Tire Speed Rating Question

Not to hijack this thread, at least not too much :), but how exactly will "low tire pressure" be proven to be the culprit? It's pretty much impossible to tell "after the fact" so any speculation is just that: speculation.

I’m sure most readers here have heard this statement. “There is the right way - the wrong way - and my way.” I don’t write my posts with the My Way. I avoid the Wrong Way. That leaves The Right Way. It often meets disapproval from a minority of readers. The antiestablishment readers oppose establishment ways. They are most often the My Way folks.

I post this often and it’s a fact. Tire manufacturers do not set the pressures for your vehicle’s tires. Vehicle manufacturers do.

The correct air pressure for your Original Equipment (OE) tires is the air pressure (s) listed as recommended tire pressures found on the vehicle’s certification label and in it’s owner’s manual. Deviations will also be found in the owner’s manual.

Load inflation charts are necessary when plus sizing up from the OE tires. Going down is not an industry consideration. Load inflation charts are also necessary for axle imbalance conditions. But, only when there is load capacity reserve air pressure available for the condition.

Those of you that do it your way are far more likely to contribute to early tire failures than those doing it the right way.

I cannot over stress how important it is to insure your trailer tires are aired to the certified recommended tire pressure (s). When you see those black tire gators on the side of the road it should be a reminder to make sure you check your tire pressures before getting underway. If someone ever compiles some statistics for trailer tire tread separations, low tire pressure will a culprit high on the chart.

FastEagle

pronstar wrote:

Francesca Knowles wrote:

Someone please correct me if I'm wrong, but the way I understand that "increase the air pressure for higher speed" thing is that it refers to recommended pressure for the load as a baseline.
Taking as an example the first tire in the chart below, if installed in a position carrying 1530 pounds of weight, 40 pounds of pressure is "correct". But running it at its 50 pound maximum would allow for the higher speed.

I interpret that to mean that if one's running it at 50 pounds already, one's good for the higher speed....is that correct?

You are absolutely correct.

The "general consensus" for many posters on RV.net is that all trailer tires should always be maxed-out for psi, but in reality I believe they should have their pressures set according to load, as the MFR recommends, just as we do with any other tire.

The key thing is the Load Range letter. I have a utility trailer that rides on "185/80-13D-ST" tires with a load range of D. There is no load range D listed on the above chart for that size tire. But the specs from the tire manufacturer tell me that I can haul 1725 (for a total of 3450 lbs) lbs when the tire is inflated to 65 psi and that is the maximum for the tire. And that allows me a maximum speed of 65 mph. Load Range D indicated that the tire has a 8 ply rating. Load Range C indicated that it has a 6 ply rating. The tire will run cooler when running its maximum rated PSI, not matter how much weight it is carrying, provided it is no overweight. The reason we run motorhome tires using the tire inflation charts is for a better ride. A trailer with ST tires does not require a softer ride.

Special Trailer (ST) Service Tires
Special Trailer Service tires are often available in multiple load ranges. The appropriate load range is identified immediately following the size's rim diameter in manufacturers descriptions.

ST-Metric sized special trailer service tires will be branded with their load range (Load Range D or LRD) on their sidewalls and list their appropriate load range letter in their descriptions as ST205/75R15 LRD.

Francesca Knowles wrote:
Looks like my (most recent) question got lost in the shuffle...it had nothing to do with running over the max tire pressure as given on the tire sidewall. Asking your forbearance, I'd like to repeat it here in hopes of getting an answer

Thanks, I hope!

pronstar wrote:
See that's the problem...
On the one hand, we're "supposed to" run ST tires at max pressure at all times.

On the other hand, we're told we can safely exceed 65 mph if we increase tire pressure.
It's a moot point when the tire pressure is already maxed out.

Someone please correct me if I'm wrong, but the way I understand that "increase the air pressure for higher speed" thing is that it refers to recommended pressure for the load as a baseline.
Taking as an example the first tire in the chart below, if installed in a position carrying 1530 pounds of weight, 40 pounds of pressure is "correct". But running it at its 50 pound maximum would allow for the higher speed.

I interpret that to mean that if one's running it at 50 pounds already, one's good for the higher speed....is that correct?

If you are at 40psi and under or at 1530 lbs you are good for max rated speed in your example. (for the LR C tire obviously)

Francesca Knowles wrote:

Someone please correct me if I'm wrong, but the way I understand that "increase the air pressure for higher speed" thing is that it refers to recommended pressure for the load as a baseline.
Taking as an example the first tire in the chart below, if installed in a position carrying 1530 pounds of weight, 40 pounds of pressure is "correct". But running it at its 50 pound maximum would allow for the higher speed.

