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Old 05-29-2015, 11:39 PM   #1
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I think I'm over-inflated... and not just my ego :)

I've read through dozens of past threads about tire pressure and axle weight, but I couldn't find an answer to my question.

Tires: Michelin 295/80R22.5 H XZA2 Energy, max PSI = 120

These are my axle weights (with full fuel and fresh water tanks):

Note: I couldn't weigh corners individually at these scales, but dividing this weight by two and adding a 5% margin for safety should compensate well enough for unequal loads left-to-right.

Steer: 13,540 lbs, 6,770 per end
Drive: 14,120. 7,060 per end
TAG: 7,040, 3,520 per end

Total weight: 34,700

Here's my question:

On both the drive an TAG axles, the weight on each axle end is so low it falls well under Michelin's tire pressure chart minimum PSI, which suggests that I run only 75 lbs of air in each of those (plus a few for a safety margin, of course).

That seems so low to me that I have a hard time believing it, so much so that I'm convinced I'm not reading something right.

Can someone straighten me out, please?

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Old 05-30-2015, 07:15 AM   #2
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105psi for the front tires. I think you read it right, although I would not go below 90psi on the rear tires till I see how it handles and what temperatures they run.

Michelin RV Tires | View Michelin RV Tires load and inflation tables for motorhomes and recreational vehicles. | Michelin RV Tires
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Old 05-30-2015, 08:31 AM   #3
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@Coma, thank you for helping me... I was completely baffled. To me, it just didn't make sense that my numbers were reporting so low when Michelin's chart started with such high numbers. Made me think I wasn't doing something right.

And the 90 lbs idea, that's a good one! I can live with 90 lbs on drive / tag axles... sounds like an excellent compromise.

Although... I stopped by CW on my way home from picking it up a few days back and had them do a tire check (it had been sitting a while). They asked me how much PSI to put in, and I had no clue since I hadn't had it weighed yet. Max PSI is 120 lbs, so I just had them fill all 8 tires to 110. Even empty it rides really smooth... didn't notice any difference with the fuel / water tanks full. I don't think going down to 90 lbs on the rears would make it perceivable smoother, so might as well leave it where it is for now.

Thanks again!
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Old 05-30-2015, 09:11 AM   #4
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Quote:
Originally Posted by Wryly Blithe View Post
@Coma, thank you for helping me... I was completely baffled. To me, it just didn't make sense that my numbers were reporting so low when Michelin's chart started with such high numbers. Made me think I wasn't doing something right.

And the 90 lbs idea, that's a good one! I can live with 90 lbs on drive / tag axles... sounds like an excellent compromise.

Although... I stopped by CW on my way home from picking it up a few days back and had them do a tire check (it had been sitting a while). They asked me how much PSI to put in, and I had no clue since I hadn't had it weighed yet. Max PSI is 120 lbs, so I just had them fill all 8 tires to 110. Even empty it rides really smooth... didn't notice any difference with the fuel / water tanks full. I don't think going down to 90 lbs on the rears would make it perceivable smoother, so might as well leave it where it is for now.

Thanks again!
YW!

If you can live with the ride that higher pressures give you, that is better. The tires will run cooler and give a bit better fuel mileage. The other benefit is that tire slip angle will be smaller so as to give you more responsive steering and tracking. The really nice thing is you have room to experiment.
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Old 05-30-2015, 11:10 AM   #5
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Coincidence? Or CW Strikes Again?

Well, I may have spoken too soon.

Remember I mentioned I had Camping World do a quick tire check for me on the way home and they filled them to 110 PSI? Well, I just checked them again for the trip today - of course - and they were all right around 90 PSI. I guess the tires weren't as cold as they thought. That's ok for the rears, but I gotta add some to the front.

Oh, and I have to add just a little to the inside dual on the roadside: it's currently sitting at 0 PSI. Yep, you read that right: ZERO.

It looked funny when I took the valve cap off... like the valve core was sticking too far out. When I tried to check it, just a whisper of air leaked out, but no PSI. I thought maybe the core was sticking out too far for me to make a seal so I manually pushed it all the way in... nothing.

I have no way of knowing if it's CW's fault... can they have accidentally yanked out the core by checking / filling the tire? In either case, my only option is Big O right down the road. Let's hope they have everyone working today.
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Old 05-30-2015, 11:28 AM   #6
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Quote:
Originally Posted by Wryly Blithe View Post
I've read through dozens of past threads about tire pressure and axle weight, but I couldn't find an answer to my question.

Tires: Michelin 295/80R22.5 H XZA2 Energy, max PSI = 120

These are my axle weights (with full fuel and fresh water tanks):

Note: I couldn't weigh corners individually at these scales, but dividing this weight by two and adding a 5% margin for safety should compensate well enough for unequal loads left-to-right.

Steer: 13,540 lbs, 6,770 per end
Drive: 14,120. 7,060 per end
TAG: 7,040, 3,520 per end

Total weight: 34,700

Here's my question:

On both the drive an TAG axles, the weight on each axle end is so low it falls well under Michelin's tire pressure chart minimum PSI, which suggests that I run only 75 lbs of air in each of those (plus a few for a safety margin, of course).

That seems so low to me that I have a hard time believing it, so much so that I'm convinced I'm not reading something right.

Can someone straighten me out, please?


When I bought my tag axle last month, I had all four corners weighed. My weights with Goodyear tire were same way for the drive and tag. Weight so low, not even on the chart. I was to worried to do that so I just followed what was on my motorhome placard for the tires. 90 on drive and 85 on tag. Drives great so I don't mess with it.
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Old 05-30-2015, 11:41 AM   #7
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Thanks, lsptpr! Good to know I wasn't the only one
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