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MPG in the rain.

April 15, 2013, 06:32:02 am

Well I drove 700 miles on Saturday, from VA to 30 mile short in the MS line on I 20. I averaged 7.6 mpg and I was going about 65 most of the way. Then Sunday I drove the rest of the way to Nac and avg about the same speed or a bit lower. No real traffic but heavy rain. Now my mpg was about 7.1 for 490 miles. Odd that I have done this before and gotten the 7.6 but this time I have to conclude either th fuel had less energy or it took more energy to drive thru the rain. Has anyone else noticed a difference in the rain?

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Re: MPG in the rain.

Reply #1 – April 15, 2013, 06:57:16 am

John. As I see it, two issues are ging on,
1-Rolling in water takes more energy than a dry road, like a concrete road will always give you better mileage than the asphault road, With asphault, you always have a wave infront of the tire your climbing over, the warmer, the more wave. 
Am expecting some flak on this one, Neal ?

2-More power from moist damp air than hot dry air.

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Reply #2 – April 15, 2013, 09:36:47 am

The "little hill" we're climbing on asphalt is so infantesimal (sp) that it couldn't figure into the discussion on a 490 mile trip. I just take the total fuel in and the total miles out...9.2 for the lift of the thing. If we're going to take the road surface into account then we need to know the humidity, the temperature, the temp of the fuel, the altitude, the number of hills or over/under passes, etc.etc,etc. Only then can we begin to figure the difference on so few miles. What's the difference, we're going to put the fuel in and drive the miles and enjoy the coaches anyway!

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Reply #3 – April 15, 2013, 10:15:01 am

Tire life varies from state to state. They all use different ingredients and depending on how much crushed lava is mixed in along with other materials drastically effects tire life. Probably shorter tire life goes includes less fuel mileage. I looked at a map of the United States with state to state tire life expectancy but can't find it now. I think Colorado was one of the worst.

With a lot of mom and pop paving companies, I can imagine the asphalt mix could even change from county to county in the same state.

In hot weather, you sure would be pushing a wave with asphalt.

Pierce

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Reply #4 – April 15, 2013, 10:44:11 am

I wonder? Rain=wet tires=cooler tires=slightly lower air pressure in tires=slightly more resistance to rolling=lower MPG???

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Reply #5 – April 15, 2013, 10:49:08 am

I find that wind direction has more influence than anything else on mileage.

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Reply #6 – April 15, 2013, 11:15:25 am

Wind direction along with speed are big factors. 65 mph into a 10 mph headwind is the same as driving 75.

Our fuel mileage (measured in the tank, vehicle level) goes from 5 to 12 mpg, depending on the terrain.

Tire pressure also makes a big difference.

Pierce

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Reply #7 – April 15, 2013, 11:50:03 am

Was a side wind most of the day.  Not too heavy but thought it was odd.  I guess it coukd. Have been quartering but that was  a Big difference. I have hit strong headwinds that brought me down to three mpg before.  Thisis the first time rain did it. 

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Reply #8 – April 15, 2013, 12:47:52 pm

also depends on which way the gravel in aspalt is facing. Just like golf, if the grain is against you it slows down the ball and you need to hit it harder!!!
 Large contractors always make the gravel lie flat so it makes a smooth surface.
John H

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