Whitey
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Hey all,
After recently fitting some custom valved Ironman Foamcell Pros to the rear of my Prado, I wanted to complete a similar exercise in the front and test some big bore hydraulic struts. Everything you want to know about the valving of the rear shocks can be found here;
http://www.pradopoint.com.au/showthr...the-Prado-rear
The reasoning behind using high critical damping at low velocity is discussed here;
http://www.pradopoint.com.au/showthr...uts-and-shocks
After reading both of those threads, you will quickly realise that my goal in pushing the limits of what can be done with strut and shock valving for the Prado is to enhance the off-road performance in a big heavily loaded up touring vehicle at GVM weight or more. I am thinking of the harshest service conditions, long hot trips along the Canning, Madigan or Talawana, hard days on the Telegraph Track or The Old Coach Road, pushing up the Carson River Track in the Kimberley, all places I want to explore in my Prado when it is loaded to the brim to survive in remote and tough conditions. If you think your Prado can’t go to these places, think again!
In that sense, Ironman big bore hydraulic foamcells are an excellent choice. These shocks are built for heavy duty performance. They are rugged large bore twin tube truck sized shocks which contain a huge amount of oil, and have a hard earned reputation for fade resistance and being able to operate at high service temperatures. The other very big plus for me with choosing Ironman Pros is you can pull them apart at home by yourself and service them and change the valving. No gas pressure complicating a strip down/revalve.
Usually when people think of hydraulics they think of Koni. Ironman go a big step further. Here’s a comparison of the 88-1712 Koni RAID with the Ironman 45710FE strut. Ironman body/shaft/piston head diameter = 65mm/20mm/45mm. Koni 88-1712 RAID = 55mm/16mm/36mm. The photo below shows my new struts;
So why revalve what is already a very good 45710FE strut!?
The biggest hurdle with correctly valving the Prado is controlling vehicle pitch in off-road conditions. The next biggest problem after pitch is body roll. If you don’t run the correct amount of rebound in your rear shocks, your Prado will handle like a pogo stick off-road. Due to the inherent scaling of the IFS motion ratio on the front, the IFS is limited to a practical maximum of around 20%C/Ccr critical damping. You can’t run a bleed shim any finer through the motion ratio scaling. The much higher nearly 1:1 motion ratio on the rear solid axle geometry allows much higher critical damping. Critical damping is how the strut/shock is valved at low velocity, and depends on both knee velocity and damping rate. Low velocity damping is what minimises undesirable kinematics such as pitch, body roll, squat etc. All of these kinematic modes become more pronounced as the sprung mass increases, and in heavily loaded tourers it can dramatically degrade off-road performance if there isn’t enough critical damping or enough rebound. Pogo stick dynamics will ensue. Due to the mid-ranged motion ratio of the IFS, the majority of the kinematic control of the Prado comes from the rear shocks. The rear shock is the most important suspension component in the Prado, and if you don’t valve it correctly you’ll never have the Prado work properly off-road. Further, as you increase the sprung mass by loading up the rear, the critical damping decreases, by around 20% up to GVM.
After testing my rear custom valved Ironman Pros with 90%C/Ccr off-road (decreases to 70% loaded), I could still feel significant squat under hard acceleration in deep sandy rutted out conditions. This tells me that the D563 Bilsteins I was running don’t have enough low velocity damping, particularly the rebound, which would minimise that undesirable squat. The D563’s are a fantastic mid-high velocity strut, but they’re missing that low velocity control. My rear Ironmans with 90%C/Ccr have gone a very long way to the performance I was looking for off-road, but the front end was definitely letting it down in certain conditions.
My starting point to fix this undesirable squat using Ironman Pros was to minimise the knee velocity as far as practical to give kinematically active struts in the 100-150mm/s range at the wheel position.
The plot below shows how this was achieved;
The solid purple line is the new custom 45710 valving compared to my old D563 valving. You can see that to achieve short knee velocities at the wheel position, you must use low knees at the strut position. In this case 50mm/s translates to around 93mm/s at the wheel position. Having the knee in the 100-150mm/s range is where you gain kinematic body control. The D563 has around 265N at 100mm/s at the wheel position. The new 45710 valving has around 720N, an additional 455N at the wheel position. There has also been an additional 210N added on the compression at 100mm/s. You can see that at mid-high velocity, the 45710 valving remains similar to the D563, with mildly softer compression and mildly harder rebound.
The effects of the additional 455N rebound and 210N compression at 100mm/s is very pronounced on the street, and I could feel the difference compared to my old D563’s immediately. There is minimal nose dive under braking, and minimal squat under hard acceleration, exactly the pitching motions I wanted to minimise during off-road conditions.
All good you’re thinking for picking up the kids from school and driving to soccer, well think again!
