Summer tire pressure and heat build-up?

[DRMousseau]

Noticed the rear tires are just slightly touching one another. I've been runnin' 65lb on the front and 70lb on the rear. Coming down here in winter, tires never even warmed up. I have a bit of concern on hot summer highways, and will be watching them closely!!! I'd be interested in any comments regarding others experience with summer tire pressures and heat buildup.

[circleD]

The only thing I can compare it to is heavy trucks. I can check the psi when I leave and 6 miles later when I get to a compressor it goes up about 5-10 psi on days over 70°. And they're warm to the touch. So I'm not to sure either if you put the right amount in, will they get higher and over inflate?  Hm?

[M & J]

Most manufacturers specify PSI cold to allow for that.

[DRMousseau]

I've seen roads buckle in heat, and tires get so hot, you can hardly touch them. This worries me ALOT on a car or truck, and scares the day lights out of me on big rigs!!! Never had problems, but I don't want max tire pressures exceeded to dangers levels either.

What's "too hot" What should "running pressures" best be to assure safety??? I've seen some indication on tires, but how hot is "hot"
And is it practical to relieve air as temp and pressures build??? I check tires and wheels at every stop,..... but that might not be enough on hot summer days in the Sourthern States.

[gpw9552]

Have a tire shop look at them.


Duals should not be touching.

[Rickf1985]

You will have the lowest heat build up at your maximum tire pressure. The more the tire flexes the more heat it builds up and that is when they come apart because the heat is being produced by the tire itself, not the road temp. The tires are designed to be run at the maximum pressure and that takes into account the fact that the pressure will rise when they get hot. BUT, That heat is radiated heat and not friction induced heat from the tire self destructing. duals should not touch, ever. You are running too low a pressure or too wide of a tire. Are these radials on rims that originally had bias?

[DRMousseau]

They're radials on standard rims (split rings rims on front only).

LT245/75R16

Tire pressure IS low,.... about 60lb right now. I last inflated them in January's sub-freezing weather to 70lbs (max cold spec is 80lbs), and this left about a 1/4 inch or so clearance between tires. Right now,.... THEY ARE TOUCHING!!! A piece of paper will not pass within an inch or more of center. NOT GOOD! No real sign of scuffing, but I haven't been runnin much either. I'll inflate to 70 or more if necessary and hope I regain my clearance!!! Something I always watch!!! Gonna have it weighed too. Although water is nearly full (was empty on trip down), rear fuel has only 10gal and main has much less. No other greatly added weight.

[Rickf1985]

That is way to wide of a tire for those rims. I would be willing to bet the rims are no more than 6 inch at best. That is the standard for most dually pick up and they all used 215/85R-16 for many years. I don't think you are going to be able to get them not to touch with that size and once you put more people in there it will be worse. What you see when it is sitting is not what you would see during travel. When moving the tires are always flexing so the bulge grows quite a bit with every dip and bump.
What is the load range on those tires? That sounds like a light truck size tire. Make sure of the max pressure before pumping them up. I hate to say it but I do not think those tires are going to be what you want on this trip.

[Froggy1936]

After pumping them up to max pressure The best way to check for kissing sidewalls is someone(you know neighbor or relative)
following you and observing the tires (may need binoculars) As they will have to be a distance behind . Kissing and excess bulgeing will cause major overheat Frank

[Oz]

Yes!  Drive like 95 mph and let the cops chase you a while and then, when they stop you, ask them if it looked like your tires were low on air...


:)rotflmao

[TerryH]

Yes!  Drive like 95 mph and let the cops chase you a while and then, when they stop you, ask them if it looked like your tires were low on air.

That is provided they can see your tires after they catch fire. Very common with duals when they go flat, bulge sideways and/or rub each other.

[DRMousseau]

ah yes,... you folks DO get me gigglin' a bit, sometimes!

I questioned tire size too.
let's see,...the rears are LT M&S 2778lbs dual rating, and 3042lbs single rating at 80PSI cold.

Had no issues in January, 70PSI spacing was fine (rear fuel and water tanks were empty), ABSOLUTELY no heat at all during the 1200mi trip to here. This is something I watch closely in whatever I'm driving in distance. Every gas stop, every rest stop,... heat, lugs, pressure, wear, spacing, whatever, it jus takes a few moments when ya stop and stretch your legs, and I feel it's important! In fact, no issues for the last few thousand miles. I recently removed both sides to service brakes, and inspected all tires carefully,... no scuffs, cracks, bulges, cuts, or unusual wear. I fact, they still have some casting whiskers on the sidewalls!!! These tires DO have a few thousand miles, but are relatively newer and in DAMN good condition.


