Front Flex
Posted: 18 Jan 2013 18:46
Pretty much ever since I got my Patrol, I have been thinking of/investigating ways of increasing the front flex to compare more equally with the rear, on the basis that more of a good thing must definately be a good thing.
Effectively, and as I am sure most of you already know, front flex is limited by the two bushes in each lower control arm fighting against flex all the time. This is bad for flex, but at the same time probably a large contributor to the Patrol's relatively good road manners when compared to the Wrangler, which is about the only production live-axle, coil-sprung 4x4 with a different front suspension layout offering markedly more flex.
Pretty much all the othrer live-axle 4x4's currently on the market have the same type of front suspenios layout, and fairly similar flexability on the front axle (there may be minor variations, but nothing spectacular).
So far I know of four systems that could offer substantially more flex, some of which are relatively simple modifications while others are a lot more complex. These are, in no particular order:
1) Superior Ingineering's Superflex arms.
2) Five-link suspension system.
3) Four-link suspension system.
4) Dobbin Xlink.
My thoughts on each are as follows:
1) Superflex:
This is the simplest system to install, and requires no permanent vehicle modification at all. It works by effectively moving the bushes closer together, thus reducing the deformation of each bush for a given flex angle. It also allows caster correction without the need for special offset bushes. A full installation (with superflex arms on both sides) will probably out-flex any shocks mounted in the standard mountings and assuming a lift of 100mm or less. However it is relatively expensive, particularly if you import it, and it is patent-protected.
Furthermore the road handling is affected to a degree (although most users claim it's not too bad), and I am a little bit concerned about axle tramp.
2) Five-links:
This effectively is modifying the front suspension into a similar layout to the rear suspension. It will allow massive amounts of flex (assuming you find a way of fitting long enough shocks) and is fitted on many competitive rock-crawlers. However I have not come across a bolt-on kit for the Patrol, and from what I can see substantial vehicle modifications are necessary, including welding brackets onto both the chassis and axle. Also, since there is very limited room on a Patrol for this, and most of these systems are home-made lashups, they frequatly result in a vehicle that handles terribly on the road. This will definately require a fairly beefy anti-sway bar to keep the car reasonably road-worthy, sort-of negating the whole exercise unless quick-disconnects are used)
3) Four-links:
I have only ever seen these on competitive pipe-car type vehicles. The system consists of two lower control arms running approximately paralel, and two upper control arms converging sharply. The convergence effectively negates the need for a panhard rod, but the joints need to be close-tolerance ball joints and rubber bushes will not work. In terms of performance and flexability, nothing (except maybe the torque-tube setup on the Unimog) will touch this, but the penalties are severe. Due to the relatively solid joints, maintenance is high and a lot of road noise is transferred to the car. Also there is limited space in a Patrol for this, and particularly so since the entire steering system needs to be re-designed if bump-steer is to be kept within reasonable limits.
4) Xlink:
Apart from Superflex arms, this is the only system I know of that is available in kit form. It works by removing the two front bushes's mounting points from the axle, and instead fitting a bar linking them together. This bar is pivoted to the axle in the middle. Thus when one arm moves up, the other is pushed down. Flex thus occurs with very little deformation in the bushes, and thus the axle flexes very easily. However, total flex is limited (to about 20 degrees) as the arm will eventually interfere with the panhard rod. Fitting the current commercially available kit is a matter of welding the arm's pivot pin to the front axle, in the correct place, and then grinding off the current front bush mounting holes from the axle. The current commercial kit can also be ordered with a lock-out pin which will lock the arm in the horizontal position, and when this is fitted road handling will not be affected at all. If the lockout pin is not used, body roll wil increase but there should not be any effect on axle tramp. By carefull placing of the pivot pin (or special arm geometry) the use of caster-correction bushes can also be avoided on lifted cars.
However, there is another factor limiting suspesion flex, and that is the amount te front shocks can extend. From extensive fiddling with a 3-d model I have developed, I suspect that the standard shocks will not allow much more flex than the standard control arm bushes, and I have no idea yet what effect standard suspension kits (such as OME etc) will have on that, although it seems that the OME shocks are only about 16mm longer than standard and have about 5mm more travel. However I suspect that any of the systems described above will out-flex any normal shock that can be fitted to the standard mounting points. Thus to gain the full advantage will probably require further modification.
