Tag Axle Tire Pressure

I plan on weighing my new to me CC this weekend and adjust the tire pressure accordingly.  I've searched a couple of forums but I've found nothing specific on how to set the pressure for the rears with a tag.  I'll be weighing at a CAT scale where I think I will only get the weight for the front an then a combined weight for the drive and tag.  I read a post where Gary RV Wizard suggested running slightly less PSI in the tag.  Is there a rule of thumb to follow when setting the rear pressures?  Placard in the coach says 120 psi front and 110 psi for drive and tag.

I was a little shocked at the pressures the dealer sent me on the road with when I drove home across Florida although the coach was empty.  Steer tires were both at 93 psi (I'm thinking 105) and drive axle and 1 tag were at 75 psi the other tag was at 65 psi.  The weight charts for my Goodyear's start at 80 psi.  I'm thinking 95 psi+/- for the rears.  All pending actual weights though.

Tires are 295/80/22.5's

Thanks
Ed

FYI - DW & I are loading the coach this week with all of our gear so it should be very close to our final traveling weight when weighed.

I've never found general rules for tag pressure - it seems to be more art than science.  Tire pressure affects how much load the tag carries and shifts weight  to/from the other axles, so it's a balancing act.  It may be complicated by the tag suspension mechanism on the chassis - some apparently have some automatic air suspension adjustment as well.  If it were a Freightliner or Spartan chassis you could get help from the factory service center, but where to find expertise on a CC Dynomax chassis?

The weight & tire placard on the wall by the driver seat should have a recommended psi for the tires on each axle. I'd start there, but never less than the minimum psi shown in the inflation table for that tire. The placard should also show the GAWR for the tag and that can be used to calculate a max load psi, useful as a sanity check on whatever else you come up with. Typically a tag has a much lower GAWR than the drive axle, so rarely would it ever need the max load inflation on its tires.


It may take multiple trips across a scale to get it dialed in.  If the trial tag pressure leaves the front or rear axles too high or  unusually low, adjust the tag tire psi and try again. A few lbs apparently can make a substantial difference.

I know of a owner with a recent model American Coach who had ride and handling problems until he took the rig to the Freightliner factory service center where they adjusted all the tire pressures to get a good balance. He drove away a much happier man, but I never learned just how FCCC adjusted things or the rationale for it.

ELeland said:

I plan on weighing my new to me CC this weekend and adjust the tire pressure accordingly.  I've searched a couple of forums but I've found nothing specific on how to set the pressure for the rears with a tag.  I'll be weighing at a CAT scale where I think I will only get the weight for the front an then a combined weight for the drive and tag.  I read a post where Gary RV Wizard suggested running slightly less PSI in the tag.  Is there a rule of thumb to follow when setting the rear pressures?  Placard in the coach says 120 psi front and 110 psi for drive and tag.

I was a little shocked at the pressures the dealer sent me on the road with when I drove home across Florida although the coach was empty.  Steer tires were both at 93 psi (I'm thinking 105) and drive axle and 1 tag were at 75 psi the other tag was at 65 psi.  The weight charts for my Goodyear's start at 80 psi.  I'm thinking 95 psi+/- for the rears.  All pending actual weights though.

Tires are 295/80/22.5's

Thanks
Ed

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LeLand, Just curious if you are using any type of Tire Pressure Monitoring System?  I am a new RVr and I went with TST. 

With that many tires it is a "necessary evil" in my mind.

Tag Axle, Sounds nice.  Have you had alot of RVs in the past? 

Welcome to Your Adventure.

John

John

X-Roughneck said:

LeLand, Just curious if you are using any type of Tire Pressure Monitoring System?  I am a new RVr and I went with TST. 

With that many tires it is a "necessary evil" in my mind.

Tag Axle, Sounds nice.  Have you had alot of RVs in the past? 

Welcome to Your Adventure.

John

John

Click to expand...

Yes John I do use a TPMS but need to have a tire shop change the valve on the tag rims so I can get my flow through sensors installed.  The only other MH I own does not have a tag.

Ed

After a 6 point weighing of our fully loaded rig.  It ended up weighing a total of just over 45K lbs.  Use 105psi in the front and 85psi in both rear axles. 

Ro and Joe said:

After a 6 point weighing of our fully loaded rig.  It ended up weighing a total of just over 45K lbs.  Use 105psi in the front and 85psi in both rear axles.

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Thanks.  I weighed yesterday and those are very close to the numbers I came up with too. 

If those pressures yield a front axle that is 1000-2000 lbs under its max (GAWR) and a drive axle that does not exceed 20,000 lbs, then I'd say you are good to go.