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Old 08-16-2007, 02:35 PM   #1
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8 ply vs 10 ply

Next year is tire time for me so I'm now going through some thoughts regarding tire plys on my next set. I've stated before in other tire threads that my 30' slide is the heaviest trailer that Airstream puts on 4 wheels. Gross weight capacity of my trailer is 9,100 lbs. It's pretty easy for me to be at least 8,000 to 8,400 lbs without water.

Given I have a choice between an 8 ply ST tire and a 10 ply ST tire, same size:

1. To get the higher weight capacity rating, I need to inflate the 10 ply over 65 lbs. to no more than 80 psi.

2. If I inflate to the 10 ply to 65 lbs. it technically has the same weight capacity as the 8 ply.

3. The 10 ply tire inflated to max load (80 lbs) will give me 300 lbs more capacity per tire.

With these three facts the questions are:

1. Will an 8 ply tire at its 65 lb max inflation run cooler than a 10 ply at 65 lbs?
a. If it runs hotter, is it still a safer tire?

2. Will the current Airstream wheels (2004 model) allow a tire with inflation up to 80 lbs?

3. Will a 10 ply tire at 80 lbs. cause a rougher ride for the trailer than an 8 ply tire at 65?

4. What about ride quality if both tires roll at 65 lbs?

Obviously the 10 ply gives me more cushion even though I won't ever load the trailer up past 9,100 lbs. which is still within the maximum capacity of the 8 ply tire. But I'm worried that if I inflate over 65 lbs. to get the extra margin will I end up popping rivets due to a rougher ride? And the issue of a hotter running tire at lower pressure is also making me wonder.

Jack
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Old 08-16-2007, 02:59 PM   #2
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The 10 ply will run hotter and increase probability of separation.
It will also give you a significantly rougher ride.

The first statement is from two different tire manufacturers. The second statement is from personal experience when I replaced 8 ply tires with 10 ply on a Suburban.
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Old 08-16-2007, 03:13 PM   #3
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Quote:
Originally Posted by jcanavera
a. If it runs hotter, is it still a safer tire?

2. Will the current Airstream wheels (2004 model) allow a tire with inflation up to 80 lbs?

3. Will a 10 ply tire at 80 lbs. cause a rougher ride for the trailer than an 8 ply tire at 65?
Jack
a. 10 ply tires aren't 'safer' than 8 ply...
2. yes
3. yes


it's interesting this post and series of questions makes no mention of the tire brand...

it's your thread but that really doesn't help folks who search here by brand name and sorta adds vagueness to the issue.

so it seems maxxis st radial tires is the focus here, not LT tires or true bias ply tires, other brands?

to begin with these maxxis tires aren't 8 or 10 ply. both of these maxxis st radial tires are the same number of plys.

that is a term used to compare the load rating to more traditional (really old) bias tire construction.

maxxis does still offer bias ply tires but only up to 6 ply.

higher pressures shouldn't result in running at hotter temps.

tire temps climb as a result of load, braking, roadway friction and temps, and side wall flex from under inflation.

yes the 30 slide is the heaviest thing on 4 wheels but much of that extra mass is tongue weight.

how much is your tongue mass? 1000 lbs, 1200 lbs or more?

so without actually weighing each of the 2 axles (or each wheel) and the tongue, this is still big time guestimation.

the actual wheel loads may be as little as 1700 lbs or a more reasonable 2000 lbs?

your alcoa forged 5 spoke 15x7j wheels are rated to 95 psi, so YES they can handle 80 psi...

but these rims are only load rated to 2200 lbs.

i don't fear wheel failure (i've got 9 of these rims alcoa rims) but they are really really light!

using tires that exceed the wheel rating by several hundred lbs isn't usually wise...

and won't increase the single wheel carry capacity of 2200 lbs.

the '8ply' equivalent tire is rated to 2500 lbs or 10,000 lbs with 4 evenly loaded...

so nothing is gained by opting for the '10ply' 2800 lb tire on a 2200 lb rated rim.

cheers
2air'
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Old 08-16-2007, 03:39 PM   #4
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Ok. Lots of ideas here. 2air, you are right the tires I am looking at are the Maxxis brand which carry a 8 or 10 ply rating. I don't believe we see any tires any more that truely are ply counts. It's all ratings. I didn't list the brand because at this point I was just trying to deal with the 8 ply/10 ply issue rather than mix brands into this.

