Tire pressure

[mikern]

on our 2016 ventana le 4037 i have not had a chance to weigh the coach 4 corners yet
dry 29700lbs gvwr 36400 lbs
very little cargo at this time full water and fuel
125 psi it rides rough
do u think it would be okay to run 100 for now
michelin X® MULTI Z - 275/70R22.5

thanks

 

[Webz]

Without knowing your actual weight, it is pretty much a guess. IMHO
You can get in the ballpark by using a CAT scale at a truck stop. At least you will know how much weight is on each axle. And for some that is sufficient.

 

[Tnedator]

I would go to a CAT scale and weigh (make sure you have your axles on different scales. Then, for each axle, multiple by .53. So, if you came out at 9300lbs on the front axle, 9300 x .53 = 4,929 and use that as the weight for both tires on that axle. Do the same with the other axle, then look up the PSI in the Michelin load chart.

The .53 is recommended when you don't have a four corner weight, as typically one side is heavier than the other, so it's about the best option you have short of a four corner weight.

 

[Rich W.]

My weights are as follows:
DF 5,750
PF 5,350
DR 10,050
PR 9600
For a total of 30,750

Using the chart from the publication below, and using the high side of each axle, I should be able to safely run 100psi in the rear, and 105psi in the front, I added 5psi to each front because I’d rather run a little firmer that softer for tire condition reasons. So my current pressures are 100psi rear, 110psi front.

You probably weigh more than 30,750 and as I said, I’m fudging on the high side for my pressures. But for guestimating your pressures in lieu of weighing I wouldn’t go below 105psi for the rears and 115psi for the fronts. Once you weigh the coach you’ll probably be able to lower it 5psi all the way around becuase you are probably not at 34,000lbs loaded. But…5psi less probably wont get you any perceivable improvement in ride and that 5psi may keep your tires cooler.

All this probably sounds like a definite maybe (because without weighing it is) but I would say that 125 is higher than necessary and high enough to contribute to a rougher ride.

In case you dont have the chart:

https://www.michelinb2b.com/wps/b2bcontent/PDF/RV_Tires_Brochure.pdf

 

[mikern]

thanks for the info

mike

 

[mikern]

I would go to a CAT scale and weigh (make sure you have your axles on different scales. Then, for each axle, multiple by .53. So, if you came out at 9300lbs on the front axle, 9300 x .53 = 4,929 and use that as the weight for both tires on that axle. Do the same with the other axle, then look up the PSI in the Michelin load chart.

The .53 is recommended when you don't have a four corner weight, as typically one side is heavier than the other, so it's about the best option you have short of a four corner weight.

i got to weigh the coach on axles only
as per michelin load chart
115 fronts and 95 rears psi
a very noticable difference in ride for sure
they had the fronts set at 131 max pressure for the mult z tire

thanks everyone

 

[Rich W.]

Since you don’t have individual weights on the rear, I’d run them at 100psi until you can do 4 corner weights. Note that I’m 450lbs heavier on my drivers side rear which puts me into the next higher tire pressure column, even though my pass side rear weight is low enough for 95psi. Also check the clearance between the duals. I seem to recall 1.5” minimum. Lower pressure will of course reduce the spacing.

When you get four corner weights, don’t interpolate - just go to the next higher pressure. So in my case, at 10,050 Im much closer to the 95psi column (9,950) but over by 100lbs and the next higher level, 10,370 is 100psi, so per the Michelin recommendation, thats what I run. Your coach is heavier than mine by at least 1700lbs, so I would think your TP would be at least as high as mine.

What were your axle weights?

 

[mikern]

Front 11464
Rear 19599

 

[Rich W.]

Front 11464
Rear 19599

So since you don’t have four corner weights, using the total axle weight x .53 (thank you Tnedator) you end up with 10,387 so I definitely run 100 in the rears until you have weights for both side. Even if you divide by two and multiply by 1.03, you’re still at 10,093 which puts you in the 100psi column. Also with four corner weights you’ll probably find you can run 110 in the fronts.

