A ? for you tire guys... - Montana Owners Club

Bluegill · 11-12-2006, 05:24 PM

Dumb question time,

My tires on my truck tell me MAX tire PSIG is 80 PSI.
Now, does max pressure mean.. that is the max the tire will handle ? Or that is the pressure that should be in them when towing at max pounds ?
Does this question make any sense at all ?

LonnieB · 11-13-2006, 01:08 AM

Good morning Blue,
The 80 psi. max. on your tires is the maximum safe inflation for the tire, regardless of load. Hope this help you out.

On Edit - There are NO dumb questions. Remember???

VanMan · 11-13-2006, 01:33 AM

With the load (Montana) applied, will the measured psi go up? In other words, should I be inflating the tire to the desired psi BEFORE hooking up? or AFTER hooking up? or does it make a difference?

ols1932 · 11-13-2006, 02:06 AM

I make sure all my tires are set to the max cold psi as specified on the tire before I hit the road. The pressure goes up as you travel. However, the tire manufacturer has taken that into consideration. That's why the "Max" psi is listed. I believe that means do not put in any more than whatever is posted. In my case it is 80 psi.

Orv

Bluegill · 11-13-2006, 02:07 AM

If 80 is MAX.... then what should it be for regular driving?
I couldnt see that printed on the tire anywhere.

I like VanMan's question too

padredw · 11-13-2006, 02:47 AM

On my Chevrolet Duramax the recommended pressure for the rear tires is 80, while that for the front tires is 55. This is on posted on the pickup, not on the tires. So I keep the pressure exactly at that: 55 on the front and 80 on the rear.

The tires are identical so the maximum would be the same for both front and rear.

Glenn and Lorraine · 11-13-2006, 03:39 AM

80 PSI is the MAX air pressure for that particular tire but not necessarily the pressure you should be carrying in that tire.

In order for you to arrive at the PROPER inflation you MUST know the load that tire is carrying. In other words weigh the vehicle. On a TV weigh the front and rear axles separately. When the trailer is attached to the TV weigh both axles again. On the trailer you can weigh both axles together but without the pin weight.

For example; The MAX capacity on an LT245/75R16E at 80 PSI is 3042 pounds per tire.
After weighing your axles you find the load to be only 2760 lbs per tire than your inflation should be only 70 PSI. This would also apply to your trailer tires as well.

Here is a tire inflation chart for ST and LT tires

Padre, you are correct about what GM/Chevy recommends for their trucks but I have found keeping 80 PSI in the rear when not towing is wearing down the center of the tires. A positive sign of over inflation. When my 2500HD is not towing my rear tires are deflated to 65 PSI. At 65 PSI I also find a lot softer ride.

Hemlockusa · 11-13-2006, 03:40 AM

Bluegill - Padredw is right along with everyone else. Tire's pressure should be adjusted when cold. On the side of the truck door post it will have the recommended pressure for regular driving and heavy load towing. That is just for a softer ride for the dear wife. Most Trucks recommend a lower pressure on the front tire's than the rear when loaded and that is for the safe handling of the truck. I run my Dually with high pressure all the time because I guess I am lazy, I do check the tire's on a weekly basis - Very important to keep the Dually's as close to equal pressure as possible for proper wear. HOWEVER I AM NOT THE EXPERT GLENN, LONNIEB and a few of the other members have the brains. Maybe you could get one of them to drop by and air your tire's up for you.... Probably cost you a large cup of coffee OR??????? Safe Travels JOhn

LonnieB · 11-13-2006, 03:42 AM

VanMan, the answer to your question is no, the pressure will not increase after load is applied. Adjust your pressure, cold, loaded or empty doesn't matter.
Blue, your question is a matter of personal preference. When unhooked I run 65 psi. in all 4, hooked up, I run 65 in front and 80 in the rear. As padredw said, look on your door panel for empty pressure.

illapah · 11-13-2006, 05:04 AM

Blue, Look at your driverside pillar between the doors for pressure recommendation.

indy roadrunner · 11-13-2006, 10:06 AM

I am in agreement with Lonnie and Glenn. I just attended a tire seminar for my trucking company and the big thing they stressed was that other than road hazards, under inflation or over inflation was the biggest reasons for tire failure. Under inflation causes the tire to run hotter and over inflation subjects the tire to failure due to lack of flexing.

padredw · 11-13-2006, 10:57 AM

Just to say that I appreciate the experience of Glenn and Lonnie and think they are right about adjusting the pressure when NOT towing. My earlier comment was related to towing which is most of my use of the pickup. Since I am not a full timer, we have an auto for most of other driving.

