Whitey
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Hey all,
While there’s usually a lot of interest and discussion about the strut open length and ball joint and CV bind on the IFS, there’s not as much discussion about limiting factors at the other end of the IFS, which is defined by the lower control arm coming into contact with the bumpstop.
As such, I thought it would be interesting to take a closer look at the bump geometry, and how it affects the strut closed length and coil working height. Of particular interest is if it is possible to collapse the front coils to solid height where the coils are all in contact with each other.
The plot below shows how the coil working height changes as a function of the strut length. Note that the working height is relative to the OEM coil seat position for the OEM 120 strut. This will change by 1-2mm for 150/FJ OEM seat position.
The lower arm contacts the bumpstop at a strut length of 468mm.
The next plot shows how the coil working height varies as a function of the lower control arm bumpstop separation;
The most important measurements to come from this data are that the lower arm touches the bumpstop at a strut length of 468mm, and a coil working height of 243mm. Many shock manufacturers will also engineer 100% bumpstop compression into the closed length of their shocks, and this closed length is 435mm from the data.
Also of note in the engineering of the 120 Prado IFS is that the strut will always be bottomed out before solid coil of after market or OEM coils can occur. Looking at typical 120 IFS coils such as Dobinsons C59-300, 302, 314 etc., the solid coil height common to these is 196mm. King and OEM coils are shorter again in solid height due to thinner wire diameter and less coil wraps.
This shows that in OEM geometry with OEM bumpstops, for the majority of Prado drivers using Dobinsons and King coils, it is not geometrically possible to get solid coil.
The OEM bumpstops can compress around 5mm under the weight of the car, and even in the worst case scenario where the bumpstop falls off/100% bumpstop compression, it is still not possible to get solid coil. The bumpstop itself is 25mm thick, and there is at least 47mm of safety margin before the typical Dobinson coil will go solid.
From a dynamic point of view, it is also obvious that it is extremely difficult to reach solid coil on ca. 600lb/in coils. There is 7.44 inches to solid coil for the C59-300, which is ca. 3.5 times the typical corner weight. You won’t achieve this under normal driving conditions, you would need to drop your Prado off a skyscraper to make this happen, Top Gear style! You can get well into bumpstop compression on the IFS with small airborne launches of the Prado, however, you will still never reach solid coil.
All of that being so, there are examples where you can easily get coil bind, well before the strut bump limits. This is achieved simply by having the incorrect coil with minimal winding gap, such as this case in post #12 for Profender coilovers;
http://www.pradopoint.com/showthread...-Prado-120-IFS
However, as mentioned above, it is a different story for potentially bottoming out a strut.
It is possible to see that Toyota have engineered close to the worst case scenario into the closed length of the OEM strut. Adding -25mm for the bumpstop falling off gives 435mm for the maximum closed length. Adding in a safety margin of around 5mm for bush flex/stretch gives 430mm. The OEM closed length is 430mm for the 120 series, and 433mm for the 150 series.
If you take a look at the Pradopoint suspension database, you’ll see that almost every after market strut is underneath 435mm closed length. For example, Bilsteins are typically 433mm, and some after market struts are almost as short as 400mm closed.
So how can you bump out an IFS strut on the Prado?
This can unfortunately be achieved with the use of after market bumpstops. One example can be seen here where it was found that after market Superbumps compressed significantly more than the OEM rubber;
http://www.fjcc.com.au/f36/superbump...-details-1413/
The compression of these after market bumpstops was greater than the thickness of the OEM bumpstop, resulting in a bumped out Bilstein (closed length right around 435mm) which resulted in a bent shaft. This would not have occurred with the OEM bumpstops in place. It is also important to note that the coil did not go solid under these conditions, only the strut bottomed out.
This strut bump failure emphasises how important it is to know the material characteristics and compression properties of after market bumpstops. The Superbumps were released into the market place with no knowledge of these properties.
Similarly for hydraulic bumpstops, they must be set carefully to avoid bumping out the struts.
Most shock manufacturers do not utilise bump out bumpstops inside their shocks, so it is not a good idea to bump a strut or shock out hard, eg, don’t turn your car into an aeroplane! However, many drivers in the rock crawling fraternity will regularly bump out their shocks during slow speed rock crawling, and do this over many years without permanently damaging their shocks.
While there is a minor difference in ball joint location, the chassis and arm dimensions are the same for 120/150/FJ, so this discussion applies to the IFS for all of these models.
I have also seen some sheared front coils recently. If someone has sheared a typical Dobinson or King front coil, it is due to manufacturing defects, and has nothing to do with the IFS geometry. Poor strut valving may have been a contributing factor due to not controlling the rate of coil motion across the defected area.
As always, take it easy on the IFS, watch out for the geometrical limits, and don’t give it a bootful with a wheel in the air!
