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Old 08-24-2015, 11:14 AM   #1
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Tire Pressures

I appologize if I am not stating the problem clearly enough.

I am running max pressure in all six tires..and I figure that is probably too much.

I know I can go as low as 40psi w/o fear of the bead letting loose. i thinkI am running 110 at the moment.

We have a local scale and I was thinking of having my front and rear axle weighed separately plus the truck as a whole. I do know my pin weight.

Is there a formula that can used to figure out approximately what psi you should be using ? I know I can do the let 15 pounds out and run it sort of situation but I was thinking there would be a more mathematical way of approaching this..

Lastly, is there any advantage of putting steer tires on the rear ?

Thanks
grassy
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Old 08-24-2015, 11:21 AM   #2
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You are correct in not running at sidewall pressure. It will jar your fillings out. Google the tire manufacturer and you will find a load chart. Weight the coach at the load you almost always carry.
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Old 08-24-2015, 02:21 PM   #3
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Thank you...discovered this when we went though a particularly bad section of highway. First I though front air bags but this route seems more logical
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Old 08-24-2015, 02:24 PM   #4
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what brand and model tires do you have?

And let us know what your weights are. I can look up the PSI loading for you.
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Old 08-24-2015, 02:32 PM   #5
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Thank you.

I am hoping to take the truck to the scales tomorrow.

grassy..
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Old 08-25-2015, 02:14 PM   #6
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The truck is a fl 60 Sport Chassis. It weighed in lighter than I thought.

Round numbers:

Front axle - 6K
Rear axle (dually) - 7900K
Total - - 13.9K

Tires Front - Goodyear G149 - 245/75R 22.5 - inflated to almost 100 psi
Tires Rear - Goodyear G159 retreds - 245/75R 22.5 - inflated to 110 psi.

Pin weight is @ 2K.. I have a McCall 6 airbag (with shocks) 5th hitch. Rear suspension air / springs. Air ride cab and seats as well. Have been thinking about air in front but want to play with the tire pressures first. We have some rough roads around here

When we start driving long distances, I think it would be a good idea to replace all rubber with all steer tires. The PO hadn't balanced the front..I did.. almost 10oz weight overall. Smoother now but I am about 50% now..and visually, still look good..no cracking, etc... I have also thought about moving to a slightly larger tire...but not sure of the efficacy in that..would like to lower the rpm in crusing speed but also give me a bit higher running speed if needed..

I am guessing that I should have a lot of flexibility here since I am no where my max hauling / weight capability.

Any / all help is appreciated.

Thanks
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Old 08-26-2015, 10:24 PM   #7
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Your tires at 75 psi can carry 3600lbs each. I would drop the fronts.
The rears figuring 2k pin puts you at 9900 lbs. For duals at 70 you are good for 3100lbs each. I would drop those to 70 aswell.
At 100 psi you are rated ~4200 each. Way to hard.
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Old 08-27-2015, 06:19 AM   #8
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Thank you ! X2 on the way too hard comment.

Only a couple of runs left for this year. Will be changing tire pressure pronto.

Grassy
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Old 09-21-2015, 06:55 PM   #9
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I dropped the rears to 70 and my fronts to 75 but it felt a bit squiggly so I upped all to 80 and the ride is perfect...thinking I don't really need air bags in the front..

I plan on replacing my tires in a year or 2 so I went looking for load ratings and there isn't much variance with this size tire...

Thanks all...

grassy
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