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Old 09-23-2009, 10:20 AM   #1
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Question Tire Pressure (Max or not to Max) Experts?

Tires are certainly an ongoing concern, and pressure is one of the leading discussions. I've been hearing so many views on this topic and did a search for previous threads on the topic. It was not clear if there is a safety or equipment concern when running tire pressure at the sidewall max.

(1) Why not keep the tires inflated at the max per load pressure on the sidewall? That way, I know I'm good up to the tire's max load. You might run a little stiff, but the peace of mind outweighs the ride softness.
(2) COLD Pressure setting in winter Montana and COLD Pressure setting in Summer Phoenix could produce a noticable difference delta.
(3) Is the tire pressure tolerance that small? Are tires so sensitive to pressure variables? Is scaring the public into precision tire pressures a way for tire manufactures to escape liabilty and merchants to sell stuff?
(4) Has the RV community created their own Tire Pressure phobia?
(5) Why not purchase 14 ply Semi tractor-trailer tires and forget about it?

Do we have any absolute answers?
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Old 09-23-2009, 10:38 AM   #2
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I found an interesting discussion at Discussions on Max tire Inflation

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Old 09-23-2009, 10:39 AM   #3
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Running overpressure will reduce traction and handling. If you're going to "set and forget", do it at the correct pressure for your weight, not the max.

joe
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Old 09-23-2009, 10:57 AM   #4
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Ah,,, that's the problem.. Where is the science? Everything I'm reading is opinion. I wonder if GoodYear or Michelin has an official statement cocerning trire pressure. Wait, they do... They provide a pressure to load table. That must be the basis and establishes a true guide to put your life on.

The article mentioned above says higher inflation (not over max) adds to tire sidewall stability (makes sense).

Thank you for the discussion
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Old 09-23-2009, 11:09 AM   #5
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Quote:
Originally Posted by Batman_777 View Post
Tires are certainly an ongoing concern, and pressure is one of the leading discussions. I've been hearing so many views on this topic and did a search for previous threads on the topic. It was not clear if there is a safety or equipment concern when running tire pressure at the sidewall max.

(1) Why not keep the tires inflated at the max per load pressure on the sidewall? That way, I know I'm good up to the tire's max load. You might run a little stiff, but the peace of mind outweighs the ride softness.
The problem here is that the tire pressure should match the tire load.. If you run a tire "Soft" (low pressure) to improve the ride, it will wear at the outer edges but the center will not wear out.. This means you get only a fraction of the life of the tire.. (And we have not even mentioned side wall damage from the strees, or handling issues, nor will I ,,, again)

Likewise if you OVER INFLATE. then the center of the tire takes the wear, and again your tire needs replacing sooner


Quote:
(2) COLD Pressure setting in winter Montana and COLD Pressure setting in Summer Phoenix could produce a noticable difference delta.
Actually.. it's not that much different Set it for cold weather (IE: 7am) where you are parked.


Quote:
(3) Is the tire pressure tolerance that small? Are tires so sensitive to pressure variables? Is scaring the public into precision tire pressures a way for tire manufactures to escape liabilty and merchants to sell stuff?
No, there is more wiggle room where safety is concerned, However far less where tire life is concerned. NOTE: Inspect tires often.

Quote:
(4) Has the RV community created their own Tire Pressure phobia?
Well. I think some folks are "Overly Concerned" and I suspect I often come off sounding that way. (I'm not) but in today's world.. Well, I can imagine a mouthpiece. ur. lawyer, checking tire presure after a crash and spouting how it's different (As well it should be) from what's on the vehicle stickers... I can also imagine an intellegent RVer tearing him a new rear opening... (See "As well it should be")

Quote:
(5) Why not purchase 14 ply Semi tractor-trailer tires and forget about it?
Now that.. is a very good question.. One answer is the ride. RV tires are designed to give a somewhat softer ride.. Another is the rims may not be spaced properly (Though this can often be taken care of by other means)

There may be other reasons which I do not know about as well.. Perhaps someone else can chime in on this one.
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Old 09-23-2009, 11:09 AM   #6
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Overpressure increases sidewall stability, but it also reduces contact patch area. And (depending on tire construction) can also cause excess wear on the center of the tire tread.

joe
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Old 09-23-2009, 11:13 AM   #7
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1. Weigh your rig and use the correct pressure for each axle. I run my rears at 85 psi based on weight even though the tires are rated at 110 psi. It does make a big difference in handling and comfort.

2. COLD means ambient. If you drive from Canada to Florida you need to recheck your pressures.

3. Not sure what stuff anyone is selling you to check your tire pressure. A more accurate gauge?

4. I don't think RV owners have a phobia about tires anymore than car and truck drivers. RV tires don't wear out they just die of old age which is the major difference.

