Tire pressure for entire rig

[rbev2308]

Ok...maybe I done fell for the age old debate that there are hundreds of different theories on what pressure to run in our tow vehicles and campers. For the record, I am driving an F-350 DRW with BF Goodrich 245/75R17 and the placard calls for 75 psi front and 65 psi rear. Now the tire itself calls for 3195 lbs max load at 80 psi so being my front axle is around 5300 lbs, it makes sense for the 75 psi rating. Where I am getting confused is on the rear. The rear axles are rated for 9500 lbs and even at that max weight on the axle, you still would not be at 80 psi since there are 4 tires x 3195 per tire Personally, I like more tire on the ground!!! The question is does the mfr set that pressure based on the max the truck can do or what...it seems that most dealers and tire places put the pressure on the placard in the tire so conventional wisdom says you are putting 3500 lbs pin weight on the rear, the placard is out the window. The math does not add up. I think with the weight I have added, I am still ok with the placard recommended psi but then that would make me wonder why the dealer and any other tire place would put that psi in the tires when the truck is empty basically running over inflated. Maybe I am reading to much into this. Looking at dozens of posts on here and various websites I get people loading 17000 lb trailers with 65 psi, to people running 80 psi no matter what the loaded weight. To me ,it makes for a scarier proposition in bad weather and other things. Basically I have drug this thing around with 60-65 since getting this thing and finally took it over the scale since I swapped out the trailer tires. I am at 7600 lbs on my rear axles and about 12,900 with truck and pin weight and 11,000 on trailer axle and trailer weight is 14,800 ish ....The 5er G614's G series are rated at 3750 at 110 psi but even with the 11,000 on trailer axle, I am not comfortable discounting that pin weight as I do not know how that axle weight is allocated since they are so close together and unknown side to side so I go with 14,800 divided by the 3750 per tire and decide to run 100-103 psi on those...My real concern is the DRW pressure.. I know I am probably going to get the same thing here cause everyone has their opinion and that's what you are going to go by.. Personally, I would rather run overinflated that under!!! Sorry for the rant!!! I should just hook up the damn thing and go down the road!!!!

[bobbecky]

I run our G614's at least 105 psi, but try to maintain 110 psi, but we are a bit heavier than you. As far as the duals on your truck, you should look at the sidewalls, and there will be two load ratings and pressures. The higher load rating, along with the higher max pressure is for running those tires as singles. The other lower load rating, along with lower max pressure is for running those tires as duals, so the placard giving you a lower pressure on the rears is probably correct.

[CWtheMan]

Do not confuse automotive tire fitments with RV trailer tire fitments. They are governed differently.

Your truck manufacturer has built-in some load capacity reserves with the axle ratings. According to you they will carry 14800#. What is your truck’s GVWR listing on it’s placard?

Tires for your truck are required to have a reserve load capacity by inflation. Here is what I get when I go to the inflation chart. Your front tires carry 3050# each at 75 psi = 6100#, lots of reserves. The rear tires must be derated for dually operation. They support 2535 each at 65 psi = 10100#, a reasonable amount above max GAWR.

Remember, as the owner you’re not supposed to exceed the truck’s GVWR. I see nothing wrong with your truck’s tire pressures.

[ReadyToRoll]

Wondering if you are reading the "reduced load" pressure for the rear. find it very unlikely that the rear pressure would be lower than the front with the max carrying capacity of the truck.
The pressure is calculated to carry the "Max" axle capacity(loaded) of the truck that is determined by the manufacturer. Many of the newer vehicles have now gotten away from the reduced load pressure because some will load the truck to it's max. capacity and not inflate the rear tires to the full load inflation and secondly, most all today have the TMPS monitoring system and the recommended pressure at max load is what it is programmed for.

