Tire pressure vs size?

[bryan]

Hello all- I’ve looked around and haven’t found a clear-cut answer, so forgive me if this question feels redundant- I have a 72 Bronco and am running BFG A/Ts size 30x9.50 R15LT w/a 2.5” suspension lift uncut fenders and manual steering (prob more info than needed)- I’m a bit confused as to what tire pressure I should be running- i drive it primarily on the highway around town, currently almost never off-road- I find that w my manual steering it becomes pretty rough to steer when tire pressure is slightly low- I aired them up to 34 earlier today and noticed an improvement in ease of steering, but they still look very slightly low? On a similar note, anyone think I could get away w larger tires w/out rubbing/damaging my sheet metal on this setup? Thx in advsnce- Bryan

 

[bryan]

Oh and I know this question is coming- I’m running stock Ford EB rims

 

[Timmy390]

It depends......

Tires generally have a max pressure noted on them. Air pressure guide lines depend on the tire load rating.....C, D, E, and it they're LT or "P" tires. Sidewall construction and load rating are the factors in the sidewall "pooch".

My last 2 sets of tires 32's and now 33's had a sweet spot of 28-30PSI for the best handling. I tend to run a few pounds more in the rear than the front as I pull a small utility trailer sometimes.

I don't think there is a solid answer for you. It's all about what your rig wants as in what pressure it handles the best at.

Tim

 

[Nothing Special]

One thing to try is to draw a chalk line across the tire and drive it for a few tire revolutions. Then look at the calk line, if it's worn more in the middle you should try less air pressure, if it's worn more on the edges you should try more. Not saying that's the "right" pressure for you, but it should get you pretty close.

 

[Broncobowsher]

You will not find a clear answer, because there isn't one.

 

[DirtDonk]

That!

And the chalk trick is the way to go as far as I'm concerned. At least if it's not perfect, it gets you right into the immediate ballpark for you to tweak a bit here and there.
For the rear you'll be within a pound or two. For the front it will depend on your alignment because most will automatically wear the chalk off more on the outside edge due to the excessive (in some cases) positive camber settings.

But it's still a great test and gauge.
I think that most of us have actually ended up in the 28 to 32 psi range in the front, and about the 25 to 30 psi range in the back. But because every Bronco is different, and ever tire/wheel combination with that Bronco is different, and everybody's "butt dyno" is different, you might be able to discern a difference with every pound or two change you make in the tires.

Definitely worth experimenting with.
And that's exactly why most people looking for clear-cut answers with Broncos don't find one in print. The only clear-cut answers really define a "range" of parameters. The final answer comes at your own experimentation.

Good luck!
And definitely let us know what you finally land on for your favorite inflation pressure so we can see how it ends up.

Thanks!

Paul

 

[73azbronco]

I use peice of white paper, roll car onto paper, back off, look see it all tread touched it.

You really cant let air out untiul all the papper looks like its touched the same, just that some part of the outer inch or so did touch the paper.

My jeep likes 26psi. I run at 30 though for mileage.

 

[Broncobowsher]

The chalk or paper test will probably yield a lower then optimal, but functional pressure. Soft ride, fast tire wear with excessive cupping. Back in the 80s some OEMs were running mid 20s for tire pressure, tire rotation was required every 3000 miles (more often then even the severe service oil changes). After the Explorer firestone disaster and the tire pressures went up to mid 30s the cupping went away, tire life went up, and the rotation went up to the more normal 15,000 miles.

So while many try to run as little pressure as possible, there is a rather large window of what works and I prefer the high side without getting into wear issues. The bad part is you may not know you have wear issues until you have wear issues, and that gets expensive.

 

[DirtDonk]

What method do you use?
I've never used the paper method, but have touted the benefits of the chalk test for a long time and haven't noted any issues with it. At least not for my own use. Not sure how everyone else's has been working out.

But either way, I've never experienced what I would consider excessive tire wear, or any indication that a too-low pressure was indicated.
Always got way more miles, and with perfect wear since using these methods. In fact I usually wear out the tire internally long before the tread is gone.

Does anyone know what the original "official" tire pressure recommendations were for EB's with the different tire options?

Paul

 

[Broncobowsher]

Somewhere I have an owners manual for an International Pickup. It has pages of tire pressures. Different tires, different weights on the tires. All going back to bias ply tires as well.

 

[blubuckaroo]

Yes, you can use the wet pavement, chalk line, or tire bulge thing, but the best way to air up your tires is how it drives.
Too much pressure will make the vehicle wander. Too little gives less control. Either to an extreme will increase tire wear.

 

[Nothing Special]

Personally I've never noticed any wander from over-inflated tires. Ride quality and traction suffer, but other than symptoms of the worse traction I've never noticed any handling issues.

And the poor traction tends to require quite a bit more pressure. I've only ever noticed that when I leave my pickups load reange E tires at 80 psi after I've been carrying a load. I run the rears at 40 psi, and that big a difference results in it being easier to light up the tires. But 50 or 60 psi will give a significantly worse ride, as well as wearing the center of the tire pretty quickly.