Why Solid Axel is Better in Off-Roading

Toyota 4Runner has gone to Independent Front Suspension (IFS) in 86. The Land Cruiser went to IFS in 98 with the Series 80. Range Rover went to IFS in 2002 with the 3rd gen. Mercedes G-Wagon will be going to IFS in 2018. As more people buy SUV for on-road use, manufacture change the design from solid axel to IFS for better handling. There is no doubt IFS handles better on-road the solid axel. What about off-road. What is it that makes solid axel better for off-roading?


All in Geometry

In summary, solid axel offers better travel than IFS strictly because of geometry. Within the confines of the design space, IFS is at a disadvantage when it comes to articulation. Engineers can only make the A-arms so long. A-arm angle can only travel up and down so much before CV joint or univrsal joints starts to bind or becomes weak. The problem with IFS is that the outboard CV joint has to run at an angle when the suspension is articulating. On top of that, when the driver turns the front wheels, the angle of the CV joint further increases. That is a double wammy. There is angle from suspension travel and in addition angle from steering. No wonder CV joints often go bust.

For more articultaion, engineers can increase the length of the a-arms. However, that will widen the car. Ford Raptor is one example. The car is quite wide, but it has good suspension travel. Is no good for tight trails though. Is really for blasting thru the dessert. Same with the Hummer H1. It is quite a wide vehicle. Great for blasting across the Iraq dessert, but not so good in the woods. Often complaint is it is too wide.

Solid axel on the other hand has less of the geometry issue. First, the CV joint only has to take care of steering angle and nothing else. The entire axel tilts for suspension articultaion. Therefore, there is almost no limit on how much it can tilt. Even with extreme tilt of the solid axel, the CV joint still only has to take care of steering. The CV joint is inherently stronger on a solid axel than IFS. The drive shaft U-joint can easily take care of the crossed up articulation of the axel because the drive shaft can be designed to be pretty long, so it does not have to angle much for suspension travel. More important than suspension travel is articulation. For articulation, the U-join on the drive shaft do not care what orientation the axel is in.

In summary, for articultaion, nothing beats solid axel all else being equal. The only reason manufacture goes to IFS is only for on-road customers.