Hey all,
I’ve noticed recently off-road that I can still observe significant low velocity heave and squat in my Prado, for example needing to accelerate hard in soft sand. As I’ve recently installed some quite high critically damped custom valved shocks in the rear, this suggests the front strut damping is not working as well as it could.
I’m running the latest modification of the D563-M2 Bilstein strut, the dyno curve is shown below;
To interpret what is going on and how the strut/shock valving Forces are connected to body kinematics such as roll, heave, pitch, squat etc., then we need to take a look at what critical damping is.
Critical damping in shock absorbers is how quickly the shock can cycle out rebound or compression motion and return the sprung/unsprung mass system to equilibrium. The part of the shock valving F vs v curve that shows what percentage of 100% critical damping the shock has occurs in the low velocity part of the curve, typically below 150mm/s where you’ll observe the knee or transition from low to high speed valving. The gradient of the F vs v curve is referred to as the damping rate, and you’ll typically see two damping rates in most shocks, low and high speed. The low velocity damping rate is the gradient which determines the %Ccr, or percent critical damping. The critical damping is characterised by a critical damping coefficient, Ccr, which is velocity dependent. The low velocity damping is what minimises sprung mass body kinematics, so the %Ccr that you have in your shocks will determine how much body roll, pitch etc. that you’ll experience in off-road conditions. You can change this low velocity part of the valving curve by modifying the valve shim in the piston head which controls low speed hydraulic bleed. Higher velocity damping Forces are typically there to control the higher frequency motion of the un-sprung mass, which in the Prado can oscillate at around ten times the frequency of the sprung mass.
To determine the %Ccr you have in your shocks, you need to utilise the passive quarter car model. From this model you can produce calculated valving curves which you can fit to your dyno data. You’ll need to know sprung and unsprung corner masses, motion ratios, wheel, tire and ride rates to calculate the critical damping coefficients for both the sprung and unsprung masses.
The image below shows the generic quarter car model and how critical damping works;
The equation of motion for the simple 1D damped oscillator model on the right is derived by summing the restoring Force on the coil, F = kx, and the Force generated by the damper, F = cv. The solutions are characterised by 100% critical damping yielding;
As the damping coefficient gets closer to 1.0, then the system will return quickly to equilibrium. Lower percentages of the critical damping coefficient means the system will take several cycles to reach equilibrium. With lower values, you’ll easily feel the kinematic effects in your car, body roll will take several cycles to completely cycle out and minimise etc. Higher values beyond 1.0 will actually take longer to settle to equilibrium.
When you hit a value of 1.0 (or 100%Ccr) for the critical damping coefficient, the system will not cycle. A great example of this is shown in this video where an off road buggy with very high critically damped shocks is dropped from a great height;
http://imgur.com/gallery/UX68xNr
For most applications, there is an old rule of thumb about critical damping from the Formula SAE and Autocross crowd. This rule of thumb suggests something like 65-70%Ccr damping rate is sufficient for the fastest lap times.
This old rule of thumb is really only a racing guideline and is not necessarily the most appropriate value. Formula 1 cars may use 120%Ccr in some circumstances, dependent on track conditions and motion ratios. Most passenger vehicles use only 10 to 20% Ccr. 4wd vehicles have different requirements again, with the most relevant use of critical damping being to control excessive body kinematics such as roll, pitch, heave etc. As an example, I’m currently using 90%Ccr in my rear shocks, and I’ll explain why this is a good thing further below.
I’ve run the Prado masses, motion ratios and rates through a rebound-compression coupled quarter car model for front and rear, so I’ll split the discussion below about critical damping between the front struts and rear shocks. If you’d like to know more about the maths and physics equations behind the quarter car model and how to make calculated valving curves, Kaz Technologies who are FSAE competitors have an excellent guide to help you develop your own model, “FSAE Damping Calculations Seminar”, which can be found here;
http://www.kaztechnologies.com/downl...nar-downloads/
1. Front struts
To understand why the front damping rate is insufficient, we not only need to model the D563-M2 dyno curve shown above, but we also need to transform it to what the valving Forces are out at the wheel. Utilising the motion ratio of the IFS will allow you to calculate the Forces at the wheel, and also calculate the wheel rate, the effective spring rate of the coil spring at the end of the lever arm. Knowledge of the front wheel rate and effective damping Forces will also allow a comparison with the rear coil rate and Forces.
