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Old 11-26-2022, 01:48 PM   #1
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Proper tire inflation

I have a 2016 Isata 3 24FW. The tire pressure stickers on the door recommend 61psi on all tires but Iím not sure if that was put on for just the chassis. I had a tire shop recommended 70psi in the front and 80psi in the rear. I decided to get it weighed and the front axel is 3680Lbs and the rear is 6860 lbs. I have Continental LT 215/85R 16. 115/112Q tires. I can not find a good chart for recommended tire pressure. Just wondering what other people are using for tire pressure.
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Old 11-26-2022, 01:55 PM   #2
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Are the tires shown on the door sticker the same size etc as the actual tires on the vehicle? If so, then 61 PSI is a good number.

If the tires are of different sizes, then refer to the tire charts, search for your tire size via Google, and you'll find the correct inflation pressure.

Bob
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Old 11-26-2022, 02:05 PM   #3
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They are the same size and manufacturer that were originally on the RV. I guess I will go with the sticker pressure. Thanks
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Old 11-26-2022, 02:28 PM   #4
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Your tire size is generally shown to carry over 2,000 lbs @61 psi cold inflation (most charts will show~2100 lbs). If you have dual wheels on your rear axle, even with the usual de-rate for duals, your fine at 61 psi-----until your rear axle weight gets up around 8,000lbs.

Many people in tire shops will recommend a "stagger" in pressures front to rear to mitigate handling problems due to oversteer. If you arent experiencing that, or manufacturer of chassis isn't showing different F/R pressures, just check and adjust pressures when cold and enjoy your travels



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Old 11-26-2022, 02:38 PM   #5
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Thanks for the reply. I obviously have them over inflated right now so I will get them back down to the 61psi.
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Old 11-26-2022, 03:52 PM   #6
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Quote:
Originally Posted by Mmspring View Post
Thanks for the reply. I obviously have them over inflated right now so I will get them back down to the 61psi.
Anything between the sticker psi and the sidewall max cold psi is properly inflated.
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Old 11-27-2022, 06:33 AM   #7
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Quote:
Originally Posted by Mmspring View Post
I have a 2016 Isata 3 24FW. The tire pressure stickers on the door recommend 61psi on all tires but Iím not sure if that was put on for just the chassis. I had a tire shop recommended 70psi in the front and 80psi in the rear. I decided to get it weighed and the front axel is 3680Lbs and the rear is 6860 lbs. I have Continental LT 215/85R 16. 115/112Q tires. I can not find a good chart for recommended tire pressure. Just wondering what other people are using for tire pressure.
Then I made you a list with my extra safe formula, and gives 90% of the calculated loadcapacity for the pressure. Your maxload is given for 99mph max, and I determined 90% using of loadcapacity for that speed, gives maximum reserves with still acceptable comfort and gripp, and no centrewear.

Was the weighing fully loaded?
And I assume rear dualload axle,and E-load AT 80 psi referencepressure.

Determining the weights is your responcibility and the most tricky part in it all, but weighing, as you did, makes it more certain.

Then you see that for your given axleloads Front 60 psi is enaugh, and Rear 65psi, but because of the maximum reserves build in 60psi, 90% of loadcapacity is only 50 lbs lower at 60 psi, so can do too for rear.
61 psi is a conversion from 4.2bar/420kPa, but vehicle maker gave it for GAWR with no reserve.


AXLEsingle/ COLD PSI/ AXLEdual
1669 lbs/ 25 psi / 3077 lbs
1964 lbs/ 30 psi / 3621 lbs
2257 lbs/ 35 psi / 4161 lbs
2548 lbs/ 40 psi / 4697 lbs
2837 lbs/ 45 psi / 5229 lbs
3124 lbs/ 50 psi / 5759 lbs
3410 lbs/ 55 psi / 6286 lbs
3694 lbs/ 60 psi / 6810 lbs/F 3680lbs
3978 lbs/ 65 psi / 7332 lbs/R 6860lbs
4260 lbs/ 70 psi / 7853 lbs
4541 lbs/ 75 psi / 8371 lbs
4822 lbs/ 80 psi / 8888 lbs/referencepressure
5101 lbs/ 85 psi / 9403 lbs
5380 lbs/ 90 psi / 9917 lbs
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Old 11-27-2022, 08:14 AM   #8
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Thanks for the list. That is a big help. The RV was loaded except but there was no water in the tanks and no passengers so I will have to add the weight of two passengers to the front and water to the back axel. With the chart I can get close instead of just guessing on the psi. Thanks again
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Old 11-27-2022, 11:30 AM   #9
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I have same rv (2 years newer). I run 61 front and 71 rear. It came that way.
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Old 11-27-2022, 02:33 PM   #10
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Because topicstarter gave enaugh, almost complete information, this tirepressure topic can stay below 20 posts. Mostly go above 100.

My made list can be used for every tire with same loadindices AT 80 psi.
So Single LI 115/ 2679 lbs AT 80 psi
Duall LI 112/ 2469 lbs AT 80 psi.

And if you have other idea about the reserves, or rather have a list per tire or axle-end, i can fill that in my made spreadsheet for it.

You can determine what comes to the axles by the persons and water, more exact.
Need to know howmuch the gravity point op watertank and persons is behind or in front of the axles, and need to know the wheelbase.

