Sprinter High Performance Bump Stops
It's inevitable...once you start modifying a vehicle platform and start to increase performance in one area, you often discover deficiencies in tangent areas. For a long time, the front suspension was the limiting factor with how hard and fast we could push a Sprinter, and our rear spring and shock upgrades were more than sufficient. But with the new levels of performance unlocked with our inverted Rally Strut up front, the rear was now struggling to keep up. We're confident in the overall tune of our spring and shock combo, but one other critical area was yet to be fully tuned: the rear bump stops.
In their simplest form, a bump stop is just that: the rubber bumper that stops the metal parts from disastrously bumping together on big suspension impacts. Many like to say 'but i'm not an aggressive driver, I don't drive on the bump stops.' That's well and good...but the road or trail gets a vote too, and some bumps come up on you faster than you think. Your bump stops are your last line of defense against damage inducing bottom outs.
Digging deeper, they are a vital part of the overall spring and damper package, and critical to overall handling and performance. From a tuning perspective, the bump stop can be used to add vital spring rate progression as the suspension cycles deep into the travel envelope. Because a bump stop is only active in the final 10-20% of wheel travel, the added spring rate is only felt then, so they do not make the ride overly harsh when properly tuned.
Properly tuning a bump stop requires extensive research time cycling, checking, disassembling, prototyping, and repetition until satisfactory results are achieved. Once the concept is proven in the lab, then its out to the track to test in the real world and assess from there. Our engineering team painstaking has to run the suspension through its full range of motion in every possible spring, shock and lift height combination to ensure correct fitment.
Ultimately, we found almost 2" of wheel travel being left on the table*, given that the factory bump setup was done before the shock travel was done. We tuned our new High Performance Bump Stop system to match this and achieve as much movement as possible from the rear suspension, simultaneously improving ride quality. In suspension engineering, anytime you can make a safe increase in overall up-travel, without sacrificing down-travel or ride height, you have a huge win on your hand for real world performance...you've just added that much more compliance to the system.
Material matters a lot in bump stops too. Taller bump stops will no doubt engage sooner, and if OE style rubber is kept ride quality would be worse overall. We use microcellular foam for several reasons, and it is actually the more common material choice on modern vehicles, especially factory models intended for off road use. Compared with rubber, microcellular foam is much more progressive in how the spring rate ramps up which allows for a softer initial feel and predictable performance. Second, foam has great natural rebound damping properties, whereas rubber does not. When a rubber bump stop is engaged, the rubber wants to instantly return back to its resting state and the result is a violent 'pogo stick' feeling with a harsh bottom out. Foam returns to its natural resting state more slowly, allowing the suspension to recover more smoothly.
The final component of this solution is re-engineering the bump stop interface on the frame. Mercedes used a simple, but oddball design to retain the original bump stop which can be extremely difficult to install. Our billet frame side mounting adapter enables the use of a more common stud mounted, cylindrical style bump stop that performs well at indirect impacts and installs easily in seconds. The lower striker pad creates a shorter, flat bump surface on the axle tube in place of the tall original 'dome' piece that is prone to falling off from off-axis impacts, since it has lots of leverage over its mounting bracket.
Overall, our Sprinter 2500 High Performance Rear Bump Stop kit addresses each shortcoming of the factory bump stop arrangement, improving overall performance and capability without compromising load carrying capacity. Get yours today and complete the total package!
*Requires Opti-Rate spring, or Opti-Rate, 2" lift and Baja Norte brackets