question on air in tires

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fair winds

question on air in tires

Post by fair winds »

Hi. I've just bought some new Firestone Transforce tires for my BF and they ride quite well. The Michelins that came with it in 2010 when I bought it were 6.5 years old this year, so it was in name of precaution that I put on new Firestone Transforce DOT dated the last month in 2013(the newest I could find), which I think I read about on this forum and have good reputation.
My question comes from the tire tech telling me that I shouldn't look at the 80 lb "suggested" on the tire itself but on the pounds listed on the door sticker of my BF. Do I run the usual 65 in front/70 in back which I used for the Michelins and is suggested on my door sticker or should I put 80 in back and maybe 75 in front?
Any information would be greatly appreciated.
I probably met some of you all at the rally in Seffner last March. If so, greetings!
Donnis Thompson
2010 BF 27' RSB

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shilohdad
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Post by shilohdad »

Tire inflation depends on the weight on the axle and whether the axle has single tires or dual tires. Here is a link to a post where you can download the tire inflation graph for Michelin tires, but is appropriate for any load range E tire for Born Free coaches: http://www.bornfreervclub.org/bulletin_ ... .php?t=394

Of course, this means you have to get your coach weighed. Most truck stops (Pilot, Flying J, TA, etc.) have scales where you can get weighed for a modest fee, giving you individual axle weights. Make sure you have your coach loaded as you will be when traveling, with all your gear, full tanks of gasoline and propane, as well as water if you will be traveling with water in the tank.

Having said that, nearly all coaches are heavy enough on the back axle to require 75 to 80 psi in the rear tires.
Joe and Lucinda
Tonto, Meadow and Shadow, the papillons
Shiloh and Morpho at Rainbow Bridge
2017 Spirit
Formerly 2006 24RB
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whemme
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Post by whemme »

Donnis,

The tire inflation graph contained in the website link noted by Joe in his post above applies to all LT225/75R16 load range E tires no matter which brands as a DOT regulation.

As a result of weighing my 2002 Born Free 26' RSB coach in down the road running condition with fuel, LP and fresh water tanks full, I run 60 psi in my front tires and 75 psi in the rear tires. After you weigh each of the four corners of your coach, your recommended inflation pressures may be different.
Bill Hemme - Spencer, Iowa
E-mail: whemme@earthlink.net
2002 Born Free (Ford E-450 V10) 26' RSB
2016 VW Golf GTI - toad
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shilohdad
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Post by shilohdad »

Bill Hemme mentioned getting all four corners weighed. Well, how do you do that? The Recreation Vehicle Safety & Education Foundation can do that. Their web site is http://rvsafety.com. Walter Cannon, the Executive Director of RVSEF often attends FMCA conventions or Good Sam rallies doing 4-corner weighings for a reasonable price. He also can do this from his home base of Merritt Island, FL, near Cape Canaveral, which is where we had our coach weighed.

We found that we pack rats run our coach at maximum capacity on the back axle, so Walter recommended 80 psi on our rear tires (we were well balanced side-to-side). We could lower our fronts from 65 psi to 60, or even 55 psi, to give us a better ride.

If you can attend a rally where Walter is doing weighings, or are ever on the central Atlantic coast of Florida, we highly recommend getting Walter to do a 4-corner weighing or your coach and discussing the results with him. He is a fount of knowledge!
Joe and Lucinda
Tonto, Meadow and Shadow, the papillons
Shiloh and Morpho at Rainbow Bridge
2017 Spirit
Formerly 2006 24RB
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bcope01
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Post by bcope01 »

I have never weighed my coach and likely never will. I just run 60-65 in the front and 75-80 in the rear and call it good.

Bill
Barb & Bill
2004 Born Free 22' Built for Two (Sold)
no longer towing a 2008 Smart ForTwo

Escondido, CA
fair winds

Post by fair winds »

Thank you everyone for the replies. I will definitely get the coach weighed and proceed accordingly. It does seem to run well at 60 front/70 rear, but nonetheless, it should be weighed so I know the status.
I think I read somewhere that on these broiling hot Florida roads, tires expand in that heat, so I don't want to get them too full I guess.
Again, thank you all, especially Mr. Hemme, because I'd never heard of Firestone Transforce until I read some of his emails on this forum. Did the research and voila! new tires. :D
Fair winds and following seas, folks.
Donnis
randallrae
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Joined: Wed May 22, 2013 7:30 pm

weight

Post by randallrae »

