Formula Renault Damper

1.0 Background Research In the earliest days of the telescopic damper design, the damper was spilt into two main design

paths in which would alter its internal workings. This was the case as it was important to deal with

the vital aspect of the oil inside of the damper. The initial design of the damper was that a piston rod

was created to slide in and out of the main body of the damper. However, this made it problematic

as a fixed quantity of oil would be present inside of a body which would ultimately change in

volume. There were two solutions created to answer this problem: the ‘twin tube’ and the

‘monotube’ (Staniforth, 2006). The twin tube had an inner and outer wall which could move parallel

to one another, this meant that the oil could pass through the gap separating the inner and outer

wall of the damper as the damper closed. The other solution was to use a compressible gas inside of

a remote chamber which resided next to the chamber which contained the oil and separated by a

piston. Nitrogen was used in this instance as it could be successfully compressed or decompressed

with piston movement. The use of valves which would control the flow rate were used for the oil as

well (Staniforth, 2006).

The method of using compressed nitrogen gas seemed short lived, and both methods included

answers such as trapping the nitrogen in a flexible bag, or moving the required ‘spare space’ to a

remote canister. The remote canister would then contain its own valve assemblies and fully floating

piston which would section of the gas cushion (Staniforth, 2006). Before the remote canister was

designed, manufactured and then created, engineers came across a number of problems with their

initial designs. These included: a large amount of heat was generated whilst the damper was

working, and valving issues. When the suspension spring was compressed by the wheel, it was

effectively turned into heat which would cause the paint of the damper to burn off, affect the oil

viscosity and alter the varying bleed hole sizes (Staniforth, 2006).

The problem which then came once the remote canister was created was how the damper would

seem to be working correctly for one speed and a certain road condition, and then completely

wrong for another. The solution to this problem was that internal valving could be made to provide a

modest ‘spread’ covering alternate speeds and road conditions. An adjustment knob was then

designed to alter the amount of strength on rebound and bound, but sometimes rebound only

(Staniforth, 2006). A step forward in the 1960’s came about when Koning in Holland produced the

‘double adjust’ originally with a bottom knob to adjust the amount of bound and a top slotted ring

for rebound (Type 8211/12). However, the ‘double adjust’ had an invisible third setting which could

be altered to control the valving strengths to 6 different ranges. Up to date dampers such as Penske

have a huge range of adjustments available to the user, both externally and internally, mechanically,

and with variable gas pressure adjustments are expensive and need highly skilled backup (Staniforth,

2006).

2.0 Introduction to the Formula Renault damper The Formula Renault damper that is currently used on the car is a gas pressure

damper which has a remote canister and is in mono-shock setup. It is also a flow

resistant damper such that it is equipped with damper valves which all work

inside an oil filled cylinder. The oil filled cylinder works in conjunction with a

nitrogen filled cylinder (Bilstein, 2014). The nitrogen resides in the cylinder

because it ensures that the oil is under constant pressure. This prevents any

cavitation within the oil which causes a reduction in the damping effect (Abdo,

2012). Gas pressure dampers are available as either a mono-shock or twin-shock

(Bilstein, 2014).

The type of damper which is currently being run on the Formula Renault is a

remote canister damper. This type of damper is currently the best on the market

for regulating heat. However, it is the most expensive damper on the market

and it requires the most maintenance. Remote canisters eradicate any problems

that are generally present in most dampers: Heat and Cavitation. The damper

stops any excessive heat from being generated by putting the gas into a separate

canister from the oil filled shock. This complete separation from the gas and oil

allows for a greater volume of oil, therefore the dissipation of heat is greater and there is a lot less

chance of any cavitation occurring. Another advantage is that the canister overcomes the

compressed to extended length trade off. As the floating piston is housed in a separate canister, a

longer piston rod can be used (ARB USA, 2010).

The inner makings of the damper can be seen below.

Figure 2 - Inner makings of damper (F1 Dictionary, 2014).

