Lower Mileage in the Rain?

[JWChessell]

Lately I've frequently been towing a 2-axle enclosed cargo trailer. In February northbound on I-5 between Lodi, CA and Medford, OR the mileage was 10. 528 MPG. In April northbound between the same two points mileage was 10. 548 MPG. All conditions were the same -- 70 PSI in the truck tires, 50 PSI in the trailer tires, about 1,000 lbs of cargo in the bed of the truck, cruise-control set at about 63 MPH, no wind -- EXCEPT: In April the trailer weighed approx 2,000 lbs less, and in April it was raining.



Does anyone know if wet pavement increases rolling resistance?

 

[Nate]

a 0. 020 difference or did you mis type that?

 

[nickleinonen]

10. 5mpg and 10. 5mpg... the 0. 02mpg difference is negligable. fuel can make that difference [different fuel supplier, winter grade fuel]



wet roads decrease rolling resistance

 

[DZink24]

Lower MPG in the rain (especially hard rain). You're pushing H2O. Even more so with tires as big as ours.

 

[mlewis73]

Another thing... you're slipping the tires ever so slightly on wet pavement, even if you don't feel it. Not efficient.

 

[Spooled-up]

I've noticed as much as 1. 0 mpg less in the rain over a tank full on a trip from Cincinnati to Lancaster, PA. It poured the whole first tank I burned, then stopped as I started in on the second tank. I filled up when I got there and sure enough, it was 1. 0 mpg off hand calculated. There's a lot of variables to mileage, but I'm convinced that the rain made a difference. You move a lot of water over the course of a tankful of fuel with a big truck.

 

[JWChessell]

Thanks for the replies, fellows. The comments about big tires moving a lot of water in the rain makes sense. And yes, the . 02 difference in MPG on those two trips is correct. Same mileage on the April trip as on the February, but towing the same trailer 2,000 lbs lighter, in the rain.

 

[Big MAK]

Weight is less a factor then resistance. Be it rolling resisitance or wind resistance. Overcoming resistance is where the most power gets spent.

 

[DJennings]

Lately I've frequently been towing a 2-axle enclosed cargo trailer. In February northbound on I-5 between Lodi, CA and Medford, OR the mileage was 10. 528 MPG. In April northbound between the same two points mileage was 10. 548 MPG. All conditions were the same -- 70 PSI in the truck tires, 50 PSI in the trailer tires, about 1,000 lbs of cargo in the bed of the truck, cruise-control set at about 63 MPH, no wind -- EXCEPT: In April the trailer weighed approx 2,000 lbs less, and in April it was raining.



Does anyone know if wet pavement increases rolling resistance?

BigMak stated the biggest difference is resistance not weight. The other thing not factored is that humid air is more dense and offers more resistance than dry air. I pull a 6. 5x12 cargo trailer that has another little trailer inside it. Total weight is only around 2200lbs and my mileage still drops ~3mpg when towing vs empty. I have loaded it to about 7k a couple of times and the mileage barely changes from when it is unloaded.



You should have waited until it was dry. You could have driven an extra 3700 feet on that tank of fuel

 

[betterthanstock]

Hitting all those raindrops slows you down too. It's kinda like getting peppered by Dick Cheney. I just had to add that one.

 

[JThiessen]

I've noticed the same thing (I live in Seattle). I had been wondering if humidity level in the air might contribute to different efficiency levels also (those of you in the south and midwest would know more about that than we do).

Due to road construction, I've been toying with different routes to work. One route is mostly stop and go, with top speed of 50mph, exactly 20 miles one way. The other morning I reset the overhead, and when I got home it read 14. 7 mpg. The other route has very few stop lights, and uses mostly freeway, 21. 5 miles one way (I though it would have been further than that). A reset in the morning, and after round trip the overhead read 19. 5mpg! I figured there would be a 1-2 mpg diff. , but not 5. I'm using the overhead just as a guage of the difference, not actual values, although its accuracy is normally within . 5 mpg.