RV Tires - Page 7 - Fiberglass RV


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Old 01-07-2013, 01:59 PM   #85
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Originally Posted by Francesca Knowles View Post
Good for you for going to the "horse's mouth", Jared.

Any word from the rim maker as to PSI limits on the wheels you bought?

Francesca
Nope. It better be 80 p.s.i.

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Originally Posted by Brian B-P View Post
Sure, but for 85 mph those "right conditions" clearly include a tire rating high enough that your load is no more than 90% of the tires standard capacity at 10 psi less than the sidewall maximum.

Using Jack's example:
  • ST205/75R14, load range C
  • maximium inflation pressure: 50 psi
  • standard tire capacity at 50 psi: 1760 lb
  • standard tire capacity at 40 psi (to allow 10 psi extra inflation for higher speed): 1530 lb
  • tire capacity at 40 psi reduced by 10% (to allow for even for higher speed): 1377 lb

Is that enough for you? It is far too low for the 3120 lb on Jack's axle, but the point here is just to illustrate the application of the adjustments for higher speed with an ST tire.

(capacity values from the standard ST load/inflation table as published by Goodyear and linked to their RV Tire Inflation / Loading page)
I think the heaviest scamp 19 was 3600, which mine will probably be on the heavier side, as I've added weight rebuilding it. Even so, maxxis has a 225/75r15 with a 2830# rating, so I would still be well within limits.

Here's the chart for maxxis:
http://www.maxxis.com/Repository/Files/m8008load.pdf

Drop the pressure to 60, that gives you 2380#,x .9 = 2142#, still plenty for me.
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Old 01-07-2013, 10:13 PM   #86
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Originally Posted by Jared J View Post
I think the heaviest scamp 19 was 3600, which mine will probably be on the heavier side, as I've added weight rebuilding it. Even so, maxxis has a 225/75r15 with a 2830# rating, so I would still be well within limits.
In Trailer Weights in the Real World the heaviest Scamp 19 is 3860 lb with 3300 lb of that on the axle.

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Originally Posted by Jared J View Post
While Jared was responding I was editing and added that same link to my post... although they're TRA standard values for ST tires so it wouldn't matter which table one uses except that Goodyear didn't include the values for over 65 psi (it looks like they don't sell Marathons for those pressures).

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Originally Posted by Jared J View Post
Drop the pressure to 60, that gives you 2380#,x .9 = 2142#, still plenty for me.
60 psi would provide full 2380 lb capacity to 65 mph, 2150 lb capacity (the normal capacity for 50 psi) to 75 mph, and 2150*0.9=1935 lb capacity to 85 mph... still enough for Jared's example.

I notice that the Scamp 19 comes from the factory on '13” C load radial' tires: assuming these are ST185/80R13 LR-C, their max capacity at 50 psi and 65 mph is only 1480 lb... even that is inadequate if loaded anywhere near the 3500 lb axle capacity, and 1300 lb at 75 mph or 1170 lb at 85 mph (both at 50 psi) are even bigger problems for anyone needing high load and speed capacity.
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Old 01-07-2013, 10:27 PM   #87
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Nope. It better be 80 p.s.i.

I was looking at your other thread and I think I read that you bought wheels for the Scamp to match your truck and that while it had been your intention to buy LT's, your tire guys persuaded you to buy ST's instead. It's my hope that since they seem to have been knowledgeable enough to have made that recommendation, they didn't overlook checking the tire rim and verifying that it was up to the PSI/load requirements for the ST's.

Still...it occurs to me to ask:

Were you considering Maxxis at that time? I ask since my look at the Maxxis in the size you gave indicates that most have a maximum PSI rating much below that of trailer tires.

A concern in my mind would be that by "matching" your truck rims you may have wound up with some that are not rated for the kind of pressure that ST tires run at, even at regular speeds, not to mention anything above 65 mph.

You haven't said what specific make/model the rims are, but I'd be most interested if you'd do so!

Francesca
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Old 01-07-2013, 11:54 PM   #88
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Originally Posted by Francesca Knowles View Post
Were you considering Maxxis at that time? I ask since my look at the Maxxis in the size you gave indicates that most have a maximum PSI rating much below that of trailer tires.
"The Maxxis"? Maxxis makes dozens of models of tires, one of which (the M8008) is an ST trailer tire; that is the tire for which Jared quoted capacity ratings and information from Maxxis. If you are seeing maximum inflation pressures mostly under 50 psi, you're likely looking at one of the several P or Euro-metric models in their Automotive / Light Truck range.

