Whitey
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Hey all,
I thought we could start an interesting thread about what the best type of suspension setup is for driving the Prado on corrugations. Hopefully many of you can chime in with your own experience from your preferred setups.
There are a few theories around on what is best, and many factors involved, including tire pressures, coil rates, and perhaps most importantly valving. Not surprisingly, there are not so many valving numbers for the “best” setups, so hopefully we can get some real dyno data in this thread to support these cases.
The tire itself acts like a coil spring, and has its own pressure dependent tire load-deflection rate. As is usually the case with suspension, there are always two sides to the argument. While you will hear many say to run tire pressures to 25-30psi for corrugations, there is also another not so well known theory that running high tire pressures is better, up to 50psi (this theory has its origins in F1 racing, and means the suspension must be softer to absorb the bumps). For each of these cases the suspension will need to be set up differently, softly for the high pressure tire case, harder for the softer pressure tire case.
There is also again the subjectivity of what one person thinks is a great setup for corrugations will not be enjoyed by someone else. Many will say to have the suspension set up softly regardless and believe the ride comfort is excellent, all the while with the sprung mass oscillating up and down.
There are also many anecdotes, such as “keep the compression hard, and the rebound soft” apparently so the soft rebound allows the suspension to “get down more easily” into the deeper parts of the corrugations, with the harder compression stopping the higher bumps lifting the vehicle too high. These types of anecdotes are usually quoted for adjustable shocks with no knowledge of the valving or the range of adjustment.
Speed is also a big factor, and one theory is that the faster you go the more easily you’ll skip or glide over the corrugations. How easily you do this can depend strongly on your suspension travel and the depth and length of the corrugations.
There are also important kinematic factors to consider, the rebound:compression ratio in the rear of the Prado is crucial to the stability of the Prado, the classic “pogo stick” dynamics are notorious. Other factors are the front:rear coil rate ratio, which will strongly affect the vehicle pitch via natural frequencies, and the ratio of front:rear ride rates.
Regarding the important rebound:compression ratio for the rear of the Prado, I believe that solid axle spec valving works the best, and valving in the 3000N:500N up to 4000N:1000N is the most common solid axle valving you will see on a wide variety of solid axle vehicles. Typical coil rates are in the 230-320lb/in range for this valving.
It is interesting for example to see the recommended settings for ARB BP-51 rear shocks yielding 4250N:920N at 0.52m/s. This is very close to the commonly used Bilstein B46-1478LT valving of 4000N:900N. It is also very close to the 3925N:910N I’m using in my custom Ironman Pros.
So it’s no real surprise to see these kinds of solid-axle valving figures for the rear for both non-adjustable and adjustable shocks. However it’s not the end of the story for the rear, and many who have adjustable shocks like the BP51’s will tweak the compression and rebound settings around dependent on their tire pressures, coil rates, and the weight of their vehicle and driving style.
In the front we are strongly limited by the IFS motion ratio in valving terms, so at the strut position it will be quite common to see struts with 2500N:1500N up to 3600N:2200N. Some struts will use even higher rebound Forces up to 5000N. Coil rates can typically vary from 600-800lb/in. In handling terms, it is better to have the front softer than the rear, something which is in any case forced upon us by the scaling nature of the IFS motion ratio. Keeping front:rear coil rates around the 700:300 ratio ensures the rear suspension frequency will be higher by around 10%, thereby minimising wheelbase length induced pitch for long spacing corrugations, while also keeping the front ride rate around 25% softer than the rear. Running a low front strut compression around 1500N leaves the IFS open to hard bump outs on taller corrugations, so keeping the compression around 2000N is preferable.
I have personally driven the 712/713 Bilstein setup on Ridepro coils with a heavy Prado over GVM on 50psi tires as a test case along the Great Central Road. The 712/713 are just copies of the OEM valving, and are considered as soft suspension on the Prado. This high tire pressure/soft suspension setup worked well, and handled nicely. I’ve also driven the complete opposite with soft tire pressure/hard suspension setup, with more like the valving discussed above, and the handling feels similar to me. In both cases I was driving at 90-100km/h.
I’d like to hear from anyone who has some feedback about their setup on corrugations, regardless of how you do it. It would be great if you could list your tire pressures, coil type/rates, strut/shock used, vehicle weight and vehicle speed, and the corrugated roads you’ve driven on. It doesn’t matter if you don’t know your coil rates and strut/shock valving, just as long as you know the manufacturer, as I can find the coil rates and valving.
Hopefully this thread will become a good tool for great suspension setups to eat up those corrugations!