I'm parked on uneven dirt right now, and as I said, tire pressure is low at only 60lbs. And I also have 25+ gal of water in back! I'm still preppin' for the journey north next week, and will air up the tires tomorrow or the next day when I get out again. I want to do this in the morning or at night when the air and pavement is cooler, the gas station is only a mile down the road. Since they ARE newer and in such good condition, I'll take 'em to 80psi and watch 'em close. Front tires are damn good too! What I thought were cracks and cord between the thick tread, was jus "indicator color". Fronts are different than rear,... 235/85R 16 on split-ring rims, with same ratings as above. I ran 'em at 65PSI in Jan, will take 'em to 75PSI now that I know they are so good.

I've noticed that excessively soft tires DO give a good bit of sway and rocking motion!!!
And at 95mph,... those soft tires SHOULD get tall and skinny!!! LoL!!!

Heard there's freezing weather tonight in Michigan, and I'll feel better leaving behind, the hot pavement in Florida!!!

[JerryP]

Low pressure tires get much hotter than properly inflated tires due to the increased flexing. Follow the tire makers recommendations, they have already factored everything into the design.

[DRMousseau]

Well, early in the morning, I adjusted tire pressure on both axles,... 80psi on rears, 75psi on fronts. I regained some perceptible spacing between the duals, but NOT what I had experienced earlier in the year. Thinkin I may have gained more weight than I might have imagined. A hundred plus pounds of water, 80lbs extra battery, 20lbs added cable, 10gals gasoline, etc.,... this and more, is above all that which I had in early January!


Throughout the short ride dashin' about all the day, I did notice a lot of heat. Nothing unusual, since I could hardly walk the hot pavement with shoes,... and barefootin' it was jus outa the question!!!


Jus something I will have to monitor more closely and make adjustments and changes if necessary.
But jus how hot, is TOO hot???

[TerryH]

If the sidewall of your tire is 'hot' to the touch as opposed to 'warm' you may have a problem, particularly with duals.
I know Rick has said earlier that hitting the tire with a bar etc. is an acquired skill, but it may work for you. Use a tire iron, breaker bar (also ideal for removing lug nuts) or whatever is handy. Rear axle - strike inner and outer tire left side - use the same amount of force for each tire. Sound return and bounce return should be identical. Flat sound/feeling - no bounce means a possible flat, and soon to be tire fire.
Same operation for right side. Then front axle.
The above is not meant as an alternative to checking tire pressure with a decent gauge. To me, virtually every stop you make should include a tire pressure check.
3 - 4 minutes of your time to check.
Tire failure = braking, steering, vehicle control, injuries to you and family and to other drivers.
My opinion, may be off topic, but..................

PS it is going to take a fairly large amount of excess weight to make your duals touch, assuming you have the correct tire and rim configuration. As well, a tire blow out, especially rear almost always causes ancillary damage. Prevention is the best cure.

[DRMousseau]

Checking tires during an extended trip has always been habit of mine,... probably due to the days when bias plys were the only tire around, and we often used "retreads". We HAD to watch 'em close, and I still do! Never cared much for radials,.. but they became the "new" standard.


Been tryin' to find all I can about the tires I'm usin. I found that I can expect about 1psi change in tire pressure for every 10 degree change in temperature. And I learned the recommended "cold" inflation is at 70F degrees and tire temperature can be expected by the manufacturer, to vary by 50F degrees or more!!


I'm pretty sure I have a weight issue I will have to address before I begin my journey Tuesday evening. My water tank is bigger than I thought. I will HAVE to weigh this and hope for weights on each axle as well as total weight. I'm planning on empty rear tanks, and empty holding tank,... I traveled here with only one usable fuel tank, so this is really no problem. I'm also planning on traveling during "cool" periods of the day here in the south, till I get further north and have cooler pavement. Cooler conditions will allow me to more easily assess increasing tire temps due to "other" conditions.


