Tire pressure variance

Topic: Tire pressure variance (Read 1360 times) previous topic - next topic

Tire pressure variance

March 12, 2017, 11:15:22 am

Finally got the coach weighed at FMCA by RVSEF. Their recommendations we're significantly different for the duals than the mfg placard. The coach had full tank of fuel and 3/4 tank of water between fresh and gray. I normally drive with half a tank of water. I have Michelins.

Drv. P. Total. WR. Rec. Placard
5150 5300 10450. 12000. 95. 97
8500. 9500. 18000. 19000 95. 83

The steering tires aren't much different than recommended. The dual are much different and it appears that I have been running under inflated by a significant amount.

If you have a similar profile are you running at the higher pressures?

Re: Tire pressure variance

Reply #1 – March 12, 2017, 11:41:06 am

I run the same levels of water and fuel. Not heavily loaded inside.
Tow a Jeep Wrangler
97 U295 36'
100 in the rear, 105 fronts.
Toyo G's
Rides like a caddy
When I was a tech, this is pretty much what customers wanted in their tires across the board
Dash plate say's 97-83 also
When Les Swab installed the tires, they had them at 95 all around.
Tires say 110 max cold, single or dual.

Re: Tire pressure variance

Reply #2 – March 12, 2017, 11:43:17 am

Thanks!

Re: Tire pressure variance

Reply #3 – March 12, 2017, 11:51:55 am

We usually weigh 22,500 to 23,000 lbs that's 3,000+ under max on those skinny Toyo's we go with 95 lbs front and back.

Re: Tire pressure variance

Reply #4 – March 12, 2017, 12:20:46 pm

George,

Which Michelins are you running? Load range?

Michelin RV Tires | View Michelin RV Tires load and inflation tables for...

The Michelin charts would generally indicate the plate is marked for load range H tires; those could be what the coach had as OEM:

12,000 GAWR front/2 -> 6000 lbs per axle end, or between 95 and 100 psi for 275/80R22.5 LRH on a single
20,000 lbs GAWR drive /2 -> 10,000 lbs per axle end which turns up just under 85 psi for 275/80R22.5 LRH on a dual

RVSEF's recommendation of 95 psi for a 5300 lb axle end on the front and a 9500 lb axle end on the rear duals corresponds to LRG tires in that size (with the usual 5-10 psi safety margin RVSEF advises).

IIRC, the plate Foretravel affixes shows the inflation recommendation for the OEM tires if the axles are at their GAWR limits.

It's important to run the inflation recommended by the tire manufacturer for your specific tires and axle weights (with a safety margin to allow for loading differences).

Re: Tire pressure variance

Reply #5 – March 12, 2017, 12:37:06 pm

Michelle

The link was very useful. We have G rated XZE and they are right on the money with their recommendation according to the table. I have used them for all our other rigs and found them to be very accurate. I was was surprised at variance.

Again thanks for the link!

Re: Tire pressure variance

Reply #6 – March 12, 2017, 02:11:01 pm

Quote from: George and Steph – March 12, 2017, 12:37:06 pm

The link was very useful. We have G rated XZE and they are right on the money with their recommendation according to the table. I have used them for all our other rigs and found them to be very accurate. I was surprised at variance.

Glad you got it weighed and now know that plate is for the OEM likely LRH tires, not the LRG you currently have.

Re: Tire pressure variance

Reply #7 – March 12, 2017, 02:39:32 pm

Does anyone know why Wayne at FT recommends lower air pressures? I am guess ride but do not know.

Re: Tire pressure variance

Reply #8 – March 12, 2017, 03:34:33 pm

Better tire contact patch. Safer in wet conditions. Versus riding on the narrower center ribs of the tires.

As the tires heat up you will add 5-10 pounds pressure I think.

My car goes from 32 cold to 35-36 at 80 degrees ambient.

