Tire Pressure

Okay, lets see where this takes us, any "real" tires experts out there????? This may get as many "opinions" as an electrical or legal question lol

Sooooo my RV has 225 75 R 16 10 Ply Load Range E Tires. The sidewalls are labeled MAX LOAD AT 80 PSI COLD

AND BY GOLLY I CARRY 80 PSI COLD AND WILL CONTINUE TO DO SO REGARDLESS even if my weight/load is wayyyyyyy less (but especially if more) then the vehicle nameplate or the tires can carry.

Butttttttttt some "dudes" claim they only run say 65 to 70 PSI either because it rides softer orrrrrrrrrrrr the vehicle nameplate says so, but that, of course, also lists an exact max load for that vehicle.

My theory is its best to err on the side of higher tire PSI (the 80 PSI cold as labeled) then the lower limit (say 65) as a squatting down tire (cuz of lower pressure) will run much hotter and the sidewalls will be flexing a lot more EVEN THOUGH YES LESS PSI MAY RIDE SOFTER

SOOOOOOOO I say its safer and you cant go wrong (even if harder ride) to run the Max load at X PSI then something less then that, REGARDLESS IF YOURE UNDERLOADED BUT ESPECIALLY IF YOURE OVERLOADED

WHAT SAY YOU???????????????????????

Why even ask if I dont plan to change anyway?? I still like to hear expert opinions I reckon

A stubborn John T

All depends on how ya want 'er to ride, John. It do make a difference.

Allan

I say keep your eye on the tread, a tire with low pressure will wear on the outside, a tire with to much pressure will wear in the center.

Hello,
Max air pressure is only needed for maximum load. But you KNOW THAT!
Here is the tool you need to keep track of your tire wear. To much pressure for the load, will wear the center of the tire, more then the rest of the tire.

Guido.

I'm not really a tire expert except that every vehicle I own has them on it. I would like to bet that of the tires you see blown out and scattered around on the roads, more of them were caused by under inflation than by over inflation. Like you said the tire runs with less heat when properly inflated.


Steven

Dave...what you say is "true", but NOT NEARLY as much so since the advent of radial tires. Now THAT comment really dates me!!

I'll respond to the "question" in a separate part to this thread.

Rick

Softer tire gives better traction in certain conditions.

Inflating to the max gives you the highest load-carrying capacity.

Car makers often shoot for a compromise with the recommended PSIs.

Bias-ply and radials wear the most even when run at the proper PSI which is determined by the weight of your vehicle and NOT the max rating.

There is no guessing on the matter. It IS how it works. Naturally not all tires act, ride, or wear exactly the same. Generally speaking - a tire lasts the longest when NOT run at the max - unless you've got your rig heavily loaded all the time.

I've got a local guy at the motor-vehicle inspection station that . . . every time I bring a car or truck there . . . he inflates every tire to the max rating and I feel like knocking him across the head.

My "credentials" are: 10 years in the "tire and rubber" industry starting with Firestone Tire & Rubber in "sales" at a company owned retail store...sales and Ser. Mgr. in a large Firestone DEALER owned store...working (I got my hands DIRTY!!) mgr. of dealer owned/operated retread shop...sales with a supplier of supplies and equipment to tire dealers and retreaders.

What JOHN T has laid out for "argument" is OK. I have NO argument and tend to kinda/sorta follow the guidelines he has laid out for myself. I will make a couple or so comments that are/are NOT directly related.

(1) An 'E' rated tire that is inflated to 'D' rated max. pressure will NOT carry 'safely' anymore than the 'D' rated tire. IE....AIR pressure is what carries the load.

(2) If you run 'lite weight' over rough roads all the time (like a scalded dog!!) with the 'heavy'
rated tires inflated to 'max' air pressure, you do increase...slightly...the chance for increased wear/tear on your vehicle's suspension. I do believe the risk is minimal though that could be attributed to just the tires.

(3) HEAT is a tire's enemy...and under inflated tires will 'heat up' faster than properly inflated tires.

(4) IF there is a 'difference' in front to rear tire pressures, I would suggest that you might do well to keep a 'difference' in the pressures. Run your fronts at 5-10 less than rear, BUT NOT LESS than vehicle placard calls for. This is a 'handling' scenario as well as a ride/comfort feature.

(5) Check air pressure in the cool part of the day BEFORE running very far so as to not heat up the tires.

