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Old 07-28-2015, 08:04 AM   #1
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Front Tire Pressure

Question for you guys. Or maybe more like postulating.

Having ideal tire pressures set based on weight is usually the recommended way, if you are lucky enough to either have your axle weights or even better your corner weights. Having the rear tires set at the max 80psi is usually what is needed on a Greyhawk, but the front?

Has anybody ever had their front axle weighted enough (or front corner) to warrant the placard 75psi? Having more patch contact w/ the ground on the steer axle would seem to be a no-brainer. Are most of you riding 75 in the front? Or are some of you riding 70?

My corner weights in the front off the factory line w/ full propane and gas were:

Lft Front: 1938
Rt Front: 2142

Per Michelin I could get away w/ 60PSI in the front !! Now, once I put my stuff in there and some bodies in the cab, it won't be the same. Not even counting unloading the front axle by gear stuffed behind the rear axle. That's why its so important to weigh if you don't have much OCCC.

But - has anybody ever really gone up to the full 5k allowed on the front? Seems to me it'd be really REALLY hard to do. Ergo - do most of you ride w/ less air in the front?
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Old 07-28-2015, 08:06 AM   #2
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I always did. The scale and tire pressure charts give you the best ride.
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Old 07-28-2015, 08:07 AM   #3
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You always went up to 5k on your front?
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Old 07-28-2015, 09:31 AM   #4
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Last time I weighed my MV they were 2450L and 2250R front. That's close enough to max weight that I just keep the tires at 75 psi as stated on the door post. The rig drives and handles really good and I don't really feel like messing around with inflating/deflatin so I just leave them alone. Underway pressures go up to around 90 psi underway so a few pounds less won't make that much difference.
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Old 07-28-2015, 09:32 AM   #5
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Wow - ok good to know.
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Old 07-28-2015, 10:44 AM   #6
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I stick with 75 psi on front and 80 psi on rear. Got 13.1 mpg last trip !
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Old 07-28-2015, 02:26 PM   #7
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I once introduced the motorhome-standard for that.
And that is that rear axle mostly gets close or even a bit over GAWR.
Then substract GAWR rear from GVWR to get the weight on the front axle, to calculate the presure for.
So for instance GAWR front your 5000 lbs and GAWR rear 9000 lbs, and GVWR of 13000 lbs the expected weight on front 13000=9000=4000 lbs on front. Your axle is 4080 lbs , so search for the GVWR and GAWR's and do this calculation to see .

The the highest load on the side is what you need for determining the pressure.
Your weightdivision L/R is 47.5/52.5% wich is pretty comon for motorhomes.
But you can probaly even add a reserve for your rightfront and still leftfront above the bumping border I determined at if real weight is 85% of weight the pressure is calculated for.

Lets do this calc for your frontaxle.
the 47.5% then is 85 % of the weight the pressure is calculated for.
Then 47.5/0.85=55,9% for wich you calculate the pressure .
Then your rightfront of 52.5% is 52.5/55.9= 93.9% of the weight the pressure is calculated for.
I call that percentage the Loadpercentage shortened L%.

So in lbs 1938/0,85=2280 lbs for wich you best calculate the pressure with my formula , or search back the loadcapacity in list of european tyre-maker.
Best not use American lists.
This still leaves a reserve for right Front of 138 lbs before tire gets overloaded and so in damage sone of above 100% L%
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Old 07-28-2015, 02:47 PM   #8
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Quote:
Originally Posted by Jopopsy View Post
You always went up to 5k on your front?
No response was to your last question about "less air pressure"...
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Old 07-28-2015, 05:09 PM   #9
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The chart on my driver side door frame says. "70 psi" front and "80 psi" rear. And that's how I have been running it.

/rick
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Old 07-28-2015, 06:52 PM   #10
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Quote:
Originally Posted by adaigle View Post
I stick with 75 psi on front and 80 psi on rear. Got 13.1 mpg last trip !
13 mpg on a Greyhawk!?! Mine averages 8.5 mpg running about 62 mph. You must have had a really long downhill stretch, with a nice tailwind, too.
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