The inner makings of the damper consist of the following:

Compression valving stack

A piston band (Teflon)

Linear compression face and linear rebound face

Rebound valving stack

The Compression valving stack regulate the amount of oil flowing past them in the compression

cycle or bump. As can be seen, they are located at the topside of the piston. During bump, the

upward movement produced by the irregularities of the road surface are absorbed through the

damper and spring. It is important that the damper is set to have enough bump stiffness during this

faze as acceleration, braking or cornering will vary due to the changing download rates (F1

Dictionary, 2015). However, if there is too much damping set up on the vehicle, it is very similar to

running the vehicle without any suspension whatsoever. Thus, any upward motion produced due to

Figure 1 - Current Mono tube shock absorber setup on the Formula Renault

irregularities in the road surface will be transmitted directly to the chassis of the vehicle. This type of

setup will also result in an increased amount of load produced on the suspension and tyres. This will

therefore result in the ride being too harsh for the driver, and will have a ‘skittish’ effect (F1

Dictionary, 2015).

The piston of the mono-tube resides directly inside of the cylinder, the contact between the two

moving parts (the piston and the cylinder) is prevented by a Teflon band. The Teflon band, or piston

band is located within a groove inside of the piston and is supported by an O-ring. This preloads the

Teflon band against the cylinder walls, thus eradicating any friction between the two moving parts.

The guide has a Teflon coated bushing surrounding it which stops metal to metal contact between

the piston rod and guide (Zuijdijk, 2013). The piston face which sits inside of the Teflon band has a

linear compression face and a linear rebound face. An example of what the piston faces look like and

how they would behave when a force against velocity graph is created can be seen in the Figure

below.

Figure 3 - Showing a common force vs velocity graph for a linear/linear piston.

The rebound valving stack controls the amount of oil flowing past them in the decompression cycle.

As can also be seen, they are located on the underside of the piston. Prior to the compression phase,

the damper will extend back to its previous position. It will move back to this position since the

spring is pushing against it (using its stored energy) (F1 Dictionary, 2015). The rebound stiffness of

the damper needs to be set at a higher setting than the bound setting as the stored energy present

in the spring is being released. If the damping is not correctly set up on the rebound setting or too

low, the wheel of the vehicle will quickly return through its static level and start to bump again (F1

Dictionary, 2015). This will therefore result in a bouncing effect that will offset the suspension giving

the driver little control. On the other hand, if the rebound setting is set too high, the wheel could

lose contact with the road for longer than intended. This will happen as the force required to push

the wheel back down is slower to react than the changing road surface. This rebound setup is not an

ideal setup, it is best to ensure that there is an optimal amount of tyre contact with the road surface

(F1 Dictionary, 2015).

Refer to the Figure below to see the entire make-up of the damper.

2.1 Possible Damper Replacements Following the initial research involving the damper currently running on the Formula Renault, it was

important to consider other types of dampers which could possibly act as a replacement. This was

essential as the group needed to find out how well the current mono-tube set up stacked up against

other types of dampers currently on the market. Although, the initial aim of the group was to

consider whether or not the current suspension setup was predictable by the means of obtaining

data from a track test using the current damper; it was considered important to research other types

of dampers as well. Thus further testing could take place using another damper, or a suspension

change could be made entirely, eradicating the damper completely. There are a few problems that

dampers can produce, so choosing the correct one is vital dependant on what the group wants from

the specific damper selected.

Initial problems to look out for

Generation of heat – this is a result of overwork and it decreases the shocks life expectancy

considerably.

Cavitation – Foaming happens and potential leaking through the valve and into the gas may

occur (ARB USA, 2010).

Benefits of having Gas Pressurisation

In a hydraulic damper, the oil inside the damper passes through the base or compression valve, and

from the outer tube which acts as a reservoir. The reservoir is partly filled with air as this allows

motion of the piston rod, hence the air is in contact with the oil. The air cannot prevent the oil from

foaming and thus causes a decrease in performance over time (Old Man Shocks, 2014).

The gas pressure shock absorber replaces the air in the reservoir with nitrogen gas. This eradicates

foaming and any decrease in efficiency over time, therefore providing a constant top of the range

performance (Old Man Shocks, 2014).

The types of dampers which could be used in the current mono-shock setup are listed and

researched below.

Figure 4 - Entire make-up of the damper (F1 Dictionary, 2015).

The Mono Tube Shock

This is the type of shock which is currently being used on the Formula Renault. This has an initial

advantage over the twin tube such that it produces less heat, this is because the entire shock is in

contact with the air (ARB USA, 2010).