[CWtheMan]

Throughout the USA tire industry the recommended cold tire pressure (s) found on a vehicle’s certification label/tire placard are the correct inflation pressure for the Original Equipment tires on that vehicle. Like sized tires will require the same inflation. The only time less tire pressures are needed is when outlined in the vehicle owner’s manual for special circumstances. Because some drivers find more comfortable riding conditions with lower tire pressures doesn’t make it right or safe. The procedure often written about in these tire forums for inflating tires to the load carried is a misconception carried over from the procedures used for over the road truckers. They are governed by other regulations, not the FMVSS which governs RV trailer tires.

Original Equipment tire fitment regulations for RV trailer tires are, like all other vehicle tire fitments, the sole responsibility of the vehicle manufacturer. So is their inflation pressures.

You already have the smallest tires sufficient to satisfy the fitment requirements of your 6750# GAWR axles. Other options are the ST235/85R16E or LRF rated at 3640# at 80 psi and 3960# at 95 psi respectively. The most popular option will be any of the LT235/85R16G hybrid trailer tires rated at 3750# at 110 psi. All of them require high pressure rims sized 16x6.5 and rated for 110 psi. All of those options are considered plus sized because they are not of the same physical size as the OE tires and will require different load inflation charts. There will be those that will say 6" wide rims will work. See if the tire manufacturer or rim manufacturer will agree and put it in an email.

Of primary importance when plus sizing your trailer tires is to maintain the load capacity of the OE tires. They will not be damaged by 100% inflation to 110 psi and that’s what I’d recommend. With large trailers capable of carrying much more than their listed load capacity it’s always going to be advantageous to use every bit of load capacity from the installed tires. The trailer manufacturer’s do.

[rbev2308]

In response to several of the threads...It is quite common to have lower psi recommendations on the rear of duallys as there are 4 tires to distribute the load. Even with my pin weight added, I am only 2000 lbs more on the rear vice the front with double the tires which makes sense... As for the trucks GVWR, I am still almost 2000 lbs under it since its listed at 14,000 lbs. As for the trailer, I have (2) 7000 lb Dexter Axles and the Sendel T09 rims are rated at 110 psi as this was the year Keystone was switching over from E to G rated tires and mine had the newer rims but the older tires so I swapped them over as part of my sale. Loaded the camper is 14600# well under the campers GVWR of 15,500 and the weight on both axles total is 10,200 and 3400 is in the truck. Following the Goodyear inflation chart for the G614 and dividing 10,200/4 does not give me a warm and fuzzy running that much of a lower pressure given the fact those two axles are so close you get total axle weight. What if one axle had 6000 and the other had 4200 no way its that I desire to assume that..I am comfortable running PSI based on total trailer weight..There is no perfect formula but underinflation does more harm than over in my book. The issue is the dually tires, even the local Goodyear dealer has a different opinion than others as he states that the mfr of the vehicle typically sets the pressure based on comfortability and adding anymore weight should result in increase psi but the math does not add up. It appears the pressure listed will support the weight to the loaded axle ratings and even with full tank of diesel, all occupants, hitch and pin weight, I am still 2000 under that!!!! This is why the tire debate is endless because you got no real hard consistency on anything and everyone else is like me, has their own opinion based on whatever their research or theory is

[CWtheMan]

Originally Posted by rbev2308

In response to several of the threads...It is quite common to have lower psi recommendations on the rear of duallys as there are 4 tires to distribute the load. Even with my pin weight added, I am only 2000 lbs more on the rear vice the front with double the tires which makes sense... As for the trucks GVWR, I am still almost 2000 lbs under it since its listed at 14,000 lbs. As for the trailer, I have (2) 7000 lb Dexter Axles and the Sendel T09 rims are rated at 110 psi as this was the year Keystone was switching over from E to G rated tires and mine had the newer rims but the older tires so I swapped them over as part of my sale. Loaded the camper is 14600# well under the campers GVWR of 15,500 and the weight on both axles total is 10,200 and 3400 is in the truck. Following the Goodyear inflation chart for the G614 and dividing 10,200/4 does not give me a warm and fuzzy running that much of a lower pressure given the fact those two axles are so close you get total axle weight. What if one axle had 6000 and the other had 4200 no way its that I desire to assume that..I am comfortable running PSI based on total trailer weight..There is no perfect formula but underinflation does more harm than over in my book. The issue is the dually tires, even the local Goodyear dealer has a different opinion than others as he states that the mfr of the vehicle typically sets the pressure based on comfortability and adding anymore weight should result in increase psi but the math does not add up. It appears the pressure listed will support the weight to the loaded axle ratings and even with full tank of diesel, all occupants, hitch and pin weight, I am still 2000 under that!!!! This is why the tire debate is endless because you got no real hard consistency on anything and everyone else is like me, has their own opinion based on whatever their research or theory is

