Tire psi question

[redneck0372]

I just had my tires mounted on my slots a couple of weeks ago. A quick psi question for you guys the tires i have say 50psi cold, I only drive my bronco on street and gravel roads no 4wheeling being done and if I was going to drive in mud or snow id air down. Yesterday I thought my tires looked a little low so I checked them and they had 35psi to me thats to little so I aired them up to 45psi my question for you guys is what would you run them at for best mpg and tire life.

 

[red71sport]

whatever the sticker in the door calls for. probably 35. However, if your tire says 50 I guess I would go with 50

 

[Pedestrian]

I wouldn't run over 30.
You need to make sure you are getting full contact of the tread to the road.
Chalk your tires and check for full contact, adjust your air pressure from there.

 

[siderbox]

What size tires? What size wheels?

The psi number on the sidewall is a max for that tire.
The numbers on the door work if your running stock size wheel and tire.
Past that it's going to be a little trial and error.

But we'll need sizes to give any 'good' opinions.

 

[DirtDonk]

whatever the sticker in the door calls for. probably 35. However, if your tire says 50 I guess I would go with 50

Sorry red71, but I'd say that's not good advice on any vehicle. Yes, sometimes you do run the max stated pressure, but that number on the sidewall is only for use as a tire manufacturers maximum safe pressure rating for that tire and may or may not have anything to do with what you run on a given vehicle.
I had a Cadillac where I ran the fronts at the full 45 psi to get the best results, while on the rear, I ran as little as 28 psi in the same tire.
With my Bronco, my Armstrong Tru-Tracs were run between 32 and the 35 psi max rating, while my Swamper Thornbirds typically like (more than) the full 30 psi max in the front, but 20 psi in the rear is almost too much.
We would never have been able to run my buddy's 255x85x16 tires at the max rating of 85 psi on his Bronco, but the same tire on my fully loaded F350 might actually like it that high.

In my opinion too, going by the car manufacturers ratings doesn't fly anymore than the tire's ratings. Again, they "might" work, but not on every combination. That pressure was for the originally supplied tires, and those tires ONLY. Any change to tire size, weight rating, and construction method (bias vs radial) might have a massive effect on what a given tire/wheel/vehicle combo needs.

So, like siderbox said.
1. What size and load rating on the tires.
2. What size wheels?
3. What, if anything, has been done to the Bronco that might have added enough weight to effect tire pressure? Winches and bumpers? Full exo-cage? Custom Dana 60's front and rear?
You know, that kind of stuff.

Use the chalk method that Pedestrian mentioned and that's a good start. If you can't get out there right away, do a quickie search here for similar discussions. We had a couple just within the last few weeks I think were a lot of people replied with the exact tire pressures they were using in their setups. Some of them might be just like what you have.

Have fun! Oh, and "your results may vary", as they say.

Paul

 

[DonsBolt]

without knowing what size tire and wheel your running hard to say, but the psi rating on the tire is a maximum you can rum in them

As a general rule do what the specs for the vehical tells you.

On my bronco with 35's BFG's I run 32 in the front 30 in the rear. When I only had mud terrains, on the street I ran 28 all the way around, if I ran the mudd terrains and higher it would ride on the center of the tread

 

[Pa PITT]

I have 285/r16....But I do run on the farm all the times and on pavement just a couple miles a day ... I'm running 18 lb.s in mine..and will let them down some more when we get to New Mexico hunting.

 

[Broncobowsher]

Read all the tire sidewall. rated for 2500 pounds at 50PSI. Something like that. If you were running with 2500 pounds on that tire, 50 PSI would be a good pressure to run at.

Since you are dealing with conditions never originally planned for, tire pressures are going to have to be determined by you. Generally about 30 PSI is a good start. Too low and it will start to get squishy and will want to feel like it wants to wonder, especially in turns. Tires will have a lot more rolling resistance and get hot. Eats gas

Too much and the ride gets hard and the contact patch of the tire will change to a little strip down the center of the tread. Less rolling resistance unless the center of the tread is blocky then it could be worse. Tire life goes away as you are only wearing the center strip of the tire instead of the whole tread. Sometimes a couple PSI hake a huge difference, other times not so much. Play with some values and see what it does.

 

[redneck0372]

tire size is 235/75/15 the bronco is a 67 with a 200 6cly in it everything else is stock

 

[Broncobowsher]

tire size is 235/75/15 the bronco is a 67 with a 200 6cly in it everything else is stock

I would give 35 a good starting point and try from there. The smaller tire will need a little more pressure then the big floatation tires most of us use.