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Old 09-21-2007, 05:30 PM   #1
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TV Tire Pressure Question

Newbie question..I have Load E 80 Pound max PSI tires. The manual states you don't get the full Load E rating unless you inflate to 80 PSI.
Any recomendations on how I should go about calculating the right PSI? What are others using????
The guy who owned the tire shop reccomended 65 in the rear and 50 in the front. This did not make a whole lotta sense to me since the whole idea of a WDH is to spit the weight between both axles. Should it be higher in the rear?
Currently have 58 in front and 62 in rear.
Any suggestions?
Thanks
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Old 09-22-2007, 02:42 AM   #2
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Quote:
Originally Posted by JOHND View Post
Newbie question..I have Load E 80 Pound max PSI tires. The manual states you don't get the full Load E rating unless you inflate to 80 PSI.
Any recomendations on how I should go about calculating the right PSI? What are others using????
The guy who owned the tire shop reccomended 65 in the rear and 50 in the front. This did not make a whole lotta sense to me since the whole idea of a WDH is to spit the weight between both axles. Should it be higher in the rear?
Currently have 58 in front and 62 in rear.
Any suggestions?
Thanks
Your question is a good one, and one that drives most people crazy. I've researched this issue several times over the years and, as far as I can find out, the front and rear pressures recommended by the manufacturer of a vehicle are calculated based on the maximum load capacity of the properly loaded vehicle. This assumes you have not installed tires other than the size and load rating your vehicle was originally equipped with. Here is some reading matter on the subject. Much more information can be found by doing a search for "tire load pressure."

http://www.tirerack.com/tires/tiretech/tirespecskey.jsp
http://www.nhtsa.dot.gov/cars/rules/.../brochure.html
http://www.automedia.com/Optimizing/...cr20010801tp/1
http://www.nhtsa.dot.gov/cars/testin...s/brochure.pdf

Consider this: Inflating your tires to their maximum rated (carrying) capacity does nothing at all to increase the load rating of the wheels, the dampening rate of the shocks, the capacity of the springs, or the load rating of the axle or other components. On the other hand, it does affect tread wear patterns, vehicle handling characteristics and ride quality.

Having said all of that, and realizing that I have opened a big can of worms, I must confess that I have been known to add a few extra psi before setting out on a towing expedition.

This is just a stray thought, but I wonder if the manufacturers somehow omitted putting information in our Operator's Manual about increasing the pressure in our tires under certain circumstances. Gosh, I suppose we should all double-check our manuals and, if it exists, report such a glaring omission to Ford, GM, Chrysler, etc.
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Old 09-22-2007, 08:04 AM   #3
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You need to go to the manufact. web site for load info. Then you need to weight each tire by itself to see what weight it is carring and inflate according to the manuf.

This is not rocket science, just hard to find the correct information. What most folks do is just inflate to the max tire pressure and head down the road. Probably won't hurt anything but if you don't need say 80psi and only need 65psi, why go with the higher pressure. As was said above there are other limiting factors in the equation, i.e. axel rating, wheel rating, springs, etc..
Me, I am like most, 80psi in the rear and about 65ish in the front. But if I took the time to weight all four corners and looked at the tables I probably would not need the max in the rears.

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Old 09-22-2007, 12:19 PM   #4
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To add to my previous post, here is a link to Goodyear. Read with care the part on over inflation. http://www.goodyeartires.com/kyt/maintaningATire/

When you think about it, it is easy to understand that as you add more psi to a tire the tire assumes a rounder cross-section, shifting the load to the center of the tire. This, in turn, means that tread is not making full (read flat) contact with the road. Why in the world would you want to do that?
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Old 07-18-2010, 02:28 PM   #5
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Quote:
Originally Posted by dimurrrw View Post
Your question is a good one, and one that drives most people crazy. I've researched this issue several times over the years and, as far as I can find out, the front and rear pressures recommended by the manufacturer of a vehicle are calculated based on the maximum load capacity of the properly loaded vehicle. This assumes you have not installed tires other than the size and load rating your vehicle was originally equipped with. Here is some reading matter on the subject. Much more information can be found by doing a search for "tire load pressure."
Good info & links, dimurrrw--and you are right about it driving me crazy. We just stepped up to a new TT, and I'll have to pay a bit more attention to weights & such.

