Restore Harmonic Stability to Your Chassis
Porpoising
End the Endless Oscillation
A guy called me up the other day and told me his Dolphin motorhome was porpoising. I told him it sounded like it was having an identity crisis (insert rim shot here).
Seriously though, porpoising is something we get quite a few calls on, and it is one of those terms that you hear about mostly with regard to RV’s. Porpoising is front to rear bounce; the front hits a bump, then the rear hits the bump, and they both bounce independently of each other, creating an oscillating motion. If the problem is severe enough, it can feel like you’re going to pull the wheels off the ground.
Don’t guess—schedule a Road Performance Assessment and let our team identify the root cause of your handling concerns.
The problem is more typical in shorter coaches (low 20-foot to low 30 foot) than long ones. You don’t have as much trouble when you head up to 37 foot and beyond, and we definitely have more problems controlling it on a short wheelbase coach. The reason is that there is more time for the bump to settle out between the front and rear wheels on a longer wheelbase coach. Anything from the springs on down is called “unsprung weight.” The heavier your axles and tires are, the more difficult it is to make them change direction. Because of the high amounts of unsprung weight on a motorhome, it’s been a real challenge for us. Between the wheel, tire and brake, you’ve got 300 lbs. there, and when it’s spinning, it’s like a gyroscope; it doesn’t want to change direction.
Changing out your shocks and sometimes your springs will usually diminish the problem significantly. On some of the IFS coaches, our Motion Control Unit (MCU) can help cut down on porpoising as well. Sometimes controlling airflow into and out of the bags can help in some applications, but not always. For example, MCU’s on some Freightliners; we’ve managed to get the side to side movement out of it, but then it started porpoising. I had a guy with a Spartan IFS chassis that he cut down some porpoising by putting on the MCU’s on the front.
On non-airbag coaches, good shocks will typically do the trick provided you’ve still got some decent springs. In situations such as these, we use the Koni FSD, and for the ultimate, the RoadKing 2-5/16 bore shock. FSD’s are good for rebound control, and the frequency selective damping takes some of the harshness out of the ride. The FSD valve is a secondary valve that they put in the piston head that dissipates the initial shock load. Most shocks are a linear rate; the harder you work them, the stiffer they get. That’s an age-old dilemma; you can make anything handle well, but it can end up riding like a lumber wagon.
We were fortunate to be involved on the protoype testing on the RoadKing. When we first experienced these shocks on a P30 chassis, it felt like we pulled 20 psi out of the tires and improved handling at the same time compared to a competitive shock. We’ve been working with King shocks for three years. What we discovered with them is, the bigger the piston the more range of control, and the smoother the transition could be from small amounts of control to great control.
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The RoadKing is a mono tube, high-pressure design which is the standard in high performance vehicles. It has the largest bore size on the market, so it has up to three times the volume of standard sized shocks. Standard pistons have 1.5 square inches of surface area; the RoadKing has 4.2 square inches—that’s 280% more surface area. The increased volume allows engineers to lower the required gas pressure in the cylinder, which gives you a smoother ride; the bigger piston also has more surface area to absorb the bumps. You also don’t have to run such tightly stacked disks in the piston head to control movement (check out roadking.com for more info). RoadKing shocks aren’t cheap, but they last longer than anything else and they’re also rebuildable. The Koni FSD’s are a 100 thousand mile shock; The RoadKings are run 350,000 or more in the trucking industry before requiring a rebuild.
great team
Our ASE-certified technicians are more than just mechanics; they are specialized experts who have been family-led since 1961.
amazing results
Our signature Road Performance Assessment (RPA), pinpoints the exact cause of your handling issues to deliver a ride that is noticeably smoother and more stable.
Competitive Pricing
We provide transparent value through our comprehensive inspections and performance assessments, giving you professional-grade results at a fair price.
Diagnosing
Issues
Our process starts with the Road Performance Assessment (RPA), where we test your vehicle under real-world conditions to see exactly how it behaves. From there, we provide specialized alignments, weight distribution adjustments, and suspension tuning tailored to your specific chassis.
Rather than just replacing parts, we use a systemic approach to identify the root causes of steering, suspension, and braking issues. Whether you’re driving a motorhome or a truck, our goal is to improve stability and reduce the physical effort required to keep your rig on the road.
We prioritize practical, engineered solutions that make your vehicle easier to drive and safer for your family.
Our
Services
The foundation of our work is the Road Performance Assessment (RPA), a systematic test drive that mimics the real-world conditions you face on the highway. Instead of guessing based on a visual inspection, we get behind the wheel to experience exactly how your vehicle behaves.
Once the assessment is complete, we use the data gathered to create a customized blueprint for your chassis. This often includes a combination of specialized alignments, weight distribution adjustments, and suspension tuning.
Our goal is to eliminate the physical effort of “white-knuckle” driving, providing practical, engineered solutions that make your rig more stable, more predictable, and safer for your family.
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We offer a comprehensive range of professional services performed to our own exacting standards. Whether you are looking for improved reliability, peak performance, or a smoother ride, our team is dedicated to providing specialized solutions tailored to your unique driving needs.
Contact us now to learn more about the expert services we provide or to schedule your appointment today.