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 > E rated tire with max psi of 65?

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CapriRacer

Somewhere in the US

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Posted: 12/03/20 06:14am Link  |  Quote  |  Print  |  Notify Moderator

There seems to be some question about where I got my information that larger sized E Load Range tires use 65 psi max pressure rather than the usual 80 psi max - and that maybe onroad/offroad has something to do with it.

I have in front of me the 2020 Tire and Rim Association (TRA) Yearbook. TRA is the source standard for the load tables (among other things!) for US based tire manufacturers. In that book are ALL the current load tables for EVERY type of tire (except aircraft - separate book - and anything non-standard)

It shows many E Load Range LT tire sizes as having 65 psi max pressures as well as the ones we normally deal with (including sizes that aren't produced!) The tables do NOT refer to onroad/offroad as one of the parameters in determining the max pressure. However, it does reference changes in load carrying capacity for various speeds. (again, no change in the max pressure!)

And lastly, why do my posts take so long to show up? I normally post in the morning - part of my daily ritual. I only recently updated to a smart phone and haven't yet figured out how to connect it to my email alerts. Plus, does this site give email alerts? More things to learn about! (edit: When I clicked to post the above, I found how to get email alerts! Now to learn how to link the phone to my email so I get alerts!)


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CapriRacer

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MFL

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Posted: 12/03/20 06:44am Link  |  Quote  |  Print  |  Notify Moderator

Good to see where your info comes from. While there are many types of tires, if you would have taken the time to read the link Burb posted, it is a hybrid type (dual purpose) tire, that by design, would work best, considering sidewall and tread at 65 psi. Other tires purpose will vary, and while e-rated, may also be less than 80 psi.

As to reading comprehension...I specifically mentioned your buddy Grit, having an issue with his posts. His post will show in the count, and at what time, but the context, and author may not be there for a day or more. It may be a phone related issue, or that a civil engineer is not a technical engineer.

In any case, whether reading posts, links, or from a book, comprehension is key!

Jerry





BurbMan

Noblesville, IN

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Posted: 12/03/20 06:45am Link  |  Quote  |  Print  |  Notify Moderator

Well I'm feeling pretty lucky right now...on out 1000 mile road trip to PA in October (maiden voyage with the newly-rebuilt camper), I had the rears aired to 80 and was seeing the TPMS tell me 85/86 going down the road at 70 mph. I'm thankful they didn't blow running that much over max.

The flip side is that I'm sure the extra air helped with stiffness and stability...so maybe they would squirm more aired to only 65?

Here is the specs page from the Nitto site for their Ridge Grappler tires.

I've added some notes:

A- This is the size that Ram puts on the truck as OEM. My truck has 18x8 rims.
B- This is the size that's on the truck now.
C- This seems like a good choice for a replacement when these wear out.

[image]

This is what Ridge Grappler looks like:

[image]


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KMLsquared

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Posted: 12/03/20 08:18am Link  |  Quote  |  Print  |  Notify Moderator

I have general tires Grabber AT on my truck in a 315/75-16 and they are an "E" rated tire at 65 PSI. I too was concerned but trusted their engineers and they have been fine. IF I still had a truck camper I would not have gotten them but the Fifth-wheel tows fine with them.


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Grit dog

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Posted: 12/03/20 10:04am Link  |  Quote  |  Print  |  Notify Moderator

MFL wrote:

We are all knowledgeable, but does not mean correct every time! If you read Burb's link, it has some good info, concerning his tires, tread, etc. It does show a little more on road capable, than off.

Do you truly know Capri, or just read of his own drum beating? Hope no relationship involved![emoticon] Roger Marble was more knowledgeable, and also had more RV type experience. Too bad, he was banned here!

Grit...just curious...why does it often take a day or more, for your posts to show up? Your post above, did not take that long, but was blank for a while? BTW...you are a knowledgeable gear head, and like me, a person who has over used trucks, and tires, while I don't recommend either.

Jerry


Idk why my posts show up late to the party. Haven’t really noticed. But one above may have been in quarantine by the mod! Lol
I don’t know Capri, but everything he’s posted that I’ve read appears to be truth and in depth knowledge.
But this is the internet. I could be more FOS than the next guy. Opinions are worth exactly what they’re worth. Although I’ve learned a lot from the “right” opinions and a fief amount from the “wrong” ones too!

Cheers MFL! And the rest of ya too...


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Grit dog

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Posted: 12/03/20 10:16am Link  |  Quote  |  Print  |  Notify Moderator

And we’ve all had experiences we learned from.
I learned about the right width rims for tires and right pressure for treadwear at the same time, same truck, 1 set of tires.
Put a nice set of 33-12.50 mudders on some 17x8 rims. Bit narrow but not bad. Then moved to Phoenix and kept them aired up more than needed, for mileage (good roads, smooth), minimize scrub on the super hot pavement etc.
thought they were the worst tires ever. Wore out in maybe 25k miles of kid carrying duties. Just the center of the treads.
Getting new tires, and commented how bad the Mickey Thompson s were and tire guy asked what pressures. I told him and he pointed out the error in my ways.