Here's how I arrived at simply following the recommended tire pressure listed on the door jamb of my truck. It says:

GVWR 6522 LB
GAWR FR 3577 LB WITH P265/70R18 TIRES 18x8.0 RIMS AT 35 PSI COLD SINGLE
GAWR RR 3800 LB WITH P265/70R18 TIRES 18x8.0 RIMS AT 35 PSI COLD SINGLE

So the total load on the rear axle can't exceed 3800 pounds. Even though my tires are marked as having a total load capacity of 2601 pounds each at 44 PSI, it seems pointless to run them that high as it will not provide an increase to the manfuacturer's rated capacity for the axle.
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Old 07-18-2010, 03:13 PM   #6
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Originally Posted by dimurrrw View Post
To add to my previous post, here is a link to Goodyear. Read with care the part on over inflation. Goodyear Tires | Know Your Tires | Maintaining a Tire

When you think about it, it is easy to understand that as you add more psi to a tire the tire assumes a rounder cross-section, shifting the load to the center of the tire. This, in turn, means that tread is not making full (read flat) contact with the road. Why in the world would you want to do that?
That was my logic (on another forum) in questioning why someone would want to run the tires @ the max' pressure as per door label & sidewall even if the truck was unloaded. I asked, "Isn't that considered overinflation?" The next poster said, "It's overinflation if you exceed the sidewall psi."

Whatever.
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Old 07-18-2010, 04:02 PM   #7
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Are the load range E tires stock? If not then you can't go by the sticker on the door jamb. I was not aware that Jeep put load range E tires on any of their vehicles (I sure wished they would have) as they are way too stiff for a good ride on cars that don't usually see heavy duty hauling.

I would go with the data put forth by the tire manufacturer not Jeep if the tires are not stock.
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Old 07-19-2010, 09:11 AM   #8
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People should always go by what the manufacturer states for recommended pressures on the door. Case in example my Ram 2500 states 60f/70r for any kind of load and 60f/45r light load which is 2 people in the truck and no load of any kind. If you lower the front tire pressure on a HD ram all you are doing is inviting the famous Death Wobble. The service manager at the dealership I go to told me 80% of the death wobble cases are caused by people underinflating the front tires to try and make these things ride better. So I have my tires at 60f/70r all the time and live with getting my teeth rattled at every railway crossing. I would never run a tire at the tire manufacturers max inflation, they should be run per the vehicle manufacturers recommendation regardless of the load range of the tire (assuming you are upgrading ie lr C to lr E and not the other way) because as has been stated it doesn't matter what you do to a vehicle you cannot change the GVWR, GCWR and tow ratings that a vehicle left the factory with and those rating are with the tires the manufaturer recommends on the placard. That is not to say you cannot upgrade the tires to say Load Range E just don't expect anything other than a rougher ride and a higher margin of safety. Case in example is the people who think they will save a few thousand dollars and buy a 1500 Megacab Dodge instead of a 2500 Megacab, they think by changing the springs and a couple other things they will have a 2500 and in reality they do but in the laws eyes they still only have a 1/2 ton and get in an accident and see what happens if it is determined the TV had anything to do with it.
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Old 07-19-2010, 02:25 PM   #9
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Quote:
Originally Posted by dimurrrw View Post
To add to my previous post, here is a link to Goodyear. Read with care the part on over inflation. Goodyear Tires | Know Your Tires | Maintaining a Tire

When you think about it, it is easy to understand that as you add more psi to a tire the tire assumes a rounder cross-section, shifting the load to the center of the tire. This, in turn, means that tread is not making full (read flat) contact with the road. Why in the world would you want to do that?
This is also a hot topic on another forum I frequent. One fellow suggested that you can put black board chalk across the tread of your tires and go for a drive. It stands to reason that it would assess the "roundness" (or lack of) of the tread. More practical than scientific, but I think it makes sense.

One thing I am certain of, if a tire can withstand higher running psi's it can only be of a higher quality construction.
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