New Tires For Big Blue

[ArdWrknTrk]

You know Gary a lot of stiff carcass (10 ply) tires are not meant to be run at ridiculous low pressures.

I'm not saying your ten year old STT's aren't ozone cracked but under inflation is far worse than over inflation and can lead to a lot of this type of damage.

Mostly because of a stiff carcass causing a lot of heat when forced to flex much more than designed.

I'm reminded of the Firestone ATX/Wilderness tire debacle with the early Exploders... and that was Ford running them only 4 psi below nominal.

Belt separation and chunking caused more than a few deaths.

If you're going to be driving "aired down" over miles of trails (instead of just airing down across challenges) I'd suggest you stop looking at the door sticker and start looking at something like a load C flotation tire.

https://ok4wd.com/blog/what-are-flotation-tires/

At least they would stand a fighting chance.

This... https://www.discounttire.com/blog/airing-tires-down

And this... https://www.takethetruck.com/blog/airing-down-tires

"One of the biggest issues with underinflating your tires is that if the pressure is too low, the inside of the tires can overheat—risking tire failure at one of the least ideal moments possible"

"Most off-road forums specify that it’s mostly safe to reduce your air pressure by 25% of your recommended PSI for comfort and traction moderate trails. For aggressive rocky terrain, dropping down between 30-35% would allow you to grip onto heavy rocks with ease."

Which would suggest 54-60 psi for the door sticker recommended 80 rear or 40-45 psi for the 60 I usually run on my truck.

I know you "want it all, and more" but I'm not at all surprised that your ten ply tires are getting destroyed when running 35 psi all the time and rock crawler pressures over many (277?) miles of trail.

ETA: a load range C tire (recommended inflation pressure 50psi) is much better suited to your 35 psi inflation, but it still shouldn't be run much below that, even off road.

 

[Rusty_S85]

Four of the K02's for the $1434, and that's $291.99/tire or $1167.96 for four. Tire Rack would get me a set to the house for $1167.96, obviously not including mounting, balancing and tax. So that's the $266 difference.

I'll be price checking 'cause they told me they'll match prices. But since the alignment was done at Tate Boys and they will redo it for free so the difference will have to be significant to make me want to change.

Dang thats pricy. When I got mine they were under $200 a tire which was the only reason why I got them.

[Gary Lewis]

You know Gary a lot of stiff carcass (10 ply) tires are not meant to be run at ridiculous low pressures.

I'm not saying your ten year old STT's aren't ozone cracked but under inflation is far worse than over inflation and can lead to a lot of this type of damage.

Mostly because of a stiff carcass causing a lot of heat when forced to flex much more than designed.

I'm reminded of the Firestone ATX/Wilderness tire debacle with the early Exploders... and that was Ford running them only 4 psi below nominal.

Belt separation and chunking caused more than a few deaths.

If you're going to be driving "aired down" over miles of trails (instead of just airing down across challenges) I'd suggest you stop looking at the door sticker and start looking at something like a load C flotation tire.

https://ok4wd.com/blog/what-are-flotation-tires/

At least they would stand a fighting chance.

Jim - I'll read up on that. We are out and about, running errands again, so I can't at the moment, but will.

[ArdWrknTrk]

Jim - I'll read up on that. We are out and about, running errands again, so I can't at the moment, but will.

This from the Wikipedia page on the Firestone tires.

These tires were brand engineered for Ford, also relating to Chad's statement above.

"Operating temperature

A tire's operating temperature will increase with higher vehicle load, speed, air temperature and with lower tire inflation pressure. The combination of inflation pressure, speed, and vehicle load could increase the tire temperature as much as 50 degrees C above the ambient air temperature.

Higher operating temperatures will increase the rate of oxidative aging. Tires that were used in southern climates were also less ductile and stiffer than tires that operated in northern climates.

Tires in warmer climates also showed higher levels of cure and had somewhat lower peel strength.

The role of air temperature would explain why geographic regions with higher air temperatures had the highest tire failure rates. These results held up even for tires that had zero percent tread wear."

By this I mean to suggest if you want the compliance of lower tire pressure perhaps you ought to consider a tire with a lower recommended tire pressure (and a more compliant carcass)

 

[Gary Lewis]

This from the Wikipedia page on the Firestone tires.

These tires were brand engineered for Ford, also relating to Chad's statement above.

"Operating temperature

A tire's operating temperature will increase with higher vehicle load, speed, air temperature and with lower tire inflation pressure. The combination of inflation pressure, speed, and vehicle load could increase the tire temperature as much as 50 degrees C above the ambient air temperature.

Higher operating temperatures will increase the rate of oxidative aging. Tires that were used in southern climates were also less ductile and stiffer than tires that operated in northern climates.

Tires in warmer climates also showed higher levels of cure and had somewhat lower peel strength.

The role of air temperature would explain why geographic regions with higher air temperatures had the highest tire failure rates. These results held up even for tires that had zero percent tread wear."