The comfort-handling relationship in suspension is inescapable. These two functions are intertwined, and the transmissibility of Force into the sprung mass is inescapable. You cannot have a smooth driving Cadillac on the street and then have a Trophy Truck off-road. Suspension does not work like that, so I want to be clear to everyone who is thinking about this suspension: you will feel this low velocity damping activate on the street on hard 40psi tire pressures. You will feel it as I said under braking and acceleration, but you will also feel it while driving at 40km/h over minor bumps/dips, it will activate and you’ll feel a small tug through the sprung mass. You’ll feel it activate through roundabouts. This is the price you pay for excellent off-road handling, you must compromise some of the comfort. You cannot have it both ways! Most of the kinematic low velocity tugging on the sprung mass you’ll feel on the street is coming from the rear shocks. As I said, the majority of kinematic control comes from the rear shock and it is the most important suspension component in the Prado. I have not compromised on this rear shock valving. It is valved to work off-road, and it is brilliant off-road and cycles superbly in the hottest and roughest tracks and conditions I could find at the time in my Prado which was well over GVM.
In the quest to satisfy both on-road comfort and off-road handling, Ironman offers two different rear shocks that fit the Prado, the 45682FE (80 series spec) and the 45682FEC (Prado spec), neither of which have enough low velocity critical damping and/or high velocity rebound.
To try and keep everyone happy, for the upcoming Ironman group buy I will be revalving the 45682FEC rear shock, which will give you the option to move back to the comfort spec valving on the street (using the same coil), as the original comfort spec valve stacks will be supplied to you, and you can put them back in yourself. You even have the option then to run comfort on the street and then switch to your off-road valving for big trips. I have been driving my Prado around with the custom off-road 90%C/Ccr low velocity damping in the rear shocks for quite a while now, and my opinion of it activating on the crappy streets of Brisbane is that it is still more comfortable to drive than my wifes Mazda. Keep in mind I like to feel what my suspension is doing, so my assometer is tuned in and I’m always feeling for the Forces and what they’re doing and how I can push the limits with them. Some of you may not notice it, feeling is subjective.
This valving will be for turning your Prado into an off-road weapon, particularly big heavy tourers in tough driving conditions. You will be able to push harder and keep on pushing through rough terrain that would have had you braking or backing off previously. If this is what you want your Prado to do then the coming group buy is for you!
In the last few days I’ve already pounded these struts across gutters and speed bumps, and they are surprisingly supple, better than my D563’s. I will be conducting some extensive off-road testing with the new struts very soon and will report all my findings back here!
Big thanks to the shock builder Kristian at Ironman for seeing this complicated and time consuming valving process through to the end!
Best
Mark
After recently fitting some custom valved Ironman Foamcell Pros to the rear of my Prado, I wanted to complete a similar exercise in the front and test some big bore hydraulic struts. Everything you want to know about the valving of the rear shocks can be found here;
http://www.pradopoint.com.au/showthr...the-Prado-rear
The reasoning behind using high critical damping at low velocity is discussed here;
http://www.pradopoint.com.au/showthr...uts-and-shocks
After reading both of those threads, you will quickly realise that my goal in pushing the limits of what can be done with strut and shock valving for the Prado is to enhance the off-road performance in a big heavily loaded up touring vehicle at GVM weight or more. I am thinking of the harshest service conditions, long hot trips along the Canning, Madigan or Talawana, hard days on the Telegraph Track or The Old Coach Road, pushing up the Carson River Track in the Kimberley, all places I want to explore in my Prado when it is loaded to the brim to survive in remote and tough conditions. If you think your Prado can’t go to these places, think again!
In that sense, Ironman big bore hydraulic foamcells are an excellent choice. These shocks are built for heavy duty performance. They are rugged large bore twin tube truck sized shocks which contain a huge amount of oil, and have a hard earned reputation for fade resistance and being able to operate at high service temperatures. The other very big plus for me with choosing Ironman Pros is you can pull them apart at home by yourself and service them and change the valving. No gas pressure complicating a strip down/revalve.
Usually when people think of hydraulics they think of Koni. Ironman go a big step further. Here’s a comparison of the 88-1712 Koni RAID with the Ironman 45710FE strut. Ironman body/shaft/piston head diameter = 65mm/20mm/45mm. Koni 88-1712 RAID = 55mm/16mm/36mm. The photo below shows my new struts;
So why revalve what is already a very good 45710FE strut!?
The biggest hurdle with correctly valving the Prado is controlling vehicle pitch in off-road conditions. The next biggest problem after pitch is body roll. If you don’t run the correct amount of rebound in your rear shocks, your Prado will handle like a pogo stick off-road. Due to the inherent scaling of the IFS motion ratio on the front, the IFS is limited to a practical maximum of around 20%C/Ccr critical damping. You can’t run a bleed shim any finer through the motion ratio scaling. The much higher nearly 1:1 motion ratio on the rear solid axle geometry allows much higher critical damping. Critical damping is how the strut/shock is valved at low velocity, and depends on both knee velocity and damping rate. Low velocity damping is what minimises undesirable kinematics such as pitch, body roll, squat etc. All of these kinematic modes become more pronounced as the sprung mass increases, and in heavily loaded tourers it can dramatically degrade off-road performance if there isn’t enough critical damping or enough rebound. Pogo stick dynamics will ensue. Due to the mid-ranged motion ratio of the IFS, the majority of the kinematic control of the Prado comes from the rear shocks. The rear shock is the most important suspension component in the Prado, and if you don’t valve it correctly you’ll never have the Prado work properly off-road. Further, as you increase the sprung mass by loading up the rear, the critical damping decreases, by around 20% up to GVM.
