Rear suspension battle - Ride quality while towing trailer on crappy highways, etc. Time for better matched shocks?

[DRAX]

While it's pretty much impossible to have a Goldilocks setup that is great for all use, I have to do something about the on-road ride while towing our trailer. The main issue is expansion joints and other "sharp" bumps in the road that basically turns my rear suspension into solid metal sticks. I suspect the shocks I have back there are the primary cause and the valving just doesn't work with high load and sharp/quick suspension hits. During the drive back to IL from KOAR yesterday it was just horrid thanks to the roads we have around here, on the slower country roads I started paying close attention to how each sharp bump felt as the front, rear, and trailer axles went over them and 90% of the harshness was from my rear axle hitting the bump.

What have other folks done if they've experienced this? When not towing the ride is ok, and towing or not the more rolling bumps and dips are fine and get soaked up just fine.

Rather than wanting to play around with trying to find a well-rounded non-adjustable rear shock I ordered something I haven't used in over 20 years...a pair for Rancho RS9000s in the appropriate length for my truck + lift. I'm hoping this will give me the ride I'm after while towing by playing with the adjustment and just be able to adjust it based on road/terrain/ride quality in general.

My rear springs (as listed in my sig) are Deaver expedition leafs that give me about 2" of lift over stock with just my topper and Decked drawers and puts me at about 1.5" over stock when the trailer is hitched up.

I thought it might be the trailer itself tugging/jarring over the bumps but it's smooth and not jerky or harsh.

Anyway, hope the different shocks take care of it (or most of it). Not sure what else to do that doesn't involve a lot more work or re-engineering.

 

[smritte]

Have you driven that route without the trailer? Suspension tuning can be a pain.

I run a set of air bags and adjustable shocks. Without the trailer I run 10 psi in the bags and my shock settings close to mid. With my trailer, I run 40 psi and a few clicks up on my rebound and dampening. My gear pretty much stays in the vehicle and I only add on two fuel cans and a water can to the tailgate. My tongue weight is around 80 lbs.
Without the fuel cans my shocks (on the highway) are a bit stiff but not bad. I don't remember the brand but one of my friends had remote adjustable shocks.
Depending on where I go, I change my settings to suit. Normally its just a few clicks one way or the other. I need to pull out my fronts and revalve a bit stiffer. My dampening is maxed out most of the time off road

If you wanted to be a bit more precise, weigh the truck (front and rear), calculate how much your rear tires and axle weighs and tongue weight. Send Deaver an email asking if their springs are proper for what your doing. They may or may not suggest adding in more spring. Most of my setups, I end up swapping out the springs a couple of times to get it right. This time I added in a set of poly bags that fit into the springs. I should have done that sooner on this rig due to the trailer.
When it comes to shocks buying the correct combo is going to be hit or miss with the valving. The shock manufactures guess what the customer will be running and make most the same. A good shock tuner will guess at what's needed and get close if he hasn't driven the vehicle. If your unhappy, he will tear it down and change it based on what you tell him.

 

[DRAX]

Have you driven that route without the trailer? Suspension tuning can be a pain.

Yup, most of the roads are similarly crappy here in Illinois.

I run a set of air bags and adjustable shocks. Without the trailer I run 10 psi in the bags and my shock settings close to mid. With my trailer, I run 40 psi and a few clicks up on my rebound and dampening. My gear pretty much stays in the vehicle and I only add on two fuel cans and a water can to the tailgate. My tongue weight is around 80 lbs.
Without the fuel cans my shocks (on the highway) are a bit stiff but not bad. I don't remember the brand but one of my friends had remote adjustable shocks.
Depending on where I go, I change my settings to suit. Normally its just a few clicks one way or the other. I need to pull out my fronts and revalve a bit stiffer. My dampening is maxed out most of the time off road

That's my plan with the RS9000s as well, figure out which settings work best on-road and off, with and without the trailer, and hopefully end up with a more well-rounded ride.

If you wanted to be a bit more precise, weigh the truck (front and rear), calculate how much your rear tires and axle weighs and tongue weight. Send Deaver an email asking if their springs are proper for what your doing. They may or may not suggest adding in more spring. Most of my setups, I end up swapping out the springs a couple of times to get it right. This time I added in a set of poly bags that fit into the springs. I should have done that sooner on this rig due to the trailer.
When it comes to shocks buying the correct combo is going to be hit or miss with the valving. The shock manufactures guess what the customer will be running and make most the same. A good shock tuner will guess at what's needed and get close if he hasn't driven the vehicle. If your unhappy, he will tear it down and change it based on what you tell him.