Taking a look at the properties of the IFS lower lever arm will show you how the spring rate and Forces can change. The figure below shows a first order simplified model of the lever arm;
Following some simple mathematics through will show the mechanical nature of the lever arm;
The valving curve at the wheel is quite simple to calculate once you run the leverage arm properties above multiplicatively through. The plot below shows the calculated valving curves for the D563-M2 strut as it sits at the strut position roughly mid-way down the lower arm, and the effective valving curve out at the wheel;
You can quickly see that the effective valving curve at the wheel is not only considerably softer in magnitude as the Forces are roughly halved at the end of the lever arm, but that the low velocity damping rate has been significantly reduced from 36%Ccr down to around 11%Ccr. This is due to the fact that the velocity is scaled by the inverse motion ratio, due to the change in arm position dB>dA and these gaps closing over the same time interval, thereby effectively doubling the velocity, and satisfying the conservation of mechanical power;
Using this equation suggests Ccr = 0.36 will reduce to 0.10, close to the quarter car model of 0.11.
Comparing the front IFS strut and coil properties at the wheel with the rear wheel properties is illuminating. The front with effective coil rate of 189lb/in and valving of 1585N:885N at 0.52m/s looks quite soft on the rebound compared to my rear with 280lb/in and 3925N:910N at 0.52m/s. Sloppy front kinematics are traditionally combated with stiffer coils, however, I think running over 700lb/in coils on the smaller sized strut bush on the 120 will be extremely hard on the bushes. I have heard of 60mm struts with up to 5000N rebound being used in the larger strut bushed 150 IFS, in combination with very stiff 960lb/in coils. However, 14mm shafts on the typical 50mm diameter Bilsteins we use limit the range of Force to around 4000N. As such, increasing rebound beyond 4000N on the front struts will require a larger body diameter strut which can utilise a shaft diameter larger than 14mm. Having a softer and more compliant front end setup compared to a stiff rear end is also a good thing for reducing understeer on the Prado, which is more noticeable on A/T type tyres. With the ride rates I currently have, my coils give me a 20% higher rear frequency for the sprung mass, something which is very desirable to control vehicle pitch.
Rather than increasing coil rate, the more effective way to combat the low damping rate at the front wheel position is to build the struts with very high critical damping at low velocity. The higher the critical damping at the strut position, then the higher it will be at the wheel position after the leverage multiplications. This can be easily achieved by throttling the bleed circuit valve shim.
The plot below shows several calculated valving curves at the strut being transformed to the wheel;
The red curve is the critical damping model for the dyno measured D563-M2 strut valving. The calculations indicate substantial gains in low velocity rebound at the wheel position can be obtained by shortening the knee velocity to around 80mm/s and increasing the critical damping up to ca. 50%. Rebound at the wheel will then double from ca. 630N to 1250N at 150mm/s, which will help greatly in minimising that squat and heave. The calculations also demonstrate it is difficult to increase the critical damping rate at the wheel beyond around 20%. I think these figures are definitely achievable with bleed circuit modifications. While the figure of 20% critical damping at the wheel appears low, it is actually relatively high for mid ranged motion ratio IFS on a 4wd. Also keep in mind I have seen many struts with very low critical damping at the strut position <30%, which would be very sloppy at the wheel.
While modifying the valving bleed circuit to obtain this level of critical damping is not that difficult, it can be difficult and expensive to do it with Bilsteins, principally due to the requirement of re-gassing. A simpler approach is to use hydraulic Ironman struts as test struts, as they can be rebuilt at home and I have already been through this procedure for my rear Ironman shocks. The Ironman front struts also utilise a large 65mm diameter threaded body with a 20mm shaft.
2. Rear shocks
The rear shocks are comparatively much simpler to model and understand, as the motion ratio is very close to 1:1 in the rear solid axle geometry, with no complicating leverage mechanics. However, there is another feature in the rear that can affect the critical damping rate, which is not present in the front. This is the extra sprung mass which can be added into the rear when we pack up the cargo area and roof rack, the majority of which ends up distributed over the rear of the Prado. This extra sprung mass can be 5-600kg extra, and can significantly alter the low velocity critical damping rate.
