Community Forums

txhood · 05-31-2014, 05:50 PM

I want to make sure I am reading the Michelin Tire Chart correctly. My tire size is 225-75-16. The front weight of my rig is 3540 lbs. and the rear is
6800 lbs. If I am reading the chart correctly, tire pressures should be 45 front and 50 rear. This is much less than the door tag which has 75 front and 65 rear. Thanks for the help.

BFlinn181 · 05-31-2014, 06:11 PM

The door tag usually is the pressure needed to support a fully loaded RV. It would be fine to increase pressure by 5 lbs over Michelin numbers. After driving for an hour, feel tires for excessive heat. If they are hot, then increase pressure another 5 lbs.

OLYLEN · 05-31-2014, 06:50 PM

The tag is also for the tires that came with the RV new. If new tires differ from the original new tire data is needed from the new tire company. That all said keep at least 5#'s over minimum on the tires from the new tire data sheet. The new tires might be a higher load rating under a lower pressure.

LEN

Ray,IN · 05-31-2014, 10:58 PM

Keep in mind the Rubber Manufactuers Association states on their website; "over 90% of all tire failures are the result of under-inflation or overloading".

Gordon Dewald · 05-31-2014, 11:16 PM

Under inflation and overloading are the same thing as long as you are between the tires minimum and maximum pressure. Both cause the tire to heat excessively which causes delamination and failure. Generally accompanied by costly damage to the coach.

The manufacturer has designed the tires for use and engineered the performance based on the maximum weight and appropriate pressure. This gives an amount of sidewall flex, rolling resistance, tire heat, traction surface and tire life. Engineers then calculate tire pressures for various loads the tire may be subjected to. This gives the tire the same characteristics for flex, rolling resistance, tire heat, etc, etc as at max pressure.

Engineers being a cautious lot have built in numerous contingencies to the chart, so there should be no real reason to add another bump to the tire pressure.

Tires require some heat in order to lubricate properly and provide maximum traction.

Tires with too much pressure ride rough, wear unevenly, have less skid resistance in adverse conditions and may not handle properly.

The best thing to do is follow the manufacturers instructions.

txhood · 06-02-2014, 07:35 AM

I really appreciate the replies so far but someone please look at the chart and double check my figures. I am concerned because the pressures I am seeing in the chart are so much lower than the door sticker.

Michelin North America RV Load & Inflation Tables

**CLIFFTALL** · 06-02-2014, 07:42 AM

Are yours the R LRE XPS RIB ?
If so , your figures are correct. Add 5 lbs as previously recommended.

R2Home · 06-02-2014, 09:03 AM

It is my understanding that 'LT' type tires should never be under 50lbs of air pressure. While the data might be OK for some situations, I would be following the tag on the door, as it is more for your vehicle. While not a motor home, the tires that I have on my 1994 Dodge with a 5.9 Cummins and snow plow mounted on it, I keep my tire pressure at 80 on the front and 75 on the rear.
For your MH, I would be kicking up the pressure quite a bit to what the door tag is showing.

BFlinn181 · 06-02-2014, 10:10 AM

Quote:

Originally Posted by R2Home

It is my understanding that 'LT' type tires should never be under 50lbs of air pressure. While the data might be OK for some situations, I would be following the tag on the door, as it is more for your vehicle. While not a motor home, the tires that I have on my 1994 Dodge with a 5.9 Cummins and snow plow mounted on it, I keep my tire pressure at 80 on the front and 75 on the rear.
For your MH, I would be kicking up the pressure quite a bit to what the door tag is showing.

Tire pressure is to be adjusted as to load. That's why each tire manufacture prints tables showing inflation vs. weight. The required label in an RV only lists one pressure for each axle position. The only way to determine the proper pressure is to weigh each wheel and set cold pressures accordingly. To inflate to the label recommendation, unless you carry maximum weight, you are almost certainly overinflated and subject to rough ride, reduced traction, and other safety concerns. Are your tires wearing more in the center of the tread than the edges? If so, you're overinflated.

Gordon Dewald · 06-02-2014, 10:15 AM

The manufacturer lists tire pressure based on the GAWR (front and rear) the vehicle is rated for. If you are loaded to the max then that is the correct pressure you should have. It should coincide with the tire manufacturers charts as well. There may be slight differences based on different tire manufacturers.

If you are under the GAWR then use the chart for the correct tire inflation pressure. Like BFlinn noted. Overinflation has detrimental effects on your tires and handling same as underinflation.

Ray,IN · 06-02-2014, 10:37 AM

The tire load/inflation charts do not reflect the "correct pressure" they only state the absolute minimum pressure for the corresponding load.

Gordon Dewald · 06-02-2014, 10:45 PM

Quote:

Originally Posted by Ray,IN

The tire load/inflation charts do not reflect the "correct pressure" they only state the absolute minimum pressure for the corresponding load.

Did some searching for inflation charts and did not find the words "correct" or "absolute minimum" but did find the following excerpt or similar wording in several places.

From the Toyo guideline:
"Find the corresponding load for the OE tire size(s) at the recommended cold inflation pressure."

Also same type of working for replacement tires. Lots of words about different tires sizes with different load range requiring different pressures to carry same load.

Sorry if I caused any confusion using the word correct.

Ray,IN · 06-03-2014, 08:43 PM

Quote:

Originally Posted by Gordon Dewald

Did some searching for inflation charts and did not find the words "correct" or "absolute minimum" but did find the following excerpt or similar wording in several places.

From the Toyo guideline:
"Find the corresponding load for the OE tire size(s) at the recommended cold inflation pressure."

Also same type of working for replacement tires. Lots of words about different tires sizes with different load range requiring different pressures to carry same load.

Sorry if I caused any confusion using the word correct.

We're good Gordon. We both used words that did not fit exactly, but they meant the same thing.

Gordon Dewald · 06-04-2014, 08:01 AM

Quote:

Originally Posted by Ray,IN

We're good Gordon. We both used words that did not fit exactly, but they meant the same thing.

Hey Ray;
I am with you. Written words are sometime difficult to interpret. I much prefer speaking directly to a person. Then when you see the confusion on their face you can explain further or in a different manner.

I am really enjoying the discussions on tires and tire pressure. I have learned a lot from the threads, questioned some of the logic used and overall come to a better understanding of how I will deal with the tires on our coach. I have always taken the high line when it comes to safety, first the DW and family ride with me and (2) I do not want my actions to be detrimental to those around me.

I am going to "try" to be more "correct" with the words I use in future posts. Big words but I will try! LOL