A downside to having the mono tube is the amount of extended length provided for a given

compression length. As the main tube of the shock houses the piston inside, there is less room for

any extended rod length. Therefore, the rod is shorter and hence the extended length becomes

shorter as well (ARB USA, 2010).

This type of shock uses a higher gas pressure when compared to a twin tube shock. The advantage of

this is that the shock is extremely responsive to road conditions, however if tuned incorrectly, it can

become harsh at low speeds causing poor performance, especially through corners (ARB USA, 2010).

The Twin Tube Shock

These type of shock absorbers use heavy steel outer tube over a more fragile inner piston tube. This

has a couple of advantages over the mono tube design. It creates a chamber for gas and oil to

expand which allows for a larger volume for both. This gives the shock a good combination of heat

capacity and a surface to area heat dissipation value. However, this type of shock generally works at

a lower pressure than the mono tube and therefore is less suited to the Formula Renaults

requirements. The Formula Renault requires a large amount of pressure inside the damper as it

needs to be very responsive (quick compression and rebound characteristics) during a race (ARB

USA, 2010).

The current research suggests that the mono tube shock is the best damper currently on the market,

which the same damper is currently running on the Formula Renault at this present stage. Therefore

testing will have to take place to conclude whether that will influence the final decision made by the

group on what the next stage is in the development and testing of the Formula Renault. As

mentioned above, the conclusion to eradicate the mono-shock system could be made, therefore

there would be no need in looking for a suitable replacement for the current Formula Renault front

damper.

2.2 Damping Adjustments The current Formula Renault front damper has three settings that can be changed to alter the way in

which it reacts to the forces generated from moving over the road surface. These settings are

revised and listed below:

Low Speed Bound – This setting is located at the top end of the

remote canister of the damper (where a dial is located and numbers

displayed). The dial indicates the number of clicks that are available

and can be changed by turning the dial clockwise (increase low speed

bound) or anticlockwise (decrease low speed bound), the total

amount of clicks on this setting that are available is 5. 1 being the

lowest amount of high speed bound (full soft), and 5 being the

highest amount of high speed bound (full hard) (Penske Racing

Shocks, 2015). This setting works for low shaft movements, for

example: corner entry, exit and power down. The oil within the

damper is displaced into the reservoir and is proportional to the area

of shaft entering the damper body. An adjustable needle and jet assembly control the

Figure 5 - Positioning of High Speed and Low Speed Bound.

amount of oil that passes through on compression. From decreasing the flow of oil, it causes

a stiffer feel in low speed circumstances. The low speed adjuster works alongside the high

speed adjuster to delay the high speed circuit (Penske Racing Shocks, 2015).

High Speed Bound – This setting can be located just below the top dial on the remote

canister. Again, this setting has a number of clicks which are available to the user which can

be altered dependent on their performance requirements. The total number of clicks

available is 14, 1 being the full soft and 14 being the firmest (clockwise and anticlockwise

adjustments remain the same for increasing and decreasing the magnitude of this setting)

(Penske Racing Shocks, 2015). This setting is used for fast shaft movement, for example;

bumps and track irregularities. This setting works by displacing oil into the reservoir at a fast

velocity. The oil is then forced to bypass the low speed needle and jet, forcing the oil to

move through another piston in which its orifices are covered by another shim stack. By

increasing the amount of clicks on this setting it makes it harder for the oil to flex the shims

and move past them. The high speed adjuster assembly is timed based on the setting that

the low speed needle is set to and the shaft velocity. For example, if the low speed needle is

set to full soft, at the higher speeds a larger amount of oil will move through the low speed

jet, thus delaying the operation of the high speed bypass mode. (Penske Racing Shocks,

2015).

Rebound – This setting is located at the base of the main shaft of the damper. From looking

at the Figure below it shows that this adjustment can be altered by inserting a pin into one

of the dials holes and turning it. Turning the dial towards the positive value increases the

amount of damping and turning the dial towards the negative value decreases the amount

of damping. This setting has a total amount of 18 clicks. 1 being the lowest amount of

damping, and 18 being the highest amount of damping (Penske Racing Shocks, 2015). This

system works by using a jet and needle combination to give the user a more linear range of

adjustment for bleed past the piston rebound. The jet uses a spring loaded poppet valve to

check the amount of oil flow. This system provides a better seal against the flow and a

quicker response time as the shaft changes direction. The needle has a curved tip which

provides for small adjustments to be made for the amount of linear damping provided by

the jet (Penske Racing Shocks, 2015).

