Learn me airing down tires

Hey all, 

like the title says, learn me airing down tires for off road driving. The car in question is a subaru crosstrek on stock wheels and tires. The surface is mixed but mostly sand and then some small rock gardens. Stock pressures are mid to low 30s.

What’s a good pressure to start with? How low can I go before I have to worry about debeading or damaging the sidewalls? If the track is smooth and I want to hustle it through the turns will that cause any problems?

Im a total off road noob. Learn me!

You don’t have bead locks, you’re not airing down much. I have a crosstrek. With stock tires, you could maybe get away with 20psi. bring a spare tire already inflated on a spare wheel though, you will likely de bead. I don’t go on the crosstrek forums anymore due to ignorance by the (m)asses, thinking the crosstrek is a rock crawler. 

In soft sand, I go down as low as 12-15psi w/o bead locks. You need to drive/corner carefully at that pressure, but I haven’t had any drama yet. On mixed surfaces, you’ll  want more pressure than that.

How soft/deep is the sand? I've done many miles of off road in the Jersey Pine Barrens (sandy soil) without airing down. If the sandy conditions are like soft beach sand, yes, airing down is a good idea. I watched a few off road newbies drive down to the waters edge at the shore with no problems and get stuck in the deep soft sand as the tide was coming in. 

If you are airing down, you should have means of airing up with you as well.

A lot of variables.... sidewall height and construction, tire width, vehicle weight....

I would be concerned about getting much below 15psi if you're carrying any speed at all.  Now just getting it unstuck I might get down to 10 but that's getting risky for pooping a bead.

I have only aired down a Jeep for dune fun.  On flotation tires I ran 8-10 rear 12-15 front.  On an old CJ the most dramatic effect was the increased ride comfort.

How much you can air down depends largely on your wheel & tire setup. For stock wheels and tires, 20 would be totally safe, you could get down into the teens but the risk of a debead would be significant.

Bigger and wider tires squeezed onto a relatively narrow wheel is the next best thing to beadlockers. My Samurai runs 31x10.5s on 15x7 wheels, and because the tires are a squeezed fit onto the wheels and the sidewalls can do a lot of the work in supporting such a light vehicle, I normally run pressures in the teens (for mixed offroad/on-road driving) and I can get down into the single digits for lower speed offroad arena events.

Where I live we have a decent bit of open beach driving on very soft sand(not like Daytona). With the lowish profile tires airing down won't do too to much. Depending on the vehicle and tire setup I've driven on sand as low as 8psi but that was a 33x11.50 on a sand rail. Driving back to a gas station to fill up was "interesting." With modern lowish profile tires I generally stick to technique over airing down.

If 20 was de-bead territory about 10% of all the cars on the road would be on the side of the road. Having said that, I wouldn't try to get much from airing down on a fairly short tire because there's not a lot of sidewall there before things get crunchy or you at least pinch it and get a bubble. I would air down to get unstuck and that's about it.  My .02

I'd be a little concerned about airing down a P-rated tire. They don't have the strongest sidewalls. 

As has been stated there are many variables.

If you just want another data point.

Jeep Wrangler TJ ~3400 lbs, 32x11.50R15 tires, on aftermarket non-beadlock aluminum wheels.  I'm comfortable at 14 PSI in mild rock crawling. 

14 PSI is noticeably grippier than 18 PSI, but without beadlocks, I'm not comfortable going much lower.  I'm not burping air at 14, but I bet I'm close.

On a Crosstrek you don't have tons of sidewall height, so it's a bit of a different game than most big off-road stuff.  I'd plan to drop 5 psi out of the tires to start.  See how they sit on the ground, see how they feel as you drive.  Adjust from there as needed, but I probably wouldn't go below 20-ish.  

Keep in mind, airing down more than necessary sacrifices ground clearance.  So I tend to only air down as much as it feels like I need to.  If I'm not getting knocked around too badly and have enough grip, there's no need to air down more.