INVERTED RALLY STRUTS
The modern adventure van has a relatively unique layout in the world of off-road vehicle suspension. It shares more in common with a modern car, instead of a truck or SUV. A MacPherson strut is the preferred layout for front suspension on the modern cargo/delivery van platforms; it is cost effective to make and offers efficient packaging. This layout uses a lower control arm to carry the steering knuckle and weight of the vehicle, then the knuckle is connected to a strut.
A MacPherson strut is a hydraulic tube that allows the suspension to compress vertically and dampen movement, rotate in the horizontal plane as the vehicle is steered, and handles all of the inward loading of the tire as the vehicle weight wants to compress. A strut is by nature a shock, but due to the loading it sees, the load bearing surfaces and housing that connects to the steering knuckle must all be significantly larger and more heavily constructed than a basic shock absorber.
Given this unique layout, we knew we needed an innovative solution; we weren’t going to be able to properly solve this engineering problem with simple off the shelf parts-binning. Looking outside the van space for inspiration, we settled on a design configuration popular in the world of rally racing, power sports and mountain bikes: the inverted damper. While our competitors have been busy adapting existing coil over and shock designs for jobs they were never intended for, we were working with Falcon on a ground-up design to a truly unique product. In a traditional strut, you basically have a heavy duty shock with a clamping bracket on it. Our inverted design flips everything upside down, and uses a specially designed damper body as the load bearing shaft, with a precision machined lower strut body housing oversized bearing surfaces, clamped to the knuckle.
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By design, a strut is in a near perfect position and orientation for proper wheel control through better damping. The proper way to solve most of the handling and sway control issues, is with damper tuning not adding spring rate (which should only come with additional damping). Getting a high performance damper in this location opens up a much wider envelope of performance and tuning possibilities. A near 1:1 motion ratio at the struts means we can control suspension velocity much more precisely and better balance high speed and low speed hits. What this translates to is better body control without sacrificing comfort on sharp hits or while off roading.
Why is it upside down?
By inverting the damper, we gain a lot of tangible benefits. The damper rod on a strut lives in a dangerous place for a sensitive hydraulic part: right near the tire. With our design, the actual damper seal is protected inside the lower strut body, and the shaft is kept isolated from contaminants and debris. Our load bearing shaft is 250% larger diameter than stock or the competition, allowing us much more bearing surface area to dissipate wear and increase lateral stability. In a conventional strut, the oil and pressure seal is being side-loaded, with the net effect of a shorter seal life. Due to the physics of fluid displacement, forcing the damper rod to work as the load bearing shaft limits its overall diameter to a much smaller size than is possible with an inverted design.
But, why are you STILL not doing a coil spring?
Quite frankly, it is the wrong solution for a Sprinter. By design, the spring and bottom out forces are loaded into the heavy gauge, stamped and boxed steel subframe. The upper strut mount loads damping forces into the much weaker sheetmetal of the body tub. A rubber bushing isolates the occupants of the vehicle from the noise, vibration, and harshness (NVH) transmitted into the chassis from the strut. Adding a coil here loads that rubber bushing in an axial direction, which is the worst way to load a round rubber donut bushing. It has a further detrimental effect of adding NVH back into the chassis.
Why do our competitors do it? It’s a simple way to add spring rate and ‘lift’, and a great bullet point to sell to people thinking they bought a ‘coil over’, which sounds like a fancy upgrade. In the end, it is a relatively negligible amount of spring rate. We are able to add a comparable amount of spring rate, in a more progressive way with upgraded jounce bumpers that direct that energy properly through the subframe and without altering the control arm geometry.
To address the increased bushing deflection and wear from the greater forces being transmitted to the strut mount bushing, we've developed our Rate Cup washer. Typically, harder bushings are used to counter increased road force in performance applications; however in our testing this approach quickly led to unacceptable levels of NVH. Our patent pending design addresses the bushing issue by preloading it with a specially machined cup to distribute damper forces more evenly across the bushing's surface area. This tightens road feel and prevents over-compression of the bushing that would lead to premature wear and tear. The Rate Cup is designed to work with the OEM strut bushing so replacement is easy and the OEM NVH characteristics are preserved. Our competitors have all completely ignored this important component, we've delivered a solution that enhances an OEM wear component.
How thoroughly is this tested?
Well, thanks to our geographic location, we are graced with a long dark winter and blazing summers. We're frequently out driving the vans year round in every harsh condition imaginable. Our test vans get driven hard in weather below 0*, throughout the triple digit heat of the summer, and all through the inclement weather of the in-between seasons.
Beyond our vans, we also have trusted local partners testing on their personal vans, since they rack up miles quicker than we can. Our red van has now covered thousands of miles in dirt chasing friends in linked and caged prerunners, offering demo rides, and doing general proving in the nearby forests. We've jumped the van hundreds of times. More than the miles alone, is the pace we're driving them at, which is faster and more composed than we even anticipated. Everyone who has ridden in one of these vans has been simply blown away by the raw performance we've achieved. All the more impressive is price point we're delivering it at!
The results speak for themselves. The difference is that we aren’t just simply taking things off the shelf and making them work, we are engineering real solutions in innovative ways. And we’re aren’t done yet. We have struts in development for ALL Sprinter applications, as well as Transit applications, and will be rolling them out over the next year.
Get more details about our 4x4/AWD Adjustable Front strut here.