I haven't spoken to Deaver directly, but this leaf pack is intended to carry more weight than stock (basically provide their stated lift amount while carrying 450LB of additional weight). I'm not having issues with too much load/weight and I'm not hitting the bump stops, the low-speed ride quality and suspension flex is great, I don't feel like the truck is over-sprung. They also claim "Combined with properly valved shock absorbers, the ride is enhanced beyond belief." and since deciding I need to do something about the ride when towing on rough pavement I started paying closer attention to the ride while not towing, specifically how the rear feels going over bridge joints, expansion joints, etc. The concern is still there when not towing, it's just not as pronounced as the chassis is better able to absorb the impact without the tongue weight of the trailer pushing down. Ever since I redid the rear suspension it has been more firm, and I've actually towed this trailer close to 10k miles so far, but the route last weekend was a little different and the expansion joints were perfectly distanced for maximum impact at cruising speed.

The shocks I ordered when I ordered the springs weren't matched, they were the only ones listed for my truck that were meant for 1.5-2 inches of lift (lift blocks) with the OEM springs. This time, rather than trying to find shocks listed for my truck and my amount of lift I ended up looking at the compressed/extended lengths needed for my lift and then ordered RS9000s that matched.

I'm pretty confident that this will really help address my ride problem, I don't recall anyone saying anything negative about their ride with Deavers, they've all been positive. Similarly, when I ran RS9000s in the past I was quite pleased with the range of damping settings they allow.

Definitely appreciate the help and working through the issue, trying to build a dual-purpose truck does have challenges. :D

 

[smritte]

Most of my leaf spring buddies run Deaver. I love how smoothly they build their progression springs. Like you said, your issue is going to be more shock related.
You stated your rear drops about an inch with the trailer. That confirms the springs are at least close.

The vehicles reaction to your drive over the expansion joints is what my industry calls "porpoising" (spelling?). One of my old trucks wheelbase was horrible on the roads out here. Now I just turn the rebound down a little.

 

[MidOH]

I'd have to drive it to diagnose.

Usually people are undersprung and extremely underdamped.

But you should feel the road. Smooth isnt safe. Good towing trucks will have a firm, but controlled ride.

Harshness is often springs and shocks that are too soft. Hitting bump stop, bouncing off the road. And/or porpoiseing or the Chevy rocking chair effect.

 

[DRAX]

I'd have to drive it to diagnose.

Usually people are undersprung and extremely underdamped.

But you should feel the road. Smooth isnt safe. Good towing trucks will have a firm, but controlled ride.

Harshness is often springs and shocks that are too soft. Hitting bump stop, bouncing off the road. And/or porpoiseing or the Chevy rocking chair effect.

I'm not new to towing (have had multiple HD diesel pickups and various trailers), definitely not undersprung, not wanting Caddy boat smooth, not hitting the bump stops (The bumps in question aren't big enough to cause full compression of the suspension anyway). Think riding a hardtail bicycle over a pressurized garden hose. The high-speed damping of my rear shocks is just too harsh and a poor match for my springs, which provide lift and are meant to carry more weight constantly compared to stock. It is 100% not porpoising or getting into a cyclic bounce, it's one hit and done. Think of someone kicking the bottom of your chair. Hard.

The harshness is still there when not towing but without the tongue weight of the trailer the chassis is able to absorb this better and not transfer it to the cab/driver, but if I pay close attention I can still feel the rear suspension just isn't compliant enough for those sharp, high-speed impacts.

The replacement shocks I ordered should arrive on Friday so hopefully I'll have an update over the weekend.

 

[MidOH]

20" wheels?

 

[DRAX]

20" wheels?

17" with 265/70R17 tires that I run between 32-35PSI most of the time.

 

[madcratebuilder]

If you don't see a improvement with the new shocks I would recommend a set of Timbren or Sumo bump stops. I have Deaver M65's, decked with 300lb load, Timbren off road stops. Recommend a chalk test for tire pressure, it makes a big difference in ride quality, I run 30psi in my 255/80 E rated rears.

 

[DRAX]

If you don't see a improvement with the new shocks I would recommend a set of Timbren or Sumo bump stops. I have Deaver M65's, decked with 300lb load, Timbren off road stops.

Buuuut those would add resistance, not help. Like I said, I'm not bottoming out. See. No clean, clear witness marks showing the bump stop is contacting the pad on the frame.

Recommend a chalk test for tire pressure, it makes a big difference in ride quality, I run 30psi in my 255/80 E rated rears.

My 265/70R17s aren't LTs and they ride well at 30-32psi even off-road. I do air down if I'm going to be traveling many miles off-road, like when we're in Colorado, just so we can go faster more comfortably, but basically running 35PSI on average has worked out very well. I haven't had to rotate my tires. Ever. They wear perfectly and evenly front to rear. Now, that may change as I installed a front lift earlier this year and I'm running Duratracs for the first time, which I can't say I'm a fan of, but we'll see. If I had LR E on my truck I'm sure I'd be running lower pressures to avoid a harsh ride.

