Whitey
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Hey all,
The 150 series Prado is a unique vehicle in the modern Toyota IFS landscape. It stands out amongst all other Toyotas with a very high OEM front coil rate of 780lb/in. In comparison, the closest OEM coil rate is the diesel 120 at 620lb/in. Not even the mighty 200 series comes close to it!
See here for my OEM coil load deflection measurements from King Coils;
http://www.pradopoint.com/showthread...a-4wd-vehicles
I have spoken with many suspension engineers, and it remains unknown why Toyota have chosen such a high coil rate for the 150. Possible causes are VSC, extra weight, known bush wearing issues with the previous model 120 etc. We may never know the reasons why without being able to ask a Japanese Toyota engineer.
A common complaint about driving the 150 Prado with OEM suspension is “boaty” or “floaty” handling. This suggests there is not enough valving force in the OEM struts to control the very high OEM 780lb/in coils.
As such, I was interested to know the factory 150 OEM strut valving, and I recently had the opportunity to dyno a new 2.8 diesel 150 strut with under 5000km driving on it.
The plot below shows the dyno valving curves;
The green line shows 150 OEM Tokico strut rebound forces as a function of velocity, the red curve the OEM compression forces.
For comparison purposes, the black lines show the rebound and compression forces for a Bilstein BE5-A712. You can easily see that the 712 strut has valving that is very close to the OEM 150 strut, which suggests that a 712 would not be well suited to a 780lb/in coil, and would struggle to control it.
The blue line shows valving curves for the 150 specific Bilstein strut from Quadrant in Melbourne. This strut has been designed specifically for the 150, and has been designed to control the motion of 670lb/in coils.
As you can see, the rebound of the 24-173032 is significantly higher than the OEM/712 struts. Low to mid velocity compression forces are also higher.
A look at the rates of after-market coils that 150 drivers are using is interesting;
http://www.pradopoint.com/showthread...il-free-length
150 drivers use coils in the range 565-984lb/in, a huge +/-200lb/in variation compared to the OEM coil rate of 780lb/in.
Unfortunately, the valving of many of the after-market 150 struts currently remains unknown, so we can only rely on road handling feedback from 150 drivers. Certainly I cannot imagine a typical after-market strut with enough valving to control a 984lb/in coil.
It is however very common for example to see 120 spec Bilstein struts matched with high coil rate 725lb/in 150 spec Dobinsons coils. Based on the valving curves above, 725lb/in coils will struggle to be controlled by 120 spec valving.
This is why there is a Bilstein strut that has been developed specifically for the 150 Prado by Quadrant.
There are many Prado, Hilux and FJ drivers who use mis-matched strut-coil combinations on the IFS, sometimes unknowingly. I know an FJ Cruiser driver who is using the 150 specific Quadrant 24-173032 strut in his FJ (a vehicle closer to 120 spec coils and weight). Initially it was matched with a Ridepro coil (586lb/in), and the handling was not the greatest. Swapping the Ridepro to a King Coil (660lb/in) made a big difference, and counter intuitively, by increasing the coil rate by 74lb/in, the driver said the front end feels softer and more compliant. On road, the extra rebound can make the handling feel stiffer, but off road, this driver said his FJ has never handled better, and he is happily driving through whoops at significantly higher speeds.
This emphasises the need for good matching between valving and coil rate, a subject which is never discussed in great detail principally due to after-market shock absorber manufacturers being elusive about releasing their valving data in a highly competitive market place. A well matched valving/coil-rate combo means the coil expends its energy smoothly to full travel and doesn’t store energy during successive bumps. Poor valving on high coil rates means an uncontrolled rate of motion (suspension frequency) when the coil releases to full travel and releases all of its stored energy. Uncontrolled coil motion translates directly into poor handling, excessive pitch and roll etc., which the poorly valved struts will never be able to cycle out. You will have to brake the Prado heavily to stop this undesirable pitch and roll. Pitch in Prados is one of the most common handling complaints.
So what is the best valving-coil rate combination for the 150 Prado IFS?