Getting the valving correct in the rear of the Prado is crucial. Both the magnitude of the valving Forces, and the critical damping rate must be considered carefully. Low magnitude for rebound Forces is responsible for the notorious pogo stick dynamics of the rear, and you will find this low rebound in shocks like 713 Bilsteins and 90-5404 Konis. The rear needs a minimum of 3000N rebound, and the rebound:compression ratio in the rear works much better for typical solid axle type valving. I’m currently running 3925N:910N at 0.52m/s in my custom valved Ironmans, shown below;
The red line is the Ironman 45682 dyno data, and the green line is a typical 1478 Bilstein dyno curve. The solid black line is the calculated valving curve for the Ironman shocks. You can see that at low velocity there is more critical damping in the Ironman shocks, around 90%Ccr compared to 70%Ccr. This ca. 4:1 rebound:compression low velocity ratio was originally developed in the 80 series Landcruiser to catch body roll. Getting the front rebound:rear compression ratio correct is another feature of the Prado suspension that needs attention, and getting this ratio correct will minimise heave and in particular squat under acceleration. As I discussed above, we are limited to around 4-5000N rebound for the front struts, limiting the ratio to around 2200N:1000N, or 2.2:1. To further optimise this front rebound:rear compression ratio requires increasing the front strut low velocity critical damping.
The effects of packing up/building in your cargo area/adding rear bar/packing up roofrack etc. modify the amount of critical damping significantly. While there is no modification of the rear valving curve with the ca. 1:1 motion ratio at the wheel, the additional 5-600kg in the rear can increase the rear sprung critical damping coefficient by ca. 25%, reducing the critical damping rate from 90%Ccr down to 70%Ccr for the Ironmans, and around 70%Ccr to 50%Ccr for the Bilsteins.
These reductions occur because the sprung mass scales through the sprung critical damping coefficient as;
The extra 5-600kg sprung mass will increase the magnitude of Ccr, decreasing the %Ccr required for the same valving Force without the additional 5-600kg. This is also intuitively obvious, the more mass the shocks need to control for the same amount of valving, the less effective they will be, and the longer they will take to cycle out the motion.
You can notice these effects easily in the rear, just go around a roundabout with a big heavily loaded up Prado and you’ll easily feel the increase in body roll and lack of kinematic control from the shocks. Before I had my Ironmans, I had around 3000N rebound 50mm twin tubes with low critical damping of 45%Ccr, and the body roll was excessive and felt quite uncomfortable with a loaded up Prado. With the higher critically damped Ironmans and higher rebound, the excessive body roll has been significantly reduced. I’m still considering a stiffer after-market swaybar to further minimise any remaining lateral load transfer.
So after plugging through all of that discussion, we can get to some simple reasons for having high critical damping in both the front struts and rear shocks for Prados. The leverage mechanics of the IFS have a significant reducing effect on both the magnitude of Force and low velocity damping rate at the wheel position. Keeping around 60%Ccr damping at the strut suggests ca. 20%Ccr damping rate at the wheel position. For the rear solid axle, packing up the rear of the Prado adds a lot of extra sprung mass that can reduce the rear critical damping to around 70-80%Ccr for touring. Minimising vehicle kinematics with valving is always a bit experimental, and before I increase the rebound further on my front struts, I will try them with much higher critical damping to observe the effects. Just increasing the critical damping may be enough to reduce that heave and squat I’ve observed. If it isn’t, then I’ll look at increasing the rebound.
Using Ironman hydraulics means it’s also easier to experiment with the valving, as the Ironman shock builder Kristian is very enthusiastic about helping on these projects, the Ironman hydraulics don’t use gas, so you can revalve them yourself at home, and they utilise a large diameter shaft which will allow for further rebound increases on the front struts in the future if necessary.
I would say at the moment that Bilstein struts are likely the highest critically damped off the shelf strut you can purchase for the Prado. The 24-173032-1 from Quadrant has the highest critical damping at the strut position with ca. 43%Ccr. We are constrained by what can be modified valving wise due to the mechanics of the leverage ratio in the IFS. With the ratio at around 2:1, the shaft velocities and Forces hit the sweet spot in terms of component strength, such as bushes, shaft, rod guide and shim plates etc. Running the leverage ratio to higher ratios, such as 3:1, or 4:1 means the velocities will decrease, but the Forces will increase, meaning components must be made stronger again. The 2:1 ratio is very common, and is used a lot in the desert racing scene. Even within the strong multiplicative mechanical reductions of the IFS leverage ratio, there is still a lot of valving performance gains and extra handling performance to be enjoyed!
Hope you are all getting the best out of your struts and shocks!
