Tire pressures on zxa-3 tires

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Tire pressures on zxa-3 tires

August 10, 2015, 04:46:01 pm

Having a local dealer install a set of "h" rated zxa-3's and wanting to see if my numbers on inflation pressures make sense?

Actual axle weights are 12,000 front and 20.233 rear fully loaded.

Based on the chart showing weight versus max pressure I get roughly 93 psi front and 91 rear.

Pretty sure that's correct. Anyone have any input of this number?

Former was "g"s at 108 front and 98 rear. Drove beautifully.

Did not like running that close to max on the front plus tires were 05 date coded on the front was my motivation plus side wall cracks had started

Thanks in advance.

Bob

Re: Tire pressures on zxa-3 tires

Reply #1 – August 10, 2015, 05:00:09 pm

Are those weights as loaded for travel including passengers in their usual seats? Do you have actual individual wheel/corner weights?

General recommendation from RV Safety is to add 5-10 psi as a safety margin to account for changes in loading, etc. and to use the heaviest axle end to determine the pressure for the tires on that axle.

Looking at Michelin's load chart for 275/80R22.5 LRH XZA3+

12000 if equally distributed is 6000 lbs per axle end, so you want 100 psi plus margin for single tire load

20233 on rear is 10115.5 lbs per axle end if equally distributed, so 90 psi plus margin for dual tire load.

If it were our coach, we would run 105 front, 95 rear. JMHO. And I would get individual wheel/corner weights as loaded and everyone in their usual spots to make sure it didn't need to be higher. Most FTs are generally just a few hundred pounds unbalanced left to right (ours is 225 lbs heavier driver front, 100 lbs heaver passenger rear), but never assume....

Re: Tire pressures on zxa-3 tires

Reply #2 – August 10, 2015, 05:16:25 pm

Round up to nearest increment of 5 and add 5

Re: Tire pressures on zxa-3 tires

Reply #3 – August 10, 2015, 05:29:50 pm

The kitchen area is the most often unballnced area,

Which reinforces why many store some items in the shower to get a more balanced load.

As always, YMMV

best, paul

Re: Tire pressures on zxa-3 tires

Reply #4 – August 10, 2015, 08:55:26 pm

On my none slide coach, I ran 105 front and 95 drive now I run 110 front on this coach.

Re: Tire pressures on zxa-3 tires

Reply #5 – August 10, 2015, 09:04:42 pm

Quote from: John S – August 10, 2015, 08:55:26 pm

On my none slide coach, I ran 105 front and 95 drive now I run 110 front on this coach.

Which may well be the correct pressure for the weight on the tires.

Slide coaches need to be weighed side to side. My neighbors tour is off by more than a 1000 pounds left to right.

Buddy suggests running one side on the scale and then the other.

When I mentioned this thread his first comment on my use of h tires versus the coaches weight was that I would be less than 100psi.

He uses a temp and pressure tire sensor system.

His comment was the tire temps changing from 50F to 150F could change the tires pressure a lot ...

Re: Tire pressures on zxa-3 tires

Reply #6 – August 10, 2015, 09:19:22 pm

Wow!! Had mine weighed (single slide) at grandvention. Was really close side to side, like off like 100 pounds

Re: Tire pressures on zxa-3 tires

Reply #7 – August 10, 2015, 09:29:53 pm

Quote from: Tim Fiedler – August 10, 2015, 09:19:22 pm

Wow!! Had mine weighed (single slide) at grandvention. Was really close side to side, like off like 100 pounds

Rare according to my guru buddy. Almost unheard of from SOB's.

I think the tour was off 1,500 pounds. Owner has been pulling his hair out trying to fix a jarring ride on cross grain highways. Bang. Changed shocks several times. Air valves.

Re: Tire pressures on zxa-3 tires

Reply #8 – August 10, 2015, 09:33:13 pm

We weighed twenty FTs at a rally. Almost all were pretty even. I am 300 pounds more on the drivers side then passenger on the fronts and very close on the drive and tag. The single slide coaches almost all broke the 20k limit on the drives if they did not have a tag.

Re: Tire pressures on zxa-3 tires

Reply #9 – August 10, 2015, 09:36:19 pm

My non slide but full liquids was 20.223 on the rear. Empty holding tanks.

Re: Tire pressures on zxa-3 tires

Reply #10 – August 10, 2015, 09:56:07 pm

Wonder if active air from hwh would help I find it sort of ironic that again but such a poorly designed coach

Re: Tire pressures on zxa-3 tires

Reply #11 – August 10, 2015, 10:28:02 pm

Well all the non slide coaches were under 20 on the rear drives. I wonder where your fuel tank is. I had mine in the first bay.

