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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #1
Hi,
Seapro brought a similar question up earlier, but decided to ask this separately so as not to confuse the two.

I'd like to lower the tire pressure on my PM RV conversion to the lowest safe level in order to improve ride -- particularly and rough and washboarded roads.

My PM is a 136 WB high roof -- on the front door it says:
Front axle max weight 4630 lbs and 65 psi infla pressure
Rear axle max weight 5291 lbs and 72 psi

My actual axle weights full up with full fuel, propane ...
Front axle 3713 lb
Rear axle 3022 lb

The tires are Vanco Fourseason 225 75R16C
121/120 R M+S
Load range E
Max single tire load 3195 lbs at 83 psi

One thing that seems wrong right off is that my rear axle load is lower than my front axle load, yet they want you to use a higher pressure in the rear tires (72 psi).

I found an article in an RV magazine showing how to use the manufacturers tire pressure vs load capacity chart to figure out how you can set your tire pressure based on your actual loads.
Looking for the chart, I found this pdf:
http://www.conti-online.com/www/dow..._info/download/technical_data_book_pdf_en.pdf

On page 24 it has the load capacity vs tire pressure for the PM Vanco...
These are converted from Kg in the chart to lbs here.

44 psi 3795 lb max load per axle (two tires)
47 psi 4037 lb
51 psi 4290 lb
54 psi 4532 lb
58 psi 4774 lb
62 psi 5005 lb
and so on up to..
83 psi 6380 lb

Note that the last 6380/2 = 3190 lb which is whats stamped on the tire as the max load.

So, it looks to me like I could use 44 psi in the rear tires and have an axle tire rating of 3795 lbs vs an actual axle weight of 3022 lb -- a 700+ lb margin of safety.
And, I could use 44 psi on the fronts with basically a small margin, or use 47 psi and have a 300+ lb margin.

I'm a little hesitant to do this as the pressures seem kind of low compared to the recommended 65 and 72 psi.
Anyone have any thoughts on this?

Also sure that the tire pres warning light would be on all the time, but I guess I could live with that.

Gary

Note: the rated axle load from the tire chart for two tires at 65 psi is 5247 lb vs the RAM allowed axle weight at 4630 lb, so they maintain a margin of about 600 lbs on their recommended pressures.
 

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Your TPMS light will definitely be on all the time. I would not lower the pressure because it will also lower the mpg. I have heard that the new stock tires, Nexan, ride a lot better than the Continentals.
 

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I have lowered mine to 64 front and back for the logic you give. No TPMS light yet. I did have two random TPS lights when the pressures were factory but several starts and 2 days ended the first and a half hour diving ended the second, both 5,000+ miles ago. I'd like to go to 60. Where does the TPMS light get triggered?
 

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The reason the door sticker lists a higher pressure for the rear is that it assumes that the van is fully loaded to max gross with the tongue weight of a trailer. At that point the load on the rear axle will be far greater than the front.

My DIY 159 inch 2500 camper has been weighted and the total is about 7000 pounds divided equally between the front and rear axles. I have the Nexen tires and I carry about 63 psi all around. The TPMS did not reset after a few days and many starts so I had the dealer reset it. When cold weather came suddenly this fall the TPMS light came on early one morning as a reminder for me to check and add air. That reminder was good as otherwise I might not have checked air.

Personally I would not feel comfortable going below about 60 psi with these tires on this van. I think it could affect handling (excessive sidewall flex) and reduce tread wear by not having the tread evenly flat on the road.

Note that as the van is both front engine and front wheel drive with all the heavy mechanicals including fuel up front the front axle will be heavier that the rear with the van empty or with just a light load.
 

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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #5
The reason the door sticker lists a higher pressure for the rear is that it assumes that the van is fully loaded to max gross with the tongue weight of a trailer. At that point the load on the rear axle will be far greater than the front.

My DIY 159 inch 2500 camper has been weighted and the total is about 7000 pounds divided equally between the front and rear axles. I have the Nexen tires and I carry about 63 psi all around. The TPMS did not reset after a few days and many starts so I had the dealer reset it. When cold weather came suddenly this fall the TPMS light came on early one morning as a reminder for me to check and add air. That reminder was good as otherwise I might not have checked air.

Personally I would not feel comfortable going below about 60 psi with these tires on this van. I think it could affect handling (excessive sidewall flex) and reduce tread wear by not having the tread evenly flat on the road.

Note that as the van is both front engine and front wheel drive with all the heavy mechanicals including fuel up front the front axle will be heavier that the rear with the van empty or with just a light load.
Hi Seapro,
Yes, mine is an RV conversion and when its fully loaded with people and all tanks full, the actual (weighed) front axle weight is 3713 lbs and back axle is 3022 lb. I don't tow anything and the loads while RVing will never exceed these.

