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Topic: How do you find Min Tire PSI  (Read 503 times) previous topic - next topic

How do you find Min Tire PSI

My FT OEM plate indicates Cold Single 115 PSI and Dual 94 PSI. I think OEM tires were Michelins.
My current tires are Toyo M170, Single 7160 lbs / 125 PSI and Dual 6610 lbs / 125 PSI.
My FT with full fresh water and diesel: Steer Axle = 11100 lbs and Drive Axel = 18900 lbs (total 30000 lbs)
Each single Steer tire needs to carry 5550 lbs and Each dual tire needs to carry 4725 lbs.
Based on these numbers do you think it is safe to have 97-98 PSI for my Steer Axle tires  and 90-91 PSI for my Drive Axle tires?
Thank you,
Al
Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)

Re: How do you find Min Tire PSI

Reply #1 –
Im running the same tires.  Im running 92lbs in the rear and 105 up front.  Im in a 34 ft. coach.  Ive only had it a month but for the 500 miles Ive driven it Ive averaged 7.8 mpg with a full tank of fuel and half a tank of water. 
06 Nimbus 34'
Build #6362

Re: How do you find Min Tire PSI

Reply #2 –
Al - I have Michelin tires and Michelin has charts that show suggested tire pressures for the weight you have on the particular type of Michelin brand tire you are using.  I looked for Toyo load inflation charts and got this link: https://www.toyotires.com/media/1475/rv_inflation_tables.pdf
Looks like they do not specify by each type tire but just have a general guideline.  You may want to search more and they may have it for your specific model Toyo tire.
Hope this helped you.
Safe travels and stay healthy!
Oscar
Oscar & Janet Valent
2023 Coach House 261XLQD
Former 2004 U320 3820 PBBS
Former 2007 Newell Coach #815
2015 Jeep Grand Cherokee Summit

Re: How do you find Min Tire PSI

Reply #3 –
Quote from: propman –

My current tires are Toyo M170, Single 7160 lbs / 125 PSI and Dual 6610 lbs / 125 PSI.


I ran into a gotcha with these toyo tires, even though they are represented as equivalents to Michelin tires originally used.  Min inflation pressure for the 125 psi max lrH M177 is 95 psi.  Not an issue in front but I found my best ride with prior tires at 75 psi on rear.  Here's the chart:

https://www.toyotires.com/media/4425/2021_commerical_loadinflationtables_v8.pdf

While I suspect the pressures were just not included for lower inflations, a call to Toyo was unhelpful in confirming or denying this. 
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS

Re: How do you find Min Tire PSI

Reply #4 –
As I recall. That chart with the two differing load and psi numbers is for the two differing ply ratings. The lower of the two that starts showing loads at 75 is blank at lower pressure because why would one buy the high load rated tire to then only run a light load. Make note of the higher max psi of the second set of numbers that goes to 125 psi where the same size tire above only goes to 120. The lower chart is simply a continuation for the higher load rating of the tire with two more plies inside.

 

Your best bet might be to call Toyo USA with your specific tire model and ask.
Jerry & Nona and Kimeru the cat that thinks she's a dog
1998 36' WTFE U320  #5314 Motorcade #17711
USAF 1975-1995
2019 Subaru Crosstrek 'toad'
2003 Subaru Legacy touring car
jerry Fincher | Flickr

Re: How do you find Min Tire PSI

Reply #5 –
Hi Al, These look like 295/75R22.5.  I don't find load/inflation tables for the Toyo M170 tires.

For Michelins see https://www.rvsafety.com/images/pdf/michelinloadandinflationrvtruck.pdf

If you are only measuring axle wt then it is prudent to assume one side might be heavier than the other by perhaps 5% of the average.  So half of your front axle wt is 5500 lbs + 5% = 5775 lbs. That is 450 lbs difference from one side to the other, probably as much as one might see. Find that load column in the table, greater then the column to the left and less than or equal to the column you are selecting. Take that pressure and add 5 psi for a cushion.

Running your tires under-inflated for the load they are carrying is the most common cause of a tire failure. Running them a bit over-inflated for the load without exceeding the max cold pressure on the tire sidewall won't hurt, ride might be a bit stiffer, mileage may improve slightly.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: How do you find Min Tire PSI

Reply #6 –
Quote from: propman –
My FT OEM plate indicates Cold Single 115 PSI and Dual 94 PSI. I think OEM tires were Michelins.
My current tires are Toyo M170, Single 7160 lbs / 125 PSI and Dual 6610 lbs / 125 PSI.
My FT with full fresh water and diesel: Steer Axle = 11100 lbs and Drive Axel = 18900 lbs (total 30000 lbs)
Each single Steer tire needs to carry 5550 lbs and Each dual tire needs to carry 4725 lbs.
Based on these numbers do you think it is safe to have 97-98 PSI for my Steer Axle tires  and 90-91 PSI for my Drive Axle tires?
Thank you,
Al
Keep in mind that the 6610 lbs for duals is at 125 psi. Lower pressure than that also lowers the maximum weight the tire will carry.

The front axle is the critical one for pressures. Since we are well under the maximum allowable weight for the front axle, the tire dealer suggested 105 psi all the way around with 120 for poor roads or hot weather. The coach rides great at these pressures. Tires are H load rated (146/143 @ 120 psi) and M rated for speed (81 mph).

The ply rating was originally for cotton plies so a 16 ply rating does not really have 16 plys.

Good read for Class 8 tires: https://az184419.vo.msecnd.net/schneider-trucks/PDF/maintenance/TireLoadRangeGvsH.pdf

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)
 

Re: How do you find Min Tire PSI

Reply #7 –
Thank you all. Based on the all the input, for my tires dual 95 & single 100 looks to be safe with +5% increase to the weigh for each tire.
Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)