Currently we have a strut-coil combination from Quadrant in Melbourne that has been dyno and road handling tested for the 150. This high rebound 24-173032 strut is matched to a 675lb/in H&R cold rolled coil.
So what about other coils? Dobinsons 150 specific coils are 725lb/in, closer in rate to the OEM figure of 780lb/in. We can already see from the above discussion and valving curves that 120 spec valving will struggle to control a 780lb/in coil.
We have to keep in mind that Dobinsons have their own 150 specific struts that have likely been matched to the 725lb/in coil rate of Dobinsons coils.
This indicates you have to be careful which manufacturers struts you match to which manufacturers coils.
For the common Bilstein/Dobinsons setup that many 150 drivers use, many will be running 120 spec Bilsteins, which are normally matched to 620lb/in coils. If you run 150 spec Dobinsons coils with 725lb/in rate, the 150 spec 24-173032 will be a better match and will control the coil better than the 120 spec struts.
There is also no reason you cannot run a 120 strut-coil combo in the 150. For example, a 120 specific 24-238762 or BE5-A712 will work well in the 150 with a 120 spec 586lb/in Dobinsons coil.
Conversely, you can run a 150 strut-coil combo in the 120 (or FJ). For example, the D563 Hilux strut has very high rebound (3385N at 0.52m/s), has a 120 size bush, and will match a 660lb/in King coil nicely. The much beefier 24-173032 with a bigger 150 bush can also be used in the 120 with the crush tube cut to 120 length.
You can see the much stronger bottom end design of the 24-173032 strut compared to a typical 120 strut below;
Another common 150 series Prado combination is Bilstein/Kings, where the 24-173032 is very nicely matched to the 660lb/in King coils.
Hopefully in the future I can get some more valving data for different after-market struts, which will help make our Suspension Database more comprehensive, and hopefully clarify well matched strut-coil setups.
Many thanks to Jim at Quadrant for providing dyno data for the 24-173032 strut, and to John up at Zordos for supplying the OEM strut.
Enjoy your 150 driving!
Best
Mark
The 150 series Prado is a unique vehicle in the modern Toyota IFS landscape. It stands out amongst all other Toyotas with a very high OEM front coil rate of 780lb/in. In comparison, the closest OEM coil rate is the diesel 120 at 620lb/in. Not even the mighty 200 series comes close to it!
See here for my OEM coil load deflection measurements from King Coils;
http://www.pradopoint.com/showthread...a-4wd-vehicles
I have spoken with many suspension engineers, and it remains unknown why Toyota have chosen such a high coil rate for the 150. Possible causes are VSC, extra weight, known bush wearing issues with the previous model 120 etc. We may never know the reasons why without being able to ask a Japanese Toyota engineer.
A common complaint about driving the 150 Prado with OEM suspension is “boaty” or “floaty” handling. This suggests there is not enough valving force in the OEM struts to control the very high OEM 780lb/in coils.
As such, I was interested to know the factory 150 OEM strut valving, and I recently had the opportunity to dyno a new 2.8 diesel 150 strut with under 5000km driving on it.
The plot below shows the dyno valving curves;
The green line shows 150 OEM Tokico strut rebound forces as a function of velocity, the red curve the OEM compression forces.
For comparison purposes, the black lines show the rebound and compression forces for a Bilstein BE5-A712. You can easily see that the 712 strut has valving that is very close to the OEM 150 strut, which suggests that a 712 would not be well suited to a 780lb/in coil, and would struggle to control it.
The blue line shows valving curves for the 150 specific Bilstein strut from Quadrant in Melbourne. This strut has been designed specifically for the 150, and has been designed to control the motion of 670lb/in coils.
As you can see, the rebound of the 24-173032 is significantly higher than the OEM/712 struts. Low to mid velocity compression forces are also higher.
A look at the rates of after-market coils that 150 drivers are using is interesting;
http://www.pradopoint.com/showthread...il-free-length
150 drivers use coils in the range 565-984lb/in, a huge +/-200lb/in variation compared to the OEM coil rate of 780lb/in.
