“Solid front axles are for rock donkeys!” “IFS stands for ‘inferior front suspension.” We’ve heard these standby beliefs bantered back and forth more times than we can count, so we thought we’d spend some time exposing some myths and sharing some truths.
If you’re looking for a clear-cut winner, this story’s subheading should be a giveaway. There isn’t one. Each style of front suspension has strengths and weaknesses, and it’s up to you to decide what to go with.
For this story, we’re sticking with 4WD solid front axles and A-arm-style IFS. The Ford Twin Traction Beam front suspension has its own merits and demerits, but there’s not enough room for a three-way comparison. This beautifully-constructed TTB buggy (below, right) made a big splash at King of the Hammers last year.
You Can’t Go Fast With a Solid Front Axle
When the Jeepspeed racing series began, many thought the term “Jeepspeed” was nothing short of an oxymoron. It turned out that the only things Jeeps needed to go fast were the right build and the right mindset. Both 2WD and 4WD frontends are used by Jeepspeed racers. This custom 2WD frontend was built by Tony Sato at Currie Enterprises, and is found under the neon-green XJ seen flying in the following photo.
How’s this for going fast and flying high? The Nissley Racing XJ Cherokee enjoyed several seasons of Jeepspeed racing before recently going to a new owner. Two of our four favorite trucks from last year (see “Looking Back,” January 2012) were also high-flying solid axle trucks, 4WD no less. Since both wheels are locked together, what affects one side will affect the other. “Driving a Jeepspeed, you have to be ready for each bump,” Chris Nissley told us. “A hit to one side can pull the whole front end to that side.”
A-Arms are Worthless on the Rocks
It turns out that almost every swipe against A-arm IFS has to do with a factory-delivered suspension. Sure, there are more moving parts in an A-arm system, but what if those moving parts are designed around performance instead of around cost spreadsheets? Shannon Campbell answered that question with a convincing win at 2011’s King of the Hammers. By the time you read this, he may well have won yet again.
Getting significant suspension travel out of a 4x4 A-arm system has historically been challenging because the stock front differential was so wide that the A-arms and CV shafts couldn’t be built to a significant length without incurring a silly-wide track width in the process. Campbell’s KOH buggy uses a Currie F9 IFS differential. The Currie F9 IFS center section measures a mere 14.5 inches wide from axle face to axle face. The narrow IFS differential means longer CV shafts and longer A-arms are possible while maintaining a reasonable track width, all with rock-and-whoop gobbling wheel travel.
Ground clearance is determined primarily by tire size, not by suspension type. Portal axles (think Unimog or H1 Hummer) are the exception to this, but that’s another story.
There is, however, a fundamental difference in the type of ground clearance you get with a solid-axle versus A-arm frontend.
It’s true that the differential hangs down on a solid axle. However, the differential also goes up and down with the suspension. As such, you can count on the same amount of ground clearance as your suspension cycles.
In contrast, the differential is mounted to the frame with an A-arm system. As the suspension cycles up and down, the ground clearance changes. These fundamental differences will influence what lines you pick on the trail, as well as influence driving style.