 

[Scotttkd2]

Mkern......My Kountry Star appears to be a lot heavier in the front (13600 on the Cat scale) and uses the same 275/70r22.5 size tires, I have to run them near max 130psi cold to cover that weight. I am concerned that is not the best idea to have engineered a design that relies on running a tire at the very top of its load range. Am looking at the possibility of fitting the 295/70r22.5 for the added margin, but no idea yet on clearance. Glad you got it sorted out!

 

[Neal]

Mkern......My Kountry Star appears to be a lot heavier in the front (13600 on the Cat scale) and uses the same 275/70r22.5 size tires, I have to run them near max 130psi cold to cover that weight. I am concerned that is not the best idea to have engineered a design that relies on running a tire at the very top of its load range. Am looking at the possibility of fitting the 295/70r22.5 for the added margin, but no idea yet on clearance. Glad you got it sorted out!

What is the weight limit on the front axle per the tag just behind the driver's seat, left wall? Take a picture and post it if you want.

 

[Scotttkd2]

I had to dig, but found a pic on my phone, 13500 front, 24000 rear with 130 front and 120 psi rear recommended on both FL label and Newmar label. Actual cat scale said 13660 front and 21800 rear. I have since offloaded a lot of weight we found we didn't need but at that time we were just starting full time so didn't know what we were or were not going to miss. I need to get it back on a scale once it's on the road again and see what our current load out looks like. Still think Newmar should have spec'ed a heavier tire for the front based on the tire chart recommendations though, I have my fingers crossed I have the clearance for the additional 2 inches in diameter, I would feel a lot better being able to run the fronts at less than max PSI rating given what has happened recently.

 

[Neal]

I think being cognizant of axle limits and getting corner weights is critical. We should not need to be running at sidewall max pressures. I'm running well above my chart mins which I think are 90 front and 75 rears. I run 105 front and 90 rears.

 

[Rich W.]

I think being cognizant of axle limits and getting corner weights is critical. We should not need to be running at sidewall max pressures. I'm running well above my chart mins which I think are 90 front and 75 rears. I run 105 front and 90 rears.

having a tag helps….a lot!

 

[Rich W.]

I had to dig, but found a pic on my phone, 13500 front, 24000 rear with 130 front and 120 psi rear recommended on both FL label and Newmar label. Actual cat scale said 13660 front and 21800 rear. I have since offloaded a lot of weight we found we didn't need but at that time we were just starting full time so didn't know what we were or were not going to miss. I need to get it back on a scale once it's on the road again and see what our current load out looks like. Still think Newmar should have spec'ed a heavier tire for the front based on the tire chart recommendations though, I have my fingers crossed I have the clearance for the additional 2 inches in diameter, I would feel a lot better being able to run the fronts at less than max PSI rating given what has happened recently.

I’d also be concerned about an under rated front axle. Wouldn’t be the first time Newmar did that. Do you have the build sheet with factory four corner weights? That would be telling.

This is page 4 (of six) of my build sheet provided by Newmar after I bought the coach used. It shows 10,050lbs on a 12,000lb axle providing a margin and some forward CCC. I don’t see how you can shed much weight off the front unless you have some heavy cargo forward.

 

[Rustymayes]

What tire temps do you guys see at your pressures? I run 95 in the rear and 115 cold in the front and I occasionally see 130 + on the inside drive tires. Of course the TPMS is constantly warning of high temps and pressures. I have yet to do a four corner weigh but I know we are going to be light as we really only weekend it the coach and have very little gear on board. I bet if I weighed every thing but water and fuel I would be under 500lbs of personal gear. I need to see if I can find my build sheet and see where my start point was. I can WAG a figure to add for gear pretty easily.

 

[BGMAC]

I run at max psi. Several reasons.
1. Tires run cooler; less friction.
2. Tires last longer; less friction.
3. Less chance of hydroplaning; tread is open up more and less flatness of the tire.
4. Less stress on the side walls when weighted down.
5. Less chance of sidewall blowout if tire hits bad pothole or something.
6. Better fuel economy. Not much of a reason on an RV, but it helps

Yes it does ride a little harder, but I drive slower to compensate.