Whitey
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Hey all,
There’s been a fair bit of discussion lately about the appropriate valving and coils to get the best handling out of the IFS.
Equally as important is the valving-coil rate setup for the rear solid axle.
Below is the valving curve for the OEM FJ Cruiser rear shock;
I’ve added the valving curve for the BE5-A713, and as you can see they are very similar in magnitude and shape. The 713 has moderately stronger valving at low-mid velocity, but at high velocity, for all intensive purposes, the OEM FJ Cruiser shock behaves just like a 713 Bilstein. Note that I’ve had to use an OEM FJ rear shock, as OEM 120 struts and shocks are too old and most have lost gas by now. I may order some new 120 struts and shocks from Amayama one day to dyno them, but they will be extremely close to the FJ valving seen here.
So Toyota have designed a rear OEM shock for FJ/Prado with 1700N:1475N at 0.52m/s, and they have matched this with a 195lb/in coil. The original BE5-A481 Bilstein sold in the European market has no doubt been developed around this type of valving. The 19mm longer A713 Bilstein sold in Australia uses the same valving as the original A481.
In Europe, the A481 is predominantly used in Prados that are not lifted and that do not use any accessories like bullbars, and as such the A481 works well in an unloaded vehicle with a soft ca. 200lb/in coil spring to give good handling. ie, the A481 shock is an OEM replacement for a stock OEM vehicle on stock OEM 200lb/in soft coils.
The 713 should be thought of in the exact same regard, as useful only for an unloaded vehicle on soft springs. The very short open length of the 713 also means it is not at all useful in a lifted geometry, and you will end up with only 50-60mm of droop at 2” lift.
So what then is more appropriate valving and coil rates for our heavier Prados that we take bush?
The valving plot below compares the 713 with a B46-1478S;
The 1478 is considered by Bilstein to be an 80 series spec shock used on the rear 80 series solid axle.
You can see that the valving differences between the 713 and the 1478 are enormous. It was recognised early on that 80 series shocks could fit in the rear of a Prado. Many put 80 series shocks in on the basis of the extra length they provide, but without any knowledge of what the valving is like.
You will find similar high rebound:low compression after market valving on a lot of vehicles using solid axle Bilstein shocks, both front and rear. After market rear 80 series coils are typically in the 250-300lb/in range, potentially up to a very high 500lb/in for a very heavily loaded vehicle. Typical after market solid-axle shock valving is in the range 2500-4000N rebound/500-1500N compression.
The rear of the 80 series is not that different to the rear of the Prado, and the OEM rear 80 series coil is even softer than the Prado at ca. 155lb/in.
As such, it isn’t immediately clear why Bilstein use dramatically different valving between the Prado rear and the 80 series rear. Kerb weights and suspension geometry are quite similar between them. I unfortunately don’t have an OEM 80 series rear shock to dyno test, but if I did I would not be at all surprised to find it is very close to 1478 valving.
This suggests Toyota have developed different rear valving for Prado and 80 series when they both have similar kerb weight, suspension geometry and coil rate. The only reason I can think why is due to the IFS on the Prado and subsequently different vehicle dynamics (roll center and center gravity etc.) on the front compared to the solid axle front on the 80 series.
On this basis, I am not at all surprised then whenever you ask a Bilstein distributor which struts/shocks to use for a Prado, they immediately reply 712/713.
This is unfortunate, as the 713 as I described above is really only valved for an unloaded OEM kerb weight Prado. It is also useless in lifted geometry, giving only around 60mm of droop at a typical 2" lift in the rear;
http://www.pradopoint.com/showthread...for-120-150-FJ
I have driven on the 712/713 combination through the Simpson in a lifted and heavily loaded 120 Prado, and the 713 could never control the 270lb/in Ridepro coil I had at the time, and the rear was very unbalanced and would force significant uncontrolled vehicle pitch which needed to be cycled out. There is simply not enough rebound in the 713 to control a high rate coil or to handle a heavily loaded rear which can run to 1800kg, which means using the brakes to slow the Prado down and kill the uncontrolled pitch, even at a miserly 20km/h.
After that experience and knowing how short the 713 is, I moved to 80 series shocks with 80 series type valving, and the difference in ride quality was night and day.
The high rebound:soft compression 80 series/solid axle type valving means a high rate coil can cycle freely.
I have also recently moved to a higher rebound setup on my IFS, and I believe my Prado has never handled better. On the front I am running D563-M2 struts with 3665N:2200N at 0.52m/s, which match extremely well with my 3300N:600N at 0.5m/s 80 series shocks. With a loaded setup, my suspension is cycling beautifully, and I can easily drive through obstacles which previously would have required slower speed and/or heavy braking with the 712/713 setup.
Regarding the range of valving and coil rate for 80 series shocks and our Prado rear, I believe the setup works very nicely in the 260-300lb/in coil rate range, and with compression under 1000N. Anything over 300lb/in or hard compression over 6-800N will start giving a stiff/bumpy feeling in the rear. I believe at least 3000-4000N of rebound is required for a heavily loaded rear.
I hope this explains a bit more why 80 series (or for that matter, most solid axle valving setups) valving works so well in the Prado rear.
