Fuel Mileage

[travelite]

JohnKlopp,

Those are great numbers. Any idea what final drive ratio you're running?

[GDeen]

Whisky Tango Foxtrot John?

How do you get mileage up in that range? Need you to come tune my fuel system or give me driving lessons.

[Jon Wehrenberg]

John has used his heat transfer engineering skills to create a negative pressure area in the front of the bus, and when combined with the positive pressure area he has set up in the rear (he takes air from the front and puts it in the back) it is the equivalent of always driving with a tailwind.

That plus he has a coach that weighs less than 20,000 pounds, combined with not towing, and using his generator to power the electric motors on the front axle wheels and he can get such god mileage. He learned the generator fuel does not get shown in the ProDriver so he now has the ability to show such good mileage.

There may be another explaination, but that's the best I can come up with.

[rahangman]

Paul, good reply, but it jogged my mind. I am thinking, how much of this crazy world can we blame on something such as you said, "I dont mind parting with that much cash, just didin't think they should make it difficult for me to do so". I think it is a core problem with the USA today

[johnklopp]

It’s simply physics!

Many things go into mileage as have been discussed on the forum. Driving style, coach weight, weight of a toad, headwinds, terrain etc. all contribute to a varying degree.

Two things are not as obvious but are some of the largest contributors to low mileage. Air resistance requires large amounts power to push the coach thru the air. Jon was correct indicating a low pressure area in the front of the coach would be beneficial. Unfortunately my experiments with creating a vortex in front of the coach have been unsuccessful.

The last item is tire rolling resistance. Tire rolling resistance is simply the force a tire must overcome to roll. A coach’s engine has to burn fuel to overcome this force to move. The less rolling resistance, the less fuel an engine burns to make the tire go round and round.

Reducing rolling resistance is a goal for those who want to achieve an improvement in fuel efficiency.

Once the tire is rolling, the rubber sidewall in a tire exhibits flex sometimes called hysteresis. Hysteresis is the main cause of energy loss associated with rolling resistance, and is attributed to the elastic deformation of the rubber.

As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy as heat rejection. That’s precisely why you can measure your tire temperatures at rest stops and quickly see if any of them are underinflated.

Load: As the load decreases, so does rolling resistance (near proportional). As load decreases, so will the deformation/deflection of the tire; less deformation means less energy loss.

Inflation Pressure: As pressure increases, rolling resistance decreases. This is attributed to less deformation and bending in the tire due to the increase in pneumatic stiffness. However, the relationship is not linear. In the typical operating inflation pressure range, an increase of 2 psi should improve rolling resistance approximately 1.5%-2%. Conversely, low inflation will cause excessive deformation and increased rolling resistance.

The bottom line in my opinion is tire inflation pressure contributed greatly toward the mileage I was able to achieve. Before departing Nashville, all of my tires were inflated to 110 PSI cold. Before departing POG 10, I increased the inflation pressure to 115 PSI cold.
Obviously the great ride our coaches are known for was compromised.

Perhaps by POG 11 I will have had time to build a clip on plastic nose cone to not only protect the bus but reduce aerodynamic drag.

[travelite]

John, that's great info, thanks. Given how exceptional your fuel mileage numbers are, you have to pardon a bit of skepticism. So here goes... Have you confirmed the accuracy of your DDEC mpg figures the old fashion way - miles driven as read from the odometer divided by gallons pumped at the filling station? Do you know what you final drive ratio is?

[travelite]

I'm sure most folks have seen the attached Caterpillar document on RV fuel mileage. If not, enjoy!

[Jon Wehrenberg]

David,

I cannot verify the accuracy of other ProDriver mileage figures but I can say mine is quite accurate. I know the miles per hour it displays when I set the cruise control is accurate when compared to my speedometer (which I calibrated using 10 miles worth of mile markers when I installed the speedometer) and my GPS. I have records of every gallon of fuel I ever pumped into my coaches for 21 years so I can pick any time period and pull out generator usage (based on the generator service logs) but not webasto usage. As near as i can determine ProDriver is really accurate.

I do not reset my ProDriver except for my service reminder periods of 5000 miles, and during those periods, the number seem to jive. I can say with conviction that measuring fuel purchases for a tank or two is a waste of time because my ability to fill to the same tank level is almost impossible. I have pumped at the slowest setting on the truck pumps and had the pump click off and had the normal filler fuel puke. I have then gone to an automobile diesel pump and gotten as much as 30 gallons more into the tank. So I calculate my mileages using a year or two of refueling figures with an estimate of generator usage pulled out of the fuel amounts.

[tskrodzki]

Wish the was the case in MA. High octane gas is 3.83 with Diesel at 4.23 recently dropped to 4.12 but the upcoming holiday is driving the price back up

[Kenneth Brewer]

John has used his heat transfer engineering skills to create a negative pressure area in the front of the bus, and when combined with the positive pressure area he has set up in the rear (he takes air from the front and puts it in the back) it is the equivalent of always driving with a tailwind.

That plus he has a coach that weighs less than 20,000 pounds, combined with not towing, and using his generator to power the electric motors on the front axle wheels and he can get such god mileage. He learned the generator fuel does not get shown in the ProDriver so he now has the ability to show such good mileage.

There may be another explaination, but that's the best I can come up with.

Sounds about right.