I'm also gonna "rotate" some tires before I leave. The outside rear tires have been marked RF and LF. Tires are identical all around except the "profile" of the current front tires. Fronts are 235 and rears are 245. This is a 1/4" difference in profile width And I'm thinkin those on the rear SHOULD be on the front. Tread diameter, load rating and all other specs the same, so this may be my answer for now to assure spacing clearance. Still, I will be VERY closely monitoring tires on this trip!!!

[TerryH]

DR, I'm a little confused here. You have 2 - 235's on the front and 4 - 245's on the rear as I understand. By putting 2 of the 245's on front and then mixing 2 - 235's and 2 - 245's on the rear, what benefit will you achieve?
My experience and understanding with duals and multi axles is you never mix sizes. Size differentials with duals will result in differences in flex, temperature build up and lowering (which affects flex), circumference and profile differential as temperature differences change the psi to tire air volume ratio. It may also affect    ( to a small degree ) braking and steering, as both are partially resultant of the tire surface actually on the road and side wall flex.
Just curious as to how you would hope to benefit from mixing sizes on duals? Granted your size mixing differences are not huge.
Thanks
Terry

[DRMousseau]

You are EXACTLY RIGHT!!! In every way.You "shouldn't" use mixed tires on duals. Slight differences in tread diameter, weight ratings, air pressure, profiles, etc., CAN have undesirable results! While big truck rigs often have different tires on the various axles, they ARE closely matched and typically bias ply which I much prefer. Bias plys have stiffer sidewalls subject to less variations and flexing due to road conditions and aren't quite the pleasant ride that radials are because of this. The flexing action of radials help keep a more constant "contact" patch and provide for better control under various driving conditions.

Bias ply tires are hardly ever found on passenger vehicles anymore. Some folks here may recall when bias plys were all we had, and the squealing of tires when turning a corner even at low speed. The result of bias plys stiff sidewall and the tire sliding laterally around the corner as the contact patch was reduced by weight transfer in the turn (yes, tire compounds contributed to this effect too). Radials are subject to sidewalls flex in the weight transfer, and this helps keep the contact patch constant. If bias began to squeal, they got louder as slip conditions worsened to the point of spinning out, allowing time for corrective action. But if radials began to squeal, chances are it's too late for corrective action,... the sidewall flex has already been grossly exceeded by lateral weight transfer with no warning. We were quite aware of the abuse we were subjecting to the tires shoulders then, unlike today. How do ya tell kids and the hot rod spouse to quite screemin' around the turns when there's no scream!!!


After considerable research, I've found all these tires to be the same in every manner, except profile,... that affecting the cross-sectional width. There is .300" difference. My greatest concern is tire diameter and I'll have to confirm this more closely when remove them today by measuring tire circumference (also differs with tread wear). A difference in diameter can cause added flexing and heat build up, as the larger tire is subject to greater load before the smaller of the two. This would cause the larger one to be overloaded depending on total axle weight and weight distribution,... NOT GOOD.

What will I GAIN??? That .300" difference in profile, will give 1/4' added clearance space between the dual tires. Spacing is currently barely perceptible and rough road conditions will cause sidewall rubbing, ensuing damage, and added heat buildup. That 1/4" may not be much, but will likely be sufficient for all but the worst bumps and rolling action of the coach. Surprisingly, the road conditions are the worst in the middle third of my journey!!!

[Rickf1985]

There is a lot more to tire size than just that width number. Check this out.

Aspect Ratio is the ratio of the height of the tire's cross-section to its width. The two-digit number after the slash mark in a tire size is the aspect ratio. For example, in a size P215/65 R15 tire, the 65 means that the height is equal to 65% of the tire's width. The bigger the aspect ratio, the bigger the tire's sidewall will be.

You will find those 235's are going to be quite a bit taller than the 245's.

The 245's will have a sidewall which is 6 3/4" high.  171.5mm   to be exact
The 235's will have a sidewall which is 7 5/8" high.  199.75mm to be exact

[Rickf1985]

Remember, the largest tire that should be on that rim is a 215/85-16. It is already pushing the limits of proper bead seating at that width.

[DRMousseau]

ACKKKKK!!!

That 235 (front) and (245) is the tread width in mm. it is the number designated before the slash. The number right after the slash is profile ratio. Sidewall height as a ratio to the above tread width.