Best
Mark
I thought we could start an interesting thread about what the best type of suspension setup is for driving the Prado on corrugations. Hopefully many of you can chime in with your own experience from your preferred setups.
There are a few theories around on what is best, and many factors involved, including tire pressures, coil rates, and perhaps most importantly valving. Not surprisingly, there are not so many valving numbers for the “best” setups, so hopefully we can get some real dyno data in this thread to support these cases.
The tire itself acts like a coil spring, and has its own pressure dependent tire load-deflection rate. As is usually the case with suspension, there are always two sides to the argument. While you will hear many say to run tire pressures to 25-30psi for corrugations, there is also another not so well known theory that running high tire pressures is better, up to 50psi (this theory has its origins in F1 racing, and means the suspension must be softer to absorb the bumps). For each of these cases the suspension will need to be set up differently, softly for the high pressure tire case, harder for the softer pressure tire case.
There is also again the subjectivity of what one person thinks is a great setup for corrugations will not be enjoyed by someone else. Many will say to have the suspension set up softly regardless and believe the ride comfort is excellent, all the while with the sprung mass oscillating up and down.
There are also many anecdotes, such as “keep the compression hard, and the rebound soft” apparently so the soft rebound allows the suspension to “get down more easily” into the deeper parts of the corrugations, with the harder compression stopping the higher bumps lifting the vehicle too high. These types of anecdotes are usually quoted for adjustable shocks with no knowledge of the valving or the range of adjustment.
Speed is also a big factor, and one theory is that the faster you go the more easily you’ll skip or glide over the corrugations. How easily you do this can depend strongly on your suspension travel and the depth and length of the corrugations.
There are also important kinematic factors to consider, the rebound:compression ratio in the rear of the Prado is crucial to the stability of the Prado, the classic “pogo stick” dynamics are notorious. Other factors are the front:rear coil rate ratio, which will strongly affect the vehicle pitch via natural frequencies, and the ratio of front:rear ride rates.
Regarding the important rebound:compression ratio for the rear of the Prado, I believe that solid axle spec valving works the best, and valving in the 3000N:500N up to 4000N:1000N is the most common solid axle valving you will see on a wide variety of solid axle vehicles. Typical coil rates are in the 230-320lb/in range for this valving.
It is interesting for example to see the recommended settings for ARB BP-51 rear shocks yielding 4250N:920N at 0.52m/s. This is very close to the commonly used Bilstein B46-1478LT valving of 4000N:900N. It is also very close to the 3925N:910N I’m using in my custom Ironman Pros.
So it’s no real surprise to see these kinds of solid-axle valving figures for the rear for both non-adjustable and adjustable shocks. However it’s not the end of the story for the rear, and many who have adjustable shocks like the BP51’s will tweak the compression and rebound settings around dependent on their tire pressures, coil rates, and the weight of their vehicle and driving style.
In the front we are strongly limited by the IFS motion ratio in valving terms, so at the strut position it will be quite common to see struts with 2500N:1500N up to 3600N:2200N. Some struts will use even higher rebound Forces up to 5000N. Coil rates can typically vary from 600-800lb/in. In handling terms, it is better to have the front softer than the rear, something which is in any case forced upon us by the scaling nature of the IFS motion ratio. Keeping front:rear coil rates around the 700:300 ratio ensures the rear suspension frequency will be higher by around 10%, thereby minimising wheelbase length induced pitch for long spacing corrugations, while also keeping the front ride rate around 25% softer than the rear. Running a low front strut compression around 1500N leaves the IFS open to hard bump outs on taller corrugations, so keeping the compression around 2000N is preferable.
I have personally driven the 712/713 Bilstein setup on Ridepro coils with a heavy Prado over GVM on 50psi tires as a test case along the Great Central Road. The 712/713 are just copies of the OEM valving, and are considered as soft suspension on the Prado. This high tire pressure/soft suspension setup worked well, and handled nicely. I’ve also driven the complete opposite with soft tire pressure/hard suspension setup, with more like the valving discussed above, and the handling feels similar to me. In both cases I was driving at 90-100km/h.
I’d like to hear from anyone who has some feedback about their setup on corrugations, regardless of how you do it. It would be great if you could list your tire pressures, coil type/rates, strut/shock used, vehicle weight and vehicle speed, and the corrugated roads you’ve driven on. It doesn’t matter if you don’t know your coil rates and strut/shock valving, just as long as you know the manufacturer, as I can find the coil rates and valving.
Hopefully this thread will become a good tool for great suspension setups to eat up those corrugations!
Best
Mark
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