Re: Tire pressure variance

Reply #9 – March 12, 2017, 04:04:16 pm

Or as Brett said in a recent suspension seminar ( hope I don't miss quote here). If your riding around on 110 lbs and the individual wheel weights say 70, don't talk to me about ride and handling.
And then on the flip side, if they should be at 110 and your at 70. Your asking for a serious problem.

Our GV is at 75 front and 85 rear per conversation with Michelin tech.

Re: Tire pressure variance

Reply #10 – March 12, 2017, 04:09:53 pm

Someone thinks that Michelin does not know how much air to put in Michelin tires?

Re: Tire pressure variance

Reply #11 – March 12, 2017, 06:00:38 pm

Mike.
How would Michelin know what to recommend for tire pressure if I had not given them the 4 corner weight of the coach? We have a free ODOT scales near our home. Prolly weighed it 3 maybe 4 times. You don't agree with the pressures ?

I don't have the figures with me but I think the heavy side in the front was 4500 or less and the heavy side in the rear was 9300 or less.

Tires are 275/80R 22.5. Michelin XZE2. Any other 95 GV owners out there with similar.

Re: Tire pressure variance

Reply #12 – March 12, 2017, 06:54:20 pm

The U280 is quite a lot heavier than the U240. Don't try to compare their tire sizes/weights/PSI.

Re: Tire pressure variance

Reply #13 – March 12, 2017, 07:30:36 pm

We keep our tires @ 95 cold....driving in FL ambient @ 80 they show 112-114..

Hans

Re: Tire pressure variance

Reply #14 – March 12, 2017, 09:06:40 pm

Quote from: Hans&Marjet – March 12, 2017, 07:30:36 pm

We keep our tires @ 95 cold....driving in FL ambient @ 80 they show 112-114..

Hans

There has been a great deal of info' on this post, I am however confused.........
Cold tire pressure.........is that June in Montana or January in Florida ?
When I fill my fuel and tanks water should I adjust my tire pressure to account for the added #1800+ lbs ?
Do they make a tire for RV's that is only for that application so you can vary the PSI without any sidewall temp. problems ?

The main reason I think I'm confused is that when I drove a 18 wheeler I never adjusted my tire pressure ( 18 tires ) to allow for being loaded or un-loaded.

Re: Tire pressure variance

Reply #15 – March 12, 2017, 09:08:56 pm

Our correct is 87/97 on LRH Xza-3's per Michelins chart.

Re: Tire pressure variance

Reply #16 – March 12, 2017, 10:36:13 pm

"The rule of thumb is for every 10° Fahrenheit change in air temperature, tire pressures will change about 2% (up with higher temperatures and down with lower). This means that light-duty, standard-pressure tires (typically inflated to 30-50 psi) used in applications on cars, vans and light trucks will change by about 1 psi; where heavy-duty, high-pressure tires (typically inflated to 80-100 psi) used in applications on recreational vehicles, busses and trucks will change by about 2 psi."

My personal opinion is set tire pressure in the morning before driving and before the sun shines on one side for many hours. If you routinely check tire pressure and have a safety margin on the high side of pressure, you "probably" will not need to adjust RV/Truck tires more than 2-3 times per year (if that). I like to set tire pressure when ambient temps are around 50-70 degrees. Add a safety margin on the high side, not the low side. Then, worst case, ride becomes a bit firmer as pressure increases. (if not exceeding *cold pressure limit * on the tire).

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=73 is a pretty good article.

Re: Tire pressure variance

Reply #17 – March 13, 2017, 12:21:39 am

Quote from: Bob & Sue – March 12, 2017, 06:00:38 pm

Tires are 275/80R 22.5. Michelin XZE2. Any other 95 GV owners out there with similar.

Bob,
We weighed our coach (sister to yours) fully loaded as we usually travel. We did not weigh corners as the Ag station we stopped at was unable to do that.
Gross was 27600
Front - 8840 or 4420ea
Rear - 18760 or 9380 per dual
We run the same size tire as you do and ours are load range H - Michellin XZE's
As per chart Front @75 and Rear @80
We set cold press at 80 front and 85 rear
When running at temp they usually increase to 85 in the front and 90 in the rears.
It steers and handles well in the cross wind, we run a TPMS and so far could not be any happier with their performance.