Your truck's manufacturer or trailer manufacturer cannot use research or theory when fitting them with the original equipment tires. They must use the directions provided in the Federal Motor Vehicle Safety Standards (FMVSS). Maybe you should read FMVSS 571.110 and FMVSS 571.120 to become more familiar with how those fitments are chosen and displayed. There are other references within those two that also play a major roll in the fitment outcome.

Footnote: Earlier I wrote that I knew you have 7000# axles. Keystone has had a number of recalls for incorrect certification label information. It is normally because they list 7000# axles with a GAWR of 7000# on the certification label and then install ST235/80R16E tires with load capacities of 3520# which is a major error. Follow-up information either on the certification label or in the trailer's owner's manual informing the owner that the load capacity of the OE tires must be maintained with any replacement tires is required. Reason: ST235/80R16E tires are manufactured in three different load capacities. 3420#, 3500#, & 3520# all at 80 psi. Without documentation of the load capacity used they all default to 3420#. The 3420# tire does not qualify for fitment on the 7000# axles. Solution: Replace the certification label with a lower GAWR such as 6750# and adjust the cargo capacity to display the proper GVWR.

[rbev2308]

I will be honest..It is all getting confusing for me..I appreciate the response but I do not plan on reading Federal Motor standards or other stuff. My unit is a 2015 with a 2014 vin as it was built during the switchover of model year and some of the stuff is different as the paint scheme and a few other internal things are 2015 layout. They put Sendel T09 wheels rated at 110 psi and 3750lbs as all the new Alpines are standard with G series tires but put the cheaper E rated tires on there since it was technically a 2014. I had them taken to a Goodyear dealer and replaced once I knew the wheel was ok for it. In theory, the GAWR is 7000 x 2 and the trailer GVWR is 15500 as obviously 15-25% and in my case 23% of the weight is in the pin and less than 11000 is spread over both axles. for total trailer weight in the 14600 range. I did check with Keystone and a dealer and with Dexter to ensure I had no open recalls on anything and got three no's I am comfortable with my weight and psi on my trailer G614's the dually was really the question mark.

[jamesmc321]

SRW guy here (ya a baby half ton truck too )

I put LT tires on my last truck (just got the '15 so haven't swapped these out yet) and got into an argument with the tire place about this same topic.

Here's the thing... the placard on the door jamb is for OE tires, or OE replacement wires... if i change from P tires to LT, the tire pressure is going to be different in them and it is going to be what is printed on the side of the tires, not the door jamb -- well after 20 minutes arguing with the tire 'professional' they set them at what I wanted (and warned against it - ooo so scared ).

From a friend at a tire manufacture (actually is the quality manager there):

"Are you going to trust the truck manufacturer or the tire manufacturer....we print on the tires what we test them and rate them too handle as far as PSI is concerned, if you choose to follow the company that builds the vehicle instead of the tire, that is your prerogative however I wouldn’t suggest it"

Think I will stick with what he is saying…

[gearhead]

Originally Posted by CWtheMan

Do not confuse automotive tire fitments with RV trailer tire fitments. They are governed differently.

Your truck manufacturer has built-in some load capacity reserves with the axle ratings. According to you they will carry 14800#. What is your truck’s GVWR listing on it’s placard?

