RV Tires

[cpaharley2008]

Recreational Vehicle Tires
How to Get the Most from Your Recreational Vehicle Tires brought to you by Michelin North America
The Importance of Air Pressure

The most important factor in maximizing the life of your tires is maintaining proper inflation. Driving on any tire that does not have the correct inflation pressure for the load of the vehicle is dangerous and may cause premature wear, tire damage, and/or loss of control of the vehicle.

A tire that is underinflated will build up excessive heat that may go beyond the prescribed limits of endurance of the rubber and the radial cords. This could result in sudden tire failure. A tire that is underinflated will also cause poor vehicle handling, rapid and/or irregular tire wear, and a decrease in its fuel economy.

Over inflation will reduce the tire's footprint or contact patch with the road, thus reducing the traction, braking capacity, and handling of the vehicle. A tire that is over inflated for the load that it is carrying will also contribute to a harsh ride, uneven tire wear, and will be susceptible to impact damage.

Maintaining correct tire inflation pressure for each loaded wheel position on your vehicle is of the utmost importance and must be a part of regular vehicle maintenance.

How Much Air Should I Carry in My Tires?

Federal law requires that the tire's maximum load rating be molded into the sidewall of the tire. On the tire's sidewall you can see the maximum load allowed for the size tire and load rating, and the minimum cold air inflation pressure needed to carry that stated maximum load. Utilizing less air pressure means a lesser load can be carried by the tire.

The amount of air pressure you need to use is dependent on the weight of your fully loaded vehicle.

It is important to note that the cold inflation pressure for the tire must never exceed the maximum inflation rating stamped on the wheel.

When Should I Check my RV's Tires' Air Pressure?

You should check the air pressure every two weeks or at least one a month and before any major trip. Your RV tires' air pressure should be checked every "drive" morning on long trips. On short trips of a day or less driving each way, your tires should be checked before you leave on your trip and again before you start your trip home. If your vehicle is stored for any length of time, air pressure should be checked prior to storage, but more importantly, when it comes out of storage.

Check your tires when they are "cold" and have not been driven for more than one mile. The stated load capacity for a given cold inflation pressure is based on ambient outside temperature. If you must check your tires when they are warm or hot, do allow for a slight increase in air pressure and make sure they are within a couple of pounds of each other on the same axle. Never let air out of a hot tire.

It is recommended you purchase a quality truck tire air gauge which has an angled dual head. This type of gauge allows you to check inflations on the inner dual wheel which has the valve stem pointing toward you, and on the outer wheel which has the valve stem pointing away from you. Nothing should restrict your ability to check a tire's air pressure daily when you are driving your RV. Pressure sealing valve caps should always be used to prevent air from escaping from the valve stem. If you use valve stem extension hoses, make sure they are good quality stainless steel braid reinforced and are securely anchored to the outer wheel. If your RV has wheel covers which must be removed to check the inflation, then consider removing them on a long trip, as the extra time and effort required may lead you to avoid checking your air pressure.

What if You Don't Check Your Air Pressure?

If a tire picks up a nail or screw that creates a slow leak and causes some air pressure loss, you might eventually spot it visually if it's a front tire. If it is an outside rear dual, you might also spot it with a visual inspection. However, if it is an inside rear dual, the chances of spotting it without an air pressure check are very slim. If you begin driving without finding it, very quickly (in most cases a few miles) your outside rear tire next to the low air pressure tire is going to heat up from carrying double its load, which will cause both tires to fail. Then you'll have two tires down on the same side and on the same axle, and a five ton or more vehicle at any speed is difficult to bring under control.

[floyd]

One thing which can be frustrating on Goodyear's site is that they obfuscate the difference between Motorhome(RV) tires and trailer (ST) tires.
Be sure to properly maintain,according to your specific tire and application.

[Borden]

Originally Posted by floyd

One thing which can be frustrating on Goodyear's site is that they obfuscate the difference between Motorhome(RV) tires and trailer (ST) tires.
Be sure to properly maintain,according to your specific tire and application.

Agree his only adds to the confusion out there

Tire limits; told by MTO we can use car, light truck tires on our trailers in Ontario but sidewall limits reduced by 10% and not recommended also the tire expert and the RV dealer both said they would not recommend it and we should get ST tires.
That is why we purchased 3 radial ST tires for on our unit.

P.S. was also told to use the recommended tire pressure inside closet door not tire max for safest ride and best tire ware

[Brian B-P]

Originally Posted by Borden

Tire limits; told by MTO we can use car, light truck tires on our trailers in Ontario but sidewall limits reduced by 10% and not recommended...