(6)DO NOT EVER LET ANY ^&%^$% TIRE JOCKEY "PLUG" A TIRE...it needs to be broken down and inspected from the inside. The tire's "tubeless" feature is its inner liner and that needs to be treated like a tube. I have broken down too many tires that were "plugged" and still leaking only to find where a nail had gone in...bent over...and damaged a much larger area than just a "simple nail hole". I can come "unglued" over that practice in just a fraction of a second. You don't "plug" tubes so why "plug" tires.


OK...John T...that's my "considered" opinion. I prefer to NOT be called an "expert" as: EX refers to being a "has been" and (S)PERT is just "a little drip under pressure".

Be safe in your journeys down life's pathway ever facing the light...RICK

Contact patch is my answer.
Put a piece of carbon paper under the tire on a clean sheet of paper and let it down on a piece of masonite. The contact patch will show just how much of the tire is on the road. I believe the patch should be about 50% of the width of the patch in length. If much less, or if foot ball shaped side to side it is over inflated. If it is more or less a rounded rectangle Cool. traction in emergency stops and cornering depend on that patch! Just my training. Jim

Not that I'm an expert but I've run 235/85/16 at 45 psi towing an they never looked low. On an RV higher pressure should result in less sway when a larger vehicle is passing, reduce(slightly) gas comsumption, should have less chance of blow out. A good tire is much more likely to have a blowout if underinflated than inflated to max pressure. Also helps if you have a slow leak that you may forget about before you leave. (not the case for you though, being the preventive maintenance nut you are :wink: )

the corect air pressure is determined by the load range, stamped on the sidewall,even if the tire is not the load range specified by the mfg. D is 60psi usually and E is 80psi,i do believe.i agree:more air is better than less air.
MARK

We started out running the max load pressure on our old Pace Arrow class A unit, until we got in some really bad roads in Oklahoma. Man, after half a day of that, we had screws rolling around on the floor and squeaks and rattles we never had before.
we pulled into the next little town with an outdoor platform scale, this was at a NH3 fertilizer plant.
The fellow on duty was kind enough to help us weigh the front then rear of the motor home.
Got the actual weight on each wheel and pulled out the motor home op manual to the tire weight / pressure section.
Turns out we were running 40-50% more pressure than what was recommended for that size tire at our load.
We adjusted tire pressure to what was recommended and our rig went from riding like an old solid rubber tire Mack dump truck, to about like an automobile or van.

Sure was a lot more plesant ride and much less damage to the coach.
Tire temp and fuel mpg changed little if any.

My credentials are not the greatest, but I"ve been in the tire industry since "74 (started as a tire tech), I"ve run as many as 43 locations in 5 states at a single time (72M annually in yearly sales before I got the he11 outta retail), and currently move about 10,000 units a month wholesale for the best tire manufacturer in the world. So, here"s my opinion, based on seeing way too many used up casings : run them at the max cold inflation, ESPECIALLY on an RV. You will ALMOST never see a radial tire wear out prematurely due to over-inflation; on the contrary, you will see thousands fail due to underinflation and impact breaks caused substantially by under-inflation. A tire"s maximum dry traction occurs at high inflations due to stiffer sidewall creating a more consistent contact patch during roll- test it with a pyrometer and you"ll see. Load carrying capacity obviously is at it"s highest at max inflaction: vehicle placards err on the side of ride comfort and may put you in jeopardy (doubt it? Just ask Firestone/Ford/ millions of Explorer owners who kept me backordered on 235/75-15 for years). Long story made very short: a tire will grip better, last longer, carry more load and just generally be safer at the maximum cold inflation based on my professional observation, which has been accepted in the courts of State of Va and the Dist of Columbia (big whoop) as expert opinion. (warning: opinions expressed here are not sanctioned by the best tire manufacturer in the world, who still wants you to run what"s printed on the door of the vehicle). PS; Nitrogen is a waste of average joe"s dough- but that"s another thread.

One thing I haven't seen mentioned is how much pressure the WHEEL is rated for. My '90 Blazer has tires that say max 60 psi, BUTTT the wheels are stamped 40 psi. I run 40, and it still has the feel of solid rubber tires.

You know what this REALLY measures? ALIGNMENT WEAR. You will spot waaaaaay more tire wear due to poor alignment with a tread depth guage than you will ever see from inflation.
You nailed it, though- a vital tool to tire maintenance. if a guy ever tries to sell you tires and does NOT have one of these in his pocket, you're talking to the wrong dude.

man, do not even get me started on plugs! The ONLY acceptable tire repair is a patch-plug installed from the inside of the tire, patching the inner liner to prevent air leakage while also sealing the puncture entry to prevent water contamination of the belt material. I am sure you saw your share of ply seprations that were actually caused by punctures or improper repairs!

