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Old 04-17-2016, 04:30 PM   #29
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Quote:
Originally Posted by RVNeophytes2 View Post
Specifically, Paragraph S6.5 Tire markings. Sub-paragraph (d)

"(d) The maximum load rating and corresponding inflation pressure of the tire, shown as follows..."

Certainly wouldn't make any sense to pump tyres up more than is necessary to carry the weight any more than reducing pressures below what is needed.
If the load is the same as the rating of the tyre, going higher compromises the tyre integrity.
If the weight is less than the rating then keeping the pressure to the sidewall marking compromises ride comfort, braking efficiency and stability.
If the load is higher than rated then you shouldn't be increasing the pressure to compensate and should instead reduce the weight or fit higher rated tyres.

I still don't see the point of MrD's oft-repeated quotes since they have no relevance to practical situations
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Old 04-17-2016, 04:47 PM   #30
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Originally Posted by johnhicks View Post

FWIW by the chart I'm 110 rear and 105 front; sticker and placards say 95...but the fact is those 1993 tires were overloaded.
I don't quite understand your post. My understanding is the sticker and placards for the pressure is for the maximum capacity of the axles. If you are inflating higher do you:

- Have different size tires than were originally installed?
- Are your axles loaded heavier than the manufacturer has specified?
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Old 04-17-2016, 04:59 PM   #31
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Quote:
Originally Posted by Tony Lee View Post
Certainly wouldn't make any sense to pump tyres up more than is necessary to carry the weight any more than reducing pressures below what is needed.
If the load is the same as the rating of the tyre, going higher compromises the tyre integrity.
If the weight is less than the rating then keeping the pressure to the sidewall marking compromises ride comfort, braking efficiency and stability.
If the load is higher than rated then you shouldn't be increasing the pressure to compensate and should instead reduce the weight or fit higher rated tyres.

I still don't see the point of MrD's oft-repeated quotes since they have no relevance to practical situations
Mr D's quotes are self explanatory. In certain circumstances the tire pressure on the sidewall can be exceeded. It is the minimum pressure for the maximum load.

An example would be the recent 2016 Dutch Star axle issue. The front axle on the 2016 Dutch Star was insufficient for the setup of the coach. With two passengers, full fuel and full water the axle was overloaded. Newmar has increased the axle capacity of the affected coaches (will be retrofitting) but not changing the tires and wheels. The tire capacity is exactly at the increased rating of the axle. So if one follows prescribed logic of adding 5 or 10 lbs for side to side variances you would exceed the tire pressure for the max loaded rating of the tire.

Newmar is not upgrading the tires on existing coaches so that would appear to be the only option available unless the current owners wish to purchase new tires and wheels at their own expense. The 2017 models are apparently being equipped with larger tires and wheels which do not have the tires at their max capacity.
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Old 04-17-2016, 11:03 PM   #32
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> I don't quite understand your post. My understanding is the sticker and
> placards for the pressure is for the maximum capacity of the axles.

My axle ratings exceed that for 110psi and I'm running 110/105 according to the weight charts. Back in 1993 when the rig was new the max pressure the Michelins were rated for was 95 and the sticker says 95. Or IOW, GAWR on the placard couldn't have been carried without overloading the tires at their max pressure. My current tires are Load Range F; the earlier ones were Load Range E.
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Old 04-18-2016, 05:04 AM   #33
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Offending Passage

Quote:
Originally Posted by l1v3fr33ord1 View Post
Mr D-

A question for you: Are there cases where you (or the manufacturers) would recommend inflating a tire over the marked tire sidewall pressure?

If not, I suggest that the definition you've provided is a statement that a tire is designed with an above-the-sidewall-marked inflation safety margin, which I think is something most everyone assumes is the case.
I don't have access to the posts of the guy who keeps saying this, but see snippets of his remarks in your quotes.

Attached is an example of what fuels this endless semantics loop we often see, here at iRV2.

I highlighted the offending passage, which is technically true but fosters a misunderstanding among users.

Notice that the publication immediately follows with an assurance that overinflation will not be achieved with their product.

Any TPMS user can easily watch the process to which they refer: For example, the Patriot Thunder is loaded to capacity on its steer axle; so, when those tires are inflated to the manufacturer's table value, it matches the sidewall psi of 120. Indeed, as we roll down the highway and tires achieve their normal 123F under standard highway conditions, the TPSM readout climbs about 20 psi.

That pressure, plus a safety margin, is engineered into the tire.

But, the higher value is moot to operators, who are restricted to the sidewall value. Inflating beyond that, and then warming the tire to operating temperature puts the net pressure into unknown territory, and a dangerous condition is generated. Despite the inherent fun of linguistic gymnastics, let's not lure operators into that rabbit hole.

I'm sure there are other sources of this misleading factoid, this is but one. Highlighting makes the passage easy to find; but, if you have time, read the whole thing. It contains some great information.

Source: Psi Tire Inflation, makers tire over-pressure fuses and of automatic inflation systems.


Fun Trivia This morning, I'm flying a Boeing 777-200IGW to South Korea. Each of my 14 tires is monitored for temp and pressure.Due to the fact that we'll load each of the mains with upwards of thirty tons and roll them along the concrete at about 180 mph, we take this stuff seriously. Interestingly, we have to inflate with nitrogen. More that one airliner that inadvertently was serviced with air has been lost, after takeoff. Similarly, we strictly adhere to a range of psi values, not just a minimum. Since I brought it up, 180 and 200 psi. And, yes, the tires are engineered for the resulting higher value when heat is applied, but it would be lethal for us to tread into that unknown terrain, for reasons I hope everyone now understands.
Attached Files
File Type: pdf PSI Tire Inflation White_Paper.pdf (444.5 KB, 10 views)
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Old 04-18-2016, 11:34 AM   #34
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Many Motor Homes are fitted with heavy truck tires and heavy truck tires called RV tires.

Motor Home tires are not fitted in accordance with trucker industry regulations. They are fitted in accordance with the Federal Motor Vehicle Safety Standards (FMVSS). Therefore the servicing and upkeep standards for them are not going to be found in truck tire/RV tire data books. They are serviced in accordance with standards for the automotive industry, FMVSS.

The trucking industry tire standards do not have recommended tire inflation pressures. Does your MH have a certification label with Recommended tire inflation pressures as required by FMVSS? I rest my case.
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