Tire PSI and Wandering

[GSP9]

Tire size is 30x9.50R15LT. I checked the spare tire and wheel on the back and there were no markings on the inside of the wheel but the wheel appears to be a 15 x 8. Not sure of the brand but it appears to be a US Wheels Daytona or a Vision D Window Wheel. Do you think I would benefit by going to a 10" wheel, possibly a different tire, or start dropping the psi with the current set up?

 

[DirtDonk]

No! You don't want a wider wheel than the tire on a truck tire like these. Even that 1" narrower wheel is at the upper edge of the recommended range for a 9.50" tire.
So if they're all 8" wide, it's not the wheel being too narrow that's giving you a crown.

Just looking at the wheel, I'd have said it was a 7" instead. Offset will fool you with looks, so that visual thing is very inaccurate unless backspacing/offset is consistent with other wheels.
But in the old days, that would have been a 7" wheel with 3 to 4 inches of backspace.
If your spare is still off, maybe get a quick measurement of how much rim is inside of the center mounting surface? More for future reference than anything critical at this point, but it's good to know that stuff sometimes.

Keep playing with pressures. I wouldn't generally go below 20, but you can get there safely at this point. If you end up spending a lot of time doing 80 in the Texas sun, more pressure would be good. But for now, I would say anything above 20 is safe still.
Just out of curiosity, what is the "max pressure" listed on the sidewall again?

And let just as much out of the rear as the front at this point. No reason to put more in the rear with most unladen EB's. Most of the weight AND weight transfer is in the front, except when loaded down with camping gear or sand or whatever you load in the back.

Keep the updates comin'!

Paul

 

[Soylent]

I thought that the tire will always have a crown at the top with the weight of the vehicle on it. Better to do the chalk test to adjust the pressure for a flat tread, right?

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[DirtDonk]

That's definitely correct. Some tires will look that way on top and be perfectly normal at the business end (on the ground).
It sill looks a bit high for that style tire, but you're right about paying more attention to the ground.

I always use the chalk test too, but was just recommending playing with the air pressures anyway as a quick-n-dirty way to see if if keeps improving.

Glad you brought us back to reality!

Paul

 

[GSP9]

Paul,

I would have assumed they were 15 x 7's as well but I ran a piece of masking tape down each side and they seem to be 15 x 8's. Back spacing seems to be 3.5 inches and I again thought they might only be 7 inch wide wheels but measured again and was coming up with 8 inches wide. Max psi is 50 cold.

 

[DirtDonk]

Hmm, sure fooled me. But that's the fickleness of just going by looks.
Just to be sure though, overall width of a wheel is INSIDE the bead edge, so a measurement taken at the outer lip is not quite correct. If you put the tape down inside though, that 8" is still going to be within 1/8" or so of right on.
If that was on the outside edge though, check how deep the lips are and see if that takes it down some. Usually that's only in the 1/2" range or less, but some wheels do have deeper curled lips than others.

Either way, still worth fiddling about with pressures. That 50 psi is typical of a modern truck tire, and would normally dictate you don't go below 25 or so for safety, but since this is likely a much lighter load than they're rated for, I still think you're safe to 20.

But the bottom line is tire wear (or the chalk line check) rather than either comfort or looking at crowns or bows or bulged sidewalls.
If the chalk line does not wear off all the way to the edge of the tread, or at least within a 1/4" of it, then either there's too much air, or just too stiff of a sidewall. That last is very common too these days, what with larger and higher load range tires the norm. Even our heavy-ish 4000 lb rigs don't begin to stress them out. Heck, with some of the tires we use, you can run them empty and not always notice extra bulge at the bottom!

The good news is that if you run them flat, you don't usually hurt the wheel. The bad news is that it's harder to tell by looks and you should check pressures now and then, and they're not always the best riding or wearing tires for our applications.

Paul

 

[GSP9]

Paul,

The measurement from edge to edge is just under 9" so take away about 1/2" per side and it leaves me with an 8" rim. I won't have much time to fool with it this week but I think what I'm going to do is fill the tires back up to 35 psi and road test. Then drop them to 30, 25, and 20 psi and road test each time. Just curious to see how varied it is and once I get it narrowed down then I'll do it in 1 or 2 psi increments. More of a curiosity think at this point as to what it will do at 35 psi. We'll see what happens......

 

[DirtDonk]

Sounds good. And unlike a pickup truck that sees heavy loads, or a car with a big trunk and light duty tires, our Broncos usually respond well to at least a few pounds less in the rear. There just isn't as much mass back there, so both ride and wear are improved with a little less.
AS always though, YRMV (your results may vary) so you doing the experimenting is the only way to find out for sure if the general rules apply.

Here's hoping for some good results!

Paul

 

[GSP9]

Made it back from vacation and spent some time taking it out last night. I pumped the tires up to 35 psi to start and took it for a drive. As I mentioned earlier, the trac bar bracket really helped and even at 35 psi, a lot of the wander was gone but there was just a little shimmy. Not bad but I did notice a little. Came back and dropped the psi to 22 psi and back out to test. Shimmy was gone and it did track better than 35 psi but I would almost equate it to having a "softer" wander.

As a side note, we go to the 4x4 beach of Carova, NC every year for vacation so I'm pretty familiar with dropping psi in my Silverado to get up the beach in the sand. My truck tires stay at 38 psi and I drop them to 25 psi to get up the beach and around town for the week down there. I've dropped those tires to 20 psi for down there but when I'm on the street, the tires have way too much roll so 25 psi is a good compromise. We've been doing that for years so I would say I have some experience in dropping psi. I've been to as low as 18 psi while down there.