2012 25' RB 8560 lbs rear 4040 lbs front wet with gear .
2012 25' rb
Ray

Post by Ray »

Just got the transforce on mine - so far really like them - Thanks Bill
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Mike Jean Bandfield
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Post by Mike Jean Bandfield »

With an IR thermometer you can get a quick relative indication of how well your tires are performing. Heat, due to excess flexing in an under-inflated tire, is what causes premature failure. Regardless of what one 'thinks' the proper pressure should be, temperature is a true indicator of the current relative risk of failure due to heat.
Mike & Jean
2005 26' RSS Diesel
Vlamgat
Posts: 152
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Re: question on air in tires

Post by Vlamgat »

Also remember that in these days of 100+ deg ambient temps and road surfaces over 160 deg, the science of LR vs tire pressure become very vague. So it's worthwhile to only carry 80% of the tire load rating and assume that the max inflation increase by roughly 2 psi per 10 deg. That means if you are at 80% of your tire load rating and it's already 85 deg when you check your tire pressure, then you need to have at least 82 psi in a LRE tire. The base reference temp is 68 deg or 20 deg C. The tire manufacturers offer no evidence of their testing that represents integrity in the maximum LR for a given tire. However there is evidence from independent tests done in the heavy truck industry and aerospace that substantiates the recommendation.

BTDT and have the bills to prove the error of my ways.
oliverpsmile
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Re: question on air in tires

Post by oliverpsmile »

Vlamgat wrote:Also remember that in these days of 100+ deg ambient temps and road surfaces over 160 deg, the science of LR vs tire pressure become very vague. So it's worthwhile to only carry 80% of the tire load rating and assume that the max inflation increase by roughly 2 psi per 10 deg. That means if you are at 80% of your tire load rating and it's already 85 deg when you check your tire pressure, then you need to have at least 82 psi in a LRE tire. The base reference temp is 68 deg or 20 deg C. The tire manufacturers offer no evidence of their testing that represents integrity in the maximum LR for a given tire. However there is evidence from independent tests done in the heavy truck industry and aerospace that substantiates the recommendation.
2 psi/10 degree and 68 degree when "cold"- Brilliant!

So with a pressure monitor and known the axles weight, someone can evaluate the status of the running tires.
Oliver P Smile
2005 26ft RSB
Vlamgat
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Re: question on air in tires

Post by Vlamgat »

Yup. I usually see anywhere from 12 to 19 psi increase depending on axle load. The highest level is at 160 surface temps, 100+ ambient and a 7500 lb axle load. I am running LRG 17.5" Bridgestones and towing 10,000 lbs with a 1250 lb hitch weight.
Ray

Re: question on air in tires

Post by Ray »

So 80 psi max cold means 92 to 99 psi hot is ok?
Vlamgat
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Joined: Sun Sep 29, 2013 9:11 pm

Re: question on air in tires

Post by Vlamgat »

Yes depending of course on your load, the ambient air temp and the road temp. The rule of thumb says that your tire temp at 92 psi assuming you started at 80 psi and +/- 70 deg will be about 130 which is not a problem and says that the road temp is something more than 130 and ambient in the high 90s.

My race car BTW typically sees temps above 150 deg and with a light load so you are not stressing the tire.
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whemme
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Re: question on air in tires

Post by whemme »

Here is my experience with my 2002 Born Free 26' RSB coach. Based on weighing all four corners of my coach I run 75 psi initial cold inflation pressures in my rear duals. I have a Pressure Pro tire pressure monitoring system that claims 0.5 psi accuracy. Typically after running 10 miles or more to bring the operating temperature of the tires up and stabilized, my two outside dual tires will then report a pressure of typically 84 psi and the inside duals will typically report 86 psi. The inside tires will always heat up more resulting in the extra 2 psi because the cooling air of running down the road cools the outside tires more than it does the inside tires.

Also, if the sun is bearing down on say the left side of the coach, that will cause the tire pressures on the left side of the coach to increase even more than on the right side.
Bill Hemme - Spencer, Iowa
E-mail: whemme@earthlink.net
2002 Born Free (Ford E-450 V10) 26' RSB
2016 VW Golf GTI - toad
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