Grit dog

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Posted: 12/03/20 10:23am Link  |  Quote  |  Print  |  Notify Moderator

@Burb.
I’d say 285-75s or 295-70s would be more ideal based on your OE rims.
And that’s about the point where capacity maxes out without going to 12” range width tires which “should” have wider rims.
FWIW, I ran 275-65-20s last set on the 07 Ram with OE 20” Ram wheels. Mainly because I’m cheap and that size isn’t so popular and $200/tire was hard to pass up for Firestone MTs. Those were all that was needed to hold up the white whale on the old Dodge. So know that you can get by with anything from the 275s on up.

N-Trouble

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Posted: 12/03/20 10:32am Link  |  Quote  |  Print  |  Notify Moderator

mich800 wrote:

twodownzero wrote:

I wouldn't get rid of them. I have the Ridge Grapplers on one of my trucks, not one I use to pull or carry a camper, and they've actually been great tires. I would, however, not air them up so much unloaded. Check your door panel for what the original tires used for pressure and back that down some. 35-40 psi is probably more than enough.


The inflation sticker is only applicable if running the size/spec tires the sticker is referencing.


Why cant people figure this out? Especially dealers and service centers. Check the freakin sidewall NOT the truck

Wider tires (generally 285 and above) will be 65psi max. A wider footprint tire doesnt need as high an air pressure as a narrower tire to support the load. This is nothing new. Been this way for years. Has nothing to do with on/off road.


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BenK

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Posted: 12/03/20 03:33pm Link  |  Quote  |  Print  |  Notify Moderator

X2....N-Trouble’s comment/thoughts

Following is more rhetorical than anything...why are folks so hung up on a tires PSI rating...when most diss the GVWR/GCWR/MTWR/etc ratings ?...and recommend that they don’t really matter...

Selective adherence to ratings IMHO...

Most get away with that mentality & recommendations because designers have dialed in some level of margin (AKA...safety margin as most think it is). How much they dialed in and how much management told them to remove is a guessing game or more aptly lucky that they haven’t found where that line is...


Off soap box...


Burbman...I’d go down in width and go to a higher aspect ratio (Larger number, which is the percentage of section width) for your setup.

A higher profile tire’s sidewall will help when you go to the beach and that sand those beaches are famous for.

Airing down will have a higher profile tire’s sidewall ‘bulge’ more, which forms both a ‘wider’ footprint...and many don’t know that the tread will also ‘cup’ inwards, which helps ‘catch’ more sand and NOT slip as much. The higher the aspect ratio (higher number, or higher percentage) will allow the sidewalls to collapse more.

Also, with a higher profile tire aired down, the ‘aparent’ tire dia will be much larger than a lower profile tire. Around some old campfires, buddies and I noodled and came to a consensus that our tires were in the effective +8 foot diameter range.



Finally, note that squared off tread to sidewall transition area needs to be rounded. Street tires with a much more squared off (sharp transition) will dig better in soft stuff (dirt, sand, etc)

Edit...for those who don’t know...airing down is for very slow going ONLY.

If you plan to drive above, say, 10MPH with aired down tires...that will shorten your tires life greatly.

Go faster and you may not make it back to pavement with the tires in good condition.

* This post was edited 12/03/20 03:46pm by BenK *


-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
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CapriRacer

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Posted: 12/04/20 04:57am Link  |  Quote  |  Print  |  Notify Moderator

MFL wrote:

...... While you SAY burst pressure the reason, then add that burst is many times the max pressure, it would seem that 80 psi rather than 65 psi, would not cause burst. .....


What's really going on here is fatigue strength. Wikipedia: Fatigue (material)

Tires are all about fatigue and in order to design a tire to go through 10's of millions of cycles (rotations), the designers uses the burst pressure as a reference and then uses a factor to increase the strength to get the desired fatigue life - which they get from an S-N Curve for the material in question.

So while tires don't burst at 80 or 100, or 150 psi, that burst pressure is an indicator as to the fatigue life.

MFL wrote:

Good to see where your info comes from. While there are many types of tires, if you would have taken the time to read the link Burb posted, it is a hybrid type (dual purpose) tire, that by design, would work best, considering sidewall and tread at 65 psi. Other tires purpose will vary, and while e-rated, may also be less than 80 psi. ......


Ah .... That's not how it works.

The simplest way to describe this is to say:

1) that the WORST condition is the onroad condition, because heat is the tire killer! So the fact that we are discussing an onroad/offroad tire still means the onroad condition is what the tire engineer has to design against.

2) that the tables were set up (over 80 years ago!) so that a construction for a given Load Range works for all tire sizes - which means that when a tire gets to a certain size, it can't withstand the stress, so the Load Range drops down to the next lower increment - in this case from 80 psi down to 65 psi.

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