I hear what you are saying, but on the other hand, the tire manufacturer publishes the chart (link in my post) that says what your tire should be inflated to for a given load, and for the actual loads on my tires they recommend 47 psi front and 44 psi back -- you would think that this should be an ideal inflation pressure for even tire wear, and the right amount of tire sidewall deflection? That is, it should be an ideal inflation pressure for that tire load?
But, as you say, its seems a bit uncomfortably low?

For whatever its worth, the method of using the tire manufacturers load vs inflation pressure chart is published in this months issue of one of the RV magazines in detail -- can't remember the name, but will take a look again next time I'm at Barnes.

I do agree that lowering the tire pressure would cost something in mpg, but I could experiment a bit and see how much as I keep records of mpg.

RD -- I did lower mine down to mid 60's and then when the cold weather came they dropped closer to 60 by themselves and the tpms light has been on all the time since they got down near 60.
I have felt the tires after long stretches at freeway speeds at 60 psi and they are barely warm.
Going to the dealer tomorrow about the brakes and will ask about the tpms.

Gary
 

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Gary,
I think you are spot on with your research. My experience suggests the high pressures are for much higher loads than we are going to see and lowering them is both safe and reasonable. I would try about 55 psi front and 50 rear if I could put up with the TPMS light etc. I just have no tolerance for such things. I mentioned earlier that Ford informed Explorer owners to lower our pressure to change the handling when they had rollover issues so those numbers on the door are not sacred. My F150 with air bags had much wider tires and would carry 3,000 lbs with 55 psi due to the contact patch being bigger. Expect the Vancos to squeal a bit cornering and to breakaway a bit earlier but with more warning. Tire life? Harder is always longer IMHO.
 

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I'd like to run the lower pressures, especially in the rear. I ran F/R at 67psi, worked great, but was getting the TPMS warning all the time. Got used to it, but tired of it this weekend. Bumped the rears up to the full load recommended pressure of 80psi. Presto... no more TPMS warning.

Not enough driving yet to comment on a change of ride quality. Hadn't thought of having the dealer reset it to a lower pressure.
 

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Last time I checked my tires, all were at 62 psi. I was checking because steering in parking lots was getting harder. I went back up to mid 60s on pressure.

I don't pump the rears higher because my loads don't require it.

I think you just have to mix in some common sense and find the pressures that work for you, and give even tire wear all around. We already know lower pressures meet the load, but in practical use, they won't likely wear right, or drive right.

I will switch to Nexen when these wear out
 

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i have NEXEN tires on my PM, i lake them a lot.
had my TPMS lights on, checked psi. front was at 57-60psi, rear was at 65-70 psi.
pumped front up to 65-68psi and rear up to 80-82psi and my TPMS light went off.

i would like to keep my rear tires at 65psi , to have softer ride, but my TPMS light probably will go on. don't like any service- warnings lights on my dashboard.

also for Winter tires decide to go with NEXEN tires. installed last week.
http://www.nexentireusa.com/tires/winter/winguard-winspike-suv
 

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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #10
i have NEXEN tires on my PM, i lake them a lot.
had my TPMS lights on, checked psi. front was at 57-60psi, rear was at 65-70 psi.
pumped front up to 65-68psi and rear up to 80-82psi and my TPMS light went off.

i would like to keep my rear tires at 65psi , to have softer ride, but my TPMS light probably will go on. don't like any service- warnings lights on my dashboard.

also for Winter tires decide to go with NEXEN tires. installed last week.
http://www.nexentireusa.com/tires/winter/winguard-winspike-suv

Hi,
I don't think you should have to inflate the backs (or fronts) to any more than the sticker on the driver door says (72 psi on mine) - and I think you could probably get away with a few psi less than that without triggering the tpms.

It would be nice to have real winter tires for our climate in that we have snow for about 5 months, but we also take trips to California and I think they would wear out in no time with that kind of use.


Gary
 

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Hi,
today just dropped rear tires pressure to 65psi with ignition on.
no TPMS light on.
all my tires now at 65psi and I have soft ride, no bumping.
 

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I run all of mine at 62 psi with no light on. I understand it can be recalibrate done but mine has never has been.
 

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I thought the whole TPMS deal was a relative thing - alerting you when one tire was reporting differently than the others, not an absolute thing wanting to see a certain pressure.
 

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That is what the service manager at my dealership told me. I then let them set the pressures and rest the TPMS to good effect. I've come to hate that system and the light and warning. Thankfully it is off right now. Would someone lower all their tires to about 55 and experiment? I'm not touching mine!
 

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When I bought my 2015 diesel 3500 EXT the dealer raised my tire pressure to 70psi(not sure what it was at before as it sat on dealer lot for 8-9 months before I purchased it) because the TPMS light was on when prepping it for me to take home. Anyhow TPMS light was still on when they handed me the keys (told me to drive it 10 miles and it should turn off).. 100 mile drive home and it never did turn off.. Finally after a few weeks (2000-3000 miles) I decided to raise the pressure to what my driver side door jam sticker says (80psi rear and 65psi front)... Get back in van and light is OFF! I now run 80psi rear and 70psi front (because I carry 2000-3000 pound loads)
So basically I think computer must have different TPMS settings based on whether it's a 1500-2500-3500..

