RV Tires - Page 2 - Fiberglass RV


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Old 12-31-2012, 08:14 PM   #15
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Thanks for posting the Goodyear link as the road to the pdf, Brian. I always assume that my computer skills are antideluvian by cf. with almost everyone else's and am never disappointed. I also know most of the habitues here are old enuf to remember how to walk their fingers up and down a bit and probably can distinguish a rank from a file.

I conclude that, from such a chart, I should be able to determine the adequate pressure to produce a balance of optimum tread wear and traction while producing an adequately-stiff side wall for miniumum rolling resistance. If I have determined rather the minimum inflation pressure, do you mean minimally adequate or the minimum that is wholly adequate or something else altogether?

jack
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Old 01-01-2013, 01:48 AM   #16
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Thanks for posting the Goodyear link as the road to the pdf, Brian. I always assume that my computer skills are antideluvian by cf. with almost everyone else's and am never disappointed. I also know most of the habitues here are old enuf to remember how to walk their fingers up and down a bit and probably can distinguish a rank from a file.

I conclude that, from such a chart, I should be able to determine the adequate pressure to produce a balance of optimum tread wear and traction while producing an adequately-stiff side wall for miniumum rolling resistance. If I have determined rather the minimum inflation pressure, do you mean minimally adequate or the minimum that is wholly adequate or something else altogether?

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Old 01-01-2013, 09:57 AM   #17
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That's right... for the minimum pressure. It might not be the best for bounce; the tire is a significant part of the suspension dynamics of a typical trailer (due to the stiff springing). Move up to 50 psi, and a somewhat higher speed would presumably be permitted.
So, given a stiff spring rate, soft tires transfer more vertical movement to the trailer than dynamited tires? Or could it be that a stiff spring rate is pretty rough on a trailer (or pickup bed) independent of tire inflation?

Floyd, I don't take my trailer out on NYEve; do you? I've never had a problem with stuff on the floor including the cast plastic sink cover which sometimes is left in place when we drag up. I'll have to take a short run with the tires at 43psi and try to determine empirically if it is indeed I whose head resides in dark place.

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Old 01-01-2013, 10:05 AM   #18
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So, given a stiff spring rate, soft tires transfer more vertical movement to the trailer than dynamited tires? Or could it be that a stiff spring rate is pretty rough on a trailer (or pickup bed) independent of tire inflation?

Floyd, I don't take my trailer out on NYEve; do you? I've never had a problem with stuff on the floor including the cast plastic sink cover which sometimes is left in place when we drag up. I'll have to take a short run with the tires at 43psi and try to determine empirically if it is indeed I whose head resides in dark place.

jack
I wasn't refering to alcohol or new years eve.... I was joking about your assessment of your computer skills.
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Old 01-01-2013, 10:56 AM   #19
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My humbled apology, Floyd. I guess my sippy cup could go tervis tumblling what with all this slamming about in unformatted territory.

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Old 01-01-2013, 02:22 PM   #20
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So, given a stiff spring rate, soft tires transfer more vertical movement to the trailer than dynamited tires? Or could it be that a stiff spring rate is pretty rough on a trailer (or pickup bed) independent of tire inflation?
The stiff springs are rough on trailers and their contents, regardless of the tires. Softer tires (for a given tire size - lower inflation pressure) can help.

The relevance of spring rate to tire pressure for bouncing is that the tires are poorly damped springs, multi-leaf spring packs are better damped (by interleaf friction), and the rubber spring rods common in egg suspensions are a bit better yet. Damping is the absorption of energy from the moving mechanical system to keep it from continuing to bounce. All are poor compared to a suspension with proper dampers (shock absorbers). If much of the movement of the system occurs in the tires, it can keep bouncing too long instead of just moving once over the bump and settling down, so soft tires may not be good.

The interaction of the tires and springs depends on the bump frequency and trailer mass, and the combined effect is not trivial, so I'm not hazarding a guess at the best pressure for ride and control.
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Old 01-01-2013, 02:38 PM   #21
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If I have determined rather the minimum inflation pressure, do you mean minimally adequate or the minimum that is wholly adequate or something else altogether?
Yes, it's the minimum for safe and reliable operation.

To put this in perspective, my Toyota van came with tires that are at their maximum load (after derating the P tires for van use, just as for a trailer) when inflated to their allowed maximum pressure and loaded to the gross rear axle weight rating. While owners complain about tire wear, there is no reliability problem with them.
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Old 01-01-2013, 03:00 PM   #22
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Great explanation, Brian. After a few thought experiments with baseballs and red rubber balls and the transfer of energy, it occured to me that soft tires might be expected to decrease the amplitude (absorb) of vertical motion from pavement discontinuities transfered thru the tire to a greater degree than would hard tires. Take the example of tennis balls which will hardly bounce (evidence of receipt of energy expressed as change of direction) when the pressure of the injected gas is lost. It seems counterintuitive to me that an object with a relatively high resistance to deformation is the best at cushioning impact but I do see a hint on the horizon that cushioning and damping may not be synonymous. As you say, compression rate and return rate (recovery from deformation) may be different for tires, springs, and shocks.

