Mileage decrease in the rain, hybrid only?

[2seater]

This is my first hybrid so