Suspension upgrades to improve handling in gusty winds

kmay

2013 Unity MB
Hello all,

I have been following the sway bar and air suspension discussions with interest. I started this Sprinter journey from a variety of info sources, one of which was the Advance RV web site. So "they" say air suspension is an important upgrade to improve handling in high crosswinds as well as eliminating the wandering from big rig bow waves and the turbulent air in their wake. I don't know if it is true or false, whether there are other alternatives and which would give one the most return on investment. I am not even sure suspension can resolve aerodynamics of a box.

First two days of our maiden voyage were beset with high winds and it took much of the joy away. In light wind, I was very happy with the suspension. I can modify driving enough to limit time in turbulence from the big rigs. I don't mind the rocking over big transitions, it seems constrained as well as a gentle reminder, this ain't a SL coupe. So I wonder if I need top shelf upgrades. Maybe just a little something to take the edge off the worst stuff.

Would someone drop a link to RV laden sprinter suspension 101? I have some car and light truck suspension experience but am unsure if any of that would apply here as we were always looking for less roll and consistent tire contact.

What would be the best suspension upgrades to improve performance in the aforementioned crosswind/turbulence?

What would help but not cost as much? I am asking for a value kit to compare against the best. Maybe a rear stabilizer kit, larger bounce stops and a front steering dampner?

Thanks,
 

NevadaBlue

Member
This will be interesting. My van will be 4x4 and the build list says it comes with some 'heavy duty' suspension parts. The machine is already a 2500 and I have found from experience that too heavy of a suspension can be worse than too light. I worked in mining all my career and we found that in general transportation use, heavy suspension beat the pickup trucks to death quicker.
Watching from here with interest.
 

calbiker

Well-known member
In order of best bang for buck:

1. Fox shocks modified for MHs. Get them from Agile Offroad.
2. Bigger sway bar.
3. Added leaf spring: Supersprings A-11.

A bigger bump stop will do nothing. Fox shocks are your best bet.
 

Old Crows

Calypso 2014 View Profile
Well, not knowing your year and model.... presume a Class C RV.

First.... BEFORE you do anything..... look at the tire pressure placard on the driver's side door sill. Do not set your TPs any higher than the suggested pressure for MAX Gross Vehicle Weight Rating. If you know you are a little 'lighter' you may back off a couple PSI. What you want is flexibility in the tire side walls.

The least expensive fix are SUMO SOLOs. Front and rear, although you could get buy with just the rear set up. That's what I have done. And, they kill the rocking side to side in all but exceptional situations. IMHO, you really don't want to increase the roll stiffness with a larger 'sway/roll' bar.

The next 'cheapest' thing you can do is to SLOW DOWN in strong winds. Faster you go, the more force that is generated on the high sides, front and rear of the RV. It already has a high center of gravity so it doesn't need any help to make it unstable.
 

Denis4x4

2013 Unity TB
Put Sumo Solos on last year and very pleased with how they perform. Best bang for the buck in my opinion.
 

calbiker

Well-known member
I don't see how Timbrens or Sumos improve handling in gusty conditions. These "rubber" springs do not get compressed when the rig leans slightly from wind push. The springs are not engaged.

You can do a simple test. Push against the side of the vehicle to get it rocking. It will rock at a 1 sec period. The ease at which it rocks is directly proportional to the amount the vehicle gets pushed off its line from wind. I've done the tests and recorded the data. These springs do not help. They have other fine attributes, but they don't help in gusty conditions.

Install the Fox shocks or the S-11 springs and you'll see a reduction of oscillations when pushing against the side of the vehicle.
 

ablock

Member
Did the Fox shocks and Sumo Springs bump stop installs yesterday on our 2016 chassis.

The Sumo Springs were super easy. You do have to jack up each wheel, but after that the job is cake: you could complete it in 5 minutes and have time for coffee. Snap out the old bump stops, push the forward tongue of the Sumo Spring into the slot, rotate the new stop upward until the aft tongue folds itself into place, done.

The shocks were a little more work. First of all, I think I read that the required somewhere socket is 19mm; it's 21mm. Once you have the tools ready (a 50-200 ft-lb ratcheting torque wrench will give you right range), the right side shock is pretty easy. The only challenge is that the modified Fox shocks are so well damped you can't change their length by hand. So you install the upper bolt first, then work the lower shock mount into place. Next, jack up the wheel until the length between the shock mounts matches the shock (i.e., when the holes line up). It took one or two raise/lower cycles to get right but it wasn't frustrating.