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Old 01-01-2013, 03:14 PM   #23
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One further thought on "minimum" inflation recs in the chart. Sad commentary on empirical science that no one is able to establish inflation pressures which are optimal (or at least balanced to give best wear, traction, ride control). Is the upper inflation limit on the Marathon STs also a "minimum"? Seems it might be as it's acceptable to the manuf. to add another 10psi to tires on rims rated for that pressure.

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Old 01-01-2013, 03:52 PM   #24
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One further thought on "minimum" inflation recs in the chart. Sad commentary on empirical science that no one is able to establish inflation pressures which are optimal (or at least balanced to give best wear, traction, ride control). Is the upper inflation limit on the Marathon STs also a "minimum"? Seems it might be as it's acceptable to the manuf. to add another 10psi to tires on rims rated for that pressure.

jack
The upper limit is just that. Since it's impractical to make vehicle-specific tires, they have to be suitable for a wide range of vehicles, so tires can be run at a variety of pressures under the stated maximum.

That's why the first thing a tire manufacturer says per pressure is "follow your vehicle maker's recommendation".

Barring access to a manufacturer's recommendation, appropriate pressure for trailer tires can be determined by the weight of the trailer itself combined with the tire manufacturer's chart of weights/pressures.

Side note:
There's a body of thought that says that exceeding a tire's stated maximum pressure (under certain conditions) by perhaps 5% is acceptable. I for one am too cautious to promote this practice...

Francesca
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Old 01-01-2013, 04:14 PM   #25
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Here's the dog whistle, Francesca. It's obvious to me from the previous discussion that no matter how sophisticated one's view of physics may be, most of us are concerned enuf about blowout at speed that we don't loose a lot of sleep over trailer tire tread wear (the side walls will crack before it's down to the markers) or the ride quality as experienced by our bedding, pots and pans (we're not iin there!). Everywhere I go, I find highly-nuanced discussions the upshot of which is always dynamite em for stiff, cool sidewalls. Add to this the caveats about constant monitoring of pressure, physical inspection of sidewall, etc. and it would seem that the worry beads are what keeps our rigs on the road.

I'd be mighty beholdin to anyone who will take my axle wgt. and tire specs and the Marathon chart at Brian's link and tell me at what pressure I should inflate. Nome sane?

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Old 01-01-2013, 04:17 PM   #26
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Originally Posted by Francesca Knowles View Post
The upper limit is just that. Since it's impractical to make vehicle-specific tires, they have to be suitable for a wide range of vehicles, so tires can be run at a variety of pressures under the stated maximum.

That's why the first thing a tire manufacturer says per pressure is "follow your vehicle maker's recommendation".
The above is very true but I would be very cautious about following a trailer manufactures recommended tire pressure if the trailer is 25 or more years old & the pressure recommendation stated by the trailer manufacture was made an equally number of years ago. The odds are the trailer tires you are buying today were not even around when the trailer manufacture made their pressure recommendations 30 years ago. IMHO in that situation you would be far better off going with what the actual tire manufacture recommends and use your actual trailer weigh as a guide.
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Old 01-01-2013, 04:26 PM   #27
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H
I'd be mighty beholdin to anyone who will take my axle wgt. and tire specs and the Marathon chart at Brian's link and tell me at what pressure I should inflate.

Nome sane?

jack
Well...part of the time I do...

Two questions per your request:

1) Are you actually using Goodyear Marathons, and if so what size?
and
2) (Axle weight being only another "capacity" number re. maximum capacity of that suspension component, it's necessary to know):
What does your trailer actually weigh?

Francesca
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Old 01-01-2013, 04:59 PM   #28
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Yes, I actually am, in size 205/75R14. wgt. on axle 3120lb. or 1560lb per tire. But, hey, I'm just having a bit of fun here about general advice and specific prescriptive advice. You don't even have to look at the Goodyear chart. I could run my tires at 43psi according to Goodyear and no suggestion anywhere that any inflation figure on there is a "minimum" figure--the numba is the numba.

So far today is the worst day of the year (surprise) and more to come so once it warms up enuf that we see the sun for two days running, maybe I'll hook up, dump the air down to 43 lb. and take a five mile run with a few items unsecured in the trailer. Couple of expansion joints should tell me all I want to know about shock absorption and damping. I should say that I am not singling out Brian and Floyd as the occasion of my little homily. Every camping and boat trailer forum has this very discussion where the blind men touch the elephant and tell you what they "saw" at least twice a month.

jack
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