Community Forums

wingnuts · 03-23-2018, 10:18 PM

Not sure how to figure out correct psi for my tires on my itasca 30w class a

placard says
front axle 7000 Lbs
Rear axle 11000 Lbs
Gvwr 18000 Lbs

My weights on the scale
Front axle 5560 Lbs
Rear axle 10420 Lbs
Total weight 15980

Tire info. .Sailun 245/70/19.5
4540 single at 110 psi
4330 duals at 110 psi

3640 single at 80 psi
3410 dual. at 80 psi

If I'm doing the math right 80 psi would be plenty but I may run 85 just to be safe on my gage

BigBillSD · 03-23-2018, 11:05 PM

Your numbers look odd. If your axle weights are correct then each front tire is carrying one half of 5560 or 2780 each approx. without corner weights its approx.

I don't see any number close to that in your numbers.. Same with the rear, I don't see anything like half of 10420 or one quarter of 10420 depending on who that manufactures chart lists the inflation pressures.
You fill the tires based on what that tire is holding up.

wingnuts · 03-23-2018, 11:59 PM

Yea. Looks like plenty of tire, my placard says 70 psi but the Sailuns minimum is 80

**Spdracr39** · 03-24-2018, 07:22 AM

can't hurt to run more than 80 as long as it is less than 110. The only thing that will be affected is a little ride quality with the higher pressure. If the minimum is 80 psi then I also would run 85 since they have plenty of load rating per your numbers.

OLYLEN · 03-24-2018, 09:35 AM

Like you said, I would run 85 both front and rear and then play with a bit more and see what the ride and stability is.

LEN

hohenwald48 · 03-24-2018, 10:18 AM

Looks like you have plenty of tire assuming you are looking at the chart for the load range tire that you own. You didn't indicate load range so we have no real way to tell for sure.

Peter M · 03-25-2018, 05:34 AM

Quote:

Originally Posted by wingnuts

Tire info. .Sailun 245/70/19.5
If I'm doing the math right 80 psi would be plenty but I may run 85 just to be safe on my gage

So what is the model Sailun tire and rating you refer to?
We need more than tire size to help

Mudfrog · 03-25-2018, 10:26 AM

Quote:

Originally Posted by wingnuts

Yea. Looks like plenty of tire, my placard says 70 psi but the Sailuns minimum is 80

I wonder if you may have a higher load range tire than originally came on the rig? Ours came with Fs and i made the mistake of buying 2 G rated Sailuns a while back. I had the roughest riding rig no matter what i did with pressure. The tire had 2, maybe 4, more plies than the Michelins i replaced. I believe this, along with having to go with a higher air pressure than my placard recommended, caused the really harsh ride.

You might check to make sure you have the right load range tires on there now.

Sweetbriar · 03-25-2018, 10:43 AM

I'm pretty much in the same spot. A lot of tire capacity with a 18,000 lbs coach. Tire charts end at 80 PSI which is the pressure I would need if I was at axle maximum loading. Unfortunately just like the OP I'm 1000 lbs or so under. Not much choice but to air up to 80.

F4Gary · 03-25-2018, 11:01 AM

Quote:

Originally Posted by Mudfrog

I wonder if you may have a higher load range tire than originally came on the rig? Ours came with Fs and i made the mistake of buying 2 G rated Sailuns a while back. I had the roughest riding rig no matter what i did with pressure. The tire had 2, maybe 4, more plies than the Michelins i replaced. I believe this, along with having to go with a higher air pressure than my placard recommended, caused the really harsh ride.

You might check to make sure you have the right load range tires on there now.

I'm wondering if this is what causes our terrible ride over even the smallest expansion joint. RV came with F range Michelins and I'm running G range Dunlops at 85 psi in the front (using the Goodyear tire chart)

wingnuts · 03-25-2018, 11:48 AM

Thanks guys, yea I went with G rated because it had H rated tires when I got it....

Rides fine to me with 85 in them, maybe because I don't know any different but way better than the motorhome we had before, plus were only weekend warriors and don't go far

hohenwald48 · 03-25-2018, 05:01 PM

Quote:

Originally Posted by Peter M

So what is the model Sailun tire and rating you refer to?
We need more than tire size to help

All tires of the same size and load range rating will have the same inflation charts regardless of who the tire manufacturer is.

wingnuts · 03-25-2018, 09:17 PM

I am kind of wondering if I could have gone with the 225/70/19.5

G rated..

Single..3960 lbs at 110 psi
Dual. 3740 lbs at 110 psi

Single 2895 at 70 psi
Dual 2720 at 70 psi

Gary RVRoamer · 03-26-2018, 07:54 AM

Quote:

If I'm doing the math right 80 psi would be plenty but I may run 85 just to be safe on my gage

80 psi is plenty, even if the load on the axles is split 60/40 rather than 50/50. The 80 psi load values are more than sufficient even if both axles were loaded to their max (GAWR).

Did you increase the tire size? Or just the load range?

Quote:

can't hurt to run more than 80 as long as it is less than 110. The only thing that will be affected is a little ride quality with the higher pressure.

I have to disagree with this statement with respect to the front (steer) axle. Excessively inflated tires on the steer axle will make the steering ultra-sensitive, with a much greater tendency to wander, track ruts, etc. Substantially over-inflating the steer tires is a poor choice.