Francesca, what Maxxis tire are you looking at and why would it not be the M8008, given Jared's posts in this thread?

Quote:
Originally Posted by Francesca Knowles View Post
... most have a maximum PSI rating much below that of trailer tires.
In fact "trailer tires" - even if considering only those conforming to ST standards - have maximum inflation pressures ranging from only 35 psi (and even less in some sizes not typically used for travel trailers or included in the M8008 range) to 80 psi (and perhaps higher). There is no inflation pressure limit which is unique to trailer tires, and no single inflation pressure limit which is characteristic of trailer tires.
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Old 01-08-2013, 03:15 AM   #89
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Originally Posted by Brian B-P View Post
60 psi would provide full 2380 lb capacity to 65 mph, 2150 lb capacity (the normal capacity for 50 psi) to 75 mph, and 2150*0.9=1935 lb capacity to 85 mph... still enough for Jared's example.

I notice that the Scamp 19 comes from the factory on '13” C load radial' tires: assuming these are ST185/80R13 LR-C, their max capacity at 50 psi and 65 mph is only 1480 lb... even that is inadequate if loaded anywhere near the 3500 lb axle capacity, and 1300 lb at 75 mph or 1170 lb at 85 mph (both at 50 psi) are even bigger problems for anyone needing high load and speed capacity.
Sorry, I was working my math backwards. I would run 80 psi, the 60 was after taking 20 off to get to that rating.

The tires on mine were 185/80r13's, just stupid.
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Old 01-08-2013, 03:21 AM   #90
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Originally Posted by Francesca Knowles View Post
I was looking at your other thread and I think I read that you bought wheels for the Scamp to match your truck and that while it had been your intention to buy LT's, your tire guys persuaded you to buy ST's instead. It's my hope that since they seem to have been knowledgeable enough to have made that recommendation, they didn't overlook checking the tire rim and verifying that it was up to the PSI/load requirements for the ST's.

Still...it occurs to me to ask:

Were you considering Maxxis at that time? I ask since my look at the Maxxis in the size you gave indicates that most have a maximum PSI rating much below that of trailer tires.

A concern in my mind would be that by "matching" your truck rims you may have wound up with some that are not rated for the kind of pressure that ST tires run at, even at regular speeds, not to mention anything above 65 mph.

You haven't said what specific make/model the rims are, but I'd be most interested if you'd do so!

Francesca
The wheels are true trailer wheels, they just make them to match the pickup ones. They're ultra nomad wheels.

http://www.ultrawheel.com/ultra-whee...1&cat=1140&s=0

My pickup tires are also rated up to 80 psi, I run them at 45 usually, and 65 towing.
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Old 01-08-2013, 12:21 PM   #91
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Sorry, I was working my math backwards. I would run 80 psi, the 60 was after taking 20 off to get to that rating.
Okay, then from the ST standard load/inflation table for ST225/75R15 LR-E
  1. 2740 lb capacity at 70 psi (subject to ST standard limit of 65 mph)
  2. so 2740 lb capacity at 80 psi and up to 75 mph (10 psi extra inflation, within tire max pressure)
  3. and 2740*0.90 = 2466 lb capacity at 80 psi and up to 85 mph

... but the Scamp 19 axle capacity is only 3500 lb, so this is much more than required, and the optimal operating pressure may be lower.
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Old 01-08-2013, 05:42 PM   #92
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IF I'm understanding this correctly....

A trailer requires a load specific load rated tire. If intended to be driven at higher speeds needs 10 psi greater pressure AND a tire that is rated to Load range greater than the specific trailer tire load by a certain percentage. Leaving aside margin of error for tire load on bumps etc.

Say I need load range C so I purchase a tire that is rated as load range C at 50 psi AND rated to load range D at around 60 psi. Then inflate to 60 psi and it should be good at the higher speed? (from Maxxis info which may be specific to them).

I should expect road bumps to transfer more energy to my suspension given this configuration.

