Airing down

[luthj]

High frequency low amplitude road variation is difficult to absorb at the damper level, its best to absorb it at the tire level. A tire is both a spring and a damper. The air pressure is the spring, and the internal friction of the rubber is the damper. Reducing tire pressure allows you to get an inch or two of soft spring travel without killing your handling, and since most of the suspension weight is "sprung" with regards to the tires pseudo spring, it has a very good response to high frequency.

 

[JPaul]

Off road hand books are typically written for neophytes, however most have a feat least a few nuggets of worth while information. I will occasionally browse one that I haven't seen (usually they just have a different cover).

Airing down to improve the off road ride indicates that, to me, that you may be running springs that are too stiff (sometimes necessary for load carrying with pickups... I long ago found short wheel base vehicles to be more maneuverable than pickups.
I have found for trucks that the ride often improves when they are moderately loaded but off road they are much easier to get stuck.

Tires with excessively stiff sidewalls also affect the ride (I have a set of load range E tires that are not fit to use for this reason).
Shocks do not have to be particularly expensive to give good ride but they do take some effort to adjust (with rebuild-able shocks) or to match the spring rate with over the counter shocks (avoid "off road and heavy duty shocks they typically have a harsh ride ride as they are often "designed"? for the higher spring rates (again harsh ride) of lift kit springs. I takes a very friendly counter guy at the parts store to get a good match of the shock length and travel along with the valving if you want to use over the counter shocks... (I used to use Monroe shocks from some GM product on a CJ along with custom assembled spring packs , to get a good ride).

It usually takes me several months to optimize the ride of a new/old vehicle. One of these days I will get around to weighing each corner of the Rubicon, then order springs and rebuildable shocks (not cheap but more adjustable) to improve the less than acceptable factory ride.

Having been both a member to the go-fast/handling community and an avid off roader I have found that mostly shocks most affect the ride (too soft or too harsh) and transitional handling while entering and leaving a corner. IMO people often over complicate shocks.

Don't get me wrong airing down has its place. but the frequency of use is usually directly related to the optimization of the vehicle.

I don't normally air down even for dry, fine (between flour and sugar) sand. however I always air down for show wheeling in deep (usually powder) mountain snow.
Part of this is because I find that a light vehicle (around 3500 pounds) helps everywhere off road, and I typically optimise my air pressure ona and off road for full tread contact (regardless of mileage)

Enjoy!

Tuning springs is an option, if it's actually an available option. Unless I want to drop several grand on converting my torsion bar IFS to a coil spring solid front axle (tempting, but out of the question for the foreseeable future), I am stuck with the spring rate the factory gave me. The rear is another story since those are leafs, but I'm not going to soften them up to improve the unladen or less laden load. Then I am stuck with having to rely on air springs to handle load over the new designs limits, and if those fail on the trail then I'll be in a really bad spot.

Unless you're building a dedicated trail rig that will always have a certain lading, you're better off leaving the springs alone.

Tuneable shocks is an option if you are ok with dropping a couple grand on those too. Again, I can only either get pretuned shocks, or adjustable shocks. I cannot simply go to the parts counter and thumb through a shock catalog unless I am ordering custom built shocks for my front suspension.

I think you're missing the point that not only do most people not have that kind of money and time, and most are building rigs that are also their daily driver so it needs to be tuned to the street as well, but also not everyone is running rigs that use super common parts that they can swap out at their whim. Anyone with an IFS (which is becoming far more common than solid axles unless you're talking about Wranglers and 3/4 ton and up trucks) is pretty limited to spring and shock choices, if they even have any.

OME used to make torsion bars for the Hummer H3 for example. But they stopped a while ago, plus you could only get ones that were stiffer. I have the Alpha with the V8 so as for the factory choices I have none, the 3.7L guys can go up the the stiffer Alpha bars to compensate for a bumper and winch though.

Plus if you're changing your spring rates then you should also be changing your shock tuning. Otherwise you will end up with over or under damped shocks, neither of which are good. So that gets pretty expensive for a good number of people. And you talk about neophytes airing down and shouldn't because they don't know how to drive offroad, but they are supposed to spend months tuning their suspension which they *definitely* won't know how to do, or paying someone else through the nose to do it for them? Not very good advice in my opinion.

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[Metcalf]

To achieve the level of tuning required for a general purpose vehicle that could see a whole range of terrain, slow technical, wash board, pavement, etc. would require multi-rate springs, e.g. progressive or stacked, and bypass shocks. It's possible to do of course but complex to tune all the circuits and very expensive. It's just more practical (and easier on budgets) to use tire pressure where it makes sense, like softening corrugation.

I think spring rates can stay consistent for a variety of terrain, but the main issue is they can't really stay the same for a variety of loads.
Multi-rate springs don't really do much for off road performance in my opinion.....and tend to make shock tuning more difficult.

I do thing there is a big difference in velocity sensitive shock tuning and position sensitive tuning ( ie a bypass ). You can do a LOT with a good linear tuned shock though. I do think that there could be some ride quality improvements to be had with a bypass, but I don't think many are tuned that way. They also have a noise factor. Internal bypass shocks is changing some of that.

I do agree that using tire pressure is the way. In my opinion, it does more than all the suspension tuning mechanisms can. The only downside is that when you start running REALLY fast off road you can't use air pressure as much as a tuning tool ( unless you stop and adjust for different terrain ). The KOH racing stuff is a good example of this. Rock section performance is suffering because you have to run more air for the really fast desert and cobble sections to prevent rim damage.

 

[billiebob]

They let you drive on some dunes in Colorado, just not at the Great Sand Dunes NP.

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Excellent pictures of where floatation tires and airing down work......
AND weight reduction.

All depends on where you wheel. Even the beaches where I live are solid. So floatation and airing down are not a factor.


On rocks a small contact patch works well. But airing down so even a skinny tire can conform to the surface is critical. I still prefer a tiny pliable footprint at 15psi to a massive floatation tire with bead locks ability to air down to 5psi. Airing down works everywhere but a massive contact patch with too low a ground pressure might act like an air mattress on marbles.

And unless you are trailering yer rig, that rig needs to be pavement friendly too. That is where I really prefer skinny tires. There is not a metric where a floatation tire outperforms a pizza cutter on pavement. Ride, mpg, traction, are all better with a skinny tire.

In the dunes, an aired down floatation tire is unbeatable. In the rocks a massive aired down floatation tire will need less focus on tire placement but often an aired down pizza cutter will keep up with skillful driving. Tire pressure is the single most important factor to a tires performance.