Best
Mark
I’ve noticed recently off-road that I can still observe significant low velocity heave and squat in my Prado, for example needing to accelerate hard in soft sand. As I’ve recently installed some quite high critically damped custom valved shocks in the rear, this suggests the front strut damping is not working as well as it could.
I’m running the latest modification of the D563-M2 Bilstein strut, the dyno curve is shown below;
To interpret what is going on and how the strut/shock valving Forces are connected to body kinematics such as roll, heave, pitch, squat etc., then we need to take a look at what critical damping is.
Critical damping in shock absorbers is how quickly the shock can cycle out rebound or compression motion and return the sprung/unsprung mass system to equilibrium. The part of the shock valving F vs v curve that shows what percentage of 100% critical damping the shock has occurs in the low velocity part of the curve, typically below 150mm/s where you’ll observe the knee or transition from low to high speed valving. The gradient of the F vs v curve is referred to as the damping rate, and you’ll typically see two damping rates in most shocks, low and high speed. The low velocity damping rate is the gradient which determines the %Ccr, or percent critical damping. The critical damping is characterised by a critical damping coefficient, Ccr, which is velocity dependent. The low velocity damping is what minimises sprung mass body kinematics, so the %Ccr that you have in your shocks will determine how much body roll, pitch etc. that you’ll experience in off-road conditions. You can change this low velocity part of the valving curve by modifying the valve shim in the piston head which controls low speed hydraulic bleed. Higher velocity damping Forces are typically there to control the higher frequency motion of the un-sprung mass, which in the Prado can oscillate at around ten times the frequency of the sprung mass.
To determine the %Ccr you have in your shocks, you need to utilise the passive quarter car model. From this model you can produce calculated valving curves which you can fit to your dyno data. You’ll need to know sprung and unsprung corner masses, motion ratios, wheel, tire and ride rates to calculate the critical damping coefficients for both the sprung and unsprung masses.
The image below shows the generic quarter car model and how critical damping works;
The equation of motion for the simple 1D damped oscillator model on the right is derived by summing the restoring Force on the coil, F = kx, and the Force generated by the damper, F = cv. The solutions are characterised by 100% critical damping yielding;
As the damping coefficient gets closer to 1.0, then the system will return quickly to equilibrium. Lower percentages of the critical damping coefficient means the system will take several cycles to reach equilibrium. With lower values, you’ll easily feel the kinematic effects in your car, body roll will take several cycles to completely cycle out and minimise etc. Higher values beyond 1.0 will actually take longer to settle to equilibrium.
When you hit a value of 1.0 (or 100%Ccr) for the critical damping coefficient, the system will not cycle. A great example of this is shown in this video where an off road buggy with very high critically damped shocks is dropped from a great height;
http://imgur.com/gallery/UX68xNr
For most applications, there is an old rule of thumb about critical damping from the Formula SAE and Autocross crowd. This rule of thumb suggests something like 65-70%Ccr damping rate is sufficient for the fastest lap times.
This old rule of thumb is really only a racing guideline and is not necessarily the most appropriate value. Formula 1 cars may use 120%Ccr in some circumstances, dependent on track conditions and motion ratios. Most passenger vehicles use only 10 to 20% Ccr. 4wd vehicles have different requirements again, with the most relevant use of critical damping being to control excessive body kinematics such as roll, pitch, heave etc. As an example, I’m currently using 90%Ccr in my rear shocks, and I’ll explain why this is a good thing further below.
I’ve run the Prado masses, motion ratios and rates through a rebound-compression coupled quarter car model for front and rear, so I’ll split the discussion below about critical damping between the front struts and rear shocks. If you’d like to know more about the maths and physics equations behind the quarter car model and how to make calculated valving curves, Kaz Technologies who are FSAE competitors have an excellent guide to help you develop your own model, “FSAE Damping Calculations Seminar”, which can be found here;
http://www.kaztechnologies.com/downl...nar-downloads/
1. Front struts
To understand why the front damping rate is insufficient, we not only need to model the D563-M2 dyno curve shown above, but we also need to transform it to what the valving Forces are out at the wheel. Utilising the motion ratio of the IFS will allow you to calculate the Forces at the wheel, and also calculate the wheel rate, the effective spring rate of the coil spring at the end of the lever arm. Knowledge of the front wheel rate and effective damping Forces will also allow a comparison with the rear coil rate and Forces.
