• I drove it and towed with it for a combined total of around 1000 miles after fixing it this summer.
• The original plan was to use LC springs to reduce the amount of work, or weight, the AHC would have to carry. With the bumpers and all the accessories we really had no payload capacity left. So changing to LC springs would give the higher capacity of the LC and give me AHC to always have the same ride height indifferent to cargo load. We also tow a 31 foot Airstream and a 28 foot race car trailer with the LX, so I didn’t want to have the AHC limiting rear height or shutting down due to high pressures (which has happened to me a couple times) This was the easy part, working with the dynamic control of the AVS side is what became a balancing act.
• AHC (Automatic Height Control) and AVS (Adaptive Vehicle Suspension) work in conjunction and have an algorithmic mapping system for controlling valve blocks, ride height while underway, and damper valve positioning. Mapping is also mathematically weighted depending on driver selectable controls (comfort/sport switch).
• The LC springs reduce the AHC pressures at normal ride height and further reduce the rate of AHC pressure increases as the springs compress. However, what I didn’t account for was the LC springs were unable to match the amount of weight reduction as the suspension traveled. As the suspension drops, the AHC works more than it does at normal or compressed ride height. This will improve as the springs break in and get softer. What ends happening is a drop in pressure during downward travel and reduced AVS ability to dampen downward travel. This is compounded with higher unsprung weight and the stronger LC springs pushing downward travel at rates that are unexpected with the AHC system. Without computer modeling of what the AVS responses would be to different spring rates and the resulting AHC working pressures of complete suspension cycles and with different velocities, I have entered uncharted territory that could’ve made it dangerous to drive.
• I knew the risks and challenges going in, and I was okay with taking the time to try and dial it in. Since the LX had a lot of additional weight on it from the accessories, I figured that would shrink the margin of difference between the LX and LC spring rates. Thus getting me closer to original LX AHC pressures. Although the vehicle would have much higher inertial mass that would require more damping force to control vertical pendular motion. The LC springs help on the compression side and AVS can respond by reducing orifice size in the valve to increase damping under these conditions.
• As of right now I have installed the LC springs and drove it. I wanted to see if the AHC would lift the LX up a little since the accessories were compressing the LC springs some. But since they were new and all stiff they didn’t squat as much as
I hoped and there is a delta margin on when the AHC will begin adjusting vehicle height. So I changed the AHC offset to increase AHC ride height. This would set the AHC to keep the truck higher and put some pressure in the system at normal height, allowing the AVS to work (which requires positive pressure to work). I ha e done this a few times to find a happy equilibrium.
• There are other ways that the LC springs have changed the operating characteristics of the AHC and AVS. They are mostly due to the arc of the spring rates on the LC springs and how that influences AHC pressures. For example, when in normal, AHC pressures are lower than normal. however, when in height mode, pressures are higher than normal and ride gets more harsh than what you would expect. It’s not radically different, but noticeable to me. This is due to the nonlinear spring rate of LC springs. The rate drops off more rapidly at spring decompression/extension than the LX springs do. This is amplified by the higher AHC offset calibration to adjust AHC pressure and increase height.
This can be compensated for by adding vehicle weight and reducing AHC offset closer to stock, or waiting for the springs to break in and soften some, then Reducing offset closer to factory.
I hope this answers your questions and is detailed enough.
I mostly wanted to keep the AHC because we tow with it. Plus, it’s just cool to have the AHC functional in such a modified state. Being able to adjust the AVS for comfort and stiffen it up when towing does add a lot of control and is a very noticable difference in handling characteristics. I have and continue to debate changing to a conventional suspension with a lift kit.
I'd like to hear details of what went into getting the AHS working with the LC springs. Did you drive the truck much, or at all, with the stock springs and all of the new equipment installed? I am curious to know if there was an improvement in ride quality with the heavier springs, or if it was more peace of mind knowing the AHS system wasn't bearing as much of the weight?
