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Old 07-22-2014, 06:18 PM   #1
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Tire Inflation - no chart

how do I know what to inflate my tires to if there's no chart? I bought Roadlux R216 225/70 19.5 last year and I checked the pressure today with a digital tire gauge at roughly 70-72.5 PSI (45 on passenger inside rear wheel and driver front at 82.5). I know I should weight it etc. to get the correct pressures but even if I do, I can't find a chart. I assumed the tire dealer inflated them correctly when they were installed but now that they're so far off from each other I'm not sure where to even begin.

The max load is 95PSI but what should I inflate to if no chart?
Can I get it weighed at my town transfer station? if not, can I get it weighed at a highway truck weigh station or are the troopers there just gonna look at me funny?
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Old 07-22-2014, 06:29 PM   #2
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Quote:
Originally Posted by Bouchbri25 View Post
how do I know what to inflate my tires to if there's no chart? I bought Roadlux R216 225/70 19.5 last year and I checked the pressure today with a digital tire gauge at roughly 70-72.5 PSI (45 on passenger inside rear wheel and driver front at 82.5). I know I should weight it etc. to get the correct pressures but even if I do, I can't find a chart. I assumed the tire dealer inflated them correctly when they were installed but now that they're so far off from each other I'm not sure where to even begin.



The max load is 95PSI but what should I inflate to if no chart?

Can I get it weighed at my town transfer station? if not, can I get it weighed at a highway truck weigh station or are the troopers there just gonna look at me funny?

If it were me, I would inflate all to 95 psi until I got it weighed. The side of the tire should also have a max weight allowed at that 95 psi both in single and double configuration. The tire should also have load rating letter. Look at several major companies inflation tables and see if one matches.


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Old 07-22-2014, 06:32 PM   #3
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Here is a contact you can ask.

ROADLUX.COM
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Old 07-22-2014, 06:33 PM   #4
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Inflate and keep tires at max psi printed on sidewall of tire, until you can determine wheel position weights. You can get an inflation chart from tire dealer or internet search. Using the iRV2 search window at the top of the page will reveal lots of previous discussion on how/where to do 4 corner weighing. This is not hard and you are doing the right thing correcting your tire pressures.
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Old 07-22-2014, 06:33 PM   #5
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You might check this website for info.
RV Safety & Education Foundation
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Old 07-22-2014, 07:01 PM   #6
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I checked RoadLux.com and found there is not an inflation chart to be found. I would suggest returning to the tire dealer you got them from and request that they provide one for you.

As far as using another manufacturers tire inflation chart, IMO it assumes that all specs are the same between the two different brands of tires. Close maybe, but not exactly.

Here's a link to a brochure from NHTSA that explains all the information printed on the tire required by law. Sadly inflation charts aren't.

Tire Safety, Brochure (DOT HS 809 361 October 2001)

Best of luck.
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Old 07-22-2014, 07:58 PM   #7
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Quote:
Originally Posted by Bouchbri25 View Post
how do I know what to inflate my tires to if there's no chart? I bought Roadlux R216 225/70 19.5 last year and I checked the pressure today with a digital tire gauge at roughly 70-72.5 PSI (45 on passenger inside rear wheel and driver front at 82.5).
The max load is 95PSI but what should I inflate to if no chart?
Is this the first time you checked the pressures in one year? The pressures need to be checked at least once a month, or at least before each trip. Roadlux's web site shows the size tire to be a F/12 ply rated tire. Which to me seems to be incorrect load range for the motor home in the OP's profile with a picture on the coach.

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Old 07-22-2014, 10:41 PM   #8
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I just checked both Michelin and Goodyear tables for 225/70R19.5 tires both have the same inflation pressures. Interesting, that tire is available in both load range F and G. Inflation pressures and load are the same for both ranges except the "G" max pressure increases above the range for the "F" to give a higher max load.
Chart here: http://www.rvtirepressure.com/assets..._Inflation.pdf

OP- you would still need to know the actual weights on each wheel.

Note that tires which have been run at 20% below the recommended pressure are considered to have been run flat and are not reliable.
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Old 07-23-2014, 05:09 AM   #9
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Originally Posted by chboone View Post
Is this the first time you checked the pressures in one year? The pressures need to be checked at least once a month, or at least before each trip. Roadlux's web site shows the size tire to be a F/12 ply rated tire. Which to me seems to be incorrect load range for the motor home in the OP's profile with a picture on the coach.

Chuck
Good question- I only used it twice last year after the tires and I've been doing extensive work on it this year so this will be the first trip with it this year. It is an F rated tire but I just went on the recommendation of the tire dealer. Why could this not be a correct load range for my RV? I appreciate info
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Old 07-23-2014, 08:20 AM   #10
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To answer your question about where to get weighted.

