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Topic: (follow up thread) Tire load ratings and inflation - G vs H (Read 671 times) previous topic - next topic

(follow up thread) Tire load ratings and inflation - G vs H

Earlier in the year I posted up a question on my G rated tires.  You can read it here:

Tire load ratings and inflation - G vs H

Today I wanted to follow up.

Last week I had a Hydralift platform lift installed along with one of my motorbikes (typically I will bring two with a total weight of around 800lbs). Right now it's just one ~310 lbs bike.  This lift is rated for 1,100lbs!

Next we headed off to the Escapees North Ranch campground where we had the coach weighed.  3/4 full diesel, full water, empty grey/black and full of everything else we need for our big trip.

Here's the results.  For reference our G rated tires are rated up to 6,175lbs for a single and 5,675 (11,350) for duals.

We have Goodyear Endurance LHS - 297/75R22.5 load range G on the steer and tag axles.  Traction tires are installed on the drive axle (Goodyear Endurance LHD - 297/75R22.5 load range G)

Right Front      5550lbs
Left Front        5475lbs

Right Rear      9200lbs
Left Rear          8875lbs

Right Tag        3700lbs
Left Tag          3500lbs

That's a total of 36,400lbs.  Our GVWR is 42,000lbs, putting us 5,600lbs UNDER weight!

All six G rated tires were well under weight their max load rating.

After checking with the manufactures tire inflation charts, I have the fronts set to 95psi.  Drive's are 70psi and the tag's are way under weight, such that there are no recommended pressures for only 3,700lbs.  70 psi @ 4,500lbs is as low as their charts go, so for now I've got them at 70... which is probably way to high. Should I try them at 55-60?

Here's a link to the Goodyear Tire Inflation Tables
https://www.goodyeartrucktires.com/pdf/resources/publications/2010_loadinflation.pdf#page=6

2003 U320 38' tag
2003 Green Jeep Wrangler

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #1 –
I had the same problem, guy at tire shop said 70 psi minimum. He said it had to do with bead sealing on the wheel.
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #2 –
Quote from: jcus –
I had the same problem, guy at tire shop said 70 psi minimum. He said it had to do with bead sealing on the wheel.

Thanks, that makes sense.  IIRC the tag has brakes so there would be a shear load between the wheel and the tire bead under braking.  Running lower pressures could cause the tire to slip on the rim and shear off the tire stem, causing the tire to rapidly deflate!

2003 U320 38' tag
2003 Green Jeep Wrangler

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #3 –
Please post your GAWR's for each axle.

Compare the % of the GAWR on each axle-- ideal is the same percent on each axle.

Which brings up the question, how is tag axle pressure determined-- separate ride height valve? percent feed off drive axle? other? Others with your model year can tell us.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #4 –
 My 03 is 14300 steer, 21000 drive and 9000 tag. If you raise your tag tire pressure to 75 psi, individual rear tire weights should be closer to equal, and still below GAWR. Might load up the front a bit more though. As HCV,s appear to feed both rear axles equally, believe my coach distributes weight equally between tag and drive because tag has only 2 bags, while drive has 4 bags, and/or by having different design airbags.  I am sure the Hydralift affects the whole equation, but not sure how.
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #5 –
Using Jim's GAWR's and the heavier wheel position on each of coloradomtn's axles:

Front axle is loaded to 79%
Drive to 88%
Tag to 82%

If tag is adjustable, loading it more would help weight distribution and improve handling.

So, on the 2003, what determines tag loading??
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #6 –
Quote from: wolfe10 –
Using Jim's GAWR's and the heavier wheel position on each of coloradomtn's axles:

Front axle is loaded to 79%
Drive to 88%
Tag to 82%

If tag is adjustable, loading it more would help weight distribution and improve handling.

So, on the 2003, what determines tag loading??
Brett, as I explained in post 4, the HCV sends the same air signal to both sets of bags, air schematic does not show any other adjustment for tag loading, so either because of bag design, or the fact tag is two bags, and drive is 4, somehow weights are proportional between axles. Might be wrong, but that's what I see.
https://www.foreforums.com/MGalleryItem.php?id=1459
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #7 –
Jim,

So, there is no separate ride height valve/linkage for the tag?

And, no pressure reducer/aduster (like Monaco used for years on their 8 outboard air bag plus tag chassis)?
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #8 –
Quote from: wolfe10 –
Jim,

So, there is no separate ride height valve/linkage for the tag?

And, no pressure reducer/aduster (like Monaco used for years on their 8 outboard air bag plus tag chassis)?
https://www.foreforums.com/MGalleryItem.php?id=1459
If you scroll down to AIR LINE CONNECTION TAG AXLE and the AIR LEVEL SCHEMATIC below it, only signal to rear tag manifold and tag air bags, appears to comes from drive axle HCV's in travel mode.
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #9 –
Jim,

So look at the LS TAG AIRBAGPRESSURESWITCH 20 PSI on page 19.

Can that be raised to 25? 30?  Clearly there is a pressure reducer involved.

Not sure I would not contact Aubry at MOT for a "how do I fine-tune" weight distribution.


Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #10 –
I have always heard 75 psi min for our RV tires (275/80R22.5)
Dan - Full timing since 2009
2003 U320 40' Tag 2 slide

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #11 –
Quote from: wolfe10 –
Jim,

So look at the LS TAG AIRBAGPRESSURESWITCH 20 PSI on page 19.

Can that be raised to 25? 30?  Clearly there is a pressure reducer involved.

There are also air bag pressure switches on front and drive axles manifolds, don't see how they could raise or decrease pressure in bag, they are just an on/off switch . Think they have more to do with the minimum  bag pressure when leveling coach or detecting travel mode.
HWH Air Leveling System Explained


Not sure I would not contact Aubry at MOT for a "how do I fine-tune" weight distribution.


Have talked to Aubry, told me no adjustments, set from factory. My coach has pretty good weight distribution on rear axles from the factory. Imagine they went to this system because all the tanks are right in front of rear axle, and with the constant load changes, they wanted a simple solution.
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.
 

Re: (follow up thread) Tire load ratings and inflation - G vs H

Reply #12 –

Another good tire pressure write up.

Tire inflation theory
Gary & Kathy 🐶 Angus

 94 GV u280 36' build #4419
Cummings c8.3m, Alison MD 3060