Tire Pressure in Itasca Sunstar 30T

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Cass Sumrall

Cass Sumrall

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Joined
Mar 5, 2012
Posts
136
I have a new (2013) 30T & have made several short trips with it but I am not sure how much pressure I should be running in the tires. I have found a lot of conflicting information from a low of 82 PSI on the sticker beside the driver's seat to 110 PSI which the dealer recommended for better handling. 110 PSI is the pressure stated on the tires for the max weight. I have not been able to weigh it but I am sure I am well shy of max allowable weight (GVWR of 18,000 lbs) by at least 500 -1000lbs. The dealer said anything from 82 - 110 PSI should be okay but that it would handle better at 110 because the tire sidewalls would not flex as much.

I know there are some owners of this model on this forum. I am hoping to hear from them what their experience has been & what they are running as a result.

Thanks,
Cass 
 
We need info on your tires - brand/style/size. Until you can get to a scale, use the GVWR to look up the correct inflation pressure in the tire manufacturer's inflation chart.

Higher inflation pressure does not necessarily equate to better handling. In our case, the dealer grossly over-inflated the tires, and the handling was terrible, until I weighed the motorhome and adjusted the tire pressures accordingly.

Here's an example in our forum library.
 
Use the weight on the tire & weight placard by the driver seat. It will be sufficient for the max axle loads your coach is capable of and is still probably more than you actually need.  Inflating to the psi shown on the tire sidewall is only rarely the right answer on motorhome tires.

And as Tom says, major over-inflation  will result in bad handling. And uneven tire wear as well.
 
Load your Sunstar with all of the stuff you would have in it for a two week (or two month) trip, top off the fuel tank, have a full propane tank and 10 or 20 gallons of water and then take it to a nearby truck stop and weigh it.

There's nothing intimidating about weighing at a truck stop:

- pull into the scales (they are one way) making sure you position front and rear axles on different scale segments, your cab area should be about even with the scale intercom

- use an umbrella or long stout stick to push the button to call the weighmaster (clerk)

- they will answer and ask if this is an initial or reweigh.  Tell them "initial"

- then they'll ask for your tractor or unit number, tell them "private RV"

- they will say okay or whatever and tell you to come inside, pay and collect your weight ticket

- pull off the scales and park, go inside to truck counter area and pay (about $9)

Here's a more professional description of the process.
 
Gary RV Roamer said:
Use the weight on the tire & weight placard by the driver seat. It will be sufficient for the max axle loads your coach is capable of and is still probably more than you actually need.  Inflating to the psi shown on the tire sidewall is only rarely the right answer on motorhome tires.

And as Tom says, major over-inflation  will result in bad handling. And uneven tire wear as well.
Click to expand...

Part of the confusion for me is that the plackard by the driver's seat says 82 PSI, but the Goodyear table for my tires says 105 PSI for about 17,000 lbs which is pretty close to what it weighs loaded. Many say to add 5 lbs to the table & that puts me at 110 PSI (which is what the dealer suggested running for better handeling).

My tires are Goodyear 245/70R19.5.  My useful load according to the plackard is 2763 lbs with a 18,000 GVWR which means my empty weight is 15,237 & I have calculated that we add about 1770 lbs to that when we are traveling with a full tank of gas, etc.  Am I figuring this wrong?

Thanks,
Cass
 
John Canfield said:
Load your Sunstar with all of the stuff you would have in it for a two week (or two month) trip, top off the fuel tank, have a full propane tank and 10 or 20 gallons of water and then take it to a nearby truck stop and weigh it.

There's nothing intimidating about weighing at a truck stop:

- pull into the scales (they are one way) making sure you position front and rear axles on different scale segments, your cab area should be about even with the scale intercom

- use an umbrella or long stout stick to push the button to call the weighmaster (clerk)

- they will answer and ask if this is an initial or reweigh.  Tell them "initial"

- then they'll ask for your tractor or unit number, tell them "private RV"

- they will say okay or whatever and tell you to come inside, pay and collect your weight ticket

- pull off the scales and park, go inside to truck counter area and pay (about $9)

Here's a more professional description of the process.
Click to expand...

I like reading these forums for just this kind of question and response, thanks to the author for the question and thanks for your response. I have been needing/wanting to weigh my motor home and yet I've been a bit intimidated...not wanting to get in the way of the professional drivers at the truck stops. I'm going to get her weighed on the way home from the shop next week, based on your response...wish me luck.
 
John Canfield said:
Cass - all of the above is really irrelevant.  You will never know how much to inflate your tires until you weigh the rig.
Click to expand...

John,

It is not irrelevant to me since I am new at this & have yet to have an opportunity to get it weighed. I am leaving tomorrow on another short trip & won't have a chance or place to get it weighed first & my tires are very difficult to fill on the road (that's another thread & still a work in progress).

I don't understand why you say the facts I stated are irrelevant - it seems to me they are better than just guessing. They are also the facts others have requested in order to answer my question.

Cass
 
Cass Sumrall said:
..I don't understand why you say the facts I stated are irrelevant..
Click to expand...
They are irrelevant vis-a-vis knowing what inflation pressure your tires need.

OscarMike - glad to have nudged you to getting your unit weighed.
 
John Canfield said:
They are irrelevant vis-a-vis knowing what inflation pressure your tires need.
Click to expand...
.

