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Tire Experts, Dual Tire Pressure Question


oldjohnt

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Having farmed and been a truck and RV dealer and 50 year user its been my experience when a dual tire blows its often (was in my experience) the inner one. Its my formed "OPINIION" that could be from one or two causes.

 

YES IM AWARE OF PROPER INFLATION AND LOADS AND WEIGHT AND RATING BUT LETS ASSUME FOR THIS DISCUSSION BOTH TIRES WERE INITIALLY AT THE CORRECT AND EQUAL COLD PRESSURE

 

1) The inner tire runs slightly hotter due to its location and air flow cooling and sometime exhaust pipe etc etc factors THEREFORE its pressure increases slightly more then the outer tire making it slightly taller therefore carrying slightly more weight then the outer tire??????

 

2) Due to the slight crown of the road for drainage, the inner tire runs on slightly higher ground therefore carries slightly more weight??????

 

 

NOW if either of the above are true?????????and if indeed the inner tire carries more weight for whatever reasons

 

 

WHY SHOULDNT A GUY INITIALLY AIR UP HIS OUTER TIRE SLIGHTLY HIGHER THEN HIS INNER TIRE???????

 

My 10 Ply Load Range E dual tires are rated for max load at 80 PSI Cold and that's where I set them. In that case its my thinking perhaps I air my outer tire to say 83 PSI and my inner to 80 PSI cold and that way when driving down the road at temperature there's a better chance each carries equal weight.

 

Tire experts???? anyone else with knowledge or ideas or opinions are appreciated

 

An ever curious Old John T

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Just something to think about.

could it possibly that the roads ar slightly crowned and puts more weight on the inner tire.

or if the road surface is warn so as to put more weight on the inner tire.

Along with your input also.

 

Just something to think about.

 

safe Travels, Vern

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Thanks Vern, hopefully other gents will "weigh in" (pun intended) on this topic also as I consider it a legitimate question as most all of us have dual wheels. Oh well I tried and will continue to study and research the legitimacy of my theory before reaching a final decision.

 

Best wishes yall travel safe now

 

John T

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So what about the tire equalizers? Will they adjust the air pressures to compensate? Not enough for the photo but the normal differences in the typical road surfaces. I am probably going to order enough for all my dual wheels this summer.

 

Rod

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Road crown doesn't overload one tire, it simply leans the vehicle to the passenger side.

That would be my thoughts also, but I'm not an expert so it is more opinion than fact. But I can't recall having had more problems with inside dual tires than outside. Is there any documentation to support the thought that inside ones fail more frequently? There must be some government study on that? I did some looking on the internet and the searches that I did came up with nothing about the subject.

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Kirk, hey big brother government has to have studied that, they have everything else lol, but like you I haven't found it. However over many years of many trucks and RV's its like always been an inside dual that blew out in my case, even under sufficient and equal pressures grrrrrrrrrrrrrr Of course, age or overloading etc etc could be another factor, but its still usually the inner.

 

Regardless if they have, perhaps some tire companies can answer my questions. 1) Does the inner tire run warmer (air flow, exhaust, brakes) ????????Does that ORRRRRRRRR the crown in the road cause the inner to be on slightly higher ground thereby carrying slightly more weight????? Could it help balance the load if slightly more air pressure was carried in the outer tire????

 

If I cant find the exact answer, research, or a sound technical argument not to do it, I may just run a few more PSI in my outers BUT THEN WATCH ONE OF THEM BLOW LOL

 

Take care yall

 

John T Live from Austin Lone Star RV Resort

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So what about the tire equalizers? Will they adjust the air pressures to compensate? Not enough for the photo but the normal differences in the typical road surfaces. I am probably going to order enough for all my dual wheels this summer.

 

Rod

I have had Crossfire tire air equalizers on my diesel pusher for more than 10 years. Had 2 blowouts. Both on the rear and on the inside. I still use the Crossfires and like them due to the convenience of one fill point instead of two. By the way, the Crossfires work as advertised in event of a blowout. In both cases, I lost very little air in the other tire.

 

Dick

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I have a friend who's driven MH'S for perhaps 30 years. He told me he always runs 10 psi more in the outer dual to compensate for road crowning and he's never had a flat on any dual wheel applications.

That's his opinion and experience, but cannot be mistaken for fact.

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I have a friend who's driven MH'S for perhaps 30 years. He told me he always runs 10 psi more in the outer dual to compensate for road crowning and he's never had a flat on any dual wheel applications.

That's his opinion and experience, but cannot be mistaken for fact.

We owned motorhomes with dual wheels for right at 25 years and never experienced any flats and I was careful to always check tire pressures before each day's travel and set mine as close to the same as I could, using a standard inflation tool and gauge. When I checked tread temperatures along the way, I was never able to detect any significant temperature difference.

 

With all of the people today running tire monitor systems that also display tire temperatures, I'd think that someone here could tell us if it is normal to have a significant temperature difference between inside and outside tires of a dual pair?

 

Where are you Jack?

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Kirk states, "With all of the people today running tire monitor systems that also display tire temperatures, I'd think that someone here could tell us if it is normal to have a significant temperature difference between inside and outside tires of a dual pair?"