Thanks, I really enjoyed the comments from the tire dealers and all the rest. I just got back from a big free fish fry, Im STUFFED. Between the big feast the Legion Hall put on Friday and tonights big fry, Im good to go until tomorrow at least.

Heck I may run my fronts at 79 lol and keep 80 in the back duals when I head out for Florida.

On so many RV's I see big time weather checking n cracking and underinflation but I guess those dudes are rookies, RV tires seldom wear out the tread its the sun and UV that gets to them. If I have any 6 to 7 yrs old I replace them, maybe sooner if on the front.

John T

Two anecdotal observations. No science or theory involved. Just what happens in real life with my tires.

One - my 92 Dodge W250. The guy I got it from ran the 235/85-16" tires at 80 PSI all the time. The centers on all four were bald and the tread near the sideways barely worn at all. To me that's ample proof that with these radial tires, over-inflation certainly made a negative difference. I still have them laying in my dump and will gladly post photos of these four tires with center bald areas if anyone wants to see.

Two - my 1983 Blazer K5 plow truck with 235/75-15" radials. I live on the steepest mountain road in town. Dirt and ice and snow covered most of the winter and it never gets salted. When I run my tires at 25 PSI I get substantially better traction then when at 44 PSI (max rating). Especially on shear ice. I soften the tires every winter due to that fact, since in bad weather it is a plow truck only and never used for long trips.

I usually just figure the guys with the advanced degrees and experience in vehicle design and the lawyers they have watching over them know what the hell they are doing. If they say 38 psi or 65 psi that is good enough for me.

I "learned" about the plug/patch units...and other stuff... when I got my education for retreading. I had a "mostly truck tire" shop to manage. We adhered pretty darn close to Firestone recommended practices. Prior to that, my experience with "patching" had been on car and light truck tires and IF it couldn't be fixed with just a patch, it got set aside as non-repairable. This was in the early 70's...radial tires just beginning to appear in passenger tire sizes and large truck tires were bias ply 10.00 x 20.

My "real education" on tire repair came from working with mfg. reps. when we made sales calls on retreaders and 'demonstrated' our product.

Rick

RYAN...Ya gotta realize this question came FROM a LAWYER and wanna be ENGINEER...but I 'hear ya'!! LOLLOL!!

Rick

I am not a tire engineer or tire expert. I do have a theory that a tire carrying a given load weight should be inflated enough to carry even pressure across the width of the tire.

For the last 17 years I have carried an infrared temperature gun (Raytek), after about 30 minutes of travel, scanned the temperatures across the tread, and adjusted tire pressures until I got even temps all the way across the tire. It has given me the best tire life in miles of anything I have tried. It is easiest to use in a vehicle that carries about the same load every day. In a vehicle that seesboth empty and loaded use, I run pressures for the heaviest load all the time.

In my work truck with LT 215-85-16E tires, it results in 80# in the front that weighs 4,500#, and 50# in the rear duals that also carries about 4,500# every day. Roads that have a higher crown will often make the right side tires run 2-3 degrees F hotter than a
lesser crown.

I have had people tell me that it takes too much
time, but it has worked well for me.

John,
I run 235's at 80 lbs cold, though the RV dealer said to carry 90 lbs. The tire dealer said not to exceed the 80 lb tire recommendation. At the price of diesel, I'm not going to wear out the tread.
I would be concerned about rolling the tire off the rim in a hard turn at lower pressure. I know they really flex and roll when I have to jack knife it in a tight spot.
C. L.

You are correct, I always run the max pressure printed on the sidewall,Your rig will drive better, sway less and get better fuel economy, and maximum wear from the tires. A lot of guys say they ride too hard, I can't tell the difference. The more plies a tire has the higher pressure it needs for less flexing and less heat, if you want a soft ride use a 4 or 6 ply and run the max in that tire.

So who is the best tire manufacturer? I think that's like trying to pick the best vehicle manufacturer. I think it would depend a lot on the specific application.

I would humbly submit that best tire manufacturer in the world is Michelin. If you"re ever near Dulles Airport, stop by- I"ll show you several thousand and explan why!

May wear more tread off the middle of the tire face. The reduction in fuel consumption will makeup for the extra tire center wear.
Better running at 80psi than 10psi less than required for the load.
Anybody remember Ford specing their Exploder with lower tire inflation pressures? Because some people complained that their truck rode like a truck.

Rick, our tire experiences are similar,lets talk.Frank

Hello jose bagge,
You mean like this?
Thanks for the kind comment.
A very inexpensive tool to prevent not only expensive repairs, but catch safety issues!
Guido.