How it relates to the Bronco is I was surprised that when I dropped all the way down to 22 psi, it still seemed to handle well on the street. I was expecting a lot of roll when going into turns and what not but they handled well. I think the wander is still there, but at 22 psi, it softens the wander. Not sure how else to describe it but I feel like I could drive the Bronco at 35 psi but my wife wouldn't want to. But at 22 psi or so, she would feel more comfortable behind the wheel because even though there is still a little wander, it's toned down enough just thru lower tire pressure to make it manageable for her.....if that makes any sense.

So I think I'll keep it at 22 psi for the time being and maybe fool with the toe in a little to see what that does. I know someone had mentioned that they felt I needed a little more toe in so I'll start there. Also after road testing last night I had a small coolant leak........if it isn't one thing it's another! Haha

 

[DirtDonk]

Glad that at least it's making a difference. Why did you go all the way to 22 right off though, instead of lowering it through the normal ranges like 25 to 28? Did you already try that and I'm just not remembering?
Just curious. Keep at it!

If the shimmy stays, maybe rotating a tire from the front to the back to see if it changes. Then do the other.
Might be worth a little driveway time to see what's up.

Paul

 

[GSP9]

I went from 35 psi to 22 psi to just cut to the chase and see how noticeable it was or wasn't. I was going to do it in 5 psi increments but really just wanted to go from one extreme to the other to see if there was a major or minor difference. It was at 25 psi before when I brought it home from the mechanic after the drop trac bar bracket was installed. So I just pumped them up to 35 psi to get started and see what it would do.

The shimmy is gone in the 22 psi to say 28 psi range so I'm just going to keep them somewhere in there for now. Pretty sure after last night that something else is causing the wandering. The lower tire pressure certainly helps by controlling it more but doesn't completely get rid of it. I'm sorta thinking out loud here but I'm kinda down to two things and that's either the C bushings being the incorrect degree or the toe in needing a little more adjusting in. I'm going to fool with the toe in, in small increments to see what that does at the current psi and then go from there. Unless anyone has any other suggestions?

 

[DirtDonk]

Sounds like you're on the right track. Definitely play with the toe-in bit by bit like you were saying. A little can sometimes be hardly noticeable, while at other times a tiny bit can be felt immediately.

Paul

 

[GSP9]

Tried fooling with the toe in tonight. Took some measurements, lifted the front end off the ground, loosened the clamp bolts but I could not get that sleeve to budge clockwise or counter clockwise. Any special tools needed? I tried pushing against the small openings in the sleeve with the end of a wrench but I just can't get that thing to budge in order to make an adjustment.

 

[DirtDonk]

Pipe Wrench.
And because this is a truck, this falls into the "bigger is better" category. A big pipe wrench has more leverage, and if yours is stuck it could be very stuck.
The good news is that once it's broken free and spinning, you likely won't ever have to fight it again. But when these things have not been messed with in decades they tend to like where they are and want to stay there.
The bad news is that the longer it's been, the harder it might be to break loose.

My own had only been in one spot for maybe 8 or 9 years (from new) but had spent that time in a very moist and rusty area. I took my biggest pipe wrench, oriented it so that lifting UP would make it grip. Put the floor jack underneath it and literally lifted the truck up off the ground with it. And even then it didn't let loose until I stood on the bumper and jumped up and down a couple of times!
It finally let loose with a bang and was good to go from then on out. I hope you don't have to go there, as it's probably not good for the rod ends to have the weight of the vehicle trying to twist them in their sockets, but at that point I figured I had nothing to lose and was going to have to buy new ones anyway. Luckily I didn't.

In that spirit of things, if you have not already I would start it soaking in penetrating lubricant to help things along when it finally decides to cooperate.

Paul

 

[GSP9]

Thanks Paul!

 

[B RON CO]

Hi, a front end shop will use a wrench like astro pnuematic 7802. This type of tool will spread the sleeve as you apply force. Pipe wrenches and vice grips will squeeze it tighter. Oil will always help. I thought the alignment shop already worked on the toe setting. Good luck

 

[edmedlin]

Just an FYI.... I went through this with DDs steps on my front end. I got the front end straightened out, then messed with the tire pressures. I didn't have the "shimmy", just a little of what I thought was bump steer, but was actually just too much air pressure and bouncing like a basketball. I was running at 34psi all round with my '75. I dropped it 2-3 psi at a time and found that 28psi all round was the sweet spot. Dropping it lower in the rear by a couple of pounds helped a bit on those "grooved" roads for some reason. I don't understand that at all. I would think that would be a function of something in the front, but if it works...... So now I have settled on 28psi front, 26psi rears and all is well. Still a brick, but a much better handling brick.

 

[DirtDonk]

That's great news! Thanks for the update.
Good detail too. Should help the next guy.

...Dropping it lower in the rear by a couple of pounds helped a bit on those "grooved" roads for some reason. I don't understand that at all. I would think that would be a function of something in the front, but if it works...

Mainly because these are short wheelbase, high center of gravity trucks with radius arms at the front.
Anything that effects the rear more than just a teensy tiny bit (official unit of measurement by the way) will transfer to the front through the frame and the radius arms, which are basically torsion bars connected between the frame and suspension/steering.
When something effects how the chassis reacts, it effects the whole chassis. Might even be as simple as changing the way it rolls side-to-side in "roll-steer", which is similar to bump-steer but brought about from a different angle.

Bunch of words adding up to blah, blah, blah, and I'm no injinear, but the real world sometimes acts different from the book anyway.;D
'Specially when Broncos are involved!

Paul