Sprinter 3500 Class C Upgrade Series: Part 1 - Rear Shocks
SS88-1889 Rear Shocks
Welcome to the first in our series of posts detailing our process of testing handling upgrades on our 2022 Winnebago Navion! We purchased the Mercedes Sprinter 3500 Class C coach as a Research and Development (R&D) project back in November of 2021, and since then we've done extensive testing on it over tens of thousands of miles.
In this series we'll take a detailed look at each of the key suspension components that we tested out on coach. First, we'll cover the rear shock absorbers.
After logging most of our RV-driving miles in larger Class A motorhomes, driving the Sprinter Class C initially felt amazingly easy due to its precise steering, small size, good ride, and decent stability on the road. However, after driving around town and pulling in and out of driveways a few times, an annoying "rock and roll" tendency became apparent. We found we could easily replicate it by driving over a set of speed bumps at an offset, with just one side of each axle going over the bump.
Once we identified the issue and an easy way to repeat it, we started looking at solutions. We did look at an anti-sway bar upgrade to help with this (look for a discussion on the sway bar in a future post), but given that a sway bar is simply a spring we really needed better shocks to slow down and stop the rocking.
This is where the shocks come in. The rear shocks on the Sprinter dual rear-wheel chassis are quite close together, which means that they aren't moving much when that low-speed rocking is occurring. We found that the factory shocks are also (unsurprisingly) not very strong. Since the force a shock exerts depends on how fast it is being compressed or extended, when the motorhome is rocking slowly the factory shocks just don't have the strength to stop the rocking right away.
Knowing that there was room for improvement on the shocks, we started testing upgrades. After testing seven different off-the-shelf options, we found that some provided a very nice ride and slight improvement in stability while others provided a significant improvement in stability but resulted in a ride that was too harsh. Nothing was quite at the "sweet spot" that we were looking for.
We contacted Koni and they began development of a custom shock for us to fill in that gap. One of their engineers flew out last August to test the first set of SS88-1889 rear shocks on our Sprinter, and after running them back to back against the best options we had to that point, we were quite impressed.
These shocks have an adjustable rebound feature, so they can be tuned to loading and user preference (an "old but good" video on the adjustment process can be found here).
At the minimum adjustment setting, we found that the ride quality was still excellent but with noticeably more control (on paper, about twice the rebound damping as the OEM shocks). We then ran them at 1.25 turns adjustment (about 75% of max, or 3.5 times as much rebound damping as OEM) and wow! On our speed bump test we had about one less full cycle of back and forth rocking. Out on the road, we also noticed much better stability - it turns out that "rock and roll" also was happening out on the road, and once it was gone it made those back road drives much more fun.
Take a look at the chart below for a comparison of our shocks vs. the OEM units, and you can really see the difference. We believe these are the best shocks out there for the Class C Sprinter motorhomes.
We expect the first production shipment in April 2023. We now have a listing for the SS88-1889 on our e-store - if you're interested, please check it out and enter your email so you can be notified once they are in stock!
Stay tuned for Part 2, in which we'll discuss our SS110 Heat Treated Rear Sway Bar.