension droops it is called “Rebound”. Turning causes the car to roll (outside tire compresses and the inside tire droops) and this is typically a low velocity occurrence of the suspension (aka low speed). Hitting a bump or curb is typically a high velocity occurrence (high speed).

      So the more adjustment knobs the better right? The tendency is to want a damper that has a knob for every function… low speed rebound, low speed compression, and high speed rebound/compression so we can fine tune but unfortunately its not that easy. We see it over and over and over again where people install complex dampers, get lost with knob turning and end up NEVER adjusting them ever again. The best laid plans get derailed by complexity. Its important to keep it simple and keep good notes.

      Öhlins dampers are competitive, not complicated. They are setup out of the box with force curves oriented towards performance driving. The clicker predominantly adjusts low speed rebound (the most important) and low speed compression is matched as necessary. This low speed adjustment helps dial in the “dynamic balance” of the car, in other words, how the car reacts when you turn. It also helps dial in grip through the turn by keeping the tire contact patch optimal over small undulations and ripples in the pavement. The Dual Flow Valve (DFV) replaces the need for high speed adjustments, it allows the damper to soak up bumps without upsetting the car and lets the tire return to the ground quickly.

      What about range of adjustment? There are typically two different use cases for aftermarket dampers and their adjustments: combo street/track cars, and dedicated track cars. It sounds enticing to buy a damper that can control a large range of spring rates to encompass multiple use cases but this approach is a major compromise. They typically end up with a small adjustment range for the springs you settle on limiting your adjustability and tuning capabilities from track to track. Everyone is a little bit different, or perhaps a lot different, which is why Öhlins offers two distinct kits, the ‘Road and Track’ and ‘Dedicated Track’, each of which are capable of handling a window of spring rates for their particular use case. No need to have your dampers re-valved if you want to make spring changes to suit your driving style or car setup. ‘Road and Track’ and ‘Dedicated Track’ are based off the same damper technology and can be converted back and forth. Custom applications are also available.

       

      Ohlins Dual Flow Valve (DFV)

      ÖHLINS DUAL FLOW VALVE (DFV) DAMPERS

      WHAT SETS THE DFV DAMPERS APART FROM THE COMPETITION?

      Dual Flow Valve Technology (DFV): Traditionally dampers control the suspension with a piston (with shim stacks) and a bleed valve. The Öhlins damper introduces a third way with it’s Dual Flow Valve. Instead of relying on the main piston and/or bleed valve to control the suspension over bumps and potholes on the street (or curbs on the track) the dual flow valve takes over in this scenario. What this does is allows the bleed valve and piston with shim stack to focus on the racecar-like feel in the turns while bumps are absorbed by the DFV. You basically get the best of both worlds. Learn more below…

      Inverted Strut Design (MacPherson Struts): This is one of the most overlooked design features of a damper. A MacPherson strut suspension incorporates the damper as one of the control arms. Vertical and cornering loads put a bending load on the damper. A traditional upright damper will flex under load causing loss of camber and steering feel. In addition, the extra load on the piston shaft causes premature internal component wear leading to the common “blown shock.” Ohlins inverts the damper which removes the cornering load on the piston shaft and puts it on the external body of the damper. This is much more rigid which reduces camber loss, enhances steering feel, and increases longevity. Learn more below…

      Temperature Compensation Bleed Valve: It is well known that when engine oil gets hot the engine will make more power because there is less drag from the hotter oil. The same thing happens in your dampers, as the oil gets hot the damping force is reduced. What this means is that your car will handle differently throughout your trip around town or during an on track session. Ohlins has solved this problem with the temperature compensation bleed valve. As the damper heats up, the special valve will close just a little to keep the damping forces the same from cold to hot. Learn more below…

      Gas Pressure Valve: Gas pressure dampers need a way to insert the gas pressure once assembled. Most dampers use Shrader valves which are not reliable at all, we’ve seen them leak hours after initial assembly. Ohlins uses self healing rubber diaphragms which lasts for years and potentially the life of the damper. Learn more below…

      Vehicle Specific Valving: Öhlins Road and Track kits are extensively developed to have the best damper valving for a specific spring rate. This method allows for very fine tune-ability of the balance of the car unlike a “catch all” damper. However, this does not mean you have to use the springs that come with the kit. You can use up to a 25% softer or stiffer spring without having to revalve the dampers. If you have a dedicated track car and want to significantly increase your spring rates, simply contact us to discuss your needs and learn more below…

