Free 7 Day Trial RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Free 7 Day Trial ×


Reply
 
Thread Tools Display Modes
Old 04-12-2011, 04:38 PM   #1
Member
 
Join Date: Dec 2010
Location: Harrisburg, PA
Posts: 70
Tire Pressure

We just returned from picking up our new Rockwood 2306 Mini-Lite from RV Wholesalers in Ohio. We were told during the PDI that the tire pressure should be set at 50 PSI and that RVW had already checked that the tires were properly inflated during the prep. After parking today, I thought the tires looked a little low and checked the pressure with a digital gauge. The tires, which are ST175/80R13, were all between 34 and 36 PSI which, I assume, means they are badly under-inflated. Shame on me for not checking this myself before we pulled away from RVW.

I'm now wondering if we were in jeopardy of having a problem due to the under-inflated tires. We had no issues on the drive home, but I assume that, if nothing else, we would've gotten better mileage if the tires had been properly inflated. My tv averaged 22 mpg on the way out and 11 mpg pulling the trailer home.

Additionally, the laminated chart attached to the rear of the tt says my tt has a dry weight of 3678 and the maximum cargo is 954 for a total weight of 4632. Does this pertain to the tires and the maximum weight they can safely carry? If so, it sounds as though it may be wise to put fourteen inch tires on my tt. Thanks for your input.

Greg
Gkconfer is offline   Reply With Quote
Old 04-12-2011, 04:43 PM   #2
Senior Member
 
DAISY BOYKIN's Avatar
 
Join Date: Jun 2010
Location: SUNSHINE STATE
Posts: 1,753
Send a message via Skype™ to DAISY BOYKIN
Tire pressure on your tt

Greg, Check the DOT and VIN stickers on the left front side of your TT. The DOT tire info sticker is yellow. This will tell you the correct pressure.
__________________
Sid & HRH MISSY, SHIH TZU
2019 WILDCAT 28 SGX
2014 F-250 KING RANCH PS 6.7L/SWD/6R140/BFT
TST Truck System Technologies TM-507SE
DAYS CAMPED 2021 16 DAYS
DAISY BOYKIN is offline   Reply With Quote
Old 04-21-2011, 09:26 PM   #3
Junior Member
 
Join Date: Apr 2011
Posts: 11
always check your tires when they are cool
Quote:
Originally Posted by Gkconfer View Post
We just returned from picking up our new Rockwood 2306 Mini-Lite from RV Wholesalers in Ohio. We were told during the PDI that the tire pressure should be set at 50 PSI and that RVW had already checked that the tires were properly inflated during the prep. After parking today, I thought the tires looked a little low and checked the pressure with a digital gauge. The tires, which are ST175/80R13, were all between 34 and 36 PSI which, I assume, means they are badly under-inflated. Shame on me for not checking this myself before we pulled away from RVW.

I'm now wondering if we were in jeopardy of having a problem due to the under-inflated tires. We had no issues on the drive home, but I assume that, if nothing else, we would've gotten better mileage if the tires had been properly inflated. My tv averaged 22 mpg on the way out and 11 mpg pulling the trailer home.

Additionally, the laminated chart attached to the rear of the tt says my tt has a dry weight of 3678 and the maximum cargo is 954 for a total weight of 4632. Does this pertain to the tires and the maximum weight they can safely carry? If so, it sounds as though it may be wise to put fourteen inch tires on my tt. Thanks for your input.

Greg
skip1955 is offline   Reply With Quote
Old 04-21-2011, 11:51 PM   #4
Moderator Emeritus
 
Join Date: Nov 2008
Location: Winston-Salem, NC
Posts: 2,381
ALWAYS READ THE SIDEWALL ON THE TIRE!!!!!! Never believe a sticker on a trailer. LOOK AT THE TIRES!!!!! The dealer may have swapped tires, factory may have installed wrong tires. LOOK AT THE TIRES!!!!. No your gas mileage would not have increased. Did I mention, READ THE SIDEWALL INFORMATION ON THE TIRES!!!!! Your weight and tire size suggest load range "B" tires, in which case 35 psi is about max. CHECK THE SIDEWALL on the tires and look for "load range" and also max "inflation pressure" Sorry if I'm over stressing this, but if you have a tire problem, they will ask what pressure you were running and where did you get the info. If you say from a sticker on the trailer, the tire manufacturer is gone because you did not follow inflation instructions printed on the tire.
__________________
LadyWindrider
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic

2008 Work and Play 18LT
LadyWindrider is offline   Reply With Quote
Old 04-22-2011, 06:51 AM   #5
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 23,170
While Skip is correct that tires are ALWAYS checked COLD, the pressure would have gone UP not down when checked hot. Boyle's Law of Gases.