Effectively, and as I am sure most of you already know, front flex is limited by the two bushes in each lower control arm fighting against flex all the time. This is bad for flex, but at the same time probably a large contributor to the Patrol's relatively good road manners when compared to the Wrangler, which is about the only production live-axle, coil-sprung 4x4 with a different front suspension layout offering markedly more flex.
Pretty much all the othrer live-axle 4x4's currently on the market have the same type of front suspenios layout, and fairly similar flexability on the front axle (there may be minor variations, but nothing spectacular).
So far I know of four systems that could offer substantially more flex, some of which are relatively simple modifications while others are a lot more complex. These are, in no particular order:
1) Superior Ingineering's Superflex arms.
2) Five-link suspension system.
3) Four-link suspension system.
4) Dobbin Xlink.
My thoughts on each are as follows:
1) Superflex:
This is the simplest system to install, and requires no permanent vehicle modification at all. It works by effectively moving the bushes closer together, thus reducing the deformation of each bush for a given flex angle. It also allows caster correction without the need for special offset bushes. A full installation (with superflex arms on both sides) will probably out-flex any shocks mounted in the standard mountings and assuming a lift of 100mm or less. However it is relatively expensive, particularly if you import it, and it is patent-protected.
Furthermore the road handling is affected to a degree (although most users claim it's not too bad), and I am a little bit concerned about axle tramp.
2) Five-links:
This effectively is modifying the front suspension into a similar layout to the rear suspension. It will allow massive amounts of flex (assuming you find a way of fitting long enough shocks) and is fitted on many competitive rock-crawlers. However I have not come across a bolt-on kit for the Patrol, and from what I can see substantial vehicle modifications are necessary, including welding brackets onto both the chassis and axle. Also, since there is very limited room on a Patrol for this, and most of these systems are home-made lashups, they frequatly result in a vehicle that handles terribly on the road. This will definately require a fairly beefy anti-sway bar to keep the car reasonably road-worthy, sort-of negating the whole exercise unless quick-disconnects are used)
3) Four-links:
I have only ever seen these on competitive pipe-car type vehicles. The system consists of two lower control arms running approximately paralel, and two upper control arms converging sharply. The convergence effectively negates the need for a panhard rod, but the joints need to be close-tolerance ball joints and rubber bushes will not work. In terms of performance and flexability, nothing (except maybe the torque-tube setup on the Unimog) will touch this, but the penalties are severe. Due to the relatively solid joints, maintenance is high and a lot of road noise is transferred to the car. Also there is limited space in a Patrol for this, and particularly so since the entire steering system needs to be re-designed if bump-steer is to be kept within reasonable limits.
4) Xlink:
Apart from Superflex arms, this is the only system I know of that is available in kit form. It works by removing the two front bushes's mounting points from the axle, and instead fitting a bar linking them together. This bar is pivoted to the axle in the middle. Thus when one arm moves up, the other is pushed down. Flex thus occurs with very little deformation in the bushes, and thus the axle flexes very easily. However, total flex is limited (to about 20 degrees) as the arm will eventually interfere with the panhard rod. Fitting the current commercially available kit is a matter of welding the arm's pivot pin to the front axle, in the correct place, and then grinding off the current front bush mounting holes from the axle. The current commercial kit can also be ordered with a lock-out pin which will lock the arm in the horizontal position, and when this is fitted road handling will not be affected at all. If the lockout pin is not used, body roll wil increase but there should not be any effect on axle tramp. By carefull placing of the pivot pin (or special arm geometry) the use of caster-correction bushes can also be avoided on lifted cars.
However, there is another factor limiting suspesion flex, and that is the amount te front shocks can extend. From extensive fiddling with a 3-d model I have developed, I suspect that the standard shocks will not allow much more flex than the standard control arm bushes, and I have no idea yet what effect standard suspension kits (such as OME etc) will have on that, although it seems that the OME shocks are only about 16mm longer than standard and have about 5mm more travel. However I suspect that any of the systems described above will out-flex any normal shock that can be fitted to the standard mounting points. Thus to gain the full advantage will probably require further modification.