Hitch weight on my trailer according to A/S is 1,250 lbs. I assume it might be heavier with 2, 30 lb lb tanks. I'm using a class V hitch.

The rim issue is interesting. Why would they give you wheels that would be rated less than the trailer's gross? If your numbers are correct those wheels have a capacity of 8,800 lbs. Short of my 9,100 rated gross.

My question on the pressure was whether the same size tire, carrying the same load, but rated differently (based on plys and maximum inflation levels), which one would run cooler? My gut would tell me the higher load rate tire, might run hotter since you are running it below its max inflation level and that possibly its mass or composition might cause that higher temperature.

We've had that question before relative to load D or load E rated tires rather than ply related measurements.

Jack
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Old 08-16-2007, 03:45 PM   #5
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I would say based on the answers so far, I don't want a rougher ride, and unless I'm willing to increase the pressure above the 65 psi range on the 10 ply tire, I might have to deal with a failure due to hotter running tires.

It looks like the 6 ply rated tire would be the better choice. So do we conceptually state across the board that higher load capacity tires do not have any advantage over the stock supplied tires 6 ply D rated tires (forgetting about quality of the manufacturers)?

Jack
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Old 08-16-2007, 03:58 PM   #6
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Originally Posted by jcanavera
..The rim issue is interesting. Why would they give you wheels that would be rated less than the trailer's gross? If your numbers are correct those wheels have a capacity of 8,800 lbs. Short of my 9,100 rated gross...Jack
that rating is stamped into the rim, i can post a pic IF you like.

the simply answer to 'why' is that that the tongue really does carry a significant amount of the gross weight.

more likely the reality is...

a/s used this rim for a LOT of years and when trailers weighed much less.

alcoa made these rims 4 all vendors but in the last few years of production ONLY for a/s.

a/s continued to buy up the rim stock even AFTER alcoa stopped production.

notice the current 30/slide is gross rated at over 10,000 lbs, 10.5 as i recall.

and no longer comes with alcoa wheels (they may NOT fit the dexter disc brakes/nev-r lube hubs)

but does still have goodyear st marathons rated to 2540 lbs ?

cheers
2air'

i suspect the 10p equivalent maxxis is 2-3 lbs heavier than the 8p...

IF this is true, that is increased rotational mass and more un sprung weight...

which, in theory would take more to balance and roughen the ride at equal pressures....

i think the only way to know with some degree of sureness about 'temps' would be to mount an 8 and a 10 on the same side and run 'em....

and expensive experiment 2 be sure.
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Old 08-16-2007, 04:12 PM   #7
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Quote:
Originally Posted by 2airishuman
that rating is stamped into the rim, i can post a pic IF you like.

the simply answer to 'why' is that that the tongue really does carry a significant amount of the gross weight.

i suspect the 10p equivalent maxxis is 2-3 lbs heavier than the 8p...

IF this is true, that is increased rotational mass and more un sprung weight...

which, in theory would take more to balance and roughen the ride at equal pressures....

i think the only way to know with some degree of sureness about 'temps' would be to mount an 8 and a 10 on the same side and run 'em....

and expensive experiment 2 be sure.

I would think that you have to be right regarding the hitch weight being the key issue here with the wheel capacities. Assuming that there can be a 50/50 split provided by the equalizing hitch, my trailer loaded to its gross capacity not hitched, would lose about 625 lbs or so of weight that would be transferred to the tow vehicle. That gets you right in line with the wheel capacity thus making the load on the wheels to be 8,475 lbs, and gives me another 325 lbs. to play with in accounting for propane tanks.

Hmmm...maybe we should have save this topic for the cold of winter. It makes a good hot stove league topic!

Jack
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