If the tire was checked hot at 36 PSI, they were severely under inflated. I hope the trip was a short one. I would complain bitterly, and yes I would be a PITA until they documented it in your jacket.

IMO, (NOT a tire guy; but have had a tread separation at speed), those tires could be damaged.;ESPECIALLY, if they were driven at high speed for a long distance.

Anecdote:
I had to get involved with my tire dealer when I bought tires for my truck. The mounting machine they use did not go to 80 PSI, so the mechanic was going to mount them at 50 PSI; the highest the machine could go. I insisted I wanted 65 in the front and 80 in the rear. The mechanic whined, "but I will have to do another step to do that!" Sheesh...
__________________
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 04-22-2011, 08:19 AM   #6
Senior Member
 
Glenn5995's Avatar
 
Join Date: Feb 2011
Location: Phoenix AZ
Posts: 926
You will be fine.

50 PSI is the maximum pressure the tire can hold. The sidewall will be marked with the maximum PSI the tire can hold and the corresponding weight the tire can bear at that pressure. As the pressure decreases, so does the tire's load bearing capability.

Here is a tire inflation chart from Goodyear which gives the the load bearing capability of their tires at given pressures.

http://www.goodyear.com/rv/pdf/rv_inflation.pdf

You had just picked it up, so it should be empty. The dry weight is 3678, but lets add 400 for optional equipment, so that brings you to 4078. Subtract about 400 for tongue weight and that leaves the axles supporting about 3678. I believe that trailer is a tandem axle, so you have four tires. Although weight is never equally distributed in an RV or most vehicles for that matter, that makes each tire roughly supporting 919.5 pounds. According to Goodyear's chart (most manufacturer's will be similar), 30 PSI is sufficient to bear that weight.

Of course, if you have the cheap Carlisle tires which come with many new RVs or any Chinese manufactured tire........you are on borrowed time anyway, but that is another story!
__________________

Glenn & Beth (Dad & Mom)
David & Audra (16 year old twins)
2006 Dodge Power Wagon (Adventure & Tow Vehicle)
2006 Rockwood 8281SS (Home away from Home)
Glenn5995 is offline   Reply With Quote
Old 04-22-2011, 08:28 AM   #7
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 23,170
Thanks Glenn, a masterful addition.
You get a thumbs up from me.
__________________
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 04-22-2011, 09:46 AM   #8
camping
 
tentcamper1's Avatar
 
Join Date: Feb 2010
Location: Elkhart, Indiana
Posts: 988
Quote:
Originally Posted by herk7769 View Post
Thanks Glenn, a masterful addition.
You get a thumbs up from me.
hit the "thanks" button!!
__________________

2007 Chevy 2500HD CC
2010 V-Lite 30WRLTS
Nights Camped 2011 -64
Nights Camped 2012 -50
"I Live in My Own World, But It's OK. They Know Me"
tentcamper1 is offline   Reply With Quote
Old 04-22-2011, 10:11 AM   #9
Senior Member
 
Join Date: Jul 2010
Location: Waynesville
Posts: 14,428
You picked it up in Ohio,and went to PA. Wonder what the tire press was from Elkhart,IN to RVW???? Youroo!!
youroo is offline   Reply With Quote
Old 04-22-2011, 12:24 PM   #10
Senior Member
 
Glenn5995's Avatar
 
Join Date: Feb 2011
Location: Phoenix AZ
Posts: 926
Tire pressures vary quite a bit with temperature. That may be part of the problem depending on the ambient temperature at which they were originally checked and the ambient temperature at which the OP checked.

When I check the "cold pressure" on the trailer tires on a 115 degree Phoenix day and then drive to a camping area at 9500' in the White Mountains of Arizona and check them the next morning at 45 degrees, they will be 10 to 12 PSI less. If I leave them alone and return to Phoenix they will be back to the original pressure. If I were to fill them back up at the colder temperature, when I return to Phoenix I will find they are now over inflated.