By this I mean to suggest if you want the compliance of lower tire pressure perhaps you ought to consider a tire with a lower recommended tire pressure (and a more compliant carcass)

Ok, I'm home now and have skimmed the material you linked to. And what you are saying makes sense, although I'm not quite sure yet what to do about or with it.

Basically my understanding is that running a tire at "reduced" inflation causes heat, and the farther you are under the target inflation # the more heat. And the faster you drive the more heat. Of course, the heat comes from energy created by burning gasoline, so having the right inflation pressure also helps MPG.

But is the "right" inflation pressure the max # on the sidewall? None of the vehicles we have recommend anywhere near the max inflation pressures for even fully loaded conditions. So when someone says "Traversing slickrock or more challenging trails with loose terrain, a 30-35% pressure reduction may be in order", are they talking about a 25% reduction from the max #?

Also, I want a 33" tall tire, and yet when I drop down to anything less than a E-rated tire they don't go that tall. Is that where the flotation tire comes in? According to the link you sent their sizes would look something like 40x13.50R17LT. But below is the table of available 16" tire sizes from Tire Rack and none of them look like that. What am I missing?

[ArdWrknTrk]

Ok, I'm home now and have skimmed the material you linked to. And what you are saying makes sense, although I'm not quite sure yet what to do about or with it.

Basically my understanding is that running a tire at "reduced" inflation causes heat, and the farther you are under the target inflation # the more heat. And the faster you drive the more heat. Of course, the heat comes from energy created by burning gasoline, so having the right inflation pressure also helps MPG.

But is the "right" inflation pressure the max # on the sidewall? None of the vehicles we have recommend anywhere near the max inflation pressures for even fully loaded conditions. So when someone says "Traversing slickrock or more challenging trails with loose terrain, a 30-35% pressure reduction may be in order", are they talking about a 25% reduction from the max #?

Also, I want a 33" tall tire, and yet when I drop down to anything less than a E-rated tire they don't go that tall. Is that where the flotation tire comes in? According to the link you sent their sizes would look something like 40x13.50R17LT. But below is the table of available 16" tire sizes from Tire Rack and none of them look like that. What am I missing?

The heat comes from the vehicle weight distorting the tire carcass.

And the stabilizing piles in that carcass flexing the rubber between plies.

Yes, speed means more distortion cycles per time, and therefore more heat input

The articles are talking about the tires rated inflation pressure...

With less than the sidewall pressure the load capacity is reduced and the self heating of the tire goes up. (WAY up if your pressure is way too low)

If pressures are too low you can spin the rim in the bead or corner your tire right off the rim.

That's why hill climb tires have bead locks and dragster tires are screwed to the rim.

They generally only have to operate for a few seconds at a time.

We used to play a lot with tire pressure and alternate inflation gasses like nitrogen when motorcycle racing.

Trying to get heat into the tire while not causing so much that it would get greasy or cook off the compound.

Or cause pressures to rise too much due to expansion.

Things are much better 40 years later....

I was suggesting you look at something like a 33 x 11.5 tire that would be a similar overall size but with a lighter carcass rated at 50psi.

I see some of the guys on Tacoma World shifting to 17" rims because 16" is basically an antiquated work truck size and only has E rated tires available.

Whatever.... unfortunately

I'm pointing out that your drastic under inflation in daily use is most likely causing a lot of the problems you're seeing with cracking and chunking. (because that heat has caused the rubber itself to cure more than the manufacturer ever intended)

You're already dangerously under pressure and "airing down" on trails is making it worse.

I don't have an answer for your tire situation.

The KO2's were available in a C construction but I guess not enough were sold so they were discontinued.

[Gary Lewis]

The heat comes from the vehicle weight distorting the tire carcass.

And the stabilizing piles in that carcass flexing the rubber between plies.

Yes, speed means more distortion cycles per time, and therefore more heat input

The articles are talking about the tires rated inflation pressure...

With less than the sidewall pressure the load capacity is reduced and the self heating of the tire goes up. (WAY up if your pressure is way too low)

If pressures are too low you can spin the rim in the bead or corner your tire right off the rim.

That's why hill climb tires have bead locks and dragster tires are screwed to the rim.

They generally only have to operate for a few seconds at a time.

We used to play a lot with tire pressure and alternate inflation gasses like nitrogen when motorcycle racing.

Trying to get heat into the tire while not causing so much that it would get greasy or cook off the compound.

Or cause pressures to rise too much due to expansion.

Things are much better 40 years later....

I was suggesting you look at something like a 33 x 11.5 tire that would be a similar overall size but with a lighter carcass rated at 50psi.

I see some of the guys on Tacoma World shifting to 17" rims because 16" is basically an antiquated work truck size and only has E rated tires available.