The left side is a bit more difficult. On our 2016 there is a linkage for a suspension length sensor (for the ESC?) that is attached to a pin that goes through the upper shock mount. You have to remove the pin to replace the shock ... but the pin is blocked by the sensor mount. The sensor mount is held in place by two 9mm nuts on studs threaded into the frame. Once you remove the nuts the sensor can be removed, but it remains connected by a fragile-looking cable. Removing the small ball end connector from the sensor linkage makes it easier to access the shock bolt. You will need a 21mm open-end wrench to keep the pin from spinning when you tighten the upper shock nut — hold it steady using the flats machined into the pin. Also, you'll need a 4" extension on your torque wrench to clear the tire.

After you reinstall the sensor, the lower mount is easy but requires the same dance with the jack.

The whole project took about 2.5 hours and was definitely worth it. Ride is significantly improved all around: coming out of driveways, cornering, and on the freeway.

Hope that helps someone.
 

calbiker

Well-known member
There is a simpler method to install the lower Fox mounting. The shock has 200 lbs of nitrogen. That makes the shock expand slowly. First install the top bolt. Then wait until the bottom bolt aligns as the shock expands.
 

Boxster1971

2012 Sprinter 3500 Ext
There is a simpler method to install the lower Fox mounting. The shock has 200 lbs of nitrogen. That makes the shock expand slowly. First install the top bolt. Then wait until the bottom bolt aligns as the shock expands.
That's what I did when installing Fox shocks on my Sprinter. But just compressing these shocks while laying on your back under my van up on ramps was a challenge. But then I'm old and weak.:lol:
 

calbiker

Well-known member
I wouldn't be able to compress the shocks I have when on my back. I stand one end on the ground and press the other end with all my weight. They'll slowly compress. Then get under the vehicle, install the top bolt and wait until the bottom bolt aligns.

I would have never guessed the vehicle needs that much damping.

That's what I did when installing Fox shocks on my Sprinter. But just compressing these shocks while laying on your back under my van up on ramps was a challenge. But then I'm old and weak.:lol:
 

Mineralfarmer

New member
I have a 2016 3500 4x4 and recently put in (on the rear only) Boss air springs and Fox shocks (from sprinterupgrades.com). The air springs (on mine, at least) are "engaged" or compressed all the time. I put 60 lbs of pressure in them to raise the back end about an inch. From the factory, the 4x4 is raised about an inch higher in the front than it is in the rear, so it sits nose-up.

They helped considerably. In addition to the height sensor on the left, which makes that side slightly more difficult, the 4x4 incorporates a spacer block for the leaf springs with a cast iron boss into which the lower bump stop is screwed. The lower bump stop has to be removed (55mm torx bit) and the boss to which it bolts has to be trimmed down about 1/4" with a grinder to allow clearance for the bottom spring plate of the Boss air springs. The upper bump stop is easily pried out, especially when lubed with silicone spray.

I have no doubt that the complete air suspension replacement, as used by Advanced RV and optional on others, would be far superior, as it eliminates the leaf springs altogether.
 

Trayscott

Member
Certainly glad nobody mentioned Koni Struts and shocks. 100 percent failure rate on my 2008 usually unloaded long and tall cargo van. The sprinter store told me the gas Bilsteins I put on up front after the second one failed, were not proper as it raises the front a bit due to the gas pressure. He must be stuck in the late 80's. Not sure I have had a non gas charged shock until I spent stupid money on the Koni's.
Still waiting on my refund for the warranteed Koni from them. Still have another to send back and as soon as the 200 bucks becomes available the rear will have the Bilstein yellows on the back.
I know traditionally yellow Bilsteins were an excellent upgrade for non sprinter motorhomes.
 

ablock

Member
There is a simpler method to install the lower Fox mounting. The shock has 200 lbs of nitrogen. That makes the shock expand slowly.
Not for me. After compressing the shock it expanded back to its resting position within about 3 seconds. Anyway there was no way to install the upper bolt and then compress the shock. I've seen guys use ratchet straps to compress the shock until the lower mount is lined up but the approach I used seemed more straightforward.

Thanks for all the advice, @calbiker.
 

Boxster1971

2012 Sprinter 3500 Ext
Not for me. After compressing the shock it expanded back to its resting position within about 3 seconds. Anyway there was no way to install the upper bolt and then compress the shock. I've seen guys use ratchet straps to compress the shock until the lower mount is lined up but the approach I used seemed more straightforward.

Thanks for all the advice, @calbiker.
Mine did the same thing which is why I compressed them under the van with great difficulty.

Ratchet strap was going to be my fall back approach but I was able to compress them by hand to get them into the bracket and then used a pry bar to get the bolt holes to line up.

I had to drive my van up on ramps to get under it to install shocks. I don't ever want to be under a vehicle when it is up on a jack.
 

jackfish

Active member
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calbiker

Well-known member
Seems your damping a little different. I have the bleeder shim/valve removed for absolute max damping.

As long as you're satisfied, that's all that matters.

Not for me. After compressing the shock it expanded back to its resting position within about 3 seconds.
 

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