Montana Sky · 11-13-2006, 11:03 AM

I run 80 psi all the way around when towing the coach or other heavy trailers. While not towing, I drop my tires down to 60psi cold. Gives the truck a much better ride, and helps the tires wear well.

JimF · 11-13-2006, 01:41 PM

The literature that came with my Michelins says 50 front 55 rear for no load and 55 front and 70 rear full load, max pressure 80 psi is only stated on the sidewall of the tire.

rickfox · 11-13-2006, 02:23 PM

By the way, most of the newer 2006 and above Montanas have the Mission tires installed. These tires are rated at 3500# at 80 psi. Previously, the tires were rated at 3042# at 80 psi.

Fully loaded, my 3400 has approximately 11,100# on the axles. I have not been able to weigh each axle separately, but if the load is fairly equally distributed, there would be less than 3000# per tire.

I have not been able to find a load chart for the new tires - 235/80R16E, but have one for the D rated tires. Per that chart, I should be running 60psi at 3000#. That is significantly less than the 80 psi that some say should be used. Perhaps most are referring to the tire sizes that used to be on the Montanas.

Glenn and Lonnie, what is right? It would sure be nice if we could come up with a load chart for the new sized tires.

Bluegill · 11-13-2006, 03:04 PM

Okay, This is great info. Lonnie & Glenn... Homeruns.

I didnt even think about looking at the door pillar. I did get my TV weighed empty so I will look at it to get an idea of where I should be.

Wrenchtraveller · 11-13-2006, 04:00 PM

Glenn and Lonnie are right on the money but remember that most construction pickups are run empty and loaded most of their lives and nobody adjusts pressure every time you unload and load up a pickup. I am not a tire expert but in the 30 years I have driven pickups I have always kept my rear tires at max because I never knew when I was going to pick up my next load.
I have never had a tire failure on any of my trucks but I always replace them before they are worn completely out and I buy Michelins as replacement tires.

LonnieB · 11-13-2006, 05:10 PM

Rick, I will look into it tomorrow, I don't have an answer off the top of my head. Glenn may have a chart handy.
Wrenchtraveller, when I was doing construction all the time, I did the same as you, for the same reason. I wasn't concerned with tire wear due to over inflation, my only concerns were a blowout due to low pressure, and not getting where I needed to be on time, because I was on the side of the road changing a tire.

Glenn and Lorraine · 11-13-2006, 11:39 PM

Quote:

quote:Originally posted by rickfox

By the way, most of the newer 2006 and above Montanas have the Mission tires installed. These tires are rated at 3500# at 80 psi. Previously, the tires were rated at 3042# at 80 psi.

Fully loaded, my 3400 has approximately 11,100# on the axles. I have not been able to weigh each axle separately, but if the load is fairly equally distributed, there would be less than 3000# per tire.

I have not been able to find a load chart for the new tires - 235/80R16E, but have one for the D rated tires. Per that chart, I should be running 60psi at 3000#. That is significantly less than the 80 psi that some say should be used. Perhaps most are referring to the tire sizes that used to be on the Montanas.

Glenn and Lonnie, what is right? It would sure be nice if we could come up with a load chart for the new sized tires.

Rick,
First of all it is not necessary to way each axle separately on the Monty. Unless you have the trailer loaded very heavy on one side than the other the weight carried per tire should be within a few pounds of one and other

We do have the load chart for the ST235/80R16"D" which goes up to 3000# at 65 PSI. Knowing that a ST235/80R16"E" is 3500# at 80 PSI as stated on the sidewall the 70 and 75 PSI numbers are in the range of 3170 at 70 PSI and 3340 at 75 PSI. Now granted this is just an educated guess but it will be in the ballpark.

Wrenchtraveller,
You are dead on the money. I also carried max pressure in the rear tires when I was using my other trucks loaded one day and empty the next. Only a fool would be adjusting tire pressure under those conditions.
The scenario I am using here is pulling the trailer or carrying just the empty hitch. Unless I plan on a long trip empty, I also DO NOT lower the PSI in the rear TV tires if I am only going to be unhooked for a week or less

ols1932 · 11-14-2006, 02:24 AM

I've had excellent results just leaving all my TV tires at max 80 psi, loaded or empty. I find that there is no abnormal wear when empty with max pressure. In the spring, we are at one place for three months with the advance staff of the Escapees for their Escapade and I do not deflate the tires. Otherwise I'm traveling pretty much steadily, only stopping for maybe a week or two at the most.

Orv

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