Whatever.... unfortunately

I'm pointing out that your drastic under inflation in daily use is most likely causing a lot of the problems you're seeing with cracking and chunking. (because that heat has caused the rubber itself to cure more than the manufacturer ever intended)

You're already dangerously under pressure and "airing down" on trails is making it worse.

I don't have an answer for your tire situation.

The KO2's were available in a C construction but I guess not enough were sold so they were discontinued.

I do understand what you are saying. Running a tire rated for a max of 80 psi at 35 psi daily is hard on it, and then airing it down to 15 psi is REALLY bad. But since I want a 33" tire on a 16" rim and the only ones appear to be E rated, I'm kinda stuck.

So perhaps I need to increase the pressure I'm running on the highway a bit, although I still want the tire to be running flat on the pavement. And maybe not go down to 15 on the trails.

The takethetruck site said:

• General off-road driving on rough dirt roads, two-track, and mild trails - a 25% reduction or 10 PSI is a good place to start

• Traversing slickrock or more challenging trails with loose terrain, a 30-35% pressure reduction may be in order

• Very soft terrain conditions such as sand or mud may benefit from up to a 50% pressure reduction

So for the trails Bret and I are going on in New Mexico, which are typically forest service roads, maybe drop to 30 psi if we are running 40 on the highway. And then on the really loose or rocky stuff down to 20. And finally, if we get the truck into really soft stuff like sand or mud we could go down to 15. But we wouldn't plan on going over maybe 20 MPH at anything south of 30 psi.

Does that sound like a reasonable plan?

[ArdWrknTrk]

I do understand what you are saying. Running a tire rated for a max of 80 psi at 35 psi daily is hard on it, and then airing it down to 15 psi is REALLY bad. But since I want a 33" tire on a 16" rim and the only ones appear to be E rated, I'm kinda stuck.

So perhaps I need to increase the pressure I'm running on the highway a bit, although I still want the tire to be running flat on the pavement. And maybe not go down to 15 on the trails.

The takethetruck site said:

• General off-road driving on rough dirt roads, two-track, and mild trails - a 25% reduction or 10 PSI is a good place to start

• Traversing slickrock or more challenging trails with loose terrain, a 30-35% pressure reduction may be in order

• Very soft terrain conditions such as sand or mud may benefit from up to a 50% pressure reduction

So for the trails Bret and I are going on in New Mexico, which are typically forest service roads, maybe drop to 30 psi if we are running 40 on the highway. And then on the really loose or rocky stuff down to 20. And finally, if we get the truck into really soft stuff like sand or mud we could go down to 15. But we wouldn't plan on going over maybe 20 MPH at anything south of 30 psi.

Does that sound like a reasonable plan?

You seem to miss the point.

10 psi from a 80 psi rated tire is 70 psi.

I'm running my tires at 25% from 80, which is 60 psi

80 minus 35% is 52 psi (an absolute minimum) and suggested for rock crawling (very low speed, and not all day long)

If you want to go down to 15 psi then even a P rated tire at 36 psi would be too much.

That's why companies like Mickey Thompson and Dick Cepek make entirely off road floatation tires for these conditions.

But you don't like noise or wear.

I mean, I don't care what you do but what "I want" and the reality of life and safety are completely at odds.

I'm only trying to point this out.

Do you wear ice skates in the house?

 

[Gary Lewis]

You seem to miss the point.

10 psi from a 80 psi rated tire is 70 psi.

I'm running my tires at 25% from 80, which is 60 psi

80 minus 35% is 52 psi (an absolute minimum) and suggested for rock crawling (very low speed, and not all day long)

If you want to go down to 15 psi then even a P rated tire at 36 psi would be too much.

That's why companies like Mickey Thompson and Dick Cepek make entirely off road floatation tires for these conditions.

But you don't like noise or wear.

I mean, I don't care what you do but what "I want" and the reality of life and safety are completely at odds.

I'm only trying to point this out.

Do you wear ice skates in the house?

LOL! No, I'm not missing the point. But I'm not going to run the tires on Big Blue at 80 psi. And maybe not as high as you are at 60. However, I will try different pressures.

But I do thank you for pointing the issues out.

And no, I don't wear ice skates in the house.

[ArdWrknTrk]

LOL! No, I'm not missing the point. But I'm not going to run the tires on Big Blue at 80 psi. And maybe not as high as you are at 60. However, I will try different pressures.

But I do thank you for pointing the issues out.

And no, I don't wear ice skates in the house.

What I'm saying is that 10 psi below your already too low 35 is NOT what those articles are suggesting.... 💡

And 35 is probably why your tires look like they do.

People that run 15 psi in deep sand are likely wearing very specialized paddle tires or if in deep mud, huge 'boggers'

50% of 32 is 16.

They don't travel 65 on the highway or expect their tires to last for years.

They tow their rig to the trailhead and likely air down for conditions. (i.e. they aren't even traversing terrain at those pressures)

You would do well to try and find some 6ply rated tires if you want to drive at 35 lbs for comfort.