Any truck stop with the CAT sign has scales, and cost usually less than $15. You can drive on the scale platforms and weigh each axle, and tell the person on the speaker pole that you want to re-weight. Drive around the lot and come back on the scale with one side of the coach off the scale to get only the front and back side tires. Then go in and the two receipts will show the one side, and totals. That will give you "almost correct" corner weights.

City transfer stations, grain elevators, gravel pits, moving and storage companies, and more places have scales.
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Old 07-23-2014, 10:45 AM   #11
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The correct tire load range is determined by the axle rating, not the actual weight. The tire max load should be sufficient to carry the max load of the axle it is installed upon. A load range F (12 ply rating) tire in the 225/70R19.5 size is good for about 3640 lbs/tire at 95 psi, so two of them would be adequate for a 7200 lb axle GAWR. Different brands and models may vary a bit, but are usually very close.

When used as duals on a rear axle, the rating is 3415/tire or 4x that for a rear dual axle.

You can use the inflation table from another manufacturer for an approximate psi but I would err on the high side to make sure it was enough. Until you get a weight, the 95 psi needed for the max tire load is the only safe pressure to use.
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Old 07-23-2014, 12:14 PM   #12
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Quote:
Originally Posted by Bouchbri25 View Post
Good question- I only used it twice last year after the tires and I've been doing extensive work on it this year so this will be the first trip with it this year. It is an F rated tire but I just went on the recommendation of the tire dealer. Why could this not be a correct load range for my RV? I appreciate info
I should have thought about it more and looked at the load chart before posting that. Generally I have seen coaches your size with G load range tires. The F load range should be well over your rear axle rating at the dual max PSI. As Hooligan and RVRoamer posted they should be fine running them at the max PSI. I looked at the Continental tires for load range F and they have the same load/psi rating as the Michelin does. Just remember to get your coach weighed loaded as you would normally use it. Four corner is best, minimum each axle. Looking at the picture in your profile the coach has a lot of overhang and would be easy to overload the rear axle.

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Old 07-23-2014, 03:29 PM   #13
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Welcome to RV lifestyle where you soon learn there is more to know than you ever thought of.

Some good references and links on tires can be found on THIS sticky.

You might also spend some time on my blog RVTireSafety.com as I have covered your questions a number of times.

To all posters.
If you spend some time looking at the details of tire Load Inflation charts you will find that well over 97% of all tires have the same ratings for Load Range and size. There are industry standards here in the US with similar standards in Europe and Asia. Since we are talking physics here the basic concept is that the volume of air (tire size) at a given pressure will support a certain load. The load capacity (carrying ability) is basically Volume at a given Pressure with the pressure carrying almost all the load not the tire.

The following applies to Motorhomes. Towables are different and should read THIS post.

RE knowing the minimum inflation needed for your tires. Once you know the actual load on each "corner" you use the tables to learn the MINIMUM cold tire inflation. It is suggested you add 10% or 10 psi to that minimum inflation to give you a cushion so you aren't chasing air pressure every day.
Check your inflation with a digital gauge the morning of every travel day and once a month when parked.


CAT scales have a policy of not wanting side to side weights as they do not like to unbalanced loading it puts on their scales. If you just get individual axle loads and assume a 45/55 side to side split and select the inflation based on the heavier loaded side you will be in good shape till you get the actual corner loads.

Please do not confuse "Load Range" with load capacity. Load Range replaced "Ply Rating" decades ago.

Dual positions do not carry 2 times the single load. There is a reduced load capacity for tires in dual application shown in the charts.

When posting questions on tires it may help if people provide info on their RV. Most RVs have a certification label showing the tire size and Load Range and inflation pressure suggested by the RV company.

DO NOT assume that other similar RVs have the same tire loading. Some people carry around a bowling ball collection while others just have a lot of shoes for the wife. This can mean 1000#s of load difference.
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Old 10-17-2014, 11:51 PM   #14
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Tireman9...Recently purchased Samson GL283A 275/70R-22.5 H rated 16 ply. Load index is 144/141, or 6175 single 5675 dual @ 120psi. Every chart I could find all listed a H rated tire at 146/144 or 6610/6175. It seems the load index for the Samsons are more of a G rated, or 14 ply, that have max @ 110psi. My RV is in the neighborhood of 26,000 pounds. These tires @ 120psi are rated at 35,000 pounds. Is there some kind of formula? I've looked everywhere I can think of on the web, but nothing.
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