The shock currently on the Formula Renault has an option to increase the fine tuning ability of the

rebound setting (see Figure below) (Staniforth, 2006).

Figure 6 - Placement of adjustment pin/screw to increase or decrease the amount of damping (Penske Racing Shocks, 2015).

Figure 7 - Showing the full rebound adjustment available on the damper as well as the needle (Staniforth, 2006).

3.0 Experiment and Analysis After fully understanding how the damper works internally and externally, it was time to detach the

damper from the Formula Renault and test it using the damper dyno available to the group during

the duration of the project. The damper was tested on all clicks which included both high and low

speed bound, and all of the rebound settings. The damper was tested to show a force vs

displacement graph for each click on all three settings and a force vs velocity graph for each click on

all three settings. The readings of minimum and maximum forces and the number of clicks for that

particular setting were measured during the test. All readings are displayed below in tables. A full

analysis of the results will be performed to conclude whether the specific damper settings show any

correlation.

Minimum and Maximum Force Values

Rebound Click Min Force (N) Max Force (N)

1 -1424.98 782.80

2 -1462.48 771.08

3 -1497.64 778.11

4 -1539.82 794.52

5 -1570.29 810.93

6 -1612.48 815.61

7 -1678.10 832.02

8 -1729.66 869.52

9 -1795.29 881.24

10 -1839.82 935.14

11 -1877.32 965.61

12 -1966.38 979.67

13 -2064.82 1007.80

14 -1293.73 2453.87

15 -1335.92 2392.94

16 -1328.89 2383.56

17 -1333.59 2385.91

18 -1331.68 2391.29 Table 1 - Measurements of Force VS Displacement recorded for when the damper was tested on all rebound clicks.

The above table shows the minimum and maximum force that was applied on the damper and its

relative click setting. In this case, the damper was tested on all rebound clicks. The results prove to

be correct as the amount of damping force increases as the clicks on the rebound setting increase as

well. This shows that the damper works correctly as when referring to the Penske Racing Shocks

Technical Manual, by turning the rebound dial towards the positive value (increasing the amount of

clicks) the amount of damping force increases (Penske Racing Shocks, 2015). However, when

referring to the rebound click settings from 14 to 18, the maximum amount of force enforced onto

the damper increases drastically (244%). From clicks 14 to 18, the maximum amount of force

required to displace the damper stays pretty constant. These readings show some correlation as the

amount of damper force required increases up to click 13, but stays around a constant force reading

from 14 to 18.


High Speed Bound Click

Min Force (N) Max Force (N)

1 -1333.58 806.24

2 -1338.26 813.27

3 -1324.20 864.83

4 -1324.20 904.68

5 -1321.86 946.86

6 -1321.86 974.99

7 -1335.92 991.39

8 -1326.54 1033.58

9 -1319.51 1061.70

10 -1352.33 1101.55

11 -1352.33 1101.55

12 -1338.26 1127.33

13 -1342.96 1143.73

14 -1335.92 1148.42 Table 2 - Showing the minimum and maximum force values required to displace the damper relative to its high speed bound click setting.

The above table shows a positive correlation for the maximum amount of force required to displace

the damper and the click setting that the damper was on. The maximum amount of force required to

displace the damper is shown to increase as the click setting for the high speed bound increases as

well. Again, referring to the Penske Racing Shocks Technical Manual, this is correct as when the

amount of clicks increase, so should the amount of damping force required to displace the damper

(Penske Racing Shocks, 2015).

Table 3 - Showing the minimum and maximum force values for the relative low speed bound clicks.