 

Just the other day a buddy told me he uses his temp gun to check his dual tire temps at every rest and fuel stop and said the inside was always higher SO I NEED TO ASK HIM THE TEMPS AND HOW MUCH HIGHER. That makes sense due to air flow and brakes and maybe exhaust pipes underneath and also hotter with more resultant PSI should make it just a tad taller and therefore carry just a tad more weight...

 

Tire experts or engineers or designers WHERE ARE YOU !!!!!!!!!!!! However, in all these years I've NEVER heard any tire dealer tell me to run more PSI in an outer dual so it may not make any sense whatsoever. Still a fun topic for discussion and as typical some will swear to one thing while another will swear to just the opposite experience lol. Plenty of opinions out there and nothing wrong with that.

 

John T

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I've stayed out of this because I don't have any data to support a position. However, some observations:

 

  1. There is not enough crown in most roads to affect road load to any extent that mattered. That is an opinion...not data that I have. But there would have to be EXTREME crown to significantly load a tire over a partner on the same wheel. Crown is not a curb, like the pic above. The axle is pretty much equally distributed over it - for the effects we are talking about. Yes, there will be some difference, but IMO not enough to matter if you are using recommended pressures. The proof that there is a difference is that when scaling a dual with a single scale you have to bring the partner tire up to the same height with a plywood riser in order to get an accurate weight. The effect of crown has to be less.
  2. Inners do run warmer, but not significantly according to my tire monitor. That is because they don't have the same airflow. But the difference is certainly not something that would harm the tire and should be dealt with....we are talking a couple of degrees.
  3. Inners - because they run warmer - also run at a slightly higher pressure. But again, not significant.
  4. IMO the things like Crossfire are important tire aids. Mainly because they ensure that you do check and air the inner properly. It is difficult to do, otherwise. And valve extenders - for the most part, have failed for me, so I do not use them.
  5. EVERYONE should run tire monitors. Again - MY opinion. There is a reason they are required on all new vehicles. They help significantly to ensure proper inflation.
  6. Tires primarily fail due to heat, and the effect of heat. Low pressure (for the weight involved) causes heat. Thus failure. Monitors, Crossfire, etc help manage the risk. If you do run monitors then you will have noticed that the "sunny" side of the coach is always hotter than the shaded. It makes a difference - always a minimum of 7 psi on my setup. Ambient air temps (and thus road temps) can modify this a little but that is about what it runs on my H rated tires.
  7. Some people obsess about all tires being the EXACT pressure. That is not necessary. If they all meet the weight table inflation's, then a 3-5 psi difference is not significant. Tire monitors are not accurate enough that you expect 1 psi accuracy. At least in my experience.

Proper inflation is obtained by knowing your weights and using the weight tables to set your pressures. I run 5-10 psi above the tables on my tires. If you don't know the weights then you have to run max pressure for the tires. Some advocate running max pressure all the time. But most tire experts and manufacturers say use the tables.

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Thanks everyone for all your experience, opinions and observations, looks like more in depth research is needed and IF (don't hold your breath lol) I find any good hard scientific studies or data (such as does the inner tire indeed carry more weight, even if slight, due to being hotter or road etc.) I will be sure and post it. In the meantime, bottom line advice as always, keep your tires properly inflated and inspected as it could save your life.

 

PS I might add if I were given ONLY TWO CHOICES to run my tires (at proper weight, temperature and pressure) at X PSI OVER rating or the same X PSI UNDER rated inflation, my choice would be OVER but to each their own choice. If I didn't happen to have the exact weight per axle or tire at the given moment to consult some chart, in the meantime until I could weigh, I would operate at the MAX load AT X PSI figure to err on the safer side even if the ride may be just a tad rougher, I'm just NOT a believer in operating at the lower end of recommended pressures as I consider under inflation and the resultant tire squat and sidewall flexing could increase the tires temperature possibly to the breaking point.

 

John T

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Kirk, I have closely monitored my tire pressures since I bought our MH. The inside dual runs about 3-5 psi higher than the outer on days when temperatures are above 75-80. They all run about 15-20 psi higher than the cold pressure on that same day.

IMO, that is insignificant pressure differences to even think about road crown.

 

oldjohnT, I totally agree. Tire manufactures and the RMA state that over 80% of tire failures are the direct result of operating underflated or overloaded. Goodyear states this running RV tires underflated is because of the incorrect assumption they will get a softer ride.

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Not directed at anyone but, why do my outter tires wear more than the inner ones?

The most common cause is installing tires of different wear. If you install a tire 1/4" larger in diameter, it will drag the smaller tire until enough rubber is ground away from each to make both the same size.

source: Mismatching dual tires, a surefire way to kill two tires at once. That article explains why, and yes it somewhat pertains to road crown, but mainly, consistent and proper air pressure.

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In my case these are factory installed new tires.

That only leaves a few causes; rims not running true-they are wobbling down the road, rims not mounted to axle correctly, lug nuts not torqued correctly or wrong lug nuts, wrong rims-some are stud-centered some hub centered.

That exhausts my memory bank, sorry.

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