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10-02-2016, 10:46 PM
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#1
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Senior Member
Join Date: Aug 2012
Posts: 1,076
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Tire question for a tire engineer?
Here's the set up-
You have a TT and C rated tires that are right at capacity load wise
You go to D rated for the extra capacity but you don't need that much load ability so you lower the air down to 55 instead of 65 psi (still above the TT weight/tire buy using the available pressure ratings from a major manufacturer.
Would this lower pressure cause enough flex at the tread/sidewall juncture to cause tread separation and tire failure?
Just thinking of the physics and thoughts from other threads here.
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10-02-2016, 10:59 PM
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#2
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Senior Member
Join Date: Nov 2015
Posts: 26,643
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Not a tire expert but I will give you a real life example.
Truck tires are good for 3195# each at 80 psi
When towing I air them up the rear tires to 80# cause I need the MAX Load Rating
When NOT towing I drop air pressure to 45# cause I don't same weight on them.
Front tires are at 55# all the time due to the less than max load on tires
I typically get 60K before I buy new tires and thread is still good.....I just change them out cause I an anal about tires
MAX Load Rating at MAX Pressure listed on sidewalls of tires is for MAX LOAD
Lower air pressure cna be used as long as it is high enough for the load on tire.
Over loaded/under inflated causes excessive heat...heat destroys tires
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Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
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10-02-2016, 11:09 PM
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#3
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Senior Member
Join Date: Jul 2005
Posts: 1,679
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Check the inflation tables for your tires. As long as you have pressure at or above the level needed for the tire load on your wheels, the sidewalls will not flex too much.
This means you need to know what the tire load is.
Excess pressure above a little margin like 5 psi means your tires are over-inflated which will crown the thread and reduce the tire patch and wear the center of your tires.
Larger tires are a good measure.
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Dale & Mark Bruss
13 Years Full-Timing Now with a 2016 Bounder 33C
40' Travel Supreme winter residence
Lots of RV Information at www.dmbruss.com
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10-03-2016, 07:17 AM
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#4
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Senior Member
Outdoors RV Owners Club
Join Date: Dec 2014
Location: Nowhere, now here. Freedom!
Posts: 4,602
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If they are ST tires, then you should run them at max pressure *especially* if you have a multiple axle trailer. The max pressure helps to prevent the problem you mentioned (flex causing tire failure) and deal with interply shear.
(I am not a tire engineer, but I learned what I know from one. I do hope that one will come in and tell us their opinion, whether that makes me right or wrong)
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ORV 19B Full Timer from '15 to '20, '14 Ram 2500 Diesel and a GSD. Vancouver, WA
de K7NOL 146.52Mhz Safety? (CLICK ME!)
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10-03-2016, 09:51 AM
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#5
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Senior Member
Join Date: Oct 2013
Posts: 191
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A D rated tire inflated to a C rated tire amount (55#) will only support a C rated load.
You're right back where you started with the C rated tire.
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10-03-2016, 10:23 AM
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#6
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Senior Member
Thor Owners Club
Join Date: Jul 2016
Location: Rainier, Or
Posts: 171
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I also am not a tire engineer, but my question is why would you want to? It seems that if a tire is built to a certain criteria that to run it at less than criteria would not be good for the integrity of the tire. After all air is free so why not use it?
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US Navy (69-90) retired
Armstrong World Industries (91-13) retired
Happily married over 45 years
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10-03-2016, 11:28 AM
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#7
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Senior Member
Join Date: Aug 2012
Posts: 1,076
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Its a hypothetical question brought about by many threads here on tires
In addition, lots of talk about STs and their failure and specifically "inter-ply shear" failure
Many threads have mentioned loading tire pressure to load on tire by using pressure load tables from a major tire company.
Granted, very low pressures (1/2 normal) will cause issues but will 15% lower cause the same?
Are STs different than LTs in this respect?
Take 205 70 15 STs and compare to 215 70 15 LTs and you see @50# less weight capacity with LTs but at 47 lbs pressure rather than 65 as in D rated STs.
As a corollary, would a lower pressure LT cause less "pounding" inside the TT (absorb more road shock) than a harder 65 lb ST tire?
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10-03-2016, 11:36 AM
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#8
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Senior Member
Winnebago Owners Club
Join Date: Mar 2014
Posts: 14,885
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IMO if you load a tire to it's max and apply the max pressure you will get a tire patch on the ground and a resultant tire flex.
If you load a tire under it's capacity and inflate it to the recommended pressure you will get the same tire patch on the ground and the same tire flex.
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Gordon and Janet
Tour 42QD/InTech Stacker
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10-03-2016, 11:41 AM
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#9
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Senior Member
Jayco Owners Club
Join Date: Mar 2012
Location: Weatherford, TX
Posts: 975
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Quote:
Originally Posted by joshuajim
A D rated tire inflated to a C rated tire amount (55#) will only support a C rated load.
You're right back where you started with the C rated tire.
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This is the best advice. The air carries the load, not the sidewall. Tandem tires share the load. If one blows the other is instantly overloaded because it's carrying twice what it was. If it's under-inflated, it's even more overloaded.
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Jack and Dee Dee Weatherford, Texas
2014 Ram 2500 Crew Cab 4X4 w/CTD 6.7
2016 Jayco White Hawk 28DSBH Travel Trailer
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10-03-2016, 11:51 AM
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#10
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Senior Member
Outdoors RV Owners Club
Join Date: Dec 2014
Location: Nowhere, now here. Freedom!
Posts: 4,602
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Quote:
Originally Posted by Cliffy
... using the available pressure ratings from a major manufacturer.
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If the table you have is from the same manufacturer that made your tires, use it. If it isn't, who is to blame for not properly inflating that particular tire you are using?
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ORV 19B Full Timer from '15 to '20, '14 Ram 2500 Diesel and a GSD. Vancouver, WA
de K7NOL 146.52Mhz Safety? (CLICK ME!)
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10-03-2016, 06:37 PM
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#11
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Senior Member
Join Date: Feb 2009
Location: Ca
Posts: 1,076
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Thing to remember is the load on all tires change as you go down the road due to bumps, curves, wind shear, etc.
My tires have a max sidewall of 80psi, and thats what they get.
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10-06-2016, 08:26 PM
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#12
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Senior Member
Jayco Owners Club
Join Date: Mar 2012
Location: Weatherford, TX
Posts: 975
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Quote:
Originally Posted by timetogo
Thing to remember is the load on all tires change as you go down the road due to bumps, curves, wind shear, etc.
My tires have a max sidewall of 80psi, and thats what they get.
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More good advise!
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Jack and Dee Dee Weatherford, Texas
2014 Ram 2500 Crew Cab 4X4 w/CTD 6.7
2016 Jayco White Hawk 28DSBH Travel Trailer
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10-07-2016, 09:05 PM
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#13
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Senior Member
Join Date: Sep 2009
Posts: 1,536
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The tire expert is your tire manufacturer. ST tires are designed to be operated at maximum sidewall pressures. They run cooled and with less stress. There is no mileage warranty to worry about and their life expectancy is somewhere between 3-5 years.
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10-08-2016, 09:18 AM
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#14
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Senior Member
Winnebago Owners Club
Join Date: Mar 2014
Posts: 14,885
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__________________
Gordon and Janet
Tour 42QD/InTech Stacker
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