How low tire pressure?

[rookieshooter]

Wondering how low can I go with tire pressure while driving in snow?
Goodyear mounted these 12.5 X 33s on 12" rims. Has a nice wide footprint.
They put 25#s in the tires. This was in the summer months. Seemed a little stiff. During the only snow we got so far I lowered them to 20# and really made a difference on the wooded trails I was riding and also on the pavement. I have no bead locks and curious just what is a safe low pressure. Maybe one pressure for trails and one for highway.

 

[rguy]

I don't drive on the street and don't have bead locks, but I run 12 lbs. on the trails in bias-ply tires.

 

[rookieshooter]

Thanks for your input. Next snow I'll try 15# and then if that works 12#. At least on the trails. If it worked so much better at 20# then 25#, I can't imagine how much nicer 12# will be. I would think mud would be the same?

 

[Anime]

You can probably get a few good suggestions from other running the same tires, but vehicle weight really comes into play, so keep that in mind. You might be able to get away with really low pressures on the trail if your rig is lighter. Be sure to air up if driving at any speed on the road and especially the highway, though, low tires build up heat, and can cause..problems. :roll:

btw, the new side mirrors = awesome. So much better than the metal cobjobs you were putting on before.

 

[gijoecam]

Here's a good rule of thumb I gleaned from the Oasis Offroad web site a few years back...

Set the tires at street pressure. (Obviously for other-than-stock tires, that specific pressure will vary) Then, measure the height of the sidewall from the ground to the lip of the rim. Then, to set the off-road pressure, lower the air pressure until the sidewall height is 75% of the height at street pressure.

That makes a good starting point. You can adjust up and down slightly as necessary. If they seem too soft under the front, put a few pounds back in. If they're still digging too much in the sand and snow instead of floating, drop a couple more pounds.

It's trial and error. Find what works for your rig and run it.

FWIW, I have a friend that runs those tires on his early (60s) Bronco. If my memory serves, he runs them around 12-14psi without a chance of blowing a bead.

-Joe

 

[rookieshooter]

Thank uguys for some really good info. It will be interesting to see what works best. And I'll do the percentage thing also and report back.
BTW, it is about 900 to 1000# lighter then a stock B2. Will be adding more weight to rear in the future, like High Jack and spare tire all mounted low.