Tires for your truck are required to have a reserve load capacity by inflation. Here is what I get when I go to the inflation chart. Your front tires carry 3050# each at 75 psi = 6100#, lots of reserves. The rear tires must be derated for dually operation. They support 2535 each at 65 psi = 10100#, a reasonable amount above max GAWR.

Remember, as the owner you’re not supposed to exceed the truck’s GVWR. I see nothing wrong with your truck’s tire pressures.

Why do the rear tires have to be derated for dually operation???

[jsmith948]

Originally Posted by jamesmc321

SRW guy here (ya a baby half ton truck too )

I

From a friend at a tire manufacture (actually is the quality manager there):

"Are you going to trust the truck manufacturer or the tire manufacturer....we print on the tires what we test them and rate them too handle as far as PSI is concerned, if you choose to follow the company that builds the vehicle instead of the tire, that is your prerogative however I wouldn’t suggest it"

Think I will stick with what he is saying…

Remember the Ford Explorer/Firestone tire debacle?
Ford set a lower pressure for the tires in order to take some of the harshness out of the vehicle's ride resulting in a degradation of handling characteristics and a propensity for roll-overs. Not to mention tire failures and the resulting roll-overs.
Our F250 calls for 75psi front and 80psi rear. That is the pressure we run. No adverse tire wear. I don't worry about the ride. It is, after all, a TRUCK. JMHO

[CWtheMan]

Originally Posted by gearhead

Why do the rear tires have to be derated for dually operation???

Road crown.

[CWtheMan]

Originally Posted by jamesmc321

"Are you going to trust the truck manufacturer or the tire manufacturer....we print on the tires what we test them and rate them too handle as far as PSI is concerned, if you choose to follow the company that builds the vehicle instead of the tire, that is your prerogative however I wouldn’t suggest it"

Think I will stick with what he is saying…

There is a problem with logic and regulations in what you say. Tire manufacturers build tires at the request of vehicle manufacturers. The vehicle manufacturer is solely responsible for setting recommended (correct) tire pressures.

All road certified tires MUST be tested to acquire the DOT on their sidewalls. They are tested for their strength in their design category.

Remember, vehicle manufacturers MUST follow safety regulations. Tire fitments are identifiable DOT safety concerns. Minimum DOT safety instructions to vehicle builders MUST be followed. The responsibility to maintain those safety concerns shifts to the vehicle owner as soon as they take position of it.

Bottom line, tire manufacturers will not trump vehicle manufacturers recommended tire inflation pressures. Exceeding the recommendations is not considered a violation. This is a short PDF. Read it carefully and you will see that not going below the vehicle manufacturers inflation recommendations is highly stressed.

http://www.trucktires.com/bridgeston.../WeighForm.pdf

Tire industry standards stress that replacement tires - even plus sized - must provide equal or greater load capacity compared to the OE tires.

[Desert185]

Originally Posted by CWtheMan

There is a problem with logic and regulations in what you say. Tire manufacturers build tires at the request of vehicle manufacturers. The vehicle manufacturer is solely responsible for setting recommended (correct) tire pressures.

All road certified tires MUST be tested to acquire the DOT on their sidewalls. They are tested for their strength in their design category.

Remember, vehicle manufacturers MUST follow safety regulations. Tire fitments are identifiable DOT safety concerns. Minimum DOT safety instructions to vehicle builders MUST be followed. The responsibility to maintain those safety concerns shifts to the vehicle owner as soon as they take position of it.

Bottom line, tire manufacturers will not trump vehicle manufacturers recommended tire inflation pressures. Exceeding the recommendations is not considered a violation. This is a short PDF. Read it carefully and you will see that not going below the vehicle manufacturers inflation recommendations is highly stressed.

http://www.trucktires.com/bridgeston.../WeighForm.pdf

Tire industry standards stress that replacement tires - even plus sized - must provide equal or greater load capacity compared to the OE tires.