I interpret that to mean that if one's running it at 50 pounds already, one's good for the higher speed....is that correct?

You are absolutely correct.

The "general consensus" for many posters on RV.net is that all trailer tires should always be maxed-out for psi, but in reality I believe they should have their pressures set according to load, as the MFR recommends, just as we do with any other tire.

Looks like my (most recent) question got lost in the shuffle...it had nothing to do with running over the max tire pressure as given on the tire sidewall. Asking your forbearance, I'd like to repeat it here in hopes of getting an answer

Thanks, I hope!

pronstar wrote:
See that's the problem...
On the one hand, we're "supposed to" run ST tires at max pressure at all times.

On the other hand, we're told we can safely exceed 65 mph if we increase tire pressure.
It's a moot point when the tire pressure is already maxed out.

Someone please correct me if I'm wrong, but the way I understand that "increase the air pressure for higher speed" thing is that it refers to recommended pressure for the load as a baseline.
Taking as an example the first tire in the chart below, if installed in a position carrying 1530 pounds of weight, 40 pounds of pressure is "correct". But running it at its 50 pound maximum would allow for the higher speed.

I interpret that to mean that if one's running it at 50 pounds already, one's good for the higher speed....is that correct?

wny_pat wrote:

full_mosey wrote:

FastEagle wrote:


The correct answer is to use the recommended air pressure value found on the tire placard.

FastEagle

Footnote: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure. (Toyo RV tires)

Think


Aren't you saying that the only approved way to travel with ST tires is to stay under 65mph?

The TT tire placard says NOTHING about speed. Why can't I drive any legal speed?

HTH;
John

You guys are mixing apples and oranges here!!! Toyo only makes commercial trailer tires, nothing smaller than 17.5". They are not a ST tire, but a "Trailer Position" catagory tire listed under their Medium Commercial Truck tires.

And both commercial trailer tires and ST tires have speed ratings. Just look at the tire specs!

Sorry I took that statement out of context. It is the stance Toyo takes with any tire aired in such a manner. Airing tires to the heaviest loaded tire puts a lot of trust in the air pressure measuring equipment.

FastEagle

Footnote: "If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure." (Toyo RV tires)

Applicability is the key to using inflation pressures outside of normal procedures. Just because a procedure is known doesn’t mean just anybody can apply it.

All LT tires can be aired to 10 psi above the maximum amount printed on the tire’s sidewall. Weight reduction to do so is not a factor. Speed is not a factor. So why would it be done? Maybe to cut down on tire flex with heavy loads? Anyhow, now you know it. What you ganna do with it?

Tire manufacturers do not set the pressures for your vehicle’s tires. Vehicle manufacturers do. They place the correct tire pressures on certification labels. In the owner’s manuals they tell you to never exceed the maximum amount of pressure shown on the tire’s sidewall. All of the tire warranty information I’ve read says to never exceed the maximum amount of tire pressure shown on the tire’s sidewall. So, when is this extraordinary event of increasing tire pressure going to happen? Can you get someone to take responsibility (tire manufacturer/vehicle manufacturer) for such radical increases in tire pressures?

If you take it upon yourself to jack your tire pressures up 10 psi beyond maximum sidewall inflation pressure and one of those tires blows off the side of your trailer, who do you think should pay the damages? Better to check with the tire and trailer builders before experimenting with tire pressures up above the normal recommendations.

FastEagle

full_mosey wrote:

FastEagle wrote:


The correct answer is to use the recommended air pressure value found on the tire placard.

FastEagle

Footnote: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure. (Toyo RV tires)

Think


Aren't you saying that the only approved way to travel with ST tires is to stay under 65mph?

The TT tire placard says NOTHING about speed. Why can't I drive any legal speed?

HTH;
John

You guys are mixing apples and oranges here!!! Toyo only makes commercial trailer tires, nothing smaller than 17.5". They are not a ST tire, but a "Trailer Position" catagory tire listed under their Medium Commercial Truck tires.

And both commercial trailer tires and ST tires have speed ratings. Just look at the tire specs!

Before pumping those tires above sidewall max pressures talk with your tire dealer first about warranty issues. Pump a tire above its pressure rating and blow the sidewall out or split the tread belts and a dealer is under no obligation to honor the warranty.

Increasing pressure in ST tires for higher speed operation has changed over the years. Goodyear tire spec sheets at one time recommended that only certain sizes of their ST tires could do this however they were required to have a reduction in load with those higher pressures and speed. I see that information has changed.