      Dual Height Adjustment Method: You have probably heard it 100s of times; if you lower your car too much you will run out of suspension travel and bottom out. Ohlins has the perfect solution to this problem, the Dual Height Adjustment. Now you can set your damper so that there is plenty of bump travel, then use the separate ride height adjuster to change the ride height of your car. Learn more below…

      Longevity and Servicability: The age old adage “you get what you pay for” couldn’t apply more with Öhlins… Between World Rally Championships, 24 hours of LeMans, and the harsh environment of Sweden, Öhlins is used to building components that survive the toughest environments in the world. The attention to quality machining and finishing processes, inverted strut design (for macPherson strut cars), and the diaphram type nitrogen valve are just a few examples of why these dampers are so robust. Learn more below…



      DUAL FLOW VALVE TECHNOLOGY

      A damper controls the upward movement (compression) and the downward movement (rebound) of the suspension. This movement is typically broken down into two levels, high speed and low speed. For example, hitting a bump on the street or the curbing on a track causes a high speed compression movement. Dropping down into a pot hole on the street or dropping off the end of track curbing causes a high speed rebound movement. Low speed movement of the suspension occurs when turning the vehicle. For example when turning to the right, the chassis will roll causing the left side suspension to compress slowly and the right side suspension to rebound slowly.

      In an ideal world we want the damper to be stiff during low speed so that the car reacts quickly to steering inputs yet be soft when we hit pot holes or track curbs. This means that the wheel and tire can quickly and effectively resume their important position back on the ground, providing grip and traction. This is what the Dual Flow Valve technology accomplishes that sets Öhlins apart from its competitors.

      Figure 1 & 2 Below "1" is compression and "2" is rebound. At low speeds oil flows mostly through the shaft jet bleed (red arrow). At moderate speeds oil mostly flows through the piston ports (blue arrow).. At high speeds oil can escape through the DFV (green arrow) increasing comfort as well as grip.



      FIGURE 3 Below: (Vehicle – no DFV) Without DFV the oil can not flow through the piston quickly enough on the rebound stroke after hitting a bump, so the tire is not able to stay in contact with the road.

      FIGURE 4 Below: (Vehicle – DFV technique) The DFV valve opens, letting the oil flow quicker through the piston on the rebound stroke after hitting a bump, enabling the tire to stay in contact with the road.

      TEMPERATURE COMPENSATION

      Figure 5 Below: As the piston moves within the damper, it generates friction – and therefore, heat. Although we can’t stop heat, we can deal with it, and this is yet another way that Öhlins differs from the competition. As the heat increases, the viscosity of the damper fluid can change, altering the car’s handling characteristics. Öhlins unique needle bleed valve expands with temperature, closing the gap that the fluid travels through, maintaining a consistent damping rate. The best thing of all? You won’t even notice! All you’ll feel is that the car responds consistently, lap after lap, turn after turn, allowing you to concentrate on braking points and apexes while the Öhlins technology takes care of the damping.



      RIDE HEIGHT ADJUSTMENT

      One the most unique features of the Öhlins Road and Track suspension kits is the dual height adjusters. Spring pre-load and ride height can be adjusted separately. On a traditional damper you can only adjust the ride height of the vehicle using the lower spring perch. The more you lower your vehicle, the less compression (bump) travel your suspension has. Lower the vehicle too much and you can bottom out the damper over even the slightest bump.


      With the Öhlins Road and Track suspension kits you can lower your car and maintain sufficient bump travel at the same time! Image you have your ride height exactly where you want it but there is only 1" of compression travel. With a traditional damper your only option to get more compression travel is to spin the lower spring perch up. Now your ride height is not at your ideal location. With the Öhlins damper you would raise the lower spring perch up to get sufficient compression travel and then adjust the ride height adjuster to lower your car back down to the desired ride height. Problem solved!

      Please note, not all applications have this dual height adjustment due to the limited diameter of the clamping ring on the front spindle.