I am having difficulty seeing how your response is helpful to me. Telling me that the numbers stated by the manufacturer are irrelevant in light of the fact as I have stated that I am leaving on a trip & can't get it weighed first leaves me with no alternatives. There are plenty of MH owners on the road who have not weighed their coach. Unless you are saying the manufacturer's weights are false, I can add the weights of the people, liquids & other things we have put on board & at least come up with a reasonable approximation just as I have done for many years with airplanes. It may not be the "best" method but I don't see how you can conclude that the figures stated are irrelevant.

Edit: Fixed quote.

 
The Goodyear load inflation tables indicate that your size tires inflated to 80 psi are suitable for weights to 3640 on doubles and 3415 on singles. If your MH weights are balanced (which is doubtful) the weight on each tire, assuming you are loaded to your maximum 18,000 pounds would be 3000 pounds for each tire, substantially less than the rating at 80 psi. That is the reasoning behind the number on the placard. The recommended psi is enough to carry the GVWR of the motorhome.

Your problem Cass, is that your figures are two tires short. The rating for doubles is for each tire.
 
Cass,
I think you are getting mixed up on the GVWR versus the axle loads and GAWR. The tire inflation tables don't deal with the whole coach weight, whether real (approx 17,000) or max (GVWR = 18000). You need to know or estimate what weight the tires are actually carrying.  The placard says 82 lbs because that is based on what the manufacturing thinks the axle loading (weight) will be. Usually they assume the axle is loaded to its max when they do that.  If your rig has an 18,000 GVWR, the rear axle is probably somewhere around 13,000-14,000 lbs and the front axle around 6000 lbs. The combined total may exceed the GVWR, providing some flexibility in where you place the load.

At 85 psi your 245/70R19.5 tires can carry 3740 lbs each as single tires on the front axle and 3515 each when paired as dual;s on the rear axle . That gives you a load capacity of 7480 lbs on the front axle and 14,060 lbs on the rear axle. If you look at the placard, it will show your max axle load ratings (GAWR) and I'll bet they are less than that.
 
Gary RV Roamer said:
Cass,
I think you are getting mixed up on the GVWR versus the axle loads and GAWR. The tire inflation tables don't deal with the whole coach weight, whether real (approx 17,000) or max (GVWR = 18000). You need to know or estimate what weight the tires are actually carrying.  The placard says 82 lbs because that is based on what the manufacturing thinks the axle loading (weight) will be. Usually they assume the axle is loaded to its max when they do that.  If your rig has an 18,000 GVWR, the rear axle is probably somewhere around 13,000-14,000 lbs and the front axle around 6000 lbs. The combined total may exceed the GVWR, providing some flexibility in where you place the load.

At 85 psi your 245/70R19.5 tires can carry 3740 lbs each as single tires on the front axle and 3515 each when paired as dual;s on the rear axle . That gives you a load capacity of 7480 lbs on the front axle and 14,060 lbs on the rear axle. If you look at the placard, it will show your max axle load ratings (GAWR) and I'll bet they are less than that.
Click to expand...
Yes, the GAWR ratings are less than that. They are 7000 front & 12000 rear.

So at 85 PSI the tires would actually be okay up to 21,540, well above my GVWR of 18000 or actual of 17000,  which means the plackard on the coach is pretty close at 82 to what would be correct for my estimated weight loaded of 17,000 lbs - am I figuring that right?

Thanks,
Cass
 
Yes, that's right. The 82 psi on the placard is actually quite high versus your actual load. That's because it has to assume that either or both axles will be loaded to 100% capacity.  And since you haven't weighed the coach, you should must assume the same thing. But you also do not want to go much higher than that, because extreme high pressures make the tire very hard, reducing its contact with the road and making the ride uncomfortable as well. Reducing the tire's contact patch (the small portion that actually touches the road) affects both steering and braking. And a too-hard tire bounces more, which is both a steering and comfort issue.
 
Thanks, Gary - good information!  :)

And very timely since I have just enough time to adjust them before hitting the road this morning.

Cass
 
Just recently purchased a '96 Jamboree Rallye as a beginner.  Got a really decent deal on a unit that had a lot going for it. Low miles, well kept, etc. Tires on front are new. We looked at date codes on the rear duallys, and found '04 codes, so we knew tires were a must, but just hadn't gotten that task done yet. Found a cracked manifold & broken bolt that set us back a couple of weeks. Today we took her down the interstate about 30 miles to get it weighed.  All was going well, when we lost the tread on the passenger side outer rear tire. Thank God no one was following close, and the damage was minimal to our vehicle. We were able to limp home, but again, our pride has taken a hit.

Yep...tires got moved right to the top of the list...

Jeff & Lora Hunt
 
Just back from our weekend trip to the other coast (of FL) & I'm happy to report that 85 PSI all around handled much better than the higher pressures we were running. The coach felt much more stable on the interstate & less squirrely with wind gusts & semis passing. Even my wife drove for a part of the trip (her first time at highway speeds) & felt very comfortable with it.

Thanks for all the good advice here!  I was apparantly getting pretty bad advice from the dealer who insisted it would handle better at 110 PSI.

Cass
 
A couple of years ago when going from ND to Arizona in January I aired up the tires at -20 degrees. As we were going down the grade into St. George, UT, the ambient temperature was going up fast and the motor home started handling funny. When I checked the air pressure the next morning, I found the pressure 15# higher than set in ND. Let air out and handling returned to normal.
 
I was apparantly getting pretty bad advice from the dealer who insisted it would handle better at 110 PSI.
Click to expand...

Hang around here awhile and you will see many examples of bad advice from dealers. Do not assume that everyone who is employed at an RV dealership is an expert, in RVs or anything else!
 
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