That is one reason some people prefer Nitrogen filled tires, they do not vary pressure as much with changes in temperature. In hot climates, I usually keep the tires a few PSI above where I think they should be and at colder climates allow them to be under a little. In moderate temperatures they will be right on. Otherwise I would constantly be changing tire pressure.
__________________

Glenn & Beth (Dad & Mom)
David & Audra (16 year old twins)
2006 Dodge Power Wagon (Adventure & Tow Vehicle)
2006 Rockwood 8281SS (Home away from Home)
Glenn5995 is offline   Reply With Quote
Old 04-22-2011, 02:30 PM   #11
Member
 
Join Date: Dec 2010
Location: Harrisburg, PA
Posts: 70
Thanks everyone for weighing in. When I checked the tires, they were cold. According to the rating chart that Glenn attached, I was well within a safe range with the weight we were pulling. The tire sidewall does indicate a max 50 psi with a max weight of 1360 lbs. That info, btw, is very difficult to read but here is what is clearly legible: Made in China. I don't know about you, but I have zero confidence in the quality of Chinese products based on the horror stories that have come out of China in recent years regarding their lack of quality control.
Gkconfer is offline   Reply With Quote
Old 04-22-2011, 03:26 PM   #12
Senior Member
 
Join Date: Mar 2008
Location: Jacksonville Florida
Posts: 1,264
I don't know if it is relevant or not, BUT I purchased a bag of Doritos in Jacksonville, Fl. where I live, and went to Tennessee on the Blue Ridge pk.way, and that un opened bag of chips was making all sorts of funny noises inside a Wal mart bag in the back seat; we kept wondering what the heck was making that noise, and discovered that bag was about ready to burst! Apparently, the air pressure when filled and sealed in sea level Florida, was so much greater at 3500 feet(guess) above sea level, it made the bag do that. Also, I recall a kid's TV show many moons ago, where they took normally inflated balloons down in a sub, and they lost all of the air in them. Upon returning to the surface, they magically went back to normal. This same thing effect tires???? HMMMMM
Randy
__________________
/SIGPIC]'08 V-lite Flagstaff 30WRLS
'06 Ram 1500 QC hemi Reese dual cam sway control,
K&N series 77 intake, Hellwig helper spgs. LT tires,
Flowmaster "true duals", 380 h.p., Bilstein shocks
08flagvlite is offline   Reply With Quote
Old 04-22-2011, 03:43 PM   #13
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 23,170
I am researching this thread regarding two "head scratchers."

1) What IS the coefficient delta between nitrogen and a 78/20 mix of oxygen and nitrogen. IE if air changes 5 PSI due to a temp change what would 100% nitrogen do under the same conditions.

2) Would anybody care if I did.
__________________
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 04-22-2011, 06:02 PM   #14
Senior Member
 
Glenn5995's Avatar
 
Join Date: Feb 2011
Location: Phoenix AZ
Posts: 926
I hope I didn't give the impression I was advocating Nitrogen for inflating tires. I was just noting that less variance with temperature is one of the claims made by its advocates. I have not figured out how much difference there would be between air which is already 78% Nitrogen and pure Nitrogen (as you noted), but there are those which swear it is so. I personally think (that's scary isn't it!) that the result is not because of it being pure nitrogen, but the fact that it is "dry", i.e no humidity/moisture. If you removed the moisture from plain old regular air, you would probably have about the same result with more consistent pressure.

Just my thinking, feel free to rally to my cause or revolt as you deem appropriate.
__________________

Glenn & Beth (Dad & Mom)
David & Audra (16 year old twins)
2006 Dodge Power Wagon (Adventure & Tow Vehicle)
2006 Rockwood 8281SS (Home away from Home)
Glenn5995 is offline   Reply With Quote
Old 04-22-2011, 06:10 PM   #15
Senior Member
 
Join Date: Mar 2008
Location: Jacksonville Florida
Posts: 1,264
1.)My POINT IS does low air in the tires change at a higher altitude, or not? And, if so, then if i topped off my 50 lb. tires at 50 lb. cold in Fl, and drove to say the smokies, or someplace like that, would my air pressure now be dangerously over pressurized, risking a blow out or not?
2.)I for one would like to know the answer to Herk's puzzling strange phenomenon.
__________________
/SIGPIC]'08 V-lite Flagstaff 30WRLS
'06 Ram 1500 QC hemi Reese dual cam sway control,
K&N series 77 intake, Hellwig helper spgs. LT tires,
Flowmaster "true duals", 380 h.p., Bilstein shocks
08flagvlite is offline   Reply With Quote
Old 04-22-2011, 07:40 PM   #16
Senior Member
 
Join Date: Sep 2010
Posts: 2,189
From everything I have read there is a slight increase in tire pressure in higher elevations, but not nearly as much as with temperature changes. I saved this formula from someone over on RV.NET which seems accurate. I have no idea if nitrogen filled tires react differently.