 

[MidOH]

Duratracs are good tires. Rotate every 10k.

Their downside is that they arent a heavy armored offroad tire. They're a soft AT carcass, easy to tear through.

 

[DRAX]

Duratracs are good tires. Rotate every 10k.

Their downside is that they arent a heavy armored offroad tire. They're a soft AT carcass, easy to tear through.

A lot of people really like them, my main complaint is their noise. Not sure how well they're going to wear yet, but compared to the Wildpeak A/T3W I ran previously the Wildpeaks were a better all-around tire.

 

[DRAX]

Ok, update time! Partial update, anyway, since I haven't testing towing yet.

After an order snafu, I received the proper shocks today and put them on this evening (What should be a 15 minute job takes about an hour thanks to GM engineers and the location of the DEF tank). Due to my lift there's not a lot of options out there specifically for my truck, so I had to go through Rancho's catalog and find the best match in terms of length with the correct mounts, which means I ended up ordering shocks that were meant for GM full-size trucks/SUVs with no lift. The piston and shaft are quite a bit larger than what you'd find on a mid-size truck so I was a little concerned that I might end up in the same boat I'm already in, however once I had one of my old shocks off I was able to feel the difference in damping between the two (RS9000 at lowest setting vs shock I took off), the RS9000 was a lot more compliant.

So, long story not so long, with the RS9000s set to their lowest setting and not towing anything (But shell on the bed, Decked drawers, etc still on the truck) the ride feels like it matches my Fox 2.0 coilovers up front exactly. Rides great on the freeway and no more feeling like the rear axle is almost solidly mounted to the frame when going over sharp bumps in the road. Super happy so far!

I plan to get the trailer out and do a tow test on Saturday to see how it feels now. If it feels too soft then I'll kick the shocks up a couple of settings.

Hooray for a positive change!

 

[DRAX]

Alright, probably my final update on this thread. I pulled the trailer out of the garage and took it on a test loop with some roads that I know were awful with the previous shocks, some lower speed (45MPH country roads) and some freeway speed (75MPH over some rough, chunky overpasses). I'd say overall there's an 80% improvement in ride quality. It's not "I can't even tell there's a trailer back there" smooth, nor would it ever be (I don't know why people say they can't tell their trailer is back there, I can always tell no matter the vehicle or the trailer), but it's a huge improvement. Feels well-planted and stable, the best test was one of the local overpasses that has been patched, has various cracks and holes, and somewhat rough joints at each end. The truck and trailer nearly floated across those bumps without a care in the world. No more feeling like I'm getting kicked in the butt over bumps.

I'd call this a success!

About the only thing I'd change, and I might have a local shop do this, is lower the front coilovers 1" or so. The springs never settled as much as Fox expected, so I'm a little higher in front vs the rear even unloaded. For those that are curious, ground to fender lip above the center of the wheels.

Unhitched:
Front: 37.8"
Rear: 36.9"

Hitched:
Front: 38.0"
Rear: 36.3"

So the front lifts 0.2" and the rear squats 0.6" when hitched. I've yet to get an accurate tongue weight for the trailer, if I had to guess it may be around 450LB.

 

[smritte]

It's going to be difficult to do better than that. You would be looking at a shock with more adjustment and playing with progressive springs. If you like it, I would count it as a win.

 

[DRAX]

It's going to be difficult to do better than that. You would be looking at a shock with more adjustment and playing with progressive springs. If you like it, I would count it as a win.

Indeed, and I'm hesitant to mess with the front coilovers. The only adjustment for height is to reduce the preload and then that will make the front softer, which is already sorta-soft since the spring rate is less than the factory coils (coilovers setup for a gas Colorado/Canyon when I have a diesel that's a little heavier. IIRC, my factory springs were 650lb and the gas are 500lb).

No such thing as perfect and my truck is also my "daily" driver (I work from home) so at this point I think I'm pretty well set up for how I use my truck.

 

[MidOH]

Preload has zero effect on spring rate, unless we're talking about extremely progressive springs.

Go ahead and lower it. If it sucks, get stiffer front springs and try again.

I jack up the truck so theres no load on the coil over, to adjust.

 

[DRAX]

Preload has zero effect on spring rate, unless we're talking about extremely progressive springs.

Go ahead and lower it.

Yeah, I had to visualize in my head what would be changing and realized it wouldn't be changing the compression of the spring with the load of the truck on it, only lowering it and changing at what point in the strut's travel it rests at.