Custom Shock Absorber Development
Source Engineering has collaborated with Bilstein to develop the shock absorbers for the very successful Ride Enhancement Kit. The shocks are carefully tuned for the RR4R chassis. Also included in the ride enhancement kit are custom air-bags and ping tank suspension components. The components have been tuned to work together to provide a comfortable smooth ride and to enhance the controllability of the motorhome as it travels over distressed and damaged roads.
Now, after months of additional design, computer modeling, fabrication and testing, Bilstein has developed a state of the art oversized mono-tube shock absorber featuring a 60mm working piston for this application. We are here at Sacramento Truck Center to document the collaborative effort between Source Engineering, Bilstein and Sacramento Truck Center to fine-tune these oversize shocks for the RR4R chassis.
These 60mm shock absorbers have a larger diameter body, working piston and rod than the 46mm units included with the standard-duty Ride Enhancement Kit. The air-valve is used on these prototype units for nitrogen charging the shocks. Having the ability to remove and recharge the gas from the shock enables the disassembly of the unit for tuning purposes. These shocks are similar to ones used on off-road fire truck applications.
The extreme-duty shocks have a larger diameter working piston than the standard shocks included with the REK.
The shock piston-rod is also of a larger diameter to accommodate extreme stress of off-road use or the most severely damaged roadways.
Udo Putzke, Senior Technician of Bilstein of America, Inc. is disassembling a shock absorber in order to adjust the inner dampening mechanism. The pre-load, compression and rebound dampening are all individually adjustable.
Here, Udo is draining the oil from the inner mechanism of the dampener. The oil is a unique type specifically designed for the Bilstein monotube shock absorber and exhibits consistent properties to temperatures of over 150 degrees C.
The inner components of the shock are adjusted in increments of as little as 5/1000 of an inch. These small changes have a significant impact on the behavior of the system under transient load.
Udo is charging the shock with nitrogen gas. The design of the Bilstein mono-tube gas-charged shock absorber prevents foaming of the oil in the shock, yielding consistent performance and reliable operation.
Installation of the prototypes required careful assessment of clearances. Fortunately, mono-tube shocks can be installed in any orientation including upside-down and achieve proper operation.
It would be very difficult to fit any larger shock absorber onto the RR4R chassis!
Assessment
A specific route along I-80 in Sacramento and including some surface streets, known for their rig-bouncing dips and transitions was mapped out. An initial trip along the route was made in my 2004 Holiday Rambler Neptune which has the Source Engineering Ride Enhancement Kit and trailing arms installed. I noted that several potholes were hit with no porpoising, and that the transient shake caused by the 1" asphalt seal-seams on the cracked concrete highway were well dampened by the system and were only barely perceptible - this is the behavior I have become accustomed to since getting the Ride Enhancement Kit installed in July. As we drove, Udo, Jim Walls and I discussed the qualities of the roads we were on, as well as how the coach handled the surface irregularities and wind sway.
We returned to Sacramento Truck Center, and Lead Technician Lawrence Cowan and his crew quickly installed the prototype shocks. We were soon back out on the same route, with very similar traffic conditions. I was careful to maintain precisely the same route - same lanes and as close to the same speed of 62.5 mph that we attained on the first run. In this first trial of the prototype shocks, we felt every one of asphalt crack seals on the highway as a continuous jarring vibration. In addition, pothole bumps were transmitted into the frame and there were a few cycles of bounce after the initial bump. Udo discussed this with us and explained the adjustments which he thought would work toward clearing up these problems. In speaking with Udo, it became clear that he has done this work dozens of times previously on various types of vehicles for major manufacturers. When one wants high-performance suspension, actually designing a proper shock absorber for the specific application is the only way to go.
Lawrence and the crew began removing the shocks and Udo disassembled them. This was my first time seeing the actual inside of a shock absorber and I was surprised at how simple it appeared to be, yet how precise and complex it became as it was further disassembled and explained by Udo. He made several changes encompassing both compression and rebound dampening, as well as pre-load. These changes consisted of exchanging one precise dimension washer for another of different thickness. The shocks have two stacks of a dozen or so of these washers, one stack for compression damping and one stack for rebound damping. The precise thickness of each washer determines the behavior of the system at a particular region of the dampening or rebound performance curve. By exchanging these washers, the dampening on both compression and rebound can be tuned to the specific characteristics of the system the shock absorber is being applied to such as the sprung and un-sprung weight, the air-bag reluctance to compression and refill time and the gross weight of the vehicle. With the extra-large tubing from the front ping-tank to the airbags, the Ride Enhancement Kit front airbags are very responsive in mitigating road impacts. Additional compression and rebound cycle dampening is determined by the shock absorber.
We returned to the road on the same route as twice before, and I was very surprised by the difference. The continuous jitter of the asphalt seams in the road was nearly eliminated - it was much closer to the ride of the rig with the standard REK shock absorbers. The ride was not the best it could be, however, now a little harsh on the pothole scale bumps and a little tendency to porpoise over swales in the roadway. Armed with this evaluation, we returned to the shop for another go-round of tuning.
With another couple of rounds of tweaking and trying, we arrived at a ride that was parallel to the base REK 46mm special shocks while adding the durability, increased damping capcity and comfort that the new 60mm shock absorber offers. The shocks, notes, tools etc. were packed up for shipment back to Poway (Bilstein USA headquarters) and the original shocks reinstalled on my coach.
During the times that the shocks were being installed on the rig, I got to look around at the shop a bit - much more perhaps than a usual customer since I was in effect working with factory reps. I was impressed with Sacramento Truck Center, the shop is clean and well equipped and well organized. The mechanics working on my rig always wore protective foot booties if they needed to enter the rig, and also applied a plastic cover to the drivers seat. I have been to shops where this was not the case. (I once took it upon myself to protect the inside of my rig during an engine swap on an old Fleetwood Flair - good thing I did, the tyvec painters tarps etc. that I used showed just how much they had protected my rig when it was all over!)
Why bother?
I have never noticed any problem with the standard Bilstein shocks included with my Ride Enhancement Kit. Why bother creating this upgrade?
The answer is simply for extreme duty applications. These shock absorbers are stronger than the standard duty components included with the standard Ride Enhancement Kit.
If you drive a lot on harsh roads or perhaps off-pavement or on dirt roads in some campsites, then the extra strength of the components used in these new shocks will provide an extra margin of tolerance for that unseen small boulder, hole in the road or continuous beating of a poorly maintained highway. Continuous operation of the shock absorbers on bad road conditions does generate heat in the shock - that is why Bilstein's unique mono-tube design uses expensive and hard to get high-temperature oil in their shocks. The larger body of the heavy duty 60mm shock absorber dissipates more heat per unit time than the smaller diameter (less surface area) 46mm body of the standard duty shocks. Considering the cost of a vacation ruined by a shock failure, if you drive in the conditions described here, you may want to invest in the extreme duty shock absorber upgrade when it becomes available. These shocks are very similar to what is used on off-road fire trucks, armored military vehicles and class8 commercial heavy trucks - that gives you an idea of the conditions they are designed to operate in.