Going way back to inflation and tire wear early in the thread, I don't think ST tires "crown" as much as most tires from higher inflation. I noticed this from filling my tires (TV vs trailer) I can see 5 extra psi in the TV tire as a distortion of the tread surface, trailer not so much if any distortion visible to the tread surface shape.

I don't have a horse in this race really, I view the speed limit as the max limit not a requirement so I'm generally not going over 65. Wear and hidden damage from heat are what I concern myself with when it comes to tire inflation.
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Old 01-08-2013, 05:55 PM   #93
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Quote:
Originally Posted by RogerDat View Post

Say I need load range C so I purchase a tire that is rated as load range C at 50 psi AND rated to load range D at around 60 psi. Then inflate to 60 psi and it should be good at the higher speed? (from Maxxis info which may be specific to them).
I'm not sure exactly what you mean by what sounds like a sort of dual rated tire, but:

If I understand you to mean that you've bought a Load range "D" tire and by load range "C" you mean you're running it at the pressure recommended for that weight range, I think your interpretation of the Goodyear bulletin/letter to be correct.

The problem I'm presently wrestling with has to do with that language about rim PSI limits...but that would only affect those of us who are running tires at or near maximum load/PSI already.

Francesca
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Old 01-08-2013, 09:01 PM   #94
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Originally Posted by RogerDat View Post
IF I'm understanding this correctly....

A trailer requires a load specific load rated tire. If intended to be driven at higher speeds needs 10 psi greater pressure AND a tire that is rated to Load range greater than the specific trailer tire load by a certain percentage.
The 10psi boost and derating to 90% of rated capacity are two separate steps - you only need the 10psi boost for up to 75 mph, and the derating in addition only to allow up to 85 mph.

How about this:
A trailer requires a tire rated to handle its load. If intended to be driven at higher speeds needs 10 psi greater pressure than it would at the normal speed limit. For even higher speeds, a tire is required that is rated to load capacity greater than the normal load capacity by a certain percentage, as well as the higher pressure.
Quote:
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Leaving aside margin of error for tire load on bumps etc.
The rated capacity considers the effect of bumps - you don't need to do this again.
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Old 01-08-2013, 09:44 PM   #95
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Say I need load range C so I purchase a tire that is rated as load range C at 50 psi AND rated to load range D at around 60 psi.
"Load range" is just a shorthand notation to indicating the highest load (and corresponding) pressure that a tire can handle. A tire has only one load range - if it is Load Range D it is not Load Range C. All tires of the same type (ST in this case) and size have the same capacity when run at the same pressure. A LR-C tire and a LR-D tire of the same size have the same capacity at 50 psi; the difference is that of the two only the LR-D tire can be inflated more for higher capacity... or to allow higher speed... so for his example RogerDat would simply get the LR-D tire (of the size he is considering).

Quote:
Originally Posted by Francesca Knowles View Post
I'm not sure exactly what you mean by what sounds like a sort of dual rated tire, but:

If I understand you to mean that you've bought a Load range "D" tire and by load range "C" you mean you're running it at the pressure recommended for that weight range...
I think the use of load ranges here is just causing confusion, and I think Francesca is interpreting the description the same way I would; there are no "dual load range" tires. RogerDat is describing the selection of a Load Range D tire to get a high enough maximum inflation pressure to allow the "extra" inflation pressure needed for higher speed, although a Load Range C tire would allow high enough inflation pressure to get enough load capacity for normal speed operation.
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Old 01-23-2013, 10:49 PM   #96
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There's more to it, but since this is beginning to sound more like a church service than a discussion I'll leave all closely held belief/doctrinal issues to folks' Individual Consciences!

Francesca
So you'll stick to chapter and verse instead?...without canonized scripture?
It seems that heresy, blasphemy, or even apostasy would be impossible in the absence of the canonization of just what the true word of godyear really is. Even then it might be open to interpretation!
Should that read Proscience in this context?
BTW...isn't 50PSI twice the inspiration of 25PSI?
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Old 01-23-2013, 11:08 PM   #97
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You've been reading Bulwer-Lytton again, haven't you, Floyd?

Francesca
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Old 01-24-2013, 12:00 PM   #98
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<_<

You've been reading Bulwer-Lytton again, haven't you, Floyd?

Francesca
I have not heard the the name nor seen it in print before today!( but Wikiawokeme)
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