Rear Wheel Spacers RTS-2000 and RTS-3000
When looking at the rear wheels of a Sprinter 3500 Class C motorhome, one thing often stands out - the wheels are pretty far inboard compared to the edge of the coach bodywork. Generally the bodywork hangs over the edge of the tire by several inches.
This difference in rear track width versus body width led Redlands Truck and RV to develop their RTS-2000 and RTS-3000 rear wheel spacers for the Sprinter chassis. There was already a precedent in place for wheel spacers being used on this chassis, given that a 4" spacer is used when running Super Single rear wheels on Sprinters, so it makes sense to run spacers to correct the track width issue on the dually chassis as well.
We knew that we needed to test these spacers on our own Navion along with the other suspension upgrades. Before installing though, we first had to determine which size to run.
The spacers mount between the hub and the inner dual wheel on each side of the back axle, so they will bring both wheels outboard on each rear corner. For this reason, the clearance must first be checked to determine how wide of a spacer can be used. While checking, it is important to remember that the wheels will move up and down when going over bumps or when cornering. The last thing you want is to cause body damage by running too wide of a spacer and having the tire rub on the body.
Once the proper size is determined, installation is fairly straightforward. The rear axle must be lifted off the ground and supported, and the wheels removed. The spacer is then installed against the hub using the supplied lug nuts, which must then be torqued to spec. Then, the wheels are installed normally using the OEM lug nuts. The nuts supplied with the spacers are tapered, which results in the spacers being very precisely centered relative to the hub of the coach (see last week's blog for more discussion on wheel centering and how it can cause vibration if not done properly!). We would still recommend using the SSWCT-001 Wheel Centering Tool when reinstalling the rear wheels, because the center of the wheels may still be enough larger in diameter that the wheel could sit slightly off center relative to the hub and spacer.
We ended up running the RTS-2000 two inch wide spacers on our coach. This increased the track width by two inches on each side, four inches total. This resulted in a much better look, with the wheels now sitting more flush with the edge of the body.
After installing the spacers, it was time for a test drive. While the difference was not as dramatic as some of the previous items we installed, we did notice a reduction in sway and improved stability on the highway. This makes sense when you consider what effect tire sidewall flex has on the overall stability of the coach. When the Sprinter is rocking back and forth coming in and out of driveways, part of the motion is coming from the flex in the tires themselves. The wider the track width, the less the body is going to rock for the same amount of give in the tires.
Another factor to consider was brought up by one of our engineer customers - by increasing the track width, you are theoretically increasing the rollover resistance of the coach. Using a very simple static calculation, it can be estimated that the rollover resistance increase is directly proportional to the increase in track width. In the case of a two inch spacer on each side, that works out to a track width increase from 62 inches (measured between the centers of each pair of dual rear wheels) to 66 inches, or about 6.5%.
While we haven't done any real-world rollover testing in our Sprinter (nor do we plan to...) to figure out the real world difference, the safety benefit of these spacers is worth considering. We thank Redlands for making this good quality product and we are glad to be able to include it in our upgrade package!
Next week, we plan to wrap up this series with a discussion on options for improving clearance in the rear suspension of the coach. Please check back with us then!
Sprinter RV Chassis - Better Steering and Handling (Filmed back in 2022, earlier in our testing process)