Best
Mark
There’s been a fair bit of discussion lately about the appropriate valving and coils to get the best handling out of the IFS.
Equally as important is the valving-coil rate setup for the rear solid axle.
Below is the valving curve for the OEM FJ Cruiser rear shock;
I’ve added the valving curve for the BE5-A713, and as you can see they are very similar in magnitude and shape. The 713 has moderately stronger valving at low-mid velocity, but at high velocity, for all intensive purposes, the OEM FJ Cruiser shock behaves just like a 713 Bilstein. Note that I’ve had to use an OEM FJ rear shock, as OEM 120 struts and shocks are too old and most have lost gas by now. I may order some new 120 struts and shocks from Amayama one day to dyno them, but they will be extremely close to the FJ valving seen here.
So Toyota have designed a rear OEM shock for FJ/Prado with 1700N:1475N at 0.52m/s, and they have matched this with a 195lb/in coil. The original BE5-A481 Bilstein sold in the European market has no doubt been developed around this type of valving. The 19mm longer A713 Bilstein sold in Australia uses the same valving as the original A481.
In Europe, the A481 is predominantly used in Prados that are not lifted and that do not use any accessories like bullbars, and as such the A481 works well in an unloaded vehicle with a soft ca. 200lb/in coil spring to give good handling. ie, the A481 shock is an OEM replacement for a stock OEM vehicle on stock OEM 200lb/in soft coils.
The 713 should be thought of in the exact same regard, as useful only for an unloaded vehicle on soft springs. The very short open length of the 713 also means it is not at all useful in a lifted geometry, and you will end up with only 50-60mm of droop at 2” lift.
So what then is more appropriate valving and coil rates for our heavier Prados that we take bush?
The valving plot below compares the 713 with a B46-1478S;
The 1478 is considered by Bilstein to be an 80 series spec shock used on the rear 80 series solid axle.
You can see that the valving differences between the 713 and the 1478 are enormous. It was recognised early on that 80 series shocks could fit in the rear of a Prado. Many put 80 series shocks in on the basis of the extra length they provide, but without any knowledge of what the valving is like.
You will find similar high rebound:low compression after market valving on a lot of vehicles using solid axle Bilstein shocks, both front and rear. After market rear 80 series coils are typically in the 250-300lb/in range, potentially up to a very high 500lb/in for a very heavily loaded vehicle. Typical after market solid-axle shock valving is in the range 2500-4000N rebound/500-1500N compression.
The rear of the 80 series is not that different to the rear of the Prado, and the OEM rear 80 series coil is even softer than the Prado at ca. 155lb/in.
As such, it isn’t immediately clear why Bilstein use dramatically different valving between the Prado rear and the 80 series rear. Kerb weights and suspension geometry are quite similar between them. I unfortunately don’t have an OEM 80 series rear shock to dyno test, but if I did I would not be at all surprised to find it is very close to 1478 valving.
This suggests Toyota have developed different rear valving for Prado and 80 series when they both have similar kerb weight, suspension geometry and coil rate. The only reason I can think why is due to the IFS on the Prado and subsequently different vehicle dynamics (roll center and center gravity etc.) on the front compared to the solid axle front on the 80 series.
On this basis, I am not at all surprised then whenever you ask a Bilstein distributor which struts/shocks to use for a Prado, they immediately reply 712/713.
This is unfortunate, as the 713 as I described above is really only valved for an unloaded OEM kerb weight Prado. It is also useless in lifted geometry, giving only around 60mm of droop at a typical 2" lift in the rear;
http://www.pradopoint.com/showthread...for-120-150-FJ
I have driven on the 712/713 combination through the Simpson in a lifted and heavily loaded 120 Prado, and the 713 could never control the 270lb/in Ridepro coil I had at the time, and the rear was very unbalanced and would force significant uncontrolled vehicle pitch which needed to be cycled out. There is simply not enough rebound in the 713 to control a high rate coil or to handle a heavily loaded rear which can run to 1800kg, which means using the brakes to slow the Prado down and kill the uncontrolled pitch, even at a miserly 20km/h.
After that experience and knowing how short the 713 is, I moved to 80 series shocks with 80 series type valving, and the difference in ride quality was night and day.
The high rebound:soft compression 80 series/solid axle type valving means a high rate coil can cycle freely.
I have also recently moved to a higher rebound setup on my IFS, and I believe my Prado has never handled better. On the front I am running D563-M2 struts with 3665N:2200N at 0.52m/s, which match extremely well with my 3300N:600N at 0.5m/s 80 series shocks. With a loaded setup, my suspension is cycling beautifully, and I can easily drive through obstacles which previously would have required slower speed and/or heavy braking with the 712/713 setup.
Regarding the range of valving and coil rate for 80 series shocks and our Prado rear, I believe the setup works very nicely in the 260-300lb/in coil rate range, and with compression under 1000N. Anything over 300lb/in or hard compression over 6-800N will start giving a stiff/bumpy feeling in the rear. I believe at least 3000-4000N of rebound is required for a heavily loaded rear.
I hope this explains a bit more why 80 series (or for that matter, most solid axle valving setups) valving works so well in the Prado rear.
Best
Mark
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