This is not unique to the Ontario Ministry of Transport (MTO), and probably not correctly stated.

The Tire and Rim Association (TRA) defines the Passenger (P), Light Truck (LT), and Special Trailer (ST) standards, which include the derating factor of 1.1 for Passenger tires in truck, van, or trailer service; it does not apply to Light Truck tires.

[rabbit]

Here's a question. Before you answer, I should tell you that I can find cavils and qualifications anywhere; answers are harder to come by. Weight on single axle 3120lb. Each ST tire rated to carry 1760lb. Max inflation 50psi. If there was a manufacturer rec sticker, it's gone or illegible. I currently inflate to max tires cold. What should I inflate to? I'm assuming for the purposes of simplification that difference in load each side is negligible. SWAGs accepted but formulas and tables prefered.

jack

[floyd]

Originally Posted by rabbit

Here's a question. Before you answer, I should tell you that I can find cavils and qualifications anywhere; answers are harder to come by. Weight on single axle 3120lb. Each ST tire rated to carry 1760lb. Max inflation 50psi. If there was a manufacturer rec sticker, it's gone or illegible. I currently inflate to max tires cold. What should I inflate to? I'm assuming for the purposes of simplification that difference in load each side is negligible. SWAGs accepted but formulas and tables prefered.

jack

Maintain at least your present inflation, and check it everyday before moving out, then touch and look at evey fuel stop. Formulas and tables are fine if you're trying to prevent a virtual flat (No really they can give you a ballpark figure)

[rabbit]

I gather from what you say, Floyd, that curb wgt 13% under the combined capacity of the tires means nothing more than inflate to the max on the sidewall. What would be the threshold at which these tires would be overinflated at 50psi? Curb wgt. 25% under the tire capacity? 50% under? Yeh, I SORT OF know the answer to that: When the trailer bounces too much and tread adhesion is lost.

jack

[Brian B-P]

Originally Posted by rabbit

What should I inflate to?

In the spirit of this sticky reference I'll avoid specific numbers and stay with general approach, but for each type and size of tire there are industry-standard load-inflation charts. Several tire manufacturers post these (on their websites) for ST, LT, and commercial tires. Find the pressure at which your tire has enough capacity, and you have the minimum (not necessarily ideal) inflation pressure. You can straight-line interpolate between chart values to get closer than the large steps of the table.

[rabbit]

Thanks Brian. I'm off to do some interpolation.

jack

[Brian B-P]

Originally Posted by rabbit

I'm assuming for the purposes of simplification that difference in load each side is negligible.

That may be valid, but load is often quite unevenly distributed side-to-side. Ideally, weigh each side separately, choose the inflation pressure for the more heavily loaded side, then use that same pressure on both sides.

[floyd]

Originally Posted by rabbit

I gather from what you say, Floyd, that curb wgt 13% under the combined capacity of the tires means nothing more than inflate to the max on the sidewall. What would be the threshold at which these tires would be overinflated at 50psi? Curb wgt. 25% under the tire capacity? 50% under? Yeh, I SORT OF know the answer to that: When the trailer bounces too much and tread adhesion is lost.

jack

The point at which the tire is overinflated might be the point at which the center of the tire starts to wear faster than the edges.
I don't buy the thought that tires ought to be considered part of the suspension, but the contact patch should be even.You might try spraying some water across a short section of your dry driveway and run the trailer across it.
My trailer weighs about 1950 pounds loaded with about 1700 pounds on the axle. The original "B" rated tires had a sidewall max of 35 PSI. Even at 1150 pound capacity, they looked marginal to me, so I ran them 26000 miles with a sustained 40PSI.
They were removed from service with about 40% tread and even wear.

They were then replaced with "C" rated tires which are run at 50PSI.

I prefer tight tires for handling, wear, and fuel economy.
I have never had a tire failure on any trailer, or car dolly, which I have owned. Could happen next week though,so diligence is prudent.

BTW, My trailer rides nice enough that I leave a roll of paper towels standing on the counter and it's there at the campsite.

[rabbit]

Here's a chart which is indexed as pertaining to Goodyear Marathons but may well be generic as the heading on the chart does not mention Goodyear. Chart didn't copy correctly to register inflation pressure in a column directly above wgt. capacity of tire. So I go to a 205/75R14 tire at the left and move over to the wgt. I believe is carried on each of my tires (1560lbs.) and then up to the inflation pressures. 1560 is between 1530 and 1640. Those are the numbers in position six and seven in the rank so up to inflation rank to find that in position six and seven are 40 and 45psi respectively. I think by a strictly linear interpolation, I could run 43lbs. and that at 65mph., avoid sidewall flex, have a full tread width footprint for maximum traction and minimum bounce. I know someone smells a rat here. What is it?