That gravitypoint of a person as sitting in a car, is aproximately at its bellybutton.
I estimate about 4 foot behind the front axle.
So weight is when wheelbase 16 foot, devided 3/4th on front axle and 1/4th on rear axle.
But you can yust measure more exact.

And the watertank you assume with its gravity point right above the rear axle, but is it realy so.
If a bit behind the axle, more weight on rear-axle and lifts up the front a little.. So try to determine that more exact.

If you then give it all here, I can give you a better estimation. But will be shifted more to the rear-axle, I suspect. Long time ago made a spreadsheet for that to, but only in Dutch.

And at last the post above this post.
That its the same RV, does not mean the weights and division over the axles are the same.
Maybe even the tires are different.

Can you at least give me the GAWR's and GVWR.
Also would like to know them from topicstarter.
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Old 11-28-2022, 12:26 PM   #11
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My GVWR is 11030 lbs. / 5003 kg
GAWR: Front 4410 lbs / 2000 kg
Rear 7720 lbs / 3502 kg
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Old 11-28-2022, 03:34 PM   #12
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Quote:
Originally Posted by Mmspring View Post
My GVWR is 11030 lbs. / 5003 kg
GAWR: Front 4410 lbs / 2000 kg
Rear 7720 lbs / 3502 kg
I think rear originally 3500kg, and with a few too and fro conversions it became these unrounded values.

When I calculate the pressure for the GAWR front with the in US used official formula for LT tires, it comes to 60.57psi, rounded to your given 61 psi. So I thought, he thats how they came to it.
But then I calculated for rear the same way, and it came to 56.27 psi so 57 psi. So I give up.
And mind that no reserve build in for things like, unequal weight R/L on the axle, wich always is, and pressure loss in time, inacurate pressure reading, etcetera.

Now Near Denvers GAWR's, so we can see if his RV is exactly the same. Most likely not.

In my list GAWR' come to 75 psi front and 70psi rear.
And this is with maximum reserves.
Chanched the list to steps of 1 psi, yust because it can. Do with it what you want, you cant measure it that acurate with the average gauge.
Axle single/ cold psi/ Axle duall / using 90% both
2316 lbs/ 36 psi / 4269 lbs
2374 lbs/ 37 psi / 4376 lbs
2432 lbs/ 38 psi / 4483 lbs
2490 lbs/ 39 psi / 4590 lbs
2548 lbs/ 40 psi / 4697 lbs
2606 lbs/ 41 psi / 4804 lbs
2664 lbs/ 42 psi / 4910 lbs
2721 lbs/ 43 psi / 5017 lbs
2779 lbs/ 44 psi / 5123 lbs
2837 lbs/ 45 psi / 5229 lbs
2894 lbs/ 46 psi / 5335 lbs
2952 lbs/ 47 psi / 5441 lbs
3009 lbs/ 48 psi / 5547 lbs
3067 lbs/ 49 psi / 5653 lbs
3124 lbs/ 50 psi / 5759 lbs
3181 lbs/ 51 psi / 5864 lbs
3239 lbs/ 52 psi / 5970 lbs
3296 lbs/ 53 psi / 6075 lbs
3353 lbs/ 54 psi / 6181 lbs
3410 lbs/ 55 psi / 6286 lbs
3467 lbs/ 56 psi / 6391 lbs
3524 lbs/ 57 psi / 6496 lbs
3581 lbs/ 58 psi / 6601 lbs
3638 lbs/ 59 psi / 6705 lbs
3694 lbs/ 60 psi / 6810 lbs
3751 lbs/ 61 psi / 6915 lbs
3808 lbs/ 62 psi / 7019 lbs
3865 lbs/ 63 psi / 7124 lbs
3921 lbs/ 64 psi / 7228 lbs
3978 lbs/ 65 psi / 7332 lbs
4034 lbs/ 66 psi / 7437 lbs
4091 lbs/ 67 psi / 7541 lbs
4147 lbs/ 68 psi / 7645 lbs
4204 lbs/ 69 psi / 7749 lbs
4260 lbs/ 70 psi / 7853 lbs
4316 lbs/ 71 psi / 7957 lbs
4373 lbs/ 72 psi / 8060 lbs
4429 lbs/ 73 psi / 8164 lbs
4485 lbs/ 74 psi / 8268 lbs
4541 lbs/ 75 psi / 8371 lbs
4598 lbs/ 76 psi / 8475 lbs
4654 lbs/ 77 psi / 8578 lbs
4710 lbs/ 78 psi / 8681 lbs
4766 lbs/ 79 psi / 8785 lbs
4822 lbs/ 80 psi / 8888 lbs
4878 lbs/ 81 psi / 8991 lbs
4934 lbs/ 82 psi / 9094 lbs
4989 lbs/ 83 psi / 9197 lbs
5045 lbs/ 84 psi / 9300 lbs
5101 lbs/ 85 psi / 9403 lbs
5157 lbs/ 86 psi / 9506 lbs
5213 lbs/ 87 psi / 9609 lbs
5268 lbs/ 88 psi / 9711 lbs
5324 lbs/ 89 psi / 9814 lbs
5380 lbs/ 90 psi / 9917 lbs
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Old 11-28-2022, 06:27 PM   #13
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With the added passenger weight I will probably go with 65 psi front and back. I would rather be a little over inflated than under inflated. And like you said the gauges are not that accurate and I am not building a watch! I just want to be close on the pressure and not guessing.
Thanks for the response and all of the work you put into the charts.
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