Tire pressure question - without scales

Topic: Tire pressure question - without scales (Read 2114 times) previous topic - next topic

Tire pressure question - without scales

March 20, 2019, 11:40:03 am

Looks like we may be the new owners of a 99 U270, its 36' without a slide so I would assume the left right balance must be pretty even. If the deal goes ahead we will not be able to weigh the unit before driving 1200 miles home.
THE QUESTION IS: what is the rule of thumb for this coach when inflating the tires, the LBS for the front and the rear.
I have been all over the forum looking for a simple answer.

Re: Tire pressure question - without scales

Reply #1 – March 20, 2019, 11:42:35 am

David,

The simple and safe answer before weighing (axle weights can be done at many truck stops) is to go by the GVWR plaque outboard of the driver's seat.

It gives proper PSI if each axle is loaded to its GAWR (Gross Axle Weight Rating).

Re: Tire pressure question - without scales

Reply #2 – March 20, 2019, 11:46:49 am

Quote from: Irish – March 20, 2019, 11:40:03 am

Looks like we may be the new owners of a 99 U270, its 36' without a slide so I would assume the left right balance must be pretty even. If the deal goes ahead we will not be able to weigh the unit before driving 1200 miles home.
THE QUESTION IS: what is the rule of thumb for this coach when inflating the tires, the LBS for the front and the rear.
I have been all over the forum looking for a simple answer.

There isn't a single simple answer. If you can weigh each axle then using the load/inllflation table for the exact tires you have set the cold inflation pressure to the minimum for your measured load plus 5 PSI as a safety margin.

One conservative approach would be to set the cold tire pressure to the minimum pressure for the maximum load, which is the pressure shown on the sidewall. This will result in minimum sidewall flex, but will also probably result in a harsher ride than is needed.

Re: Tire pressure question - without scales

Reply #3 – March 20, 2019, 11:47:05 am

This is great news! Also, you will find that the coach is pretty well balanced so you don't really need to worry much about how you load it before you get actual weights. Need to see some photos of that baby when you get goin'.
jor

Re: Tire pressure question - without scales

Reply #4 – March 20, 2019, 11:50:40 am

Quote from: Irish – March 20, 2019, 11:40:03 am

Looks like we may be the new owners of a 99 U270, its 36' without a slide so I would assume the left right balance must be pretty even. If the deal goes ahead we will not be able to weigh the unit before driving 1200 miles home.
THE QUESTION IS: what is the rule of thumb for this coach when inflating the tires, the LBS for the front and the rear.
I have been all over the forum looking for a simple answer.

If your generator is on the driver's side, the propane and diesel fuel tanks are on the passenger's side and don't go all the way across the vehicle. So, as you use fuel and propane, the left and right weights change. Multiply 150 gallons of diesel by a rounded figure of 7 lbs per gallon and you can see that there is quite a bit off difference possible on not only the front tires but also a smaller difference in the back.

So, what difference does this make in tire pressures? None to me.

Pierce

Re: Tire pressure question - without scales

Reply #5 – March 20, 2019, 11:56:39 am

Quote from: wolfe10 – March 20, 2019, 11:42:35 am

David,

The simple and safe answer before weighing (axle weights can be done at many truck stops) is to go by the GVWR plaque outboard of the driver's seat.

It gives proper PSI if each axle is loaded to its GAWR (Gross Axle Weight Rating).

This answer is accurate if the coach still has the same brand, size and load-rating tires as it came with originally. If not, then it might not be accurate.

Re: Tire pressure question - without scales

Reply #6 – March 20, 2019, 11:58:33 am

Brett's answer is right......to a point. The GAWR is just that, a rating. Who knows how much 'stuff' is on board? Who knows if things have been changed in the coach? (battery type and placement comes to mind, as well as different tires)). It's worth the money to weigh all four corners, individually. Then you can either talk with the tire guy or go on-line to find the load rating and PSI for the particular tire. Case in point; when we bought this coach, she rode real hard, had it weighed, checked with Michelin and found the tires were overinflated by 20 psi! Went to 85 front, 80 stern and got my smooth ride back!

Re: Tire pressure question - without scales

Reply #7 – March 20, 2019, 12:20:08 pm

I would use Brett's answer 9as usual) until you can get a four corner weight.

On the way home, you can spend a few bucks at a truckstop with a "CAT" brand scale and get a total weight and a per axle weight if you want something that is more accurate.

Coaches are usually weighed as follows:

Fuel - Fuel
Propane - Full
Fresh Water - Full
Black Tank - Empty
Grey Tank - Empty

Normal occupants on board.

Have a great time - where are you taking delivery?

Re: Tire pressure question - without scales

Reply #8 – March 20, 2019, 12:22:36 pm

Quote from: Irish – March 20, 2019, 11:40:03 am

we will not be able to weigh the unit before driving 1200 miles home.

You should be able to weigh it enroute. Most truckstops have scales, or a weigh station that's closed may leave the scale on. Run the maximum amount of air according to the sidewall info until you get to a scale, assuming that the tires are the correct ones for your rig and not outdated.

Re: Tire pressure question - without scales

Reply #9 – March 20, 2019, 12:38:09 pm

What Tim said, X-2. Except I added this to ours (as per Brett): 1/2 tank of grey water & half of black. It all counts.

