RE: Correct Tire Pressure

[mrdrnac]

RE: Correct Tire Pressure

Can anyone give me some beginning recomendations for the air pressure to run on a early Bronco with a set of 37X14.5X15 Toyo Open Country M/T tires? And should the front tires be inflated more than the back? No top, no extra weight in the back.
Thanks

 

[Broncobowsher]

That's a big tire. Are you looking for highway pressures or trail pressures?

At this point you are probably just going to have to play around and see what works. I really hate seeing anything under mid 20's on the highway. The lowest tire pressure spec I can think of on modern tires was 26, and Explorers were known to loose tires and roll over at highway speeds running that low of a pressure. Too much flex caused tread separation.

Even things like the width of the rim play a factor. As the rim narrows the center of the tread crowns out like running too much pressure. Causes a small contact patch and excessive center tire wear.

Sorry, there isn't a quick way of knowing the exact right pressure. There are estimates and rules of thumb. Enough air the tire doesn't look low is a great starting point. Go up and down, drive it. I have had noticeable changes in handling with as little as 2PSI change. I could pull out of my neighborhood and tell that the tires were low (26 instead of the normal 28). although going from 30 to 28 to correct early signs of excessive pressure tire wear didn't cause any significant changes in handling. That was on only 33s. You have a lot taller tire on the same 15" wheel.

Low pressures tend to make a wallowing feel. Adding pressure firms up the tires.

Need a starting point? Start at 30 and go from there. It is a safe pressure even if not optimal.

 

[ENDLIFE]

I watched my friend do it for a guy with 44's on his rig, it took a little time, but he went to school to be a car guru. He would fill to the tire to the recommended tire pressure on the side of the tire, this would cause the tire to balloon and ride the middle of the tire. He would hook up a remote deflator to the tire, lay on the ground, and deflate the tire till the full width of the tread was on the ground then let out 2 to 5 PSI more. He would record the tire pressure for his customer so they could set the pressure back if they deflated the tires for any reason. It's the way I do my tires now, and I love it.

 

[Doyle]

We've always used playground chalk to get a starting point for oversize tires. Color a inch wide stripe across the tread and drive in a straight line till you can see the rub patern. If middle rubs off first drop pressure, if sides first add pressure. This will get you close on having the same pressure on the width of the tread. With that wide of a tire you may be in the teens to get any pressure on the edges, depends some on rim width.

 

[bknbronco]

a lot depends on the tires, vehicle weight, etc. I have ran 35" all terrrains at 65psi on my excursion, but I pulled a large trailer on a daily basis. On my bronco id never run them same tires at that high a pressure. I like to stick around 25-30psi. When we air up are tires after a day on the trail we go to 32 but that takes into account that CO2 leaks out of the tires slowly.

 

[TN1776]

I run my 37" tires at around 30psi on the highway, drop them to 15 on the trail. I've run them higher and lower but 30 seems to be about right on the road. The suggestions above are great though.. got me thinking I need to snag some chalk from my niece and see where I'm at.

 

[mrdrnac]

Thanks for the good answers they all helped. FYI the rim width is 10" and I was intersted in suggestions for the Highway. The install shop put 35lbs. in all of them and I thought that would be a little high for these tires on a Bronco.
i'll start at 30 and try the chalk test. Thanks!

 

[mortimersnerd]

We've always used playground chalk to get a starting point for oversize tires. Color a inch wide stripe across the tread and drive in a straight line till you can see the rub patern. If middle rubs off first drop pressure, if sides first add pressure. This will get you close on having the same pressure on the width of the tread. With that wide of a tire you may be in the teens to get any pressure on the edges, depends some on rim width.

This. I run my 35x13.5s around 28 front and 26 rear to get a proper contact patch. As was said above, 2 psi can make a big difference.

 

[Apogee]

My brother runs his 35x13.5x15 Toyo MT's on his Toyota (~4200 lb) at 26 psi.

 

[73azbronco]

Have to agree with the comment about not going to low on pressure even if it looks or feels right.

I run 35 12.5 17 Toyo open Country. E range tires on A Jeep JK. At rated pressure of 40psi, my wife described it best, it's like driving a Great Dane puppy, all over the road. Got great milage though. I then tried the chalk trick, which meant 21 psi to get the right tread contact, bad news was the tires heated up even running around town. I then started raising pressure until I found a sweet spot, reasonably good mileage, reasonably good drivability, and contact is 95 % across the tread and that pressure is 30psi. But if I road trip, I jack it up to 35 as that's where I note no heat being made from tire flex and it still drives pretty well.

My biggest point learned, avoid buying tires with load ratings above the vehicle your using them on. My next tire will be a C rated tire for the jeep. These Toyos are going on the bronco.

 

[Amac70]

I rarely run above 26 on the fronts and 24 in the rears. don't have any heat issues. when i air down im around 6 airing up to head back to camp im usually around 15.