jraffler

Tire Pressure Recommendation

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jraffler   

Have Clas "A" 2003 Fleetwood Southwind R35. Just purchased new tires (6) Uniroyal RS20 size 245/70R19.5. Recommended psi cold is 110. I keep hearing from other Motorhome owners that I shouldn't inflate to maximum recommended psi. Current psi on all my 6 tires is 100. Does anyone one know a safe rule of thumb of what psi is allowable below manufacturers recomended air pressure. Appreciate any assistance.

Cheers, John

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Until you get it weighed go with the max of 110 psi.  I don't know why anyone would tell you not to run at that pressure.  You should have a data plate somewhere near the driver side that will give you the GVWR and until it is weighed that is what you should use.

I ran 110 on all tires for several years because I couldn't find a four corner weight place. Finally in Oregon I used the weigh scales that were closed. Run of one with all tires/axles, then run over the next with only passenger side. Use the differences to determine you individual weights. Max psi will not hurt the RV, but may give you a much stiffer ride.

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wolfe10   
4 hours ago, wayne77590 said:

Until you get it weighed go with the max of 110 psi. 

You should have a data plate somewhere near the driver side that will give you the GVWR and until it is weighed that is what you should use.

OK, those two statements MAY be similar, or may be well different.

So, let's look at them:

The sidewall of the tire indicates the PSI needed for the tire to carry its maximum designed weight.

The GVWR sticker indicates the PSI needed for each axle when loaded to maximum GAWR (Gross Axle Weight Rating).

Unless you have information indicating that your coach has axles loaded to more than GAWR, I would start with the PSI recommendations on the GVWR sticker. 

There are very few towns in the country that do not have scales-- truck stops, dumps, moving companies.  DO IT SOON, then you will know you have the correct PSI.

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Picky picky! Yep, sidewall will say, for example 5400  lbs at 110 psi for a 255/80R22.5 for a single tire and 9370 lbs for duals at 110 psi per tire.

That would be the Maximum load & pressure on sidewall for a 255/80R22.5

A single 255/80R22.5 could carry a max load of 5400 lbs and a max pressure of 110 psi. The single tires on an axle, if the weight were distributed evenly, would be able to carry 10800 lbs with each tire inflated to 110 psi. Dual tires on an axle evenly distributed could carry 18740 lbs with 110 psi in each tire.

So what I was trying to say is that as long as the load for the axle is is below max (after weighing the axle only (GAWR)), say for example a person is unable to get individual corner weights and the front axle combined weight is 9400 lbs, then inflating the tires to 110 psi is not going to hurt the tires and is a better option because corner weight are unknown and one side could be 5000 lb an the other 4400.

Hmmm! Did I say that right. It's better to not exceed the max load rating of the tire nor the max inflation pressure of the tire. If the weight is unknown it is better to run at 110 psi until weights can be gotten.

I have not traveled extensively but I have covered 46 of the 48 contiguous U.S and Oregon is the only state i was in that I knew for sure had scales open even when truckers were not required to stop at them. If there are other states that have open scales it would be a nice list to have.

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7 hours ago, wayne77590 said:

I have not traveled extensively but I have covered 46 of the 48 contiguous U.S and Oregon is the only state i was in that I knew for sure had scales open even when truckers were not required to stop at them. If there are other states that have open scales it would be a nice list to have.

That would be a nice list to have. 

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I want to get four corner weights and so far I've not found a place in central Texas to do that. There are lots of scales but they all have bollards placed close to the scale edges.

Any suggestions? And no, I'm not driving to Oregon.

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wolfe10   

Jim,

Just do a search for "truck scales" and your location. Getting axle weights is easy-- lots of truck stops have them.

Getting individual wheel weights (more accurate, as few motorhomes have perfect left/right weight distribution) is more difficult to find.

With axle only weights assume 45/55 weight distribution and use the 55% side to go to your tire manufacturer's inflation table to determine the minimum PSI for all tires on that axle.

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wolfe10   
2 hours ago, elkhartjim said:

Thanks, Brett. I have the axle weights but I would like to confirm I'm not something like 30/70. Using your 45/55 ratio, would that apply for the tag also?

Certainly if you have a single ride height valve for the tag axle, I would assume that would be a reasonable first cut at it.

Yes, some floorplans such as galley slides where the weight of the slide, appliances, cabinets, pantry and cookware are on one side "offset" by a Eurolounger on the other side, one can exceed the 45/55 rule.  In most cases, you can look at weight of heavy components and make a rough guess in terms of left/right distribution.

The exception is on the axle with two ride height valves.  If mis-adjusted, they can transfer a LOT of weight side to side.  That is why checking ride height at least once a year is a good idea.

Last point-- with a tag, on many chassis, it is possible to balance weight on each axle by adjusting weight on the tag.  Ideal is to have the same PERCENT of each axle's GAWR on each axle. 

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Alabama DOT uses portable scales, if you happen on one of the setups, you can ask the officer to to do a four corner, and if they are not too busy at the time, they will. The truckers here never know where to expect them to be, but most commonly found on roads where there is a lot of pulpwooding going on.

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LOL...thanks Kay but there isn't a whole lot of pulp wooding going on in the Texas hill country. 

Brett, I feel pretty confident my weight is fairly well balanced but its one of those things I'm anal about. I'll hopefully run across a scale some day that I can get the corners or drive to the Escapees in Livingston. 

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tireman9   
7 hours ago, elkhartjim said:

I want to get four corner weights and so far I've not found a place in central Texas to do that. There are lots of scales but they all have bollards placed close to the scale edges.

Any suggestions? And no, I'm not driving to Oregon.

Until you can get "4 corner weights" I suggest getting individual axle weights. Then assume one end is carrying 53% of the total. Use that number when consulting the Load Infl tables. That's your minimum cold inflation but I also suggest you add 10% (but not exceed tire max) to give a margin.

 

I also suggest you start reading my RV Tire Blog. Also put Perry GA next March on your calendar and come to both of my RV tire seminars.

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wolfe10   

Jim,

Being in Texas (like we are), check with your local DPS office and talk with their truck enforcement guy.  They use the same individual wheel position scales as RVSEF, Escapees, etc.

You should be able to arrange to meet them at their HQ at beginning or end of shift to do the individual wheel weighing.

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wolfe10   

Jim S,

Since you already have axle weights, you would need to check with any of the public scales to see if they are set up to allow side/individual wheel position weighing.  Most are not, as the area around most scales is graded away from them and weighing on a slant is not really that accurate.

DO contact the DPS and let us know if they will allow you to show up for individual wheel position weighing.  Suspect that would be very doable-- probably happy that someone really cares enough about safety to ask for their help.

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