      INVERTED MACPHERSON STRUT DESIGN

      There are two different types of damper (aka shock) designs within MacPherson strut suspensions There is an upright design and an inverted design. The damper essentially acts like one of the control arms in the suspension system. Vertical and cornering loads put a bending load on the damper. You want the damper to be as rigid as possible in bending for many reasons, but most importantly it provides better steering feel, ensures camber settings stay in spec under load, and greater longevity of the internal damper components.

      GAS PRESSURE VALVE

      Mono tube dampers use gas pressure to keep the oil inside the shock from cavitating. This ensures the damping forces stay consistent in all scenarios, especially during high speed occurences. Traditionally, dampers use shrader valves to fill the damper with nitrogen which is very inconsistent and can leak over time. Ohlins uses a rubber diaphragm retain the nitrogen and is filled by a needle tool. Once the needle begins to be extracted, the diaphram seals itself not allowing any gas to escape.

      Figure 1
      Figure 1

      Figure 2
      Figure 2

      Figure 3
      Figure 3

      Figure 1: The needle valve is inserted in order to fill the gas chamber

      Figure 2: As soon as the needle starts to be extracted, the diaphragm seals itself, holding the exact pressure as seen on the gauge.

      Figure 3: Once the needle is fully removed the diaphragm stays sealed with no chance of leaking throughout the service life of the damper. A screw is then inserted to keep contaminates from wearing out the diaphragm.

      Figure 4
      Figure 4

      Figure 5
      Figure 5

      A schrader valve has many intricate parts that can lead to failure. As gas pressure is added, the valve is opened (Figure 4). Once the valve is closed (Figure 5), it relies on a perfectly clean seal (Red Arrow) to retain the gas pressure. The slightest contaminate or degradation in the seal can cause the gas pressure to escape. A slightly bent plunger can also lead to a bad seal.

      DEVELOPMENT PHILOSOPHY AND PROCEDURE

      Despite what other suspension manufacturers may tell you, comfort is king, even when you are trying to set-up a competition machine. Ohlins' vast experience on events like the World Rally Championship, Nürburgring and Isle of Man TT races has shown them that the fastest drivers and riders are those that aren’t being shaken to bits. The ‘science of compliance’ is a hugely important part of their design work.

      Development is a step by step process which starts with their test drivers driving the car on public roads just outside Stockholm, and on their racetrack to set a benchmark. The goal is to collect enough data about the current setup from driving on the racetrack and public roads.

      What data is of their interest? They measure all specific parameters of the suspension, such as the motion ratios, ride-height, roll-centre etc. They are also performing a corner-weight of the car. This data is vital for the next stages of Their development process.

      With their purpose-built software, they develop an initial setting with feedback from their test drivers. From the first setting, they can begin to build an early proposal damper-setting and spring stiffness. When the computer-based model is developed, it’s time to build and fit the first Öhlins Road & Track prototypes to the car.

      With the prototypes fitted to the car their technicians and engineers hand over the car to their test drivers again. A first shakedown performed on the racetrack to make sure that we have a safe product.

      After the shakedown, they begin to stress the dampers with high-speed maneuvers, and they also find out if the computer modelling of the damper-settings and spring stiffness are correct. Though the dampers are primarily intended to be used on the racetrack, their engineers and test drivers spend much time to find a comfort-setting for road use. The Road & Track dampers from Öhlins are often more comfortable than the standard suspension.

      The process to find the optimum track setting and road setting may take some time. Öhlins is a perfectionist company, and that is clear in their development process. If their test drivers and engineers are not pleased with a particular setting, they change it until they are sure that this is the best possible match between Road & Track.

      The final step in the Öhlins Road & Track Development Process is to finalize and prepare the dampers for production. All documentation and prototypes used during the development phases are saved for regulatory compliance to meet legal demands.

      The Öhlins Road & Track Development Process is executed for every single car model. Every setting is tailor-made and evaluated thoroughly before being transferred to series production. Their test drivers put in thousands of test kilometers to ensure the perfect handling combined with comfort. They develop their dampers after careful calculations to secure a high-quality product, which is safe to use when driving on the absolute edge. All in all, Öhlins Road & Track group takes care of testing and development to find the optimum performance so you can focus on driving your car with a smile! Drive safe!