KOV... What does your door sticker say pressure should be at? I know if I put 62 psi in my van light would be on again for sure!
 

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I've been told flatly 'no' to re-calibrating the computer to accept lower pressures.

After battling cold weather all winter triggering the idiot-light, come springtime I chose a bright sunny warmish (not hot) day and drove interstate speeds for 20 minutes to get tire temperature up then set the tire pressure to 1/2 PSI above the door sticker settings of 65/72. Note the written commandments all say NOT to set tire pressure when hot, but on this nearly empty van it sure makes a difference doing errands when the tires never have a chance to warm up, there is no/low scrub to parking lot turns and the pressure is still up enough highway mileage is not affected. I've not checked pressures cold to see what they drop to but it is/was a nice compromise until next winter!

Another thing noticed here is a vehicle parked in 1/2 a days worth of sunshine, the sunnyside tires will read 1 to 1-1/2 PSI high versus the shadyside tires... which then translates to being 1-1/2 PSI low come the next morning, just enough to trigger the idiot-light IF we've arbitrarily lowered pressures for a softer ride.
 

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SeaPro wrote: (on reducing F/R monitored pressures to 63 psi...)
Mine was successfully reset by the dealer.
If so then your dealer is an exception, two of two here act like it is the first time they've ever been asked, many others in this forum report the same: the liability across multiple drivers/owners on derating the factory tire pressures versus load capacity is/was not acceptable corporate policy to them.

What dealership in Virginia, I'll be back there sooner or later...
 

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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #20
Hi,
Seapro brought a similar question up earlier, but decided to ask this separately so as not to confuse the two.

I'd like to lower the tire pressure on my PM RV conversion to the lowest safe level in order to improve ride -- particularly and rough and washboarded roads.

My PM is a 136 WB high roof -- on the front door it says:
Front axle max weight 4630 lbs and 65 psi infla pressure
Rear axle max weight 5291 lbs and 72 psi

My actual axle weights full up with full fuel, propane ...
Front axle 3713 lb
Rear axle 3022 lb

The tires are Vanco Fourseason 225 75R16C
121/120 R M+S
Load range E
Max single tire load 3195 lbs at 83 psi

One thing that seems wrong right off is that my rear axle load is lower than my front axle load, yet they want you to use a higher pressure in the rear tires (72 psi).

I found an article in an RV magazine showing how to use the manufacturers tire pressure vs load capacity chart to figure out how you can set your tire pressure based on your actual loads.
Looking for the chart, I found this pdf:
http://www.conti-online.com/www/dow..._info/download/technical_data_book_pdf_en.pdf

On page 24 it has the load capacity vs tire pressure for the PM Vanco...
These are converted from Kg in the chart to lbs here.

44 psi 3795 lb max load per axle (two tires)
47 psi 4037 lb
51 psi 4290 lb
54 psi 4532 lb
58 psi 4774 lb
62 psi 5005 lb
and so on up to..
83 psi 6380 lb

Note that the last 6380/2 = 3190 lb which is whats stamped on the tire as the max load.

So, it looks to me like I could use 44 psi in the rear tires and have an axle tire rating of 3795 lbs vs an actual axle weight of 3022 lb -- a 700+ lb margin of safety.
And, I could use 44 psi on the fronts with basically a small margin, or use 47 psi and have a 300+ lb margin.

I'm a little hesitant to do this as the pressures seem kind of low compared to the recommended 65 and 72 psi.
Anyone have any thoughts on this?

Also sure that the tire pres warning light would be on all the time, but I guess I could live with that.

Gary

Note: the rated axle load from the tire chart for two tires at 65 psi is 5247 lb vs the RAM allowed axle weight at 4630 lb, so they maintain a margin of about 600 lbs on their recommended pressures.
So, I took this a bit further on the last trip.

First lowered all the tires to about 64 psi and drove it this way for a day.
Did not really notice much difference -- maybe a little less harshness in the ride.
TPMS light did not come on.

The 2nd day we camped at a beautiful place, but at the end of a pretty rough 20 mile gravel road.
On the way back out, I lowered the pressure in all tires to 56 psi.
This seemed to make a noticeable and welcome improvement in the harshness of the ride -- particularly on the rough gravel, but also on bumpier paved roads.
The TPMS light came on and stayed on.

Using the tire pressure vs load curve for the Vancos, I'm still using a tire pressure that is well above the actual load on the tires for my van, so I'm going to try going down to about 50 psi and evaluate that.

Actually averaged 20.5 mpg for the full trip (Bozeman, MT -> Yellowstone -> Grand Tetons -> Wind River Range, WY), so does not seem to be seriously effecting mpg.

Any thoughts/advice on this?

Gary
 
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