Re: Tire pressures on zxa-3 tires

Reply #12 – August 10, 2015, 10:43:22 pm

Ours is a '96 U320 (no slide). We are 6100/6000 & 10200/10200 (L/R, F/R) fully, fully loaded, including driver, passenger and (large) furry friend. For the XZA3+ H, this suggests 97# and 87#. I use 105# up front, 95-100# on the rear. Ride is fine and seems to be on the safe side.

Re: Tire pressures on zxa-3 tires

Reply #13 – August 10, 2015, 11:24:47 pm

Quote from: Grant L – August 10, 2015, 10:43:22 pm

Ours is a '96 U320 (no slide). We are 6100/6000 & 10200/10200 (L/R, F/R) fully, fully loaded, including driver, passenger and (large) furry friend. For the XZA3+ H, this suggests 97# and 87#. I use 105# up front, 95-100# on the rear. Ride is fine and seems to be on the safe side.

Hard to measure tiny things but over time a tire measurement of wear might give some input on any differences?

I got 93 and 92 same weight and tires? Did I figure wrong?

84% of the front load

76%? Of the rear

Re: Tire pressures on zxa-3 tires

Reply #14 – August 10, 2015, 11:26:48 pm

Quote from: Tim Fiedler – August 10, 2015, 09:56:07 pm

Wonder if active air from hwh would help I find it sort of ironic that again but such a poorly designed coach

They are selling floorplans

Re: Tire pressures on zxa-3 tires

Reply #15 – August 11, 2015, 06:59:34 am

A guru I meant to say

Re: Tire pressures on zxa-3 tires

Reply #16 – August 11, 2015, 02:58:07 pm

Quote from: Caflashbob – August 10, 2015, 11:24:47 pm

Hard to measure tiny things but over time a tire measurement of wear might give some input on any differences?

I got 93 and 92 same weight and tires? Did I figure wrong?

84% of the front load

76%? Of the rear

Looking again at my calculations, I still get around 97 psi for the front and 87 psi for the rear. Not sure why we're getting different numbers.

Re: Tire pressures on zxa-3 tires

Reply #17 – August 11, 2015, 08:37:12 pm

6610 X 4 for dual installations on h rated =26440

Actual weight is 20233.

76%

76% of 120 = 91 psi

7160 X 2 for single = 14320

Actual is 12,000

83%

83% of 120 is 100 rounded off.

So I get 100 on fronts, 91 on rear?

My math better?

Re: Tire pressures on zxa-3 tires

Reply #18 – August 11, 2015, 09:48:55 pm

Bob, I can see how you came up with the pressures you did. I went about it a little differently.

Front axle: 12100 lb; from table below - 11880 is 95psi, 12380 is 100psi, so 12,100 is about 97psi
Rear axle: 20400 lb; from table below - 20600 is 85psi, 21000 is 90psi, so 20400 is about 87psi

It may be the difference between recommended and maximum; not sure. It looks like we get to same practical outcome.

275/80R22.5 H XDE®2+ XZA3®+ EVERTREAD® XZE®

Re: Tire pressures on zxa-3 tires

Reply #19 – August 11, 2015, 10:51:31 pm

Quote from: Grant L – August 11, 2015, 09:48:55 pm

Bob, I can see how you came up with the pressures you did. I went about it a little differently.

Front axlwe: 12100 lb; from table below - 11880 is 95psi, 12380 is 100psi, so 12,100 is about 97psi
Rear axle: 20400 lb; from table below - 20600 is 85psi, 21000 is 90psi, so 20400 is about 87psi

It may be the difference between recommended and maximum; not sure. It looks like we get to same practical outcome.

275/80R22.5 H XDE®2+ XZA3®+ EVERTREAD® XZE®

Cool. Love double checks.

The giant volume truck shop guy mentioned I would like the h's for ride and steering versus the 108 psi g's I have now on the front. And the 90 psi rears versus the 98's I have now. 16 plies.

Re: Tire pressures on zxa-3 tires

Reply #20 – August 12, 2015, 04:35:26 pm

Correct tire pressures are elusive and personal.
We measured several times over the years, weighing coach on 9 scale positions: left front, right front, left rear, right rear, left side, right side, front axle, rear axle & all four tires on scale. We put scale readings in spreadsheets along with axle, wheel and tire limits.
Our chosen 100 psi for all six LR-H XZA+ Michelin tire positions includes added PSI to account for cold mornings, high altitudes, side winds, turns, etc.
We quickly check tire pressures with our dash mounted Pressure Pro display before & during traveling and often while parked. Pressure Pro will display current pressures while parked and alert to a slow leak or theft, so we never turn it off.

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