Optimizing suspension for washboard?

[pappawheely]

"Suspension" has many moving parts. The most important thing is your spring rate. Then it's the correct valving in your shocks. Most people are nowhere near where they need to be. The simplest fix is like many have said; to air down. To be honest, I've never tried 4-HI. I will give that a shot. Most of the roads I am on are trails and have much bigger bumps.

 

[*TRD*]

There are four things that impact performance on washboard:

Tire "spring rate" - eg, airing down is better
Suspension Spring Rate - Most lift kits are way too stiff IMO
Shock Valving - Lots of opportunity for improvement here, will expand on this
Suspension Geometry - steep angles can transmit harshness

When it comes to shock valving there are a lot of trade offs. Super soft shocks ride great on washboard but will bottom out too easily. We can optimize washboard performance with some of our new valving techniques while retaining decent bottoming control. But someone concerned with mixed terrain that includes long stretches of washboard are still best suited to an adjustable shock.

A slightly related note is that washboard absolutely kills shocks due to the extremely fast movement and heat build up. Most expo rigs probably need 2.5's if they're going to hit washboard at moderate speeds.

 

[Betarocker]

I've noticed on my new 29er mountain bike that the larger tires roll over obstacles which my 26er would either jam into or require a wheelie to smooth out the transition. The same would apply to trucks as a smaller tire would impact higher on the tire.

 

[comptiger5000]

Anything with lots of unsprung weight will be rougher on washboard. Suspension can mitigate it some, but the less unsprung weight your suspension has (axles, wheels, tires, etc.) relative to the sprung weight riding on it, the better it'll ride on washboards (the suspension will be more able to soak it up and control it).

 

[Martinjmpr]

WRT airing down, it's strange to me how many people are so resistant to it.
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In our camping group, there are a lot of people who have 4wd trucks and SUVs (we are based in Colorado, after all) but most of them are not "4 wheelers" in the sense that they rarely (if ever) actually deliberately go on a 4wd trail. Instead, they have 4wd for snow and ice, or because 4wd trucks/SUVs are generally considered to be better for towing.
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On many of our group's camping trips, I'll lead a "day ride" to some interesting or scenic place (on our last one it was to the slot canyons along Hole-in-the-rock road, but previously we've gone through Cathedral Valley at Capitol Reef NP and back in May we took a great trip along the old railroad bed that followed the Navajo River from Colorado into Dulce, NM.)
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If we're on a rough or washboard-y road (which is often) I'll always recommend to everyone that they air down their tires. And I always offer them the use of my compressor when we get done. And yet, the only people who ever air down are those who are experienced 4 wheelers (and who usually have their own compressors anyway.) I've tried telling people, again and again, that if they'd just air their tires down, they'd have a much better time but they still refuse to do so.

 

[Comanche Scott]

Last weekend the '07 Ram 2500 4x4 cc/sb got weighed on a CAT scale. The front axle alone was 4,480lbs...
That is heavier than some of my previous rigs total weight.
It really made me think about the amount of energy stored/released in the springs. Also made me think about the punishment the tires will see on the trail.
I'm definitely looking forward to following Regcabguy's thought on tire pressure, since our rigs are probably fairly similar in weight on the front axle.
Initially I was thinking to try 35psi, but after reading that post will probably start at 30psi.
Another advantage to airing down is the increase in puncture resistance.

Thanks to Regcabguy. :beer:

 

[Trikebubble]

I'm in the middle of building my Tundra for extended backcountry forestry road type travel, which will always include a lot of washboard type travel. I have a Four Wheel Camper in the production line as I type, and I have outfitted my truck with all new suspension components. After way too much research and talking with people I went with ADS Racing Shocks all around. 700 pound coils up front to handle the bumper and winch, front's with external adjustable reservoirs, and rears with external reservoirs and triple bypasses. I also added OME Dakar leaf packs and airbags to help with the added load. I spoke with MCM Fab (where I ordered my ADS stuff from), they recommended the particular shocks and coilovers and set them up for the type of travel we most see ourselves traversing.
I don
t have the Four Wheel Camper yet, but I've traveled some good wahsboard so far, and I have to say these ADS Racing shocks soak it up very well.

 

[Stryder106]

As others have mentioned - 1) Air down to about 25 (don't go below that if you are going to be trying to run at something above low speed); 2) 4Hi - power to the ground at both ends smoothes and stabilizes the vehicle; 3) Increase the speed (trial and error based on your setup); 4) Suspension - namely shocks. Not sure of your budget, but the Eibach Pro Truck Sport shocks were designed using my Avalanche and the 66 miles of roundtrip washboard to The Racetrack (and back) in Death Valley.
//
FWIW in my Avalanche, aired down to 25, 4Hi, with the Eibach's and fully loaded - I was running the DV washboard at 45-60 - smooth as could be. But, as mentioned - watch for dips - and don't use your brakes - just let off the throttle.

 

[txmxer]

Stock replacement coilovers with proper valving will make a world of difference, there are certain things you can do with valving stacks that will allow to soak up chatter bumps and little low speed bumps better.

 

[comptiger5000]

A caution when airing down for travel at any significant speed: monitor your tire temperatures. If you're running decently fast and the tires aren't massively over-speced in load carrying ability, you may not be able to air down a whole lot before tire heat (and damage) becomes a concern. In other cases, you'll have lots of wiggle room.

 

[LandCruiserPhil]

Airing down does not begin until 20psi YMMV

 

[hemifoot]

i'd pay money to watch someone run washboard with less than 20 psi.

 

[ExplorerTom]

i'd pay money to watch someone run washboard with less than 20 psi.

No video, but I ran the Colorado BDR north of I-70 at 15 psi. Most of it was dirt roads- some of it was washboard. Lots of it was done at 50+ mph.

 

[rruff]

I'm in the middle of building my Tundra for extended backcountry forestry road type travel.... I've traveled some good wahsboard so far, and I have to say these ADS Racing shocks soak it up very well.

I was surprised at how well my Tundra rides on washboard after I got new bigger tires. Stock was 255/70r18 (32x10)and I now have 325/65r18 (35x13). The new tires are LT also, and I do notice a little harsher ride on pavement, but it seems smooth on washboard for some reason, though I haven't been on really bad washboard yet. No load I'm running 35 psi front and 30 psi rear.

From what I've read airing down works the best. The bigger your tires for the load, the more you can air down generally. I think 20psi would be plenty for mine at 7200lb loaded; might go even lower. Need to make the tires your suspension, because it's too hard for springs and shocks to respond that quickly.

 

[comptiger5000]

Airing down does not begin until 20psi YMMV

No... Just no. Airing down is any time you reduce your tire pressures noticeably below "normal" for street use with a given amount of weight on them. If 60psi is "normal" for your rig, running at 40 counts as aired down.