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Old 07-28-2015, 07:03 PM   #11
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Originally Posted by NC Roamer View Post
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.
Exactly what I get NC and that's after 6000 cross country miles. Now that we've hijacked the thread...
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Old 07-28-2015, 07:09 PM   #12
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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%
Huh!? Me thinks getting the actual weights of the loaded rig and adjusting the tires according to the tire pressure tables is a tad easier.
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Old 07-29-2015, 02:54 PM   #13
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@ hoppers4

Looking in pressure/loadcapacity lists of American make, gives higher loadcapacity for the pressure then in European lists, and if you use the formula that to my conclusion comes closest to the ever to be constructed ideal formula, even lower loadcapacity for the same pressure.

So lookin back in lists gives to low pressure advice, with to much deflection so heatproduction.
What I do in my made spreadsheets is calculate the pressure with a formula that is savest and then even add a percentage for maximum reserve , but still acceptable comfort and gripp.
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Old 07-30-2015, 09:20 AM   #14
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I do not run with the AC on. I use cruise on level roads. Make sure I speed up a little before going up hill. Travel at 55 MPH on highway. I try to run between 2000 and 2500 RPM. 70% of time I travel at 2000 RPM, 20% at 2500 RPM and 10% above 2500 RPM. Got 15.1 MPG from Bangor to Bar Harbor, ME. From Bar Harbor to Calais, ME. I got 13.1 MPG because I got stuck behind an accident and idled for 45 minutes had to keep AC on it was really hot !!!
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Old 07-30-2015, 09:25 AM   #15
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55mph probably has a lot to do w/ it. Its wind resistance more than anything that sinks the mileage on these things.
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Old 08-05-2015, 07:11 AM   #16
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Originally Posted by GrayHawk51 View Post
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
Really? I've not yet seen a Greyhawk w/ 70 listed for the front. 5k pounds on the front axle calls for 75. You sure?
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Old 08-05-2015, 10:48 PM   #17
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Jopopsy, just for grins I weighed the rig again today as I was driving by a closed Oregon state weigh station anyway (they leave the display on all the time). My weights today were LF=2450 RF=2350 LR=4550 RR=4450. These weights seem to agree with the door post (75F/80R) and Michelin's weight table. These weights are with half tank of water, half tank of gas, full propane, and both front seats occupied.

Yeah, I know, I'm overweight on the LR by 50 lbs. As far as I'm concerned it's rather difficult to keep these large class Cs at the proper weight even with a judicious packout. And the weight police are really going to be after me when I take my family for a ride.
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Old 08-06-2015, 07:32 AM   #18
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Wow - that's pretty amazing Don. I'm not packing heavy at all but I had so much capacity on my axles off the line - and your's is the same model year.

Glad I asked the question.
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Old 08-06-2015, 09:11 AM   #19
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This weight problem is what kept me from buying a large class C for years. We've had two other MHs, the first one being a short Jayco C on the E450 chassis (I had 2K lbs left over after a full loadout) and a class A on an 18000 lb F53 chassis. I never reached the limits on the class A but was closer than the first Jayco.
At any rate we bought this one because 1) the wife liked it 2) I really like the ride and handling (so much better than either previous rig) 3) the wife liked it 4) it has amenities such as levelers and a large galley.
Soooo, I just have to accept the fact that I'll be pushing into the safety zone of the advertised weight limits. Have fun out there Jopopsy!
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Old 08-06-2015, 09:18 AM   #20
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Originally Posted by hoppers4 View Post
This weight problem is what kept me from buying a large class C for years. We've had two other MHs, the first one being a short Jayco C on the E450 chassis (I had 2K lbs left over after a full loadout) and a class A on an 18000 lb F53 chassis. I never reached the limits on the class A but was closer than the first Jayco.
At any rate we bought this one because 1) the wife liked it 2) I really like the ride and handling (so much better than either previous rig) 3) the wife liked it 4) it has amenities such as levelers and a large galley.
Soooo, I just have to accept the fact that I'll be pushing into the safety zone of the advertised weight limits. Have fun out there Jopopsy!
Hmmm, you mention "the wife liked it" twice.
You are wise beyond your years
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