Re: Tire pressure question - without scales

Reply #10 – March 20, 2019, 02:25:52 pm

Quote from: Travelin' Man – March 20, 2019, 12:22:36 pm

You should be able to weigh it enroute. Most truckstops have scales, or a weigh station that's closed may leave the scale on. Run the maximum amount of air according to the sidewall info until you get to a scale, assuming that the tires are the correct ones for your rig and not outdated.

I know, in Washington & Oregon, they leave the scales on. By turning the coach around, it can be weighed on each of all fours.

Re: Tire pressure question - without scales

Reply #11 – March 20, 2019, 03:30:10 pm

Glad you found one David.

Re: Tire pressure question - without scales

Reply #12 – March 20, 2019, 03:38:54 pm

I imagine the 99 weight is very similar to my 97. If so, you will be pleased by the cargo carrying capacity. This 97 weighs 26.5K fully loaded as Tim indicated above. The GVWR is 30K, leaving an extra 3,500 pounds capacity. I never have understood how they arrive at these capacities. For example, our 95 300 (bigger engine & trans) had the same GVWR of 30K but when fully loaded we only had about 1K capacity remaining. Our 320 had a GVWR of 34,880#. It gets really interesting when you figure horsepower to weight ratios and different gearing. I asked Triana about it one time but he said he didn't know how it's figured. Glad you got your motorhome!
jor

Re: Tire pressure question - without scales

Reply #13 – March 20, 2019, 04:20:40 pm

As it's your delivery trip just inflate to the recommended pressures as Brett says. Better to be over than under inflated as that's what causes tire to overheat and fail. Have the coach weighed then you can decide on proper pressures as per the manufacture pressure chart. Make sure that the tire sizes are the same as on the plate by the drivers seat.

Keith

Re: Tire pressure question - without scales

Reply #14 – March 20, 2019, 04:44:29 pm

GVRW is the sum of the axle ratings I believe
My coach has a 9k front axle and a 17.5k rear so GVRW is 26.5k. coach weighed about 22k with pots, pans, basic tools and other stuff when I drove it home.

Re: Tire pressure question - without scales

Reply #15 – March 20, 2019, 05:11:29 pm

Congratulations on the new coach. Enjoy and yeah what they all said

Larry

Re: Tire pressure question - without scales

Reply #16 – March 20, 2019, 05:28:11 pm

The sidewall pressures will be way too much air. Just go with what is on the plaque on the wall next to the driver seat. After having mine weighed on four corners, it ended up needing just that pressure, plus 5 psi for safety. And you can get it weighed per axle just about anywhere.

By the way, mine is just about dead even side to side.

Re: Tire pressure question - without scales

Reply #17 – March 20, 2019, 10:22:59 pm

We try to keep about 100 psi in each of our Michelin xza-3 load-range-H tires. All deduced from 9 weigh points done a several closed truck weigh stations and at feed stores.

Here is our Excel spreadsheet that puts our nine points of measurements together to make information out of data. . .

Re: Tire pressure question - without scales

Reply #18 – March 20, 2019, 11:49:59 pm

We had our coach weighed at Escapees in Livingston, TX. Using the weights and the Michelin charts AND after adding 5 extra pounds, our pressures are:

Front: 105 psi,

Rear: 85 psi.

The balance from the side-to-side weights seemed to impress the technician.

Trent

Re: Tire pressure question - without scales

Reply #19 – March 22, 2019, 06:09:10 am

I do not weigh my U270, and SIMPLY use 105 PSI cold in ALL tires because pressure varies with temperature due to:

- Asymmetrical sunshine
- Daily temperature variation
- Driving

There were no issues in last 12,000 miles.
My tires are rated at 120PSI cold maximum, and I don't succumb to "Pressure Shaming".

I HIGHLY recommend a TPMS.

Re: Tire pressure question - without scales

Reply #20 – March 22, 2019, 09:05:39 am

I was looking at Barry's spreadsheet and seeing the rear axle being overloaded. I have never weighed our and wondering if mine is overloaded also

Re: Tire pressure question - without scales

Reply #21 – March 22, 2019, 10:02:41 am

We got our coach 4-corner weighed at Escapees in Livingston, TX. Found out we are slightly overweight on our front axel, and 900 pounds over the total GVWR. We weighed with full water and fuel tanks, and 1/2 tank of propane. The tech suggested we could travel with less fresh water on board to reduce overall weight. We have since adopted that procedure. We also upgraded from the old G rated tires we had, to new H rated tires. This gave us some additional safety factor in the tire load department. I figure (hope) the axle ratings are probably pretty conservative, and our placarded GVWR looks suspiciously low to me...especially when compared to the same model year U300:

Foretravel Vehicle Weight

Regardless of what method a driver uses to set tire pressures, getting 4-corner weighed is a interesting exercise. Like most other reports, our side-to-side balance was fairly close. I guess Foretravel got that part of the engineering right!

Hanging At Camp FOT

Re: Tire pressure question - without scales

Reply #22 – March 22, 2019, 10:31:36 am

Whenever I hear those stories about coaches being overweight, I think of that scene in 'The Long Long Trailer' where Desi discovers Lucy's rock collection!

Re: Tire pressure question - without scales

Reply #23 – March 22, 2019, 02:50:55 pm

If you don't know! Go with Max pressure on side wall of tire. Example g rated 110psi

Re: Tire pressure question - without scales

Reply #24 – March 22, 2019, 03:23:53 pm

When I didn't know, I went tire FT placard pressures plus five psi. Still under sidewall Max.

Affiliate Notice