Best
Mark
While there’s usually a lot of interest and discussion about the strut open length and ball joint and CV bind on the IFS, there’s not as much discussion about limiting factors at the other end of the IFS, which is defined by the lower control arm coming into contact with the bumpstop.
As such, I thought it would be interesting to take a closer look at the bump geometry, and how it affects the strut closed length and coil working height. Of particular interest is if it is possible to collapse the front coils to solid height where the coils are all in contact with each other.
The plot below shows how the coil working height changes as a function of the strut length. Note that the working height is relative to the OEM coil seat position for the OEM 120 strut. This will change by 1-2mm for 150/FJ OEM seat position.
The lower arm contacts the bumpstop at a strut length of 468mm.
The next plot shows how the coil working height varies as a function of the lower control arm bumpstop separation;
The most important measurements to come from this data are that the lower arm touches the bumpstop at a strut length of 468mm, and a coil working height of 243mm. Many shock manufacturers will also engineer 100% bumpstop compression into the closed length of their shocks, and this closed length is 435mm from the data.
Also of note in the engineering of the 120 Prado IFS is that the strut will always be bottomed out before solid coil of after market or OEM coils can occur. Looking at typical 120 IFS coils such as Dobinsons C59-300, 302, 314 etc., the solid coil height common to these is 196mm. King and OEM coils are shorter again in solid height due to thinner wire diameter and less coil wraps.
This shows that in OEM geometry with OEM bumpstops, for the majority of Prado drivers using Dobinsons and King coils, it is not geometrically possible to get solid coil.
The OEM bumpstops can compress around 5mm under the weight of the car, and even in the worst case scenario where the bumpstop falls off/100% bumpstop compression, it is still not possible to get solid coil. The bumpstop itself is 25mm thick, and there is at least 47mm of safety margin before the typical Dobinson coil will go solid.
From a dynamic point of view, it is also obvious that it is extremely difficult to reach solid coil on ca. 600lb/in coils. There is 7.44 inches to solid coil for the C59-300, which is ca. 3.5 times the typical corner weight. You won’t achieve this under normal driving conditions, you would need to drop your Prado off a skyscraper to make this happen, Top Gear style! You can get well into bumpstop compression on the IFS with small airborne launches of the Prado, however, you will still never reach solid coil.
All of that being so, there are examples where you can easily get coil bind, well before the strut bump limits. This is achieved simply by having the incorrect coil with minimal winding gap, such as this case in post #12 for Profender coilovers;
http://www.pradopoint.com/showthread...-Prado-120-IFS
However, as mentioned above, it is a different story for potentially bottoming out a strut.
It is possible to see that Toyota have engineered close to the worst case scenario into the closed length of the OEM strut. Adding -25mm for the bumpstop falling off gives 435mm for the maximum closed length. Adding in a safety margin of around 5mm for bush flex/stretch gives 430mm. The OEM closed length is 430mm for the 120 series, and 433mm for the 150 series.
If you take a look at the Pradopoint suspension database, you’ll see that almost every after market strut is underneath 435mm closed length. For example, Bilsteins are typically 433mm, and some after market struts are almost as short as 400mm closed.
So how can you bump out an IFS strut on the Prado?
This can unfortunately be achieved with the use of after market bumpstops. One example can be seen here where it was found that after market Superbumps compressed significantly more than the OEM rubber;
http://www.fjcc.com.au/f36/superbump...-details-1413/
The compression of these after market bumpstops was greater than the thickness of the OEM bumpstop, resulting in a bumped out Bilstein (closed length right around 435mm) which resulted in a bent shaft. This would not have occurred with the OEM bumpstops in place. It is also important to note that the coil did not go solid under these conditions, only the strut bottomed out.
This strut bump failure emphasises how important it is to know the material characteristics and compression properties of after market bumpstops. The Superbumps were released into the market place with no knowledge of these properties.
Similarly for hydraulic bumpstops, they must be set carefully to avoid bumping out the struts.
Most shock manufacturers do not utilise bump out bumpstops inside their shocks, so it is not a good idea to bump a strut or shock out hard, eg, don’t turn your car into an aeroplane! However, many drivers in the rock crawling fraternity will regularly bump out their shocks during slow speed rock crawling, and do this over many years without permanently damaging their shocks.
While there is a minor difference in ball joint location, the chassis and arm dimensions are the same for 120/150/FJ, so this discussion applies to the IFS for all of these models.
I have also seen some sheared front coils recently. If someone has sheared a typical Dobinson or King front coil, it is due to manufacturing defects, and has nothing to do with the IFS geometry. Poor strut valving may have been a contributing factor due to not controlling the rate of coil motion across the defected area.
As always, take it easy on the IFS, watch out for the geometrical limits, and don’t give it a bootful with a wheel in the air!
Best
Mark
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