Re: Tire pressure variance

Reply #18 – March 13, 2017, 07:01:37 am

Set it and get on down the road. I run Continentals and air up at 85 psi to 90 then don't worry about it. It all fits into the range for my weight and speed. Speaking of weight, I noticed you had a 1000 lbs difference from left to right in rear. We had that same difference three years ago with no explanation from those doing the weighing. This year, same people, we had less than 100 lb difference with nothing changed. I really think they need to check their scales and procedure. Have no idea where the 900 lbs went.

Have a friend who checks his tires at each stop. Yes, breakfast, lunch and dinner. after a week he is worried where the air is going. It's going into the guage. Can't get him to see this.

Re: Tire pressure variance

Reply #19 – March 13, 2017, 08:53:30 am

Quote from: Michelle – March 12, 2017, 12:20:46 pm

The Michelin charts would generally indicate the plate is marked for load range H tires; those could be what the coach had as OEM:

12,000 GAWR front/2 -> 6000 lbs per axle end, or between 95 and 100 psi for 275/80R22.5 LRH on a single
20,000 lbs GAWR drive /2 -> 10,000 lbs per axle end which turns up just under 85 psi for 275/80R22.5 LRH on a dual

Based upon our measured axle weights we run our 1995 U320 (Michelin 275/80R22.5 LRH) with the cold (that means just before driving at whatever our location happens to be) tire pressure at 95 Front and 90 Rear and have a very comfortable ride. The ride quality degrades significantly if I set the tire pressures more than about 5 PSI above these values.

Re: Tire pressure variance

Reply #20 – March 13, 2017, 11:52:32 am

Quote from: wolfe10 – March 12, 2017, 06:54:20 pm

The U280 is quite a lot heavier than the U240. Don't try to compare their tire sizes/weights/PSI.

My mistake. So the U280 has a whole different frame/suspension making it heavier?

Re: Tire pressure variance

Reply #21 – March 13, 2017, 12:42:55 pm

Yes

Re: Tire pressure variance

Reply #22 – March 13, 2017, 12:53:07 pm

Quote from: mike leary – March 13, 2017, 11:52:32 am

My mistake. So the U280 has a whole different frame/suspension making it heavier?

That is correct. It's a bit of an oversimplification, but think of the U280 (and U300) as "full-size" coaches, and think of the U240 (and U225) as mid-size coaches.

Re: Tire pressure variance

Reply #23 – March 14, 2017, 10:31:07 am

DJ,
I found exactly the same thing on my '95.
Just adding 5psi above the tire chart pressure did make the ride harder.

Re: Tire pressure variance

Reply #24 – March 14, 2017, 03:22:39 pm

Quote from: Olde English – March 12, 2017, 09:06:40 pm

There has been a great deal of info' on this post, I am however confused.........
Cold tire pressure.........is that June in Montana or January in Florida ?
When I fill my fuel and tanks water should I adjust my tire pressure to account for the added #1800+ lbs ?
Do they make a tire for RV's that is only for that application so you can vary the PSI without any sidewall temp. problems ?

The main reason I think I'm confused is that when I drove a 18 wheeler I never adjusted my tire pressure ( 18 tires ) to allow for being loaded or un-loaded.

I adjusted my 18 wheelers tire pressure to my normal max weight when loaded. As I was a contractor for FedEx, We ran really light loads (60,000Lbs) even when both trailers were full as well as 250 gallons of fuel. Michelin recommended that I drop tire pressure on my drive axle tires to 65-70PSI. I would normally have just 19,000lbs on dual drive axles (8 tires) that are DOT allowed to handle 36,000lbs that's only 2375 lbs per tire instead of the 4500lbs at max allowed DOT load. My SUV's tires can handle 1700@51 max PSI.

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