LOAD/INFLATION INFORMATION FOR RV ST METRIC TIRES
Max
Speed
Tire Rating Inflation Pressure - PSI
Size (MPH) 15 20 25 30 35 40 45 50 55 60 65

ST175/80R13 65 670 795 905 1000

1100( 1190 1270 1360(C)

ST185/80R13 65 740 870 990 1100

1200( 1300 1400 1480(C)

ST205/75R14 65 860 1030 1170 1300

1430( 1530 1640 1760(C)

ST215/75R14 65 953 1110 1270 1410

1520( 1660 1790 1870(C)

ST205/75R15 65 905 1070 1220 1360

1480( 1610 1720 1820(C)

ST225/75R15 65 1060 1260 1430 1600 1760 1880 2020

2150(C) 2270 2380 2540(D)

ST235/80R16 65 1720 1920 2090 2270 2430 2600 2730 2870

3000(D)

Tire Single (S) Inflation Pressure - PSI
Size Dual (D) 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
LT215/75R15 S 1345 1475 1600

1765(C) 1845 1960 2095(D)

D 1225 1340 1455

1610(C) 1680 1785 1930(D)

LT235/75R15 S 1530 1680 1825

1895(C) 2100 2230 2335(D)

D 1390 1530 1660

1820(C) 1910 2030 2150(D)

LT225/75R16 S 1500 1650 1790

1940(C) 2060 2190 2335(D) 2440 2560 2680(E)

D 1365 1500 1630

1765(C) 1875 1995 2150(D) 2200 2330 2470(E)

LT245/75R16 S 1700 1865 2030

2205(C) 2335 2480 2623(D) 2765 2900 3042(E)

D 1545 1695 1845

2006(C) 2125 2255 2381(D) 2515 2640 2778(E)

LT215/85R16 S 1495 1640 1785

1940(C) 2050 2180 2335(D) 2430 2550 2680(E)

D 1360 1490 1625

1765(C) 1865 1985 2150(D) 2210 2320 2470(E)

LT235/85R16 S 1700 1870 2030 2205 2335 2485

2623(D) 2765 2905 3042(E) 3170 3300 3415 3550 3675 3750(G)

D 1545 1700 1845 2006 2125 2260

2381(D) 2515 2645 2778(E) 2885 3005 3085 3230 3345 3415(G)

7.50R16LT S 1620 1770 1930

2040(C) 2190 2310 2470(D) 2560 2670 2755(E)

D 1430 1565 1690

1820(C) 1930 2040 2150(D) 2245 2345 2470(E)

8.75R16.5 S 2240 2405 2470 2570

2680(E)

D 1970 2095 2175 2260

2405(E)

LOAD/INFLATION INFORMATION FOR RV TIRES

[Brian B-P]

Originally Posted by rabbit

Here's a chart which is indexed as pertaining to Goodyear Marathons but may well be generic as the heading on the chart does not mention Goodyear

Correct - this is the standard ST table, although showing only sizes offered by Goodyear.

Originally Posted by rabbit

Chart didn't copy correctly to register inflation pressure in a column directly above wgt. capacity of tire...

Since the current FiberglassRV forum software does not support tables, this sort of information is not reasonable to present. I think it makes more sense to just link to the source: Tire Inflation and Loading... and perhaps attach the PDF file.

[Brian B-P]

Originally Posted by rabbit

So I go to a 205/75R14 tire at the left and move over to the wgt. I believe is carried on each of my tires (1560lbs.) and then up to the inflation pressures. 1560 is between 1530 and 1640. Those are the numbers in position six and seven in the rank so up to inflation rank to find that in position six and seven are 40 and 45psi respectively. I think by a strictly linear interpolation, I could run 43lbs. and that at 65mph., avoid sidewall flex, have a full tread width footprint for maximum traction and minimum bounce. I know someone smells a rat here. What is it?

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.

[rabbit]

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

[floyd]

Originally Posted by rabbit

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

So keep your drinks on the floor!

[rabbit]

Originally Posted by Brian B-P

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.

jack

[floyd]

Originally Posted by rabbit

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.

[rabbit]

My humbled apology, Floyd. I guess my sippy cup could go tervis tumblling what with all this slamming about in unformatted territory.

jack

[Brian B-P]

Originally Posted by rabbit

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.