      SERVICABILITY

      All Öhlins units are fully serviceable and adjustable, making sure that they give faithful and dynamic service for years to come. Between World Rally Championships, 24 hours of LeMans, and the harsh environment of Sweden, Öhlins is used to building components that survive the toughest environments in the world. The choice of materials used is one of the key factors behind Öhlins' success. Each component is surface treated to ensure reduced friction and superior performance. The carbon steels bodies are salt spray tested meeting ISO 9227 Standards. These are real-world units for daily driven cars.

      Having said that, it is a common misconception that once you buy a damper it will last forever. Dampers have moving parts and oil just like your engine and brakes. You change the oil in your engine and bleed your brakes regularly don't you? Depending on the type and level of use, dampers can go many years before they need servicing. This applies to any and all OEM and aftermarket dampers.


      Inverted MacPherson Strut Design

      INVERTED STRUT DESIGN
      In this article we will go over how an inverted strut design works and the benefits of the design versus a standard upright strut.

      MACPHERSON STRUT DESIGNS
      Figure A: MacPherson Strut Design
      Figure A: MacPherson Strut Design

      Figure B: Upright Design Damper
      Figure B: Upright Design Damper

      Figure C: Inverted Design Damper
      Figure C: Inverted Design Damper

      There are two different types of damper (aka shock) designs within MacPherson strut suspensions (Figure A). There is an upright design (Figure B) and an inverted design (Figure C). The damper essentially acts like one of the control arms in the suspension system. In addition to vertical loads over bumps, the damper also sees bending loads from cornering. You want the damper to be as rigid as possible in bending for many reasons, but most importantly it provides better steering feel, ensures camber settings stay in spec under load, and greater longevity of the internal damper components.

      RIGIDITY IN BENDING: UPRIGHT STRUT VS INVERTED STRUT
      standard gas pressure.JPG
      Upright Strut

      An upright strut takes the bending load on the actual piston shaft itself. The piston shaft is supported by the upper guide bushing (green) and the piston (purple). The piston shaft is typically anywhere from .5" to .75" in diameter depending on the damper brand. This is not ideal for taking bending loads.




      Inverted Strut

      An inverted strut takes the bending load on the outside of the damper body. The damper body is supported by two guide bushings (yellow) in an outer tube whose sole purpose is to support bending loads. A typical inverted struts body is about 1.75" in diameter. This makes for a MUCH stiffer design in bending.

      WHY ARE OEM DAMPERS UPRIGHT IF INVERTED IS BETTER?
      spring angle.jpg
      Upright OEM Damper

      In a nutshell, they are cheaper to produce. One way to combat the bending load on the damper is with the spring. Have you ever noticed how the spring sits at an angle on your OEM strut? The force generated by the angled spring helps counter the bending loads placed on the damper during cornering and this is what helps an upright design work in a MacPherson strut. When we "upgrade" to performance oriented suspension kits with adjustable height springs (coil overs) we loose the aid of an angled spring.

      OTHER BENEFITS TO INVERTED DESIGN
      inverted compressed.JPG
      Guide Bushings and Seals

      Because the outer body of an inverted damper is taking the bending load, this means the piston shaft nor the piston itself have any side loading like an upright damper. This means the piston shaft guide bushing (green) lasts much longer before it needs replacing. The piston shaft also has seals that keep the pressurized oil from escaping the damper. The same applies to the seals, since there are no side loads from the piston shaft, the seals last much longer than an upright damper. The seals are also protected by the outer support tube which virtually eliminates the possibility of debris contamination.

      standard gas pressure.JPG
      Fluid Displacement and Gas Pressure Upright Strut

      On an upright damper, one way to increase bending rigidity is to increase the diameter of the piston shaft. Unfortunately, the larger the piston shaft, the less room there is for oil in the damper housing (white). Additionally, the larger the piston shaft displaces more fluid when compressed which in turn compresses the high pressure gas even more. In the diagram you will see where blue = uncompressed and Red = compressed too much. This increase in gas pressure results in extra unwanted forces and friction. Ideally you only want the gas pressure to be high enough to keep the fluid from cavitating and that is it.





      inverted gas pressure.JPG
      Fluid Displacement and Gas Pressure Inverted Strut

      Since the piston shaft of an inverted strut sees no side loading, the piston shaft can be very small in diameter. This in turn allows for more fluid in the damper and prevents the gas pressure from becoming a factor at any point in the suspension travel. In the diagram you will see the where blue in both scenarios has a large enough volume to prevent high gas pressure.