Help with tires pressure question:

Fakrwee · 07-21-2007, 11:52 AM

I just downloaded the Michelin inflation chart for RV usage and was surprised at the recommended tire pressure for my MH. It seems to me a little low.
I weighed my loaded MH on all 4 corners and the results were:

Driver front-3540 lbs.
Passenger front-3580 lbs.
Total front- 7120 lbs. (GAWR 7,500 lbs.)

Driver rear-6540 lbs.
Passenger rear-6900 lbs.
Total rear 13,440 lbs. (GAWR 14,500 lbs.)

Michelin inflation chart shows:
Front Single 3875 lbs. @ 70 psi. Or 7,750 lbs. total (Multiplied lbs. X 2)
Rear Dual 7050 lbs. @ 70 psi. Or 14,100 lbs. total (Multiplied lbs. X 2)
GVWR @ 70 psi. 21,850 lbs. (MH GVWR 22,000 lbs.)

I am currently running 85 psi. Front and 90 psi. Rear. I have noticed that on rough roads it does feel a bit choppy. I was wondering if I an interpreting the chart right.

I'm going to Alaska and some of the roads have permafrost road heaves, even though I'll be on the alert and driving as slow as possible there's always the chance of hitting one off guard. I'm afraid of sidewall damage on one of the heaves. I'd like to lower them to 70lbs. because of a smother ride but am also apprehensive. Maybe I'll just split the difference.

Any thoughts or advice would be greatly appreciated.
Thanks
Tom

Fakrwee · 07-21-2007, 11:52 AM

I just downloaded the Michelin inflation chart for RV usage and was surprised at the recommended tire pressure for my MH. It seems to me a little low.
I weighed my loaded MH on all 4 corners and the results were:

Driver front-3540 lbs.
Passenger front-3580 lbs.
Total front- 7120 lbs. (GAWR 7,500 lbs.)

Driver rear-6540 lbs.
Passenger rear-6900 lbs.
Total rear 13,440 lbs. (GAWR 14,500 lbs.)

Michelin inflation chart shows:
Front Single 3875 lbs. @ 70 psi. Or 7,750 lbs. total (Multiplied lbs. X 2)
Rear Dual 7050 lbs. @ 70 psi. Or 14,100 lbs. total (Multiplied lbs. X 2)
GVWR @ 70 psi. 21,850 lbs. (MH GVWR 22,000 lbs.)

I am currently running 85 psi. Front and 90 psi. Rear. I have noticed that on rough roads it does feel a bit choppy. I was wondering if I an interpreting the chart right.

I'm going to Alaska and some of the roads have permafrost road heaves, even though I'll be on the alert and driving as slow as possible there's always the chance of hitting one off guard. I'm afraid of sidewall damage on one of the heaves. I'd like to lower them to 70lbs. because of a smother ride but am also apprehensive. Maybe I'll just split the difference.

Any thoughts or advice would be greatly appreciated.
Thanks
Tom

skigramp · 07-21-2007, 12:21 PM

Tom ...

I think you are interpreting the chart correctly ...

I lowered the pressure in my tires after weighing and downloading the chart ... I have certainly gotten a noticeably better ride ... and I think the handling is better too ...

I did this about 40,000 miles ago ... I had it aligned at the same time

BobD · 07-21-2007, 06:20 PM

I also had my coach weighed and the Michelin chart said to run 80 pounds and I run 85 pounds and it seems to be a really nice ride.

ichn2go · 07-22-2007, 12:20 AM

Tom, the general consensus is use the chart #'s and add 5 lbs for fudging and safety. A lower pressure will give a better ride and handling as stated.

You will get some grief from some folks about adding the extra 5 lbs. They will tell you the chart means what is says and you are doing your tires a disservice by adding 5. I like to have that cushion for whatever reason and know that I have a little fudging I can do on the weights.

Good Miles

Fakrwee · 07-22-2007, 12:04 PM

Thanks guys...I forgot to mention tire size,

Michelin LRG 255/80R22.5

Went to the MH to check and measure tire pressure, I was wrong on tire pressure stated above, I've been running 85 psi front and 90 psi rear. Got those numbers from the Winnebago tire pressure posted on the door.

Does anyone know why there is such a big difference between what Winnebago recommends and the Michelin chart? 15 and 20 pound difference is substantial. Someone is either very, very wrong or they are both wrong. I don't trust big Corporations anymore.

Thanks
Tom

Pusherman · 07-22-2007, 02:05 PM

Winnebago does not know how you will load your coach. Therefore they quote tire pressures assuming the coach is loaded at maximum Gross Vehicle Weight Rating - or max tire inflation psi for the tire max weight rating.

The correct way to air your tires is as everyone (including yourself) has stated -- weigh the coach and go by the tire vendor's recommendation on air pressure.

Fakrwee · 07-22-2007, 03:18 PM

Thanks for the insight Don, looking at it that way the tire pressure listed for all MH of a given model is based on the biggest unit in the lineup. The 85 psi front and 90 psi rear on my door jam is the correct psi for the 38T model.

Now I feel better.

They print the max psi no matter the rig size.

David and Fran · 07-22-2007, 03:27 PM

I am totally confused and worried about this whole issue over weights and inflation pressures. I do understand all to well that it is important to carry the correct pressure in the tires. We have an 07 Vectra. We are relatively new to MHs, although we towed a TT before selling it and moving into a MH. I have looked at the gold tag that is in our Owner's Bag. First of all it says, "Incomplete Vehicle Manufactured by Freightliner..." What does that mean? Then in the table it talks about the suitable pressure for the GVWR. Question here is, are they assuming packed to the gills with everything we can put in it as well as full fuel tank, full fresh water and assumed empty or near empty black and grey water? And does this mean the MH is "completed" now?

skigramp · 07-22-2007, 05:49 PM

David and Fran ...