Again, the above table shows

the maximum amount of force

required to displace the

damper relative to the low

speed click value that the

damper is set to. The values do not show a clear positive correlation relative to the click settings in

this case. The values are firstly shown to decrease from click 1 to click 2 and then slowly increase



Low Speed Bound Click


14 1 -1333.58 1171.86

14 2 -1345.29 1160.14

14 3 -1307.79 1181.23

14 4 -1317.17 1183.59

14 5 -1317.17 1188.27

from click 2 up to click 5. This may be due to a slight maintenance issue as the valve shims have not

been replaced on the damper recently and it is required that they, as well as some other internal

components (shaft seal O-ring, shaft bearing O-ring, Piston O-ring et cetera) are replaced yearly or

for every 30 hours of track time (Penske Racing Shocks, 2015). When comparing the bump and

rebound settings on the damper, it shows that the maximum amount of force required to displace

the damper on the rebound setting is 2392.94N, and the maximum amount of force required to

displace the damper on the bound setting is 1188.27N. This is a correct correlation as according to

Staniforth (2006, p.170) it states that the rebound setting on a damper is two to four times the

strength of the bump. Although in some competition settings the readings may be a 1:1 ratio.

For a full explanation of a Force VS Displacement graph and the transient response of the damper

when force is applied to it, refer to the Figure and explanation below.

The above graph shows the minimum and maximum amount of force applied on the damper and its

full range of displacement. The damper has a full displacement range of 25.6mm. The minimum

amount of force was measured, the minimum amount of force on a Force VS Displacement graph is

when the damper is moving through rebound. Therefore, the rebound shims would be reacting and

the damper would be moving towards its maximum range of displacement (negative displacement in

this instance) (Staniforth, 2006). When the damper is in a maximum negative value of displacement,

at bottom dead centre (BDC) the rebound shims close and the compression shims begin to react.

The damper would then be moving through bound (bump) as the amount of force required to move

the damper increases. When the damper moves through bump and reaches the maximum amount

of force required to displace the damper the compression shims will be reacting. At the point where

the maximum amount of force is applied on the damper, the displacement will be equal to zero.

When the displacement is equal to zero, it is known that the damper is moving through its point of

Figure 8 - Showing a Force VS Displacement graph for the damper when tested on the damper dyno.

equilibrium (or natural ride height). Following this, the damper will still be tested in bound but will

be moving towards its maximum displacement value. At the maximum displacement value, the

compression shims will close and the rebound shims will begin to react. To see how the damper

oscillates and how it links to the above graph in terms of the quadrant it is in, refer to the Figure

below.

The next objective whilst using the damper dyno was to extract the data for Velocity VS Force. See

the tables below for the minimum and maximum force values and relative click settings for the high

speed and low speed bound, and rebound.


Rebound Click Min Force (N) Max Force (N)

1 -1462.48 771.08

2 -1678.10 832.02

3 -1539.82 794.52

4 -1678.10 832.02

Figure 9 - Showing the oscillation of the piston inside of the damper walls relative to the force vs displacement graph (Staniforth, 2006).

5 -1612.48 815.61

6 -1754.23 876.54

7 -1839.82 935.14

8 -1795.29 881.24

9 -1839.82 935.14

10 -1877.32 965.61

11 -1966.38 979.67

12 -1966.38 979.67

13 -917.05 981.56

14 -1335.92 985.17

15 -1328.89 985.92

16 -1729.66 869.52

17 -1321.86 998.11

18 -1358.32 997.23 Table 4 - Showing the minimum and maximum values for when the damper was tested on all clicks in the rebound setting.

The above table shows similar values to the force values gathered when testing the amount of force

required to displace the damper when the damper was set up on all rebound clicks. The data cannot

be said to have a positive correlation (force increasing as the clicks increase) even though the results

of the amount of force are generally increasing, there are some mixed values. An anomaly can be

seen to be present for the maximum force value on click 16. Although the damper has a linear

compression face, the values of the maximum force should increase quickly for possible low speed

damping and then slowly increase. However, this is not the case. It can be concluded that this may

be down to a maintenance issue as the shims in the damper have remained inside of the damper for

a longer period of time than recommended by Penske (Penske Racing Shocks, 2015).


High Speed Bound Click Min Force (N) Max Force (N)

1 -1319.51 1061.70

2 -1324.20 864.83

3 -1342.95 1143.73

4 -1321.86 946.86

5 -1321.86 974.99

6 -1321.86 974.99

7 -1321.86 974.99

8 -1326.54 1033.58

9 -1352.33 1101.55

10 -1321.86 1087.49

11 -1338.26 1127.33

12 -1338.26 1127.33

13 -1342.95 1143.73

14 -1342.95 1143.73 Table 5 - Showing the minimum and maximum force readings gathered for when the damper was tested on all high speed bound clicks.