Taking a look at the properties of the IFS lower lever arm will show you how the spring rate and Forces can change. The figure below shows a first order simplified model of the lever arm;
Following some simple mathematics through will show the mechanical nature of the lever arm;
The valving curve at the wheel is quite simple to calculate once you run the leverage arm properties above multiplicatively through. The plot below shows the calculated valving curves for the D563-M2 strut as it sits at the strut position roughly mid-way down the lower arm, and the effective valving curve out at the wheel;
You can quickly see that the effective valving curve at the wheel is not only considerably softer in magnitude as the Forces are roughly halved at the end of the lever arm, but that the low velocity damping rate has been significantly reduced from 36%Ccr down to around 11%Ccr. This is due to the fact that the velocity is scaled by the inverse motion ratio, due to the change in arm position dB>dA and these gaps closing over the same time interval, thereby effectively doubling the velocity, and satisfying the conservation of mechanical power;
Using this equation suggests Ccr = 0.36 will reduce to 0.10, close to the quarter car model of 0.11.
Comparing the front IFS strut and coil properties at the wheel with the rear wheel properties is illuminating. The front with effective coil rate of 189lb/in and valving of 1585N:885N at 0.52m/s looks quite soft on the rebound compared to my rear with 280lb/in and 3925N:910N at 0.52m/s. Sloppy front kinematics are traditionally combated with stiffer coils, however, I think running over 700lb/in coils on the smaller sized strut bush on the 120 will be extremely hard on the bushes. I have heard of 60mm struts with up to 5000N rebound being used in the larger strut bushed 150 IFS, in combination with very stiff 960lb/in coils. However, 14mm shafts on the typical 50mm diameter Bilsteins we use limit the range of Force to around 4000N. As such, increasing rebound beyond 4000N on the front struts will require a larger body diameter strut which can utilise a shaft diameter larger than 14mm. Having a softer and more compliant front end setup compared to a stiff rear end is also a good thing for reducing understeer on the Prado, which is more noticeable on A/T type tyres. With the ride rates I currently have, my coils give me a 20% higher rear frequency for the sprung mass, something which is very desirable to control vehicle pitch.
Rather than increasing coil rate, the more effective way to combat the low damping rate at the front wheel position is to build the struts with very high critical damping at low velocity. The higher the critical damping at the strut position, then the higher it will be at the wheel position after the leverage multiplications. This can be easily achieved by throttling the bleed circuit valve shim.
The plot below shows several calculated valving curves at the strut being transformed to the wheel;
The red curve is the critical damping model for the dyno measured D563-M2 strut valving. The calculations indicate substantial gains in low velocity rebound at the wheel position can be obtained by shortening the knee velocity to around 80mm/s and increasing the critical damping up to ca. 50%. Rebound at the wheel will then double from ca. 630N to 1250N at 150mm/s, which will help greatly in minimising that squat and heave. The calculations also demonstrate it is difficult to increase the critical damping rate at the wheel beyond around 20%. I think these figures are definitely achievable with bleed circuit modifications. While the figure of 20% critical damping at the wheel appears low, it is actually relatively high for mid ranged motion ratio IFS on a 4wd. Also keep in mind I have seen many struts with very low critical damping at the strut position <30%, which would be very sloppy at the wheel.
While modifying the valving bleed circuit to obtain this level of critical damping is not that difficult, it can be difficult and expensive to do it with Bilsteins, principally due to the requirement of re-gassing. A simpler approach is to use hydraulic Ironman struts as test struts, as they can be rebuilt at home and I have already been through this procedure for my rear Ironman shocks. The Ironman front struts also utilise a large 65mm diameter threaded body with a 20mm shaft.
2. Rear shocks
The rear shocks are comparatively much simpler to model and understand, as the motion ratio is very close to 1:1 in the rear solid axle geometry, with no complicating leverage mechanics. However, there is another feature in the rear that can affect the critical damping rate, which is not present in the front. This is the extra sprung mass which can be added into the rear when we pack up the cargo area and roof rack, the majority of which ends up distributed over the rear of the Prado. This extra sprung mass can be 5-600kg extra, and can significantly alter the low velocity critical damping rate.
