Bronco Sport First Edition in SoCal Desert

[fdes]

It's to keep the tires from cutting down into the sand. Deflating makes the tires wider.

The wider the tires are, the larger the area that the load is distributed across, and therefore the less stress is placed on the sand (stress is force/area). The lower you keep the stresses on the sand surface, the less likely it is to "break" (i.e. have the tires cut down), and the more traction you'll have and the less barriers (ruts) you'll need to move through.

You'll sometimes hear this called "flotation" because the tires "float" on top of the sand, but that's kind of a misleading term.

So, yeah, traction, but a bit more nuanced than that.

Thanks for the great explanation. Any downsides to airing down, wouldn’t it expose the sidewalls to possible cuts if there are any sharp rocks or is it really not a concern?

Do you guys air down whenever you go through sand, or stay at normal pressure to see if needed first?

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[jofer]

Any downsides to airing down, wouldn’t it expose the sidewalls to possible cuts if there are any sharp rocks or is it really not a concern?

Take all of this with a grain of salt, I'm hardly an expert, but here's my $0.02 if it helps...

Airing down limits performance (including safety-critical things like stopping distance) on pavement significantly. That's the biggest concern. There's a reason you don't want it that way all the time.

If you expect to be going back and forth between roads and sand/etc pretty frequently during the trip and don't want to air up/down repeatedly during the day it's often best to compromise in both directions. Yeah, you have a higher risk of getting stuck by only dropping your tire pressure to, say, 20psi, but it's better in sand than 35psi and way better on the pavement than 10psi. Just air back up before you take that highway drive home.

In general, tires are less likely to take damage/cuts/etc when _underinflated_ than when overinflated. Basically, a stiffer tire (higher air pressure) is more likely to break/get cut/etc on rough terrain. A tire will bend around that sharp rock sticking out of the sand at low pressure, and get cut at high pressure.

However, airing down too much on tires that weren't meant to operate that way can definitely cause issues.

Like you said, you're putting the sidewall in contact with the ground, and all-season tires aren't designed for that. (All terrain tires usually have extra tread on the sidewall specifically so they work well when aired down.) Similarly, if you air down too much in any tire, to the point where the sidewall actually folds tightly, you'll definitely damage the tires. For that to happen, you've got to have the air pressure really low, though.

Broadly speaking, look at the tires. You want a soft bulge, but never a fold. You don't want to see the smooth part of the sidewall sitting on the ground. Don't pay too much attention to exact PSIs, as it will depend a lot on the tires/etc, but you probably shouldn't go below or even fully down to 10psi if you're not running off-road tires. Things start to come off the rim at low pressure, too.

Do you guys air down whenever you go through sand, or stay at normal pressure to see if needed first?

Personally, it depends on what I'm driving on. If everything (including the access road) is hard-packed, you don't need to air down. As soon as you get into the soft stuff, though, it makes a huge difference. If you're not going far and you know it's hard packed, sure, don't bother airing down. If you don't know or if you're going a long distance, air down. The second you need to pass someone or drive around something and wind up in the softer sand, you can get stuck really quickly.


On a side note, it's worth getting a better-than-average air compressor (as well as tire deflators, so you don't have to stand there with a stick gauge and wait for the pressure to go down) if you want to drive in the sand frequently. Next, bring a shovel. Airing down and having a shovel will get you out of most of the issues you'll get into in the sand. Traction boards are great, but a shovel is more important and really cheap.

 

[fdes]

Thanks again Jofer, great advice!

 

[Cactusjk]

I have BFO KO2s (245/65/17) and plan on airing down to 18 psi using Stauns for general purpose off road.

Off-Roadeo recommended 20 psi but having set Stauns before I am going with the preset.

Any issues?

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