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Old 05-13-2015, 11:43 AM   #1
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Tire Pressure Question

Is there an "engraved in stone" tire pressure to maintain? I have Toyo tires on my '05 Alpine Coach 40ft FDTS. I have had so many differing opinions on what to inflate the tires to. I now carry 105 all around. Is that close or am I way off? I need some good advice.
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Mike
Reno, Nevada
07 Yukon Toad
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Old 05-13-2015, 11:50 AM   #2
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Mike,

On an RV, the BEST way to determine correct tire pressure:

Weigh each wheel position with the coach loaded as it goes down the road (including full fuel). Using the heavier wheel position on each axle, go to your tire manufacturer's Inflation Table which will tell you the MINIMUM PSI for a given load. Add 5-10 PSI to that minimum as long as you do not exceed what is stamped on the sidewall or wheel specs.

Next best is to weight axles and do as above. But, this ASSUMES perfect left/right weight distribution which is unlikely. Particularly unlikely if you have a galley slide. So, you will need to add more air than axle weight would suggest to account for this.

Next best is to go by the GAWR sticker for your coach which gives the correct pressure if each axle is loaded to its GAWR. Hopefully, that will be sell more than you need. Said another way, it the sticker PSI is the correct PSI, it means you have no Carrying Capacity left/no safety reserve. Unlikely, at least we have quite a lot of capacity left on our 38' between actual and GAWR's.

Brett
2003 Alpine 38'

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Old 05-13-2015, 05:11 PM   #3
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Weighing is the way to go, and you should do this soon, as my fronts require 120psi.
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Old 05-13-2015, 05:18 PM   #4
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Quote:
Originally Posted by wolfe10 View Post
Mike,

On an RV, the BEST way to determine correct tire pressure:

Weigh each wheel position with the coach loaded as it goes down the road (including full fuel). Using the heavier wheel position on each axle, go to your tire manufacturer's Inflation Table which will tell you the MINIMUM PSI for a given load. Add 5-10 PSI to that minimum as long as you do not exceed what is stamped on the sidewall or wheel specs.

Next best is to weight axles and do as above. But, this ASSUMES perfect left/right weight distribution which is unlikely. Particularly unlikely if you have a galley slide. So, you will need to add more air than axle weight would suggest to account for this.

Next best is to go by the GAWR sticker for your coach which gives the correct pressure if each axle is loaded to its GAWR. Hopefully, that will be sell more than you need. Said another way, it the sticker PSI is the correct PSI, it means you have no Carrying Capacity left/no safety reserve. Unlikely, at least we have quite a lot of capacity left on our 38' between actual and GAWR's.

Brett
2003 Alpine 38'

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Hi Brett

On our Magna CC says to run the pressures on the weight sticker and not go by the actual weight. So far that's worked fine for us as the tires run very cool.

Deen
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Old 05-13-2015, 05:31 PM   #5
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Deen,

How close to GAWR are you? At GAWR, both methods end up with the exact same recommendation.

BTW, good seeing you in Tonopah this winter.
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Old 07-02-2016, 02:18 PM   #6
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Toyo says ...

Wrote to Toyo with this question: "Have M122 tires on the front with an axle rating of 12,000 lbs. And duel M627's on the rear with an axle rating 19,000 lbs. What is the correct inflation pressure?" Toyo's response: "Based off of the load information you have provided the recommended cold tire pressures are 110 front and rear axle at 90 PSI for the 295/75R22.5 M122 tire."
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Old 07-02-2016, 02:24 PM   #7
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Wrote to Toyo with this question: "Have M122 tires on the front with an axle rating of 12,000 lbs. And duel M627's on the rear with an axle rating 19,000 lbs. What is the correct inflation pressure?" Toyo's response: "Based off of the load information you have provided the recommended cold tire pressures are 110 front and rear axle at 90 PSI for the 295/75R22.5 M122 tire."
Here is the source Toyo consulted to give you a response.

https://www.toyotires.com/assets/lib...ion_tables.pdf
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Old 07-02-2016, 03:52 PM   #8
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Recommended tire pressure is based on ACTUAL WEIGHT, not GAWR (Gross Axle Weigh Rating).

Hopefully your actual weight will be well under GAWR (meaning you have a safety reserve).

SO, best answer: Weigh individual wheel positions and use the heavier wheel position on each axle to go to your tire manufacturer's inflation chart to determine the MINIMUM PSI for all tires on that axle.

I add a 5 PSI fudge factor so full fuel, water and gear doesn't overload/underinflate the tires.

Said a different way, inflating based on GAWR will very likely have your tires OVERinflated.

Brett
2003 Alpine 38FDDS
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Old 07-02-2016, 05:13 PM   #9
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If you do not weigh 4 corners you are hoping they are not overloaded. "Hoping" is not an acceptable plan. Get your coach weighed so you know what YOU have, not what the manufacturer rolled out the door. Folks have a way of accumulating "stuff" that can cause one corner to be out of whack with its opposite side. Overweight with slightly worn tires is a recipe for disaster. If you ever see a blown tire on a motor coach at highway speeds you will do everything you can to avoid it. The damage to the metal and fiberglass is significant and if there is some wiring running through the area it is not pretty.

Knowing your weighs is important for YOUR safety. Once you have the weights as previously suggested go to the tire manufacturers charts and determine the proper inflation, then add a bit so you do not run under inflated.
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Old 07-03-2016, 01:12 PM   #10
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Dave, you are absolutely correct. Spend a minute on YouTube and see the consequences of a tire failure on a motorhome at highway speeds. THAT will make a believer out of you. Currently using axle weight rating as a baseline for tire inflation until I able to locate a scale in out area.
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Old 07-03-2016, 10:27 PM   #11
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In addition to checking tire inflation prior to every trip, I take a reading immediately after picking up the coach from the shop. Twice I found someone messed with the pressure.
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