5. A lot of people use truck tires on their rigs rather than expensive RV tires. I have Yokohama steer tires on my coach and they work great. About half the price of G670.
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Old 09-23-2009, 11:32 AM   #8
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One note:
I noticed the max air pressure on the tire is 125 psi.. The rim, however; is 120 psi max
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Old 09-23-2009, 01:01 PM   #9
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Using max sidewall pressure is easy to keep up with and a good starting point. If you are into it, finding weight on each tire and consulting a manufacturer's table, calculating a proper consideration for temperature and pressure and planned transient loading and tire age and so forth can make for a good hobby but won't gain you much as far as efficiency or safety or tire longevity.

The traction argument is bogus in most circumstances. Yes, contact area is reduced but the force on that area is increased (you can weigh your rig by measuring contact area and multiplying by tire pressure). Friction is determined by both the normal force and the area over which it is applied. The differences in pressure being talked about in this context are not sufficient to bring in any significant contributions from other factors in most conditions.

Tire wear is the usual indicator of over inflated tires - more wear in the center of the tread. RV tires are seldom subject to sufficiently high mileage use to have a concern about this. But do keep an eye on tread wear as it will tell you if your pressure philosophy is off for your rig and circumstances and also if you have some other problems with suspension and alignment.

RV loading is usually rather consistent and towards the upper end of the rated capacities. There is something to be said for the ease of using max sidewall PSI rather than trying to continually adjust for what you think the actual load on a particular tire is and then trying to get the pressure right for that particular brand and make of tire as guestimated by the manufacturer under ideal conditions.

You do not run a safety risk by having max sidewall PSI in the tires (do check to make sure you don't exceed max pressure ratings of the wheels). You do gain benefits of lower tire heating, which is the major cause of tire failure. The stiffer tire might improve handling and reduce sway as well. Fuel efficiency can be improved. These benefits are why racing vehicles often run at enhanced pressure.

Easy means more likely to get done and getting sufficient air in your tires is something that really really needs to get done.
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Old 09-24-2009, 02:37 PM   #10
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If ppl are more likely to maintain air pressure at near sidewall max, not over and not exceed rim max, then that seems like the best practice.

Complicating the effort by adjusting for load balances, load distribution, scale weights, etc etc etc will probably mean it will not get done.
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Old 09-24-2009, 03:45 PM   #11
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If you're going to pick one pressure to maintain, why not pick one that has some semblance of appropriateness for the job? Sidewall max on my main and tag axles is 120. The correct pressure(s) for my weight is 85 main/90 tag. No way does it make sense to use the sidewall max.

It's closer for my steer axle. 120 max, 105 actual. We had it at 120 before we got weighed the first time. The difference in ride quality is amazing. At 120 it felt like our fillings were going to fall out on a rough road.

joe
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Old 09-24-2009, 03:58 PM   #12
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I attended a seminar at Spartan given by two Michelin engineers and a man from RVSEF. The question was asked about running tires at maximum side wall pressure instead of weighing each wheel and setting tire pressure according to the tire manufacturers' charts.

The engineers said the tires will wear out quicker in the center of the thread, the motorhome can become squirmy and tiring to drive, wind will blow the motorhome more, the ride will be rougher, due to road shock more items in the motorhome will come loose and break, there will be less road contact which will affect handling and braking on wet roads, there can be increased tire damage when the tire hits an object, the shocks will do more work and wear out quicker and the front suspension will wear out quicker.

If you want to ignore the above problems - pump the tires to the maximum and have a safe trip.
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Old 09-24-2009, 06:04 PM   #13
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Tires should wear in a smooth, even pattern. If tires are not at proper inflation levels, it can have a drastic effect on treadwear.

Underinflation and overinflation can cause tires to wear unevenly, and ultimately, reduce the tire’s overall life. That’s why it’s important to inflate your RV tires to the proper pressure so the wear rate is at its best.
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Old 09-24-2009, 10:57 PM   #14
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I attended a seminar at Spartan given by two Michelin engineers and a man from RVSEF. The question was asked about running tires at maximum side wall pressure instead of weighing each wheel and setting tire pressure according to the tire manufacturers' charts.

The engineers said the tires will wear out quicker in the center of the thread, the motorhome can become squirmy and tiring to drive, wind will blow the motorhome more, the ride will be rougher, due to road shock more items in the motorhome will come loose and break, there will be less road contact which will affect handling and braking on wet roads, there can be increased tire damage when the tire hits an object, the shocks will do more work and wear out quicker and the front suspension will wear out quicker.


If you want to ignore the above problems - pump the tires to the maximum and have a safe trip.
With the tires at max you do all of the above and chance loss of control on rough roads. Max out a tire to 120 on a load that only requires 65 and you can find your wheels dribbling like basketballs after a chatter bump and taking you right off the outside of the next turn in the road.
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