"
The complete formula is (P1 * V1)/T1 = (P2 * V2)/T2. It's fairly safe to assume the volume doesn't change in a relatively minor change in temperature. Normally, the "T" number is Fahrenheit Absolute, which is regular F +460.

As an example, if you set the pressure at 120 psi when it's 40 F and the recheck it at 80F, and ignore the tire volume, P2 woud be 120*540/500, or 129.6

"
__________________

2011 Flagstaff 831FKBSS
2010 F250 4X4 5.4L 3.73 LS
EQUALIZER E4 1200/12000
lbrjet is online now   Reply With Quote
Old 04-22-2011, 08:37 PM   #17
Senior Member
 
Glenn5995's Avatar
 
Join Date: Feb 2011
Location: Phoenix AZ
Posts: 926
My understanding, and this is not an area in which I claim a lot knowledge, so correct me if I am wrong, is that there is no change in pressure in a SEALED container with changes in elevation assuming all other variables remain constant.

In the example of a sealed chip bag, when the chips were placed in the bag, no air was pressurized into the bag. The air inside was at atmospheric pressure, which matched the exterior pressure and so they canceled each other and the bag was pliable. Once you went up in elevation the atmospheric pressure decreased. The bag still contained the original higher atmospheric pressure, but now the pressure on the exterior of the bag has decreased and so the pressure inside the bag is greater than that outside and the bag expands under the force of the greater pressure, but the pressure in the bag stayed the same. This is assuming all other variables remain constant.

The change in pressure in tires is primarily from changes in temperature.
__________________

Glenn & Beth (Dad & Mom)
David & Audra (16 year old twins)
2006 Dodge Power Wagon (Adventure & Tow Vehicle)
2006 Rockwood 8281SS (Home away from Home)
Glenn5995 is offline   Reply With Quote
Old 04-22-2011, 10:55 PM   #18
Site Team - Lou
 
Herk7769's Avatar
 
Join Date: Oct 2009
Location: South Eastern PA
Posts: 23,170
Quote:
Originally Posted by lbrjet View Post
The complete formula is (P1 * V1)/T1 = (P2 * V2)/T2. It's fairly safe to assume the volume doesn't change in a relatively minor change in temperature. Normally, the "T" number is Fahrenheit Absolute, which is regular F +460.

As an example, if you set the pressure at 120 psi when it's 40 F and the recheck it at 80F, and ignore the tire volume, P2 would be 120*540/500, or 129.6
"
Gas laws - Wikipedia, the free encyclopedia

We could go crazy here with formulas, but the question posed has more to do with the "pure Nitrogen" vs "Air" debate of which there are over a hundred separate threads on this forum alone.

It is true, that if you keep the volume of a gas constant (ie in a fixed non-inflateable tire) and increase temperature, the pressure will rise. Decrease temperature and the pressure will fall.

Similarly, in a fixed volume, raising or lowering the pressure OUTSIDE the container; NOTHING inside the container changes. Pressure stays the same since the volume of the tire is fixed.

If the tire was flexible enough to inflate like a balloon, it would expand until the pressure inside was the same as the pressure outside (or it popped). If you put it underwater it would deflate as the outside pressure increased. However tires are not that flexible so temperature is the only thing that changes internal pressure.
__________________
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW
Herk7769 is offline   Reply With Quote
Old 04-23-2011, 06:59 AM   #19
Moderator Emeritus
 
MtnGuy's Avatar
 
Join Date: Sep 2008
Location: Shenandoah Valley of Virginia
Posts: 9,280
FWIW, it is almost impossible to get 100% (pure) N2 in tires. Unless there is some way to completely purge the existing air out of a tire, a 95% N2 fill is about all that can be expected.
__________________

Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS
MtnGuy is offline   Reply With Quote
Old 04-23-2011, 09:20 AM   #20
Senior Member
 
Glenn5995's Avatar
 
Join Date: Feb 2011
Location: Phoenix AZ
Posts: 926
Lou,

Sorry, I have not been on the forum long and did not realize there was a "nitrogen vs air" debate. I wasn't trying to start anything.

Also, thank you for explaining what I was attempting to say about the laws of gas far more clearly than I did.

I generally try to confine my comments to things about which I have knowledge, but after awhile the silence gets to me and I have to say something.......regret it.......start the process over.

Glenn
__________________

Glenn & Beth (Dad & Mom)
David & Audra (16 year old twins)
2006 Dodge Power Wagon (Adventure & Tow Vehicle)
2006 Rockwood 8281SS (Home away from Home)
Glenn5995 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Forest River, Inc. or any of its affiliates. This is an independent, unofficial site.



All times are GMT -5. The time now is 05:56 PM.