The above table shows that the maximum force values generally increase as the clicks increase.

Although this is the case, again there cannot possibly be any positive correlation between the

increasing amounts of clicks set on the damper relative to the maximum force readings gathered for

that specific setting.



Low Speed Bound Click


14 1 -1345.29 1160.14

14 2 -1350.11 1090.78

14 3 -1335.92 991.39

14 4 -1352.33 1101.55

14 5 -1342.95 1143.73 Table 6 - Showing the minimum and maximum force values for when the damper was tested on all 5 clicks on the low speed bound setting and at the highest amount of clicks for the high speed bound setting.

The table above again shows no correlation between the values obtained for the maximum amount

of force gathered from the various click settings gathered from the test. Due to mixed results and

many results being concluded to be wrong due to maintenance issues, the damper will need a

complete service to change all of its inner components which effect the results obtained from the

damper dyno. The components that will need maintenance, or replacing are as follows:

Oil

Shaft seal

O-ring

Wiper

Shaft bearing O-ring

Reservoir cap O-ring

Piston ring O-ring

Valve shims

(Penske Racing Shocks, 2015).

Further tests would then be required for all click settings when comparing Force VS Displacement

and Force VS Velocity.

When analysing the Force VS Velocity graph it can be seen that the compression and rebound face of

the piston is a linear/linear piston. Both parts of the curve can be tuned dependant on the

requirements of the user. A comparison on the maximum and minimum adjustment settings can be

seen in the following Figure.

Figure 10 - Comparison between total amount of 'elbow-room' of force between adjustments on bound and rebound.

As can be seen from the above figure, the maximum force (when the damper is in bound) for the low

speed bound (click 1) setting is 1160.14N and the maximum force for the rebound setting (click 1) is

771.08N. The minimum force (when the damper is in rebound) for the low speed bound (click 1)

setting is -1345.29N and the minimum force for the rebound setting (click 1) is -1462.48N. Therefore,

the total ‘elbow-room’ for the bound adjustment is a total of 1160.14N - 771.08N = 389.06N; and

the total ‘elbow-room’ for the rebound adjustment is a total of 1462.48N – 1345.29N = 117.19N.

Hence, the adjustment of the bound available to the user is greater than the adjustment of the

rebound. Refer to the table below for the percentage of adjustments available to the user for the

bound and rebound of the damper.

Percentage of Adjustment Available to the User

Bound 33.5%

Rebound 8% Table 7 - Adjustment percentage of bound and rebound available to the user.

4.0 Final Proposal Due to the reliability of the damper being poor, the final proposal will be to fully service the damper.

As the damper used on the Formula Renault is currently the best on the market for regulating heat

and responding to changes in road conditions such as bumps or irregularities, the cost of fully

replacing the damper would not be a clever option since the vital parts (which need to be replaced)

can be purchased online. By following the Penske Racing Shocks Technical Manual and by replacing

the necessary components, the damper would be working as expected and the group could furtherly

test the car.

References Abdo, E., 2012. Modern Motorcycle Technology. 2nd ed. New York: Cengage Learning.

ARB USA, 2010. Selecting Shocks. [Online]

Available at: http://arbusa.com/Getting-Started/Selecting-Shocks.aspx

[Accessed 28 November 2014].

Bilstein, 2014. Technology: basic suspension know how made easy. [Online]

Available at: http://www.bilstein.de/en-uk/technology/basic-know-how/


F1 Dictionary, 2014. Shock Absorbers. [Online]

Available at: http://www.formula1-dictionary.net/damper_shock_absorber.html


F1 Dictionary, 2015. Shock Absorbers. [Online]

Available at: http://www.formula1-dictionary.net/damper_shock_absorber.html

[Accessed 21 April 2015].

Penske Racing Shocks, 2015. Technical Manual Adjustable Shocks (8100, 8660, 8760 Series). [Online]

Available at: http://www.penskeshocks.co.uk/downloads/AdjustableTechManual.pdf

[Accessed 20 April 2015].

Staniforth, A., 2006. Competition Car Suspension. 4th ed. Yeovil: Haynes Publishing.

Zuijdijk, J., 2013. Vehicle Dynamics and Damping. 1st ed. Bloomington: AuthorHouse.

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Formula Renault Damper