If you were to visit Forest City, IA you would find a big lot full of chassises (frame, engine, axles, wheels,tires, steering wheel, fuel tank, etc) that is the "incomplete" vehicle manufactured by Freightliner ... it was probably manufactured 4 to 8 months before Winnebago installed the fresh water and holding tanks, the floor, walls, roof, appliances, etc) ... that is the "complete" vehicle.

Fakrwee · 07-22-2007, 08:40 PM

Hi David and Fran, sorry to confuse the issue. Just go with the recommended psi either on driver's door or in your manual. The psi recommended assumes your rig is at max GAWR (Gross Axle Weight Restriction). The important thing is to weigh your rig, if possible all 4 corners, and make sure you're within specs.

I too went from TT to MH and it's a completely different animal. Luckily you've found one of the best sites to learn and share about your rig.

Once you weigh your rig post the results and you'll get a lot of help figuring things out. Other than that, relax and have fun. That's one beautiful rig.

Tom

David and Fran · 07-23-2007, 02:45 AM

SkiGramp and Tom, Thank you for your responses. I am going to put about 1/3 of a tank of fresh water (because we will be dry camping for the first 2 days) and refill the fuel tank. Then there is one place in town that weighs (other than the grainaries) and we will go directly there and weigh. Hopefully we will be able to do an easy 4 corners weight (I had already ordered the new Michelin book for RV tires). Then I will for sure come back and post the results.

Yes it is a beautiful rig and we are looking forward to many years of fun motorhoming.

Thanks again!

Pusherman · 07-23-2007, 05:32 AM

David and Fran -- one suggestion before weighing -- fill your water tank full, have your coach loaded as you would travel, including the total number of people you typically travel with (I assume this is 2).

Fill your fuel tank (as you have stated). Your grey/black tanks can be empty, as 1) this is how I typically travel, and 2) as your fresh water tank empties, it will compensate for the weight of the filling black/grey.

I normally travel with full fuel/fresh water, and empty grey/black tanks, so this is how I have the coach weighed.

Paul T · 07-23-2007, 05:43 AM

My four corner weight with full petrol, propane, and water came in well within limits but fairly lopsided in the rear with the right side, (where most of my fresh water tank weight is), quite a bit heavier than the left. I have rationalized the differential as being OK once a good portion of the fresh water has found its way into the black/grey tanks however, I haven't re-weighed under those circumstances. Does anyone think this logic might be close to logical?

Fakrwee · 07-23-2007, 01:28 PM

Hi Paul, I have a +40 lb. difference on passenger front (No jokes please!) and a +360 lb. difference on the passenger rear. I'm pretty sure it has to be the basement AC which sits on the rear passenger side of the coach. I also have the kitchen on that side. I'm not too worried about a 400 lb. difference compared to the GVWR (Gross Vehicle Weight Restriction) of 22,000 lbs.

Tom

Tom N · 07-29-2007, 07:17 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ichn2go:
Tom, the general consensus is use the chart #'s and add 5 lbs for fudging and safety.
</div></BLOCKQUOTE>

I have never seen a tire manufacturers pressure chart state add 5#s for "fudging and safety".

Inflating over the manufactures load/pressure charts can be unsafe. Over inflating can lead to tire wear, hydroplaning and the tire can become more susceptible to impact damage.

See the online Michelin RV tire guide for confirmation and more negative information on adding more than the chart's recommend pressure.

-Tom

ichn2go · 07-30-2007, 01:28 AM

Tom, I think we have been around with this before. I have pored over the tire charts both for Michelin and Goodyear many times for three coaches and one new set of tires.

Hypothetical,,,3450 lbs calls for 85lbs. You weight the coach and its at 3350 you have a 100lbs to spare. THEN,,you throw a few more things on the coach,,maybe add a couple of people and your weight goes up to 3550. Now you are over for 85psi. You have two choices, go have it reweighed and use the EXACT psi or you add five lbs for fudge and safety..

I know tire charts do not say anything about adding 5lbs. There are many things that people do that deviates from the instructions some what But many of the old timers on the net do and these are very knowledgeable folks.(I am not trying to say you are not knowledgeble,cause I respect many of your opinions.)
I druther know that I can carry a little more weight than be under inflated. I think under inflation is the worse of the two evils.

Everyone has to operate his own coach in the manner that he feels is the safest. I don't think there is a right or wrong, but I did mention consensus and I think 5 extra lbs is the best for me...You run yours on the line and you won't get any grief from me. Happy days, Be Safe and

Fakrwee · 07-30-2007, 05:50 PM

Thanks to you both, (Ichn2go & Tom N), I read and respect both your opinions. One of the things I enjoy is reading both sides of the story to reach a conclusion. You are both right depending how you read and interpret the info. In my case I can go 5 lbs. over and still be within my max psi. If I were at max weight and max psi I would try and not go over limit on GVWR if possible. If I had no choice the call to add 5 for just in case would depend on many conditions such as weather, type of road, speed, and how I feel that day. There are always 3 sides to any story, yours, mine, and the correct one. You guy's are great and thanks for the sincere info.

SacsTC · 07-30-2007, 06:53 PM

The thing to remember about those charts is that the given pressures are the minimum pressures required to cary the given weight.

ichn2go · 07-31-2007, 02:46 AM

Fakrwee, thanks for the compliments. We all try hard to help. Good Miles