After a 500-mile day of solo driving over nearly every type of road imaginable — from interstate highways to winding narrow mountain roads — I now have a rather complete driver's perspective of how LiquidSpring’s “Compressible Liquid Adaptive Suspension System“ (CLASS) has changed my motorhome's ride and handling. And I’ll try to describe it thoroughly, but let me start with my most important conclusion:
Listen to what your body is telling you.
The first hint, just shortly after starting my trip, was a seat-of-the-pants sensation that there was less vibration, even on smooth roads. Then, as I drove at higher speeds, this became obvious to my ears — I wasn’t hearing the usual rattles and creaking from the back of the coach. As the day wore on, my hands registered the most surprising difference of all: they remained relaxed. Even when the pavement got rough or the roads became narrow and twisting, there was just no white-knuckle driving. Ten hours spent in the driver’s seat would normally leave me exhausted, and the tension usually lingers on as a stiff back and tight shoulders. But when I pulled into my campsite late yesterday, I was not tired or tense or sore, just hungry.
That was Friday. I spent part of Saturday trying to figure out why a rear suspension mod should have made that much of a difference to my comfort in the front. And rather than having you rely on what my body was telling me, I’m going to try to explain that with a little experiment and some data analysis.
First, let’s re-cap my setup as a way to understand the experimental design: My 34-foot-long motorhome is a 2017 Tiffin Allegro Open Road 32SA, built on a Ford F53 gas chassis. It has the following suspension and handling modifications: Sumo Springs, which should help control side-to-side sway; Koni shock absorbers, which should result in a softer ride than the original shocks; and a Safe-T-Plus steering stabilizer, which helps keep the coach tracking straight and reduces steering wheel corrections while driving. I’ve had a front wheel alignment, and my tire pressures have been properly adjusted based on front and rear axle weights. All of these individual changes introduced improvements in the ride and handling, but all were incremental – and none were sufficient to compensate for the ride on poor highways. That’s the problem I have been trying to solve, as I wrote about in part 1: “the jarring, bouncing, and swaying in response to rough road surfaces.”
Now for the experiment itself: Just before dropping off my coach at the LiquidSpring factory, I found a stretch of Indiana’s I-65 that had straight, level roads in good condition, occasionally punctuated by bridges that had concrete surfaces in poor condition. I set my cruise control to 60 mph, got in the right lane, and took advantage of my iPhone’s built-in 3-axis accelerometer to record motion/vibration data as I drove. The app I used (“Vibroscope”) records side-to-side motion (X axis), front-to-back motion (Y axis), and up-and-down motion (Z axis). I placed the iPhone on the carpeted floor near my right foot so that I could record the chassis movement that was being transmitted to the driver’s seat. After the LiquidSpring crew installed my new rear suspension system, I drove the same section of highway again. Because of the timing of both the “before” and “after” tests, I was driving a coach with the identical load (including the amounts in my propane, gasoline, and water tanks), the same speed and lane (got lucky with the traffic), the same negligible wind, and the same tire temperatures and pressures. So I'm hoping you can see that this is meant to be a controlled experiment designed to test the effects of changing just one variable: replacement of my original rear suspension by the LiquidSpring CLASS.
Finally, the results: I’m going to save you time by focusing only on the measurements that showed a substantial difference with LiquidSpring. This was rather surprising to me, because it’s all about the X-axis data, measuring side-to-side motion. You can visualize this motion in the graphs below:
The jagged peaks you see in these tracings correspond to measurements of the side-to-side movement at the driver’s location in the coach. Regardless of whether the peaks are pointed up or down, their size (how far they extend from the baseline in the middle) correlates with the intensity of the vibration; and the more closely packed the peaks are, the higher the vibration frequency. At first glance, these traces look similar because I’m traveling the same stretch of road at the same speed, but it’s the differences that are worth a closer look. First, let’s focus on the data as I drove over the rougher pavement on the bridge, hitting expansion joints at the beginning and end:
There are a couple of key observations here, and the first is to see the effects of driving over an expansion joint. The duration, number, and size of the large peaks at those spots on the graph show that the LiquidSpring suspension reduces the front end motion after the initial hit. This matches the impression I had while driving — I could still feel the initial jolt of the expansion joint, but the “aftershocks” were subdued. Once I was driving on the rough pavement of this bridge, another difference can be seen in the tracings: there are fewer, smaller peaks after the LiquidSpring modification, giving the graph a less “busy” look. This correlates with my sensation of a gentler and smoother ride over the bridge’s rough pavement. Since we’re measuring side-to-side motion, it makes sense that I also found it easier to control the steering while going over harsh bumps or over generally rough pavement.