AND,... the profile ratio IS different. DAMN!!! How could I not notice!!!
85R's on the front 75R's on the back duals!!!
By rough figures, there's nearly 3/4" difference in sidewall height for a total of nearly 1 1/2" diameter difference, all else the same. there are tread, weight, and air pressure differences right now, and I physically measure nearly the same for diameter difference and this gives too much circumference difference.

SOOOOOO,... scratch that!!! Back to closely monitoring temps and pressures as is!!!
Think I find an electronic IR temp gauge,... these work pretty good for surface temps.

[Rickf1985]

The problem is that you cannot measure the temperature where the damage is being done, between the tires and the damage is done very quickly every time they rub together at speed and then they cool down till the next hit, This will harden the rubber on the inside but leave it soft on the outside. I know you are trying to rationalize using those tires but at what expense? Maybe nothing will happen, or...................... , Your vehicle, your family, your call.

Putting more air in radial tires will not change the shape of the outside of the tire due to the radial construction of the belts. They are built specifically for that reason.

[Oz]

I'm impressed with how much consideration and detail is really involved in this and glad everyone has taken the time to enlighten us with it!  From a much less adept about such things RVer, what I get from it all is to go with what is known to be correct, and be safe rather than sorry.  Does that make sense as a rule of thumb, or is it there more to be considered?

[Rickf1985]

Bingo!

[DRMousseau]

Soooooo,..... after 2400mi of travel on various roads (Indiana being the WORST), everything is fine.

I've learned from those who know, that tires are built to exceed their "safe" ratings. While I did buy a digital IR temp gauge, (I find it useful for MANY purposes and had lost the one I had), it gave me the reassurance that my tires, while VERY hot on southern summer roads, did not exceed unsafe temps. On my return from Florida to Michigan, I took advantage of rainy weather and avoided hot daytime roads in the south as much as possible.

And the biggest, most important factor,.... is proper inflation for the load carried!!! Surprisingly, I found my FRONT tires to run hotter than the rear duals!!! Those "road 'gators" along the highway? They are typically the result of underinflation! And not necessarily because of load,... apparently, they are often left behind by empty trailers hauled at speed by truckers. AND,... are more common on the hot southern roads where tires are a big concern for truckers and especially for passenger busses!!! (I noticed CONSIDERABLY more trucks on the road during the night when daytime roads were hot)

I learned that tires rarely "blow" because of over inflation, even when inflation pressure dramatically rises with heat. They are designed with this factor in mind. But excessive heat alone, for whatever reason, will cause sever damage and dramatic tire failure!

Sooooo,.... how hot is TOO HOT?

I was told that tires can be expected to reach surface temps of up to 50 degrees above ambient temperatures. On a hot 100 degree day in the south,.... THAT'S A LOT!!!! Internal temperatures are even more!!!! Tire pressure rises approximately 1psi for every 10 degree increase in temperature. But inflation comparisons between hot and "cold" running tires, will be inconsistent with tire surface temp readings. Argggg!!!!!!

Again,... HOW HOT is TOO HOT???

Not an easy straight answer to get from "those who know"!!! Best I got was, "If you see ANY temps exceed 200 degrees in your tires in ANY way,.... you should be concerned. The best indicators were the tires themselves." Any sign of non-uniformity in any part of the tire, is a sign of damage and imminent failure. A bulge, a bump, a ripple or dimple,... ANYTHING unusual and not uniform may be a sign of internal damage. Tread will often be seen "rising" in some manner, being higher on one side than the other. A sure sign of imminent catastrophic failure!!!!Not all damage may be heat related,... all kinds of road hazards can also cause damage that shows in non-uniformity and will result in tire failure.

"Hard tires" have an "uncomfortable" ride,... radials were designed with safety in mind by maintaining more uniform contact with road surface with varying tire pressures. Jus so happens, that they have a more comfortable, "softer" feel in a ride that many prefer. Bias ply tires are "stiff" by design,... proper inflation is key to maintaining uniform contact with road surface. Over and under inflation is easily seen in the tread wear of all tires,... center wear caused by over-inflation, uniform shoulder wear usually from under-inflation. I'm told again,.... "proper inflation to load requirements are the key to safety! And not because of tire pressure!!!" Confusing? Contradicting??? Not really,... because I have a better understanding now.

Oh,... and the spacing of my rear duals??? Marginally acceptable!!! NOT suggested, but as long as they dont bear on on another, it should be of less concern than inflation/load considerations that would affect it much more!

Thank-you! Never really a simple answer, is there?!?