Getting the valving correct in the rear of the Prado is crucial. Both the magnitude of the valving Forces, and the critical damping rate must be considered carefully. Low magnitude for rebound Forces is responsible for the notorious pogo stick dynamics of the rear, and you will find this low rebound in shocks like 713 Bilsteins and 90-5404 Konis. The rear needs a minimum of 3000N rebound, and the rebound:compression ratio in the rear works much better for typical solid axle type valving. I’m currently running 3925N:910N at 0.52m/s in my custom valved Ironmans, shown below;
The red line is the Ironman 45682 dyno data, and the green line is a typical 1478 Bilstein dyno curve. The solid black line is the calculated valving curve for the Ironman shocks. You can see that at low velocity there is more critical damping in the Ironman shocks, around 90%Ccr compared to 70%Ccr. This ca. 4:1 rebound:compression low velocity ratio was originally developed in the 80 series Landcruiser to catch body roll. Getting the front rebound:rear compression ratio correct is another feature of the Prado suspension that needs attention, and getting this ratio correct will minimise heave and in particular squat under acceleration. As I discussed above, we are limited to around 4-5000N rebound for the front struts, limiting the ratio to around 2200N:1000N, or 2.2:1. To further optimise this front rebound:rear compression ratio requires increasing the front strut low velocity critical damping.
The effects of packing up/building in your cargo area/adding rear bar/packing up roofrack etc. modify the amount of critical damping significantly. While there is no modification of the rear valving curve with the ca. 1:1 motion ratio at the wheel, the additional 5-600kg in the rear can increase the rear sprung critical damping coefficient by ca. 25%, reducing the critical damping rate from 90%Ccr down to 70%Ccr for the Ironmans, and around 70%Ccr to 50%Ccr for the Bilsteins.
These reductions occur because the sprung mass scales through the sprung critical damping coefficient as;
The extra 5-600kg sprung mass will increase the magnitude of Ccr, decreasing the %Ccr required for the same valving Force without the additional 5-600kg. This is also intuitively obvious, the more mass the shocks need to control for the same amount of valving, the less effective they will be, and the longer they will take to cycle out the motion.
You can notice these effects easily in the rear, just go around a roundabout with a big heavily loaded up Prado and you’ll easily feel the increase in body roll and lack of kinematic control from the shocks. Before I had my Ironmans, I had around 3000N rebound 50mm twin tubes with low critical damping of 45%Ccr, and the body roll was excessive and felt quite uncomfortable with a loaded up Prado. With the higher critically damped Ironmans and higher rebound, the excessive body roll has been significantly reduced. I’m still considering a stiffer after-market swaybar to further minimise any remaining lateral load transfer.
So after plugging through all of that discussion, we can get to some simple reasons for having high critical damping in both the front struts and rear shocks for Prados. The leverage mechanics of the IFS have a significant reducing effect on both the magnitude of Force and low velocity damping rate at the wheel position. Keeping around 60%Ccr damping at the strut suggests ca. 20%Ccr damping rate at the wheel position. For the rear solid axle, packing up the rear of the Prado adds a lot of extra sprung mass that can reduce the rear critical damping to around 70-80%Ccr for touring. Minimising vehicle kinematics with valving is always a bit experimental, and before I increase the rebound further on my front struts, I will try them with much higher critical damping to observe the effects. Just increasing the critical damping may be enough to reduce that heave and squat I’ve observed. If it isn’t, then I’ll look at increasing the rebound.
Using Ironman hydraulics means it’s also easier to experiment with the valving, as the Ironman shock builder Kristian is very enthusiastic about helping on these projects, the Ironman hydraulics don’t use gas, so you can revalve them yourself at home, and they utilise a large diameter shaft which will allow for further rebound increases on the front struts in the future if necessary.
I would say at the moment that Bilstein struts are likely the highest critically damped off the shelf strut you can purchase for the Prado. The 24-173032-1 from Quadrant has the highest critical damping at the strut position with ca. 43%Ccr. We are constrained by what can be modified valving wise due to the mechanics of the leverage ratio in the IFS. With the ratio at around 2:1, the shaft velocities and Forces hit the sweet spot in terms of component strength, such as bushes, shaft, rod guide and shim plates etc. Running the leverage ratio to higher ratios, such as 3:1, or 4:1 means the velocities will decrease, but the Forces will increase, meaning components must be made stronger again. The 2:1 ratio is very common, and is used a lot in the desert racing scene. Even within the strong multiplicative mechanical reductions of the IFS leverage ratio, there is still a lot of valving performance gains and extra handling performance to be enjoyed!
Hope you are all getting the best out of your struts and shocks!
Best
Mark
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