After testing my rear custom valved Ironman Pros with 90%C/Ccr off-road (decreases to 70% loaded), I could still feel significant squat under hard acceleration in deep sandy rutted out conditions. This tells me that the D563 Bilsteins I was running don’t have enough low velocity damping, particularly the rebound, which would minimise that undesirable squat. The D563’s are a fantastic mid-high velocity strut, but they’re missing that low velocity control. My rear Ironmans with 90%C/Ccr have gone a very long way to the performance I was looking for off-road, but the front end was definitely letting it down in certain conditions.
My starting point to fix this undesirable squat using Ironman Pros was to minimise the knee velocity as far as practical to give kinematically active struts in the 100-150mm/s range at the wheel position.
The plot below shows how this was achieved;
The solid purple line is the new custom 45710 valving compared to my old D563 valving. You can see that to achieve short knee velocities at the wheel position, you must use low knees at the strut position. In this case 50mm/s translates to around 93mm/s at the wheel position. Having the knee in the 100-150mm/s range is where you gain kinematic body control. The D563 has around 265N at 100mm/s at the wheel position. The new 45710 valving has around 720N, an additional 455N at the wheel position. There has also been an additional 210N added on the compression at 100mm/s. You can see that at mid-high velocity, the 45710 valving remains similar to the D563, with mildly softer compression and mildly harder rebound.
The effects of the additional 455N rebound and 210N compression at 100mm/s is very pronounced on the street, and I could feel the difference compared to my old D563’s immediately. There is minimal nose dive under braking, and minimal squat under hard acceleration, exactly the pitching motions I wanted to minimise during off-road conditions.
All good you’re thinking for picking up the kids from school and driving to soccer, well think again!
The comfort-handling relationship in suspension is inescapable. These two functions are intertwined, and the transmissibility of Force into the sprung mass is inescapable. You cannot have a smooth driving Cadillac on the street and then have a Trophy Truck off-road. Suspension does not work like that, so I want to be clear to everyone who is thinking about this suspension: you will feel this low velocity damping activate on the street on hard 40psi tire pressures. You will feel it as I said under braking and acceleration, but you will also feel it while driving at 40km/h over minor bumps/dips, it will activate and you’ll feel a small tug through the sprung mass. You’ll feel it activate through roundabouts. This is the price you pay for excellent off-road handling, you must compromise some of the comfort. You cannot have it both ways! Most of the kinematic low velocity tugging on the sprung mass you’ll feel on the street is coming from the rear shocks. As I said, the majority of kinematic control comes from the rear shock and it is the most important suspension component in the Prado. I have not compromised on this rear shock valving. It is valved to work off-road, and it is brilliant off-road and cycles superbly in the hottest and roughest tracks and conditions I could find at the time in my Prado which was well over GVM.
In the quest to satisfy both on-road comfort and off-road handling, Ironman offers two different rear shocks that fit the Prado, the 45682FE (80 series spec) and the 45682FEC (Prado spec), neither of which have enough low velocity critical damping and/or high velocity rebound.
To try and keep everyone happy, for the upcoming Ironman group buy I will be revalving the 45682FEC rear shock, which will give you the option to move back to the comfort spec valving on the street (using the same coil), as the original comfort spec valve stacks will be supplied to you, and you can put them back in yourself. You even have the option then to run comfort on the street and then switch to your off-road valving for big trips. I have been driving my Prado around with the custom off-road 90%C/Ccr low velocity damping in the rear shocks for quite a while now, and my opinion of it activating on the crappy streets of Brisbane is that it is still more comfortable to drive than my wifes Mazda. Keep in mind I like to feel what my suspension is doing, so my assometer is tuned in and I’m always feeling for the Forces and what they’re doing and how I can push the limits with them. Some of you may not notice it, feeling is subjective.
This valving will be for turning your Prado into an off-road weapon, particularly big heavy tourers in tough driving conditions. You will be able to push harder and keep on pushing through rough terrain that would have had you braking or backing off previously. If this is what you want your Prado to do then the coming group buy is for you!
In the last few days I’ve already pounded these struts across gutters and speed bumps, and they are surprisingly supple, better than my D563’s. I will be conducting some extensive off-road testing with the new struts very soon and will report all my findings back here!
Big thanks to the shock builder Kristian at Ironman for seeing this complicated and time consuming valving process through to the end!
Best
Mark
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