Tire pressure; 8 x 17.5"

[The_Handier_Man1]

From: dave76Chieftain  (Original Message)
Sent: 7/1/2003 12:47 PM

Now that I have my Winnie finally sitting in my driveway, I discovered that the original GVW sticker has faded and I can no longer read the information on it so that I can determine correct tire pressures.  I believe that a 77 M400 chassis has a total GVW of 12,000, but I have no idea how that is distributed between front to rear.  This is a 1978 24' Chieftain on a 77 M400 chassis with a 440.   It has 8x17.5 Load Range E Radial tires (Bridgestone) on it.  Hmm, comes to mind that the wheelbase may also be needed to establish the correct front/rear weight ratio, but I haven't measured it yet.  Anyone have any info they can pass on?

Dave
The project begins (not for the faint hearted )



From: BoatNut
Sent: 7/1/2003 1:21 PM

My personal opinion on tire pressure is too read the side of the tire and apply whatever is the maximum pressure recommended. I believe on that tire (I have some also) the max is 80 PSI. Mine drive fine and handle well @ that pressure.

Chuck (the Boat Nut)



From: beach
Sent: 7/1/2003 5:50 PM

look on the tires



From: chip
Sent: 7/1/2003 6:46 PM

check the rims also. i know in the past there was an issue about the tire rating vs. a particular rim. someone else can probably post the correct info.



From: denison
Sent: 7/1/2003 7:58 PM

My 72 M400s, both of them, have GVWR of 13000 lbs. I run about 5 psi below the tire max on the dualies, about 10 psi below the tire max on the front tires, just because their max pressure is 90 psi, while the back tires have a sidewall max pressure listed as 65. Those back tires are now worn down to the tread wear indicators, after 40k miles, and 12 years. I did change the inner tubes after 6 or 7 years. My front axle is rated at 5000, my back axle rated at 10000. My winnies both weigh about 10000 empty, and I estimate the weight distribution as 2/3rds rear, 1/3 front. This is based on the spring curvature, which is the same on front and rear axles. I believe a fully loaded spring is one whose top leaf is straight by the way. To really know your weight distribution you need to find a truck stop and pay them for a weighing - per axle. denison 



From: dave76Chieftain
Sent: 7/2/2003 8:02 AM

I plan on having it weighed once I get it fit for inspection Denison.  The fronts looked low so I wanted to get them close.  I at least know for my M400 the GVWR is 12000.  Dodge redesignated the M300, M350, M400 to M300, M400 and M500 in 1975 which is why mine is only 12000 vs 13000.  I did see a 72 M300 with a  GVWR rating of 11000 and GAWR of 4500 (F) and 7500 (R) locally.  Guess I will use a ratio estimate based on that until I can get it weighed.  Thanks for the input though.

Oh, another question.  Should the converter battery charge output voltage be getting as high as 16 volts?  That seems way to high to me.  House load voltage is around 12.5 volts on the converter.  I am thinking the charge circuit may have a problem.

Dave



From: elandan2
Sent: 7/2/2003 1:45 PM

Hi Dave,
There is an issue for Budd disc wheels.  Unless the Budd part number is preceeded by an  "R" , then the wheels were not designed for radial tires.  Dodge issued a service bulletin many years ago addressing this problem.  In short,  you can only load the wheels to 2500 lbs. apiece, and a maximum pressure of 75 PSI.  If you exceed that pressure you are risking making  your own "split rim" wheels.  Personally I have found that the Michelin X, Load Range F tire will carry 2500lbs. at 75PSI or less.  There may be other tires out there that will fit the bill, just check the manufacturers web sites for their Load Inflation tables for their tires. Another added bonus for inflating the tires to the pressure required to carry the load in your situation, is a smoother ride, not that these old Winnies ride stiff or anything.  Sorry for the long post but this issue can be dangerous.  Rick



From: denison
Sent: 7/2/2003 2:40 PM

dave76chieftain: I believe the voltage measured at the battery should Not be 16 volts, more like 13.75 to 14.5, but make sure you are measuring it across the battery, not across the wires leading through half a dozen connections and 20 feet away from the battery. A charge voltage of 16 is what I would expect if it werent connected to the battery, or was connected through a small gauge wire - awg 20 or so. That would actually be an rms average of the rectified voltage, like you get with an analog meter. If you read an unloaded battery charger with a peak-reading digital vom it might read over 20 volts.

rick - elandan2. I am going to check my 17 inch wheels, some of which are Budd, some by Kelsey Hayes and another maker, for the part numbers. Do you know where that service bulletin might be found? I dont have any plan to run radials, but if there is a pressure limit on the wheels, I certainly want to observe it. I once tried lowering my tire pressures on one side of the rear axle by 10 psi, to see if they ran much warmer over a couple hundred miles in hot weather. I was just able to tell they were warmer - it wasnt by much. denison



From: BoatNut
Sent: 7/2/2003 3:23 PM

To Dave,
Some of the older converters have what is called poor regulation, as a function of their design. What that means is that with no load they put out 16 volts. As soon as you turn something on they only put out 14 volts or so. The more you load them the less the voltage. That is normal for them. I have one also. Some years ago I went through some cheep florescent lights pretty fast, because of that. However the regular RV florescents seem to do fine with it.

Chuck 



From: elandan2
Sent: 7/3/2003 12:44 AM

Hi Denison,  The service bulletin may still be available at the Dodge dealer.  The problem was with the disc, not split rim wheels.  If you are running bias ply tires on disc wheels,  they are good for what is stamped on the wheel.  I'll keep looking for the service bulletin and if I can find it I will post it. Rick