But it’s not just rough road surfaces that show this difference of the LiquidSpring suspension. Let's shift our focus to the smooth road section that I drove right after leaving that bridge:
The graphs show that the LiquidSpring suspension resulted in an overall decrease in side-to-side movement, even on smooth road surfaces. What all these data are showing is that the front of the coach is normally experiencing a significant amount of side-to-side instability, presumably a result of the lateral motion that is inherent in a leaf spring suspension. The LiquidSpring conversion changes that to a much more stable suspension system in the rear, and that stabilization around the rear axle (which carries most of the motorhome weight) is apparently having a noticeable effect on the lateral stability in the front. The reduced side-to-side vibration must be what is giving me the sensation of a more comfortable, lower vibration ride on even a smooth road.
There are two other LiquidSpring benefits that are worth mentioning here, and both relate to a control panel interface mounted just below the dashboard display (see photos below). The first benefit has to do with controlling the ride and handling by selecting either a smoother ride (“Comfort” mode) or better handling (“Sport” mode). I chose the “Comfort” mode for the test shown above and for most of my highway driving, where I wanted to insure the smoothest possible ride when the road unexpectedly became rough. During the last 90 minutes of my trip, I was exclusively on winding two-lane mountain roads, and I switched to the “Sport” mode for better handling. The effect was very noticeable — the usual leaning around tight curves was very limited, and when I sharply changed directions, the typical side-to-side swaying was greatly reduced. Sumo Springs also help with this, but this is a major improvement over what my Sumo Springs were ever able to do. Frankly, I never suspected that my coach could ever handle like this on winding, twisty roads. And I should point out that even without switching from one mode to another, CLASS is constantly modifying its response based on sensors that are evaluating the road surface and how you’re steering.
The second benefit from the LiquidSpring control panel is the ability to adjust the rear coach height up or down by 6-7 inches. If you are driving out from a steep driveway and want to avoid scraping the bottom rear of the motorhome, a single button press will raise the coach over the rear axle in a matter of seconds; it will then reset to normal height as soon as your speed reaches 10 mph. These height adjustments can also be helpful when camping on a non-level site. It’s important to have the motorhome leveled before extending the slide-outs, but I have been at campsites where the only way to be level is if the automatic leveling jacks lift the rear tires off the ground. That’s not safe, since your parking brake is working only on the back wheels. The LiquidSpring system allows the rear tires to extend much further, helping to stabilize the coach on a non-level surface.
Unfortunately, there are still some questions that my limited experience doesn’t let me answer (yet):
- How is the ride in the back of the coach? This is, of course, where LiquidSpring’s rear suspension modification should be having its greatest impact, but my solo road test didn’t allow me to evaluate that (other than noticing the reduced rattling and creaking from behind me).
- Does this system help the motorhome deal with crosswind gusts? My entire driving day had little or no wind, so I don’t know the answer yet.
- How does this compare to other rear suspension modifications? There are many other choices for gas chassis rear suspension enhancements (such as the Sumo Springs that I traded out), including upgrades for sway bars, shock absorbers, trac bars, etc. As I mentioned in part 1, the big difference between all of those solutions and CLASS is that they are passive rather than active systems. Even though they may improve the ride or handling, they are optimized to help over a narrow range of driving parameters — not to constantly adjust to road conditions like the LiquidSpring system.
- Is CLASS as good as an airbag suspension? Having never driven a vehicle with airbags, I have no idea. And as I’ve pointed out previously, there are no aftermarket airbags available for Tiffin gas chassis motorhomes.
- Will this system be adopted as an option for factory installation at Tiffin? That would certainly make installation easier and cheaper, since it could be done to the chassis before the rest of the coach parts are in place. But I have no idea whether Tiffin would consider this from a marketing standpoint. After all, they sell every Allegro Open Road motorhome they manufacture even without offering this system.
- And finally, the magic question: Is it worth $12,000? For me, yes, since we have been traveling close to 15,000 miles each year in our motorhome, and a lot of that has been over less than ideal highways. Had CLASS been a factory-installed option from Tiffin, I would have selected it, since I think this is still a very small investment compared to choosing a similarly outfitted diesel chassis motorhome with an airbag suspension.
Those are my initial impressions, and I hope they give you a sense of what LiquidSpring CLASS does, at least from the driver’s seat perspective. My limited road test has already convinced me that this is a fundamental improvement in ride and handling, with the net result being a more relaxed and comfortable driving experience. Yes, it’s priced accordingly, but right now I think it is the best single suspension improvement you can make for a gas chassis motorhome.