Unfortunately, the valving of many of the after-market 150 struts currently remains unknown, so we can only rely on road handling feedback from 150 drivers. Certainly I cannot imagine a typical after-market strut with enough valving to control a 984lb/in coil.
It is however very common for example to see 120 spec Bilstein struts matched with high coil rate 725lb/in 150 spec Dobinsons coils. Based on the valving curves above, 725lb/in coils will struggle to be controlled by 120 spec valving.
This is why there is a Bilstein strut that has been developed specifically for the 150 Prado by Quadrant.
There are many Prado, Hilux and FJ drivers who use mis-matched strut-coil combinations on the IFS, sometimes unknowingly. I know an FJ Cruiser driver who is using the 150 specific Quadrant 24-173032 strut in his FJ (a vehicle closer to 120 spec coils and weight). Initially it was matched with a Ridepro coil (586lb/in), and the handling was not the greatest. Swapping the Ridepro to a King Coil (660lb/in) made a big difference, and counter intuitively, by increasing the coil rate by 74lb/in, the driver said the front end feels softer and more compliant. On road, the extra rebound can make the handling feel stiffer, but off road, this driver said his FJ has never handled better, and he is happily driving through whoops at significantly higher speeds.
This emphasises the need for good matching between valving and coil rate, a subject which is never discussed in great detail principally due to after-market shock absorber manufacturers being elusive about releasing their valving data in a highly competitive market place. A well matched valving/coil-rate combo means the coil expends its energy smoothly to full travel and doesn’t store energy during successive bumps. Poor valving on high coil rates means an uncontrolled rate of motion (suspension frequency) when the coil releases to full travel and releases all of its stored energy. Uncontrolled coil motion translates directly into poor handling, excessive pitch and roll etc., which the poorly valved struts will never be able to cycle out. You will have to brake the Prado heavily to stop this undesirable pitch and roll. Pitch in Prados is one of the most common handling complaints.
So what is the best valving-coil rate combination for the 150 Prado IFS?
Currently we have a strut-coil combination from Quadrant in Melbourne that has been dyno and road handling tested for the 150. This high rebound 24-173032 strut is matched to a 675lb/in H&R cold rolled coil.
So what about other coils? Dobinsons 150 specific coils are 725lb/in, closer in rate to the OEM figure of 780lb/in. We can already see from the above discussion and valving curves that 120 spec valving will struggle to control a 780lb/in coil.
We have to keep in mind that Dobinsons have their own 150 specific struts that have likely been matched to the 725lb/in coil rate of Dobinsons coils.
This indicates you have to be careful which manufacturers struts you match to which manufacturers coils.
For the common Bilstein/Dobinsons setup that many 150 drivers use, many will be running 120 spec Bilsteins, which are normally matched to 620lb/in coils. If you run 150 spec Dobinsons coils with 725lb/in rate, the 150 spec 24-173032 will be a better match and will control the coil better than the 120 spec struts.
There is also no reason you cannot run a 120 strut-coil combo in the 150. For example, a 120 specific 24-238762 or BE5-A712 will work well in the 150 with a 120 spec 586lb/in Dobinsons coil.
Conversely, you can run a 150 strut-coil combo in the 120 (or FJ). For example, the D563 Hilux strut has very high rebound (3385N at 0.52m/s), has a 120 size bush, and will match a 660lb/in King coil nicely. The much beefier 24-173032 with a bigger 150 bush can also be used in the 120 with the crush tube cut to 120 length.
You can see the much stronger bottom end design of the 24-173032 strut compared to a typical 120 strut below;
Another common 150 series Prado combination is Bilstein/Kings, where the 24-173032 is very nicely matched to the 660lb/in King coils.
Hopefully in the future I can get some more valving data for different after-market struts, which will help make our Suspension Database more comprehensive, and hopefully clarify well matched strut-coil setups.
Many thanks to Jim at Quadrant for providing dyno data for the 24-173032 strut, and to John up at Zordos for supplying the OEM strut.
Enjoy your 150 driving!
Best
Mark
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