Since the title of that link is "Travel Trailer and RV", I interpret it as NOT applying to the pickup tow vehicle. So, inflate to max tire rated pressure on the trailer and max on the rear of the pickup when towing. When not towing, deflate rear tires to a lesser PSI in agreement with the door sticker...a procedure I have done for decades without any consequences other than decently high mileage realized on pickup tires not generally used for towing. Even though a grandpa, I don't drive like a grandpa/grandma...FWIW.

In my case with LT265/75-16 LRE driving over 300,000 miles on multiple sets of Michelin or Bridgestone tires:

Not towing: 60 front; 55 rear
Towing: 60 front; 80 rear

[gearhead]

Originally Posted by CWtheMan

Road crown.

I guess I'm dumber than I thought.
Tell me more....

[CWtheMan]

Originally Posted by gearhead

I guess I'm dumber than I thought.
Tell me more....

Sorry, I often give the impression of a know it all with my tire posts. Probably relates to my more than 31 years of active duty military.

I write most of my posts from the top of my head and not from archived posts I've previously written. That way each post is tailored to the thread I'm posting in.

I have references for everything I post but I've found most wont read them. Here is a case in point about some of the information I've posted in this thread about tire pressures.

The following is from the current (2015) Bridgestone truck tire data book. Stuff presented in such publications follow tire industry standards. .

Owner’s Obligations
It is your obligation to maintain proper tire inflation pressures
as specified by the vehicle manufacturer and to operate the
vehicle within tire/vehicle load capacity and speed limitations.


Tire Inflation Pressure
Tires need proper inflation pressure to operate effectively and
perform as intended. Tires carry the vehicle, passenger, and
cargo loads and transmit the braking, acceleration, and turning
forces. The vehicle manufacturer recommends the inflation
pressures for the tires mounted on your vehicle.

In a dual assembly tire fitments, the load limit is reduced slightly, to compensate for small differences in tire loading and inflation pressure. Even road crown can put more load on one of your duals than on the other.

It's 134 pages and most readers that are not researchers are not going to read all of it.

http://www.trucktires.com/bridgeston...ckDataBook.pdf

[buckeyebobhockingcamper]

ok here is my problem,when leaving ohio in december i fill my
tires to 80 rear ,60 front on tow vehicle(srw)i leave ohio and when i get into fkorida heat the tpms on my truck says warning check tire pressure.rears are at 92-95 psi,should i stop and let some air out and take them back to 80?also rear truck rims are too hot to hold,is this heat normal.?i have noticed tires wear like overinflation in center of tread(firestone tranzforce)my new 5er is 500 more lbs on pin weight at 2250.i am gonna install airbags on tv2007 chevy d/a i guess my main question is should i let air out,i see lots of people with more pin weight on srw trucks than i am running

[gearhead]

Originally Posted by CWtheMan

Sorry, I often give the impression of a know it all with my tire posts. Probably relates to my more than 31 years of active duty military.

I write most of my posts from the top of my head and not from archived posts I've previously written. That way each post is tailored to the thread I'm posting in.

I have references for everything I post but I've found most wont read them. Here is a case in point about some of the information I've posted in this thread about tire pressures.

The following is from the current (2015) Bridgestone truck tire data book. Stuff presented in such publications follow tire industry standards. .

Owner’s Obligations
It is your obligation to maintain proper tire inflation pressures
as specified by the vehicle manufacturer and to operate the
vehicle within tire/vehicle load capacity and speed limitations.


Tire Inflation Pressure
Tires need proper inflation pressure to operate effectively and
perform as intended. Tires carry the vehicle, passenger, and
cargo loads and transmit the braking, acceleration, and turning
forces. The vehicle manufacturer recommends the inflation
pressures for the tires mounted on your vehicle.

In a dual assembly tire fitments, the load limit is reduced slightly, to compensate for small differences in tire loading and inflation pressure. Even road crown can put more load on one of your duals than on the other.

It's 134 pages and most readers that are not researchers are not going to read all of it.

http://www.trucktires.com/bridgeston...ckDataBook.pdf

No man, you're fine. That's why I'm on here...to learn from those who are more knowledgeable, than me anyway. What we used to call "content matter expert". You're "it" for tires.
I see how road crown would lean the vehicle over and put more load on one side of the vehicle. Just me, but why wouldn't that have the same effect on a single? My calculus teacher is still asleep, but thinking of the angle of road crown being fairly low and how much weight would be transferred, I wonder if someone has some actual data to show how much a tire would be over loaded? If that is the case, why wouldn't you want the tire to be inflated for max capacity, rather than under inflated with less rated capacity?
The question or issue that maybe hasn't been expressed clearly, is that folks just run max single inflation on dual rears which gives reserve capacity. That seems to make more sense than running a tire less inflated, regardless of what is stamped on the sidewall.
The road crown issue sounds illogical to me.
More comments without much thought.....are manufacturers guarding against someone using the bad logic of looking at max single load and multiplying that times 4 to come to a load of 16,000 pounds in the back of a F350 dually, disregarding Fords vehicle capacity?

[CWtheMan]

Originally Posted by buckeyebobhockingcamper

ok here is my problem,when leaving ohio in december i fill my
tires to 80 rear ,60 front on tow vehicle(srw)i leave ohio and when i get into fkorida heat the tpms on my truck says warning check tire pressure.rears are at 92-95 psi,should i stop and let some air out and take them back to 80?also rear truck rims are too hot to hold,is this heat normal.?i have noticed tires wear like overinflation in center of tread(firestone tranzforce)my new 5er is 500 more lbs on pin weight at 2250.i am gonna install airbags on tv2007 chevy d/a i guess my main question is should i let air out,i see lots of people with more pin weight on srw trucks than i am running

No, you should not let air out of tires that were known to be properly inflated before they were used on the road. Tire engineers use a thermal equilibrium formula to account for such inflation pressure increases.

There is probably something else going on with your tires. Excessive heat is a product of under inflation, over loading and excessive speed. Any single or combination of those factors can cause the condition you have described. If you haven’t actually got some scaled weights you should find out if those hot tires are overloaded.

Keystone has established a pin weight of 2225# for your fully loaded trailer. Fiver owners usually put a high percentage of their cargo forward of the axles which leads to a much higher pin weight. And, owners tend to overlook the fact that truck cargo figures must be calculated to determine what their acceptable pin weight capability is.

http://www.keystonerv.com/montana-high-country/#/specs

[CWtheMan]

Originally Posted by gearhead

More comments without much thought.....are manufacturers guarding against someone using the bad logic of looking at max single load and multiplying that times 4 to come to a load of 16,000 pounds in the back of a F350 dually, disregarding Fords vehicle capacity?

This is the kind of question that often pits me against trained tire experts. My answers are from the safety regulations vehicle manufacturers must abide when fitting the running gear to your truck. There are more than half a dozen lengthily ones and I’m not going to reference them here.

Get the actual figures from your truck’s tire placard for GVWR and total GAWR. The GAWR is going to exceed the GVWR. That’s normal because the truck manufacture has used axles that provide a reserve load capacity to insure the GVWR is always supported. Tires are fitted to each GAWR and are also required to provide load capacity reserves via inflation pressures. Get the load inflation charts for the installed tires and do some math. You will find that the recommended inflation figures on the tire placard exceed the GAWR which exceeds the truck’s GVWR. Points to remember. With dual rear wheel configurations the load capacity is reduced and is provided on the inflation charts. Many half ton trucks are equipped with Passenger type tires. Those tires must be derated by dividing the maximum load capacity on their sidewalls by 1.1. Vehicle manufacturers using such fitment configurations will automatically derate the passenger tires.

Bottom line: A vehicle’s limiting factor is it’s GVWR.