Taller tire, smaller wheel, or both?

Kevin B.

Not often wrong. Never quite right.
Moderator
Location
Stinkwater
On Black Dragon this weekend I burped a bead and lost a bunch of air in one tire, and then later coming out of Copper Globe I nearly pinchflatted two more, to the point I don't trust them. The tires are Rubicon takeoffs, 255/75r17 BFG KM load range C, I was at roughly 20 PSI. The easy out is obviously to hit KSL for another used KM or two, they can be had pretty cheap. But I'm not sure I'm a fan of these tires on this truck - great traction, but not enough sidewall I think, both in terms of height and strength. So I need to look at options. The truck is an F150, pretty much stock, that sees daily driving and family camping duty. It probably pushes 6000 pounds with family and gear loaded. This weekend is the hardest I've pushed it yet and probably the hardest I ever will, but it'll still see it's fair share of rough roads and light crawling in remote locations, and I want tires I trust to get me in and out.

1) Buy new? Taller tires would give me more sidewall to work with. There are two tall skinnies with an E load range available that I know of for a 17" wheel, the BFG KM2 and the Cooper ST MAXX. I'm a huge fan of the KM2, but they're nearly $250 a pop and might be outside the budget. I thought I liked the Coopers but watched a buddy with a very similar truck struggle with those tires on this weekend, so I'm maybe not as high on them anymore? If I decide to buy new they're still on the short list, but not on top like they would have been a month ago. Those are $200 or so each in the size I want. There are a grip of AT and MT E rated tires in the 285/70 range, but those tend to be more expensive than my precious skinnies, so most of those are going to be further down the list (money talks, though, the right price could bump any of them up). I think 265 and 275 series are all too small, and bigger than 285 would require mods to fit that I don't wanna get into.

2) Smaller wheel? Dropping to a 16" wheel also gives me more sidewall. I've been thinking I'll want a 35 or 37 for the 4Runner if/when I ever get around to finishing the engine swap, so I wouldn't be adverse to robbing the 255/85r16 KM2s that are on it now (my favoritest tire ever) for the F150. Those would be slightly taller than my current tire, on a smaller wheel, with the E load range I want. I'd need to find a set of 16" wheels with the elusive 5x135mm bolt pattern to put them on, but that's cheaper than a new set of tires.

So I'm conflicted - stick with what I've got and tone down the offroadish activites, buy new tires (and what kind?) and kill the pocketbook and piss off the wife, or rob the KM2s from the 4Runner and postpone the pocketbook-killing and wife-pissing-off until later. What would you guys do?
 

dutchman

KI7KSV
Location
Boise, Id
If you're talking about my truck struggling with the Cooper ST Maxx I'm not sure it's a completely fair assessment of the tires. Mine still have ok tread but are fairly worn and I stayed at street pressure (about 45 psi) all the way through the trail. Are you set on a mud-terrain tire?
 

Kevin B.

Not often wrong. Never quite right.
Moderator
Location
Stinkwater
You never aired down? That makes a difference. What size is on Chief?

I'm not set on MTs, but I'm pretty hung up on E rated and I really do like me a skinny.
 
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sawtooth4x4

Totally Awesome
Put some load range D's or E's on. Then you don't need to worry about the tire as much. They have a much stronger sidewall then the Load Range C's you have.

I've been doing it for a long time and have not lost a sidewall since switching to a higher load range.
 

sixstringsteve

Well-Known Member
Location
UT
Too much sidewall could actually lead to more burping. What wheels are you running? I dig the original KM1s. I dig my cooper ST Maxx's even more.

I agree with needing a heavier rated tire for such a heavy truck. D rated at least, but I think an E rated tire would do better.

When you say "around 20 psi", is this judging with the eyeball?
 

frieed

Jeepless in Draper
Supporting Member
Location
Draper, UT
Kevin,

I think you were under-inflated for those KMs and that heavy a truck.
I had my Michelin LTX MS2s (E rated) aired down to 40 psi and cannot recall any spot on that trail where I was lacking traction. (although with occasional help from the rear locker when crossed up)
 

mesha

By endurance we conquer
Location
A.F.
Always go with a taller tire. :)

seriously though, on a heavy rig 20 lbs will seem like 10 lbs on a light rig. If you are losing beads on black dragon you need more air.
 

Kevin B.

Not often wrong. Never quite right.
Moderator
Location
Stinkwater
Too much sidewall could actually lead to more burping. What wheels are you running? I dig the original KM1s. I dig my cooper ST Maxx's even more.

I agree with needing a heavier rated tire for such a heavy truck. D rated at least, but I think an E rated tire would do better.

When you say "around 20 psi", is this judging with the eyeball?

Pretty much. My deflators are set for 15 PSI, I pulled them a minute or two early.

I hadn't considered that I might have been running too low a PSI. I'm still learning this heavier truck, and I've been kinda feeling that the 15-20 range was giving me the best comfort and traction of what I've tried, you guys think that's maybe just too low huh?
 

DAA

Well-Known Member
Supporting Member
For your C rated tires, perhaps. I don't think 20 would be too low with E's though.

I've run my 20" wheel, hardly any sidewall, Duratrac E's at 30 quite a bit and never had a burp or a pinch that I could ever see. They're like skinny 34's, but on 20" wheels I dare not take them lower.

But, I used to take the factory tires that came on my Jeep, old style MT/R's that were only 31's, which were load range E, but on 16" wheels, down to 12 psi all the time, never had any issue. Granted, my Jeep is about a thousand pounds lighter, and, the Rubicon factory wheels seemed really good at holding a bead, but, still, I don't see how 20 is going to be too low for you on a 16" or 17" wheel with an E or maybe even a D.

- DAA
 

glockman

I hate Jeep trucks
Location
Pleasant Grove
I had the same truck with 16" wheels and ran 35" bfg mt load range D tires at 15 to 20 psi all the time. Never lost a bead or a sidewall.
 

Gravy

Ant Anstead of Dirtbikes
Supporting Member
What does the inner safety bead profile look like on the 17's on your F-150? That is what I would suspect to be the issue before the tires.
I've lost beads on my Jeep when I had non beadlock 16.5 (which had almost no inner safety bead) at over 25 psi.

If that is the case (little to no inner bead) just invest in some better wheels.
 

thefirstzukman

Finding Utah
Supporting Member
I used to run a 31x13.50-15 Swamper tsl sx tire on my samurai, heavy sidewall tire.. it used to rush air all the time out the sidewall, I tried 8,10 & 12" wide wheels on it and had it happen on all three widths. I talked to my tire distributor and he told me it was because of the thick stiff sidewall, when it folds it pushes the bead. He said thats why most off road tires wont have more than a 3 ply sidewall, might have worse problems with a E rated tire
 

Kevin B.

Not often wrong. Never quite right.
Moderator
Location
Stinkwater
The rubi tires are no better nor worse than any other.

Oh, I'm sure the tires are fine in and of themselves. I bought them used, I'm thinking older broken in tires with C rated sidewalls on a heavy truck and maybe I didn't have enough air all added up to my trouble. If the tire burped when I think it did, it was the outside wall anyway.

But I'm taking the tires and wheels off the truck in the next couple days, I'll break a bead and have a look because you've got me curious.
 
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