Can a leaf-sprung vehicle be endowed with the ride and compliance of a coil-sprung vehicle?

After installing a set of Terrain Tamer parabolic spring on our 1973 FJ40 Land Cruiser, I’d answer that question with: Close. Astonishingly close. Just one anecdote—when I first took Roseann for a ride after the installation, we’d not even got off our neighborhood byway onto a main street before she said, “Wow.”

First, if you’re not familiar with the concept, please read this, then this. But, briefly, a parabolic leaf spring is shaped in such a way that a single leaf can provide progressive resistance as it is compressed—it is, in essence, an extremely elongated parabola, thus its name. By comparison, the traditional standard leaf, stamped from flat bar stock, requires several additional, increasingly shorter leaves to provide progressive resistance, and those additional leaves produce substantial interleaf friction, reducing compliance and ride quality—especially in the case of a heavy-duty spring pack for a 4x4 vehicle, which might comprise eight, ten, or even more individual leaves. Theoretically a parabolic spring can be built with just a single leaf, but most systems use two or sometimes three, to provide backup in the event of one leaf breaking. But those leaves only contact each other at the very ends, via a thick anti-friction pad, so interleaf friction is nearly nonexistent. In fact, shocks for parabolic springs are valved more firmly to compensate for that reduced friction and the lack of self-dampening. Like a coil spring, a parabolic spring would continue to oscillate for some time after a bump if not damped.

Terrain Tamer has been making parabolic spring kits for Series Land Rovers, Hiluxes, and several other (mostly non-USA) vehicles for some time; not long ago they added applications for 40-series Land Cruisers, and offered to provide me with a set. The kit is exhaustively complete: four springs, four nitrogen-charged twin-tube shock absorbers, a steering damper, greasable anti-inversion shackles, and U-bolts. My kit also included TT’s own synthetic elastomer Pro bushings, which the company claims combine the vibration-absorbing properties of natural rubber with the durability of polyurethane. The bushings come with a specific molybdenum disulphide grease.

Terrain Tamer’s shock absorbers have an excellent reputation; however, I had an opportunity to try a set of Koni’s Heavy Track shocks. Koni’s Heavy Track Raid is the best expedition shock absorber I have ever used on overloaded Defender 110s in East Africa, so I jumped at the chance to install the slightly lighter-duty version on the 40.

Installation of everything was completely straightforward, with the additional benefit that the Konis are not nitrogen-charged and thus do not have to be forcibly compressed to fit them. Weighing the OME springs, then the parabolics, drove home one of the salient advantages of the latter: the swap removed 80 pounds from the Land Cruiser.

With it all bolted up, the Land Cruiser’s fender height was within a quarter inch of where it had been with the OME springs installed—the (to me) ideal 50mm/two-inch lift for an FJ40 intended for all-around use. Trying to suppress unrealistically high expectations—this is still after all a leaf-spring suspension—I headed out for a short drive.

I needn’t have suppressed any expectations. The ride was, in a word, transformed. One might demur by pointing out that the evicted OME springs were five years old, but I’d replaced and lubed their anti-friction pads not long before, and regularly greased the shackle bushings. No—this was a transformation. Harshness over minor irregularities in the road surface was simply gone, with the partial result that normal rattles and buzzes in the 40 seemed cut in half. Suspension action over larger holes and humps was astonishingly compliant.

I turned around and went back to the house to take Roseann for a ride, and she was just as impressed.

I let the suspension “settle” for a few weeks. From the side I then noticed a very slight droop at the rear—no more than a half inch, but I loathe a non-level vehicle. This was undoubtedly due to the substantial rear rack on the 40. So I installed a set of OME rear shackles, which are about an inch longer than the Terrain Tamer versions. “Problem” solved.

A few days ago we took the 40 up into Redington Pass, east of Tucson. This route combines a severely degraded dirt road up the pass with several challenging 4x4 trails off it. The Terrain Tamer parabolics—along with the Konis—simply took 90 percent of the sting out of corrugations and potholes that were punishing with standard leaf springs. Once on the trail, the extra compliance was obvious, keeping all four tires in contact with the surface in spots where I typically lift a wheel. Impressive. Even in a video of a simple drive-by (see the Firestone M/T2 tire review) you can see how much easier the ride is.

Over my entire 40-plus-years ownership of the FJ40, no modification I’ve done has had anywhere near such a profound effect on the very nature of the vehicle. Obviously it will be some time before I can attest to the durability of these springs, but the technology has been around long enough to be well-proven. If you own a leaf-sprung Land Cruiser or Land Rover, I cannot recommend Terrain Tamer parabolic springs highly enough.

Terrain Tamer is here. The (just announced) U.S. importer, Valley Hybrids, is here. Query regarding availability.