Community Forums

bobthebob · 10-27-2007, 02:31 PM

Hello Folks....

Here is a question for you folks.....

Which one i can trust.......Yesterday i have had my Trek Weighted.

From the number i got now if i go to the Michelin table chart the front tire should be set at 75lbs and the rear one at 70lbs but in the wall near the driver seat i can see in the lable there that the front tire are supposed to be set at 95lbs and the rear at 80.....which one i can trust.....20lbs difference for the front tire is, i think,a huge difference.isn't it.....

Talking about the lable.....Does it mean the maximum the tires should be inflated when the Trek is loaded or is it a minimum inflation i have to respect all the time.
Thanks

Bobthebob
2006 28RB
W-18 chassis
Outback Lodge

bobthebob · 10-27-2007, 02:31 PM

Hello Folks....

Here is a question for you folks.....

Which one i can trust.......Yesterday i have had my Trek Weighted.

From the number i got now if i go to the Michelin table chart the front tire should be set at 75lbs and the rear one at 70lbs but in the wall near the driver seat i can see in the lable there that the front tire are supposed to be set at 95lbs and the rear at 80.....which one i can trust.....20lbs difference for the front tire is, i think,a huge difference.isn't it.....

Talking about the lable.....Does it mean the maximum the tires should be inflated when the Trek is loaded or is it a minimum inflation i have to respect all the time.
Thanks

Bobthebob
2006 28RB
W-18 chassis
Outback Lodge

RV Wizard · 10-27-2007, 04:36 PM

The pressures on the data tag are for the GVWR with the size and brand of tires that were OEM. So if you are not at the GVWR weight or it now has different tires this may change. As long as you do not exceed the pressure rating on the wheels or tires, do not exceed the GVWR and keep the pressure on each axle at the tires manufacturer's pressure chart according to the tires carring weight you will be fine.

Norm Payne · 10-27-2007, 05:00 PM

Michelin recommends adding about 5 pounds more than the chart shows for safety. So if the chart shows 75 and 70 pounds you want to run with 80 and 75 pounds.

Pusherman · 10-27-2007, 05:26 PM

Always go with actual weights. Then correlate with your tire vendor's inflation table. This is the safest way to go. Adding 5psi is a good safety margin.

The labels in your coach are most likely based on maximum weight ratings (GVWR). That's why most likely the label states to inflate to a higher pressure, assuming your actual weights are below max.

Tom N · 10-28-2007, 03:07 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Norm Payne:
Michelin recommends adding about 5 pounds more than the chart shows for safety. So if the chart shows 75 and 70 pounds you want to run with 80 and 75 pounds. </div></BLOCKQUOTE>

Where does Michelin recommend this?? In the RV Tire Guide?? Please cite your Michelin source.

This is what the Michelin RV Tire Guide says about adding more than their pressure tables. (I realize there are many RVer's that think more pressure than the Michelin load tables recommends is safer.)

"Overinflation, on the other hand, will reduce the tire's contact area with the road, which
reduces traction, braking ability, and handling. A tire that's overinflated for the weight
it's carrying is more prone to a harsh ride, uneven tire wear, and impact damage."

[Source: Michelin RV Tire Guide ]

-Tom

Route 66 · 10-28-2007, 03:38 AM

I've always "heard" that you should add 5# of air pressure for "safety".

But, you are correct in that Michelin does not state that in their RV tire info.

Perhaps it's just an old wives tale or perhaps years ago, it was recommended, but no more.

If your tires are at the correct pressure when starting a trip, they will soon heat up and air pressures will rise anyway.

Unless documentation shows up stating otherwise, I'm going to chalk this one up to "urban legend".

So, IMHO, go with the recommended air pressures and enjoy a better ride, and less tire wear.

Norm Payne · 10-28-2007, 11:18 AM

Tom, your are right, Michelin has dropped adding 5 pounds for safety in their latest RV Tire Guide. It was in earlier versions of their guide but gone now.

I have attended three Michelin seminars and in all three they said to add 5 pounds for safety. When I bought new tires for my 2000 Dutch Star the pressures and weights on the sidewalls did not match Michelin's chart so I called them. An engineer sent me the new pressure and loading chart for my tires that were not in their guide yet and he told me to add 5 pounds for safety.

The last RVSEF seminar I attended gave some interesting information along with a handout. They said a motorhome never weighs the same and can vary up to 200 pounds per wheel. They said if they weigh a motorhome and drive it off the scales and drive it back on the weights are always different and up to 200 pounds per wheel so they recommend 5 additional pounds for safety.

Another thing to think about is temperature. If it is 80 degrees when you set tire pressures according to the chart and when you hit the road in the morning it is 50 degrees. The tire pressure will drop about 3 pounds so you are running under inflated.

Many people seem to add more stuff (weight) to their motorhome and if you are going by the weighing you had done a year ago you may be under inflated.

For all these reasons I always add 5 pounds for safety. My motorhome has been weighed by wheel position four times and the last time it showed I need 100 pounds in the front and 80 in the rear. I run 105 and 85 and I don't think I am over inflated to a point that effects handling, stopping and excessive tire wear.

But you are correct that the Michelin Guide no longer says to add 5 psi for safety. I just feel more comfortable adding 5 pounds.

Oemtech · 10-28-2007, 11:51 AM

I bought a set of scales off Ebay... I weigh my rig on the 4 corners, then take the heaviest corner on the front/rear,add 500 lbs to it and check the charts for the correct pressure.

JavaJelly · 10-29-2007, 12:09 AM

I got frustrated trying to get this question answered. Newmar, Spartan and Michelin all had different answers, not to mentions fellow RVers w/actual road experience.

I decided to trust Spartan. Had them weigh the coach w/me at the driver's seat and told them the weight of my family. They weighed the corners and wrote the recommended PSI on the readout for me. In my case 105 front, 80 rear.

Regarding tire pressure change. I just installed pressure pro. I am amazed at how much the psi changes both from ambient temp changes and then once you start rolling.

For example, by mid-morning the tires on the sun side will be 3 psi different than shade side. Also, tires will increase in pressure by 10 psi while driving.

Given how temperate the weather is in the midwest right now, I could spend all day adjusting psi, i.e. more air in the a.m. and less in the afternoon.

Oemtech · 10-29-2007, 04:00 AM

Not only does the pressure change on the "sunny side" the temp may change as much as 20 degrees. I use a IR temp probe to check the tires right after I hit a rest stop.

Route 66 · 10-29-2007, 04:24 AM

The inside duals also run hotter than the outside duals.

SargeW · 10-29-2007, 04:40 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The inside duals also run hotter than the outside duals.
</div></BLOCKQUOTE>

Is that because the inside duals do not get as much fresh air exposure? Do you have any idea how much hotter an inside may run as compared to an outside tire?

cwg · 10-31-2007, 08:56 AM

According to my Pressure Pro monitor, the inside tire generally runs 2-3 lbs higher pressure. On a similar note, even the tires on the sunny side of the road may run a little bit higher pressure. Of course one does not set the air pressure guessing what the inside dual tire may be; I just set them in accordance to the pressures recommended after weighing the coach.