Hello all,

Two part question.

1) I was trying to figure out the power to weight ratio using the GVW or I guess also known as the GVWR of the Barth's with all the different engines. I was trying to figure performance differences between the years of the same model and also how the different models differ in power.

I used as an example a Caterpillar 3116 with 250 HP/650 lb-ft of torque in a Regency on a Gillig Chassis with a GVWR of 29,640. The Gillig Chassis was rated with higher GVWR with 3890 lbs of more gross weight than the Spartan chassis from what sky posted a few years back.

I was reading on another forum ( forgive me Bill N.Y and Dave for I have sinned by going to another forum ) and a person on there talks about using the 100lbs/HP ratio for a start to figure out if you motor coach has enough power.

http://forums.trailerlifedirec...57681/print/true.cfm

Since the 3116 CAT has 250 HP ( I have read some say it is 240HP?) then the Regency on a Gillig Chassis with a GVWR of 29,640 should be underpowered if loaded to the max GVWR. Using the formula with the 3116 cat then the GVWR shouldn't go over about 25,000 to still have good performance?   

I think the Spartan chassis has a GVWR of about 25,800 as per sky's post from a few years ago? So a Regency with a 3116 CAT a Gillig chassis could be underpowered because the Gillig chassis can carry more weight. But on the Spartan chassis the power to weight ratio is better, so to say, because it can carry less weight. What I take away from this, if true, it is better for Gillig chassis to have a 300+ HP engine than a 250HP engine.

Part 2

2) I learned from one of Bill N.Y. posts that the maximum weight is actually determined by the tires load capacity which for the  single 12R 22.5 ( can carry about 5250 lbs at 85 psi) is more than the 11R 22.5. ( about 4900 at 85 psi)  (please verify this... I am no expert).

Dual tire load limits are set at a lower rating than single tires is that tires paired up as duals do not always contact the road surface equally. For doubles 12R 22.5 per tire ( can carry about 5000 lbs at 85 psi) is more than the 11R 22.5. ( about 4700 at 85 psi) (please verify this... I am no expert).

I think that works out a tire load of about 10,000 lbs up front and 20,000 lbs ont the back. 

I have read that 295/75R 22.5 low profile can carry slighly more weight than the 11R 22.5 as per Goodyear charts?

A gallon of diesel fuel weighs about 7.3 lbs, I think the GVWR includes fuel. 1992 Regency holds 147 gallons of diesel equals 1073 lbs. of fuel plus generator fuel needs to be added plus water storage ( water 8.35 lbs a gallon) and waste water storage.

Fuel Capacity: 147 gallons = 1073 lbs
LPG: 165 lb (approx 42 gal. 4.23 lbs a gallon) = 177 lbs. 
Potable water: approx 80 gallons = 668 lbs.
Black water: approx 60 gallon = 501 lbs.
Gray water: approx 40 gallons = 334 lbs.

Total liquid capacity weight =   About 2753 lbs 

That is over a ton (2240 lbs) of liquid capacity, worst case

In any case I was wondering what the real world experience to see if this formula of 100 lbs/HP actually works to see if the motor coach has enough power?

Only thing I can't find is the gross weight of an empty 1990's Barth Regency with a Gillig chassis and a Spartan chassis.

Thanks,

Corco

GVW is the maximum the coach should weigh to remain within design specs. Empty weights will be all over the place, depending on the engine, transmission, features like dual-pane windows, appliances, and accessories.

Your calculation of liquid load has an error: There should be no case where fresh water and black and grey water would be topped off.

HP/weight ratio can be misleading, in that acceleration/hill climbing depends more on torque. This can be affected by the engine's torque output, transmission ratios, and differential ratio.

Rusty,

Thank you for the information. I don't know how I would learn right from wrong without the help of the members of this forum. Not easy learning all this stuff.

Don't know where you got the weight for 11R22.5, but they are usually rated at 6600 lbs for single and somewhat less for dual. This is for load range G. 12R is somewhat higher. Load range H is about 7000 per tire. 11R22.5 is a standard truck tire size. Many highway buses used 12R22.5 for a better ride.

Federal DOT is 600 pounds of load per 1 inch of tire, therefore 11R is 6600lbs. Our 8R19.5 would be 4800lbs.

GVW is far more than tires. Based on the tire size a P30 GM chassis could carry 9000 pounds on the front and 1600 pounds on the rear or a total of 25,000 pounds. Don't try it.

Thanks Gary for the info.

I found this document called "RV Tire Guide" provided by Michelin at the following link. I found it helpful for a newbie like me.

http://www.michelinrvtires.com...ference-material.jsp

I found this in the Michelin Advantage discount program for FMCA members in the January 2012 Family Motor Coaching magizine on page 112 or at http://www.fmcmagazine.com/bac...ember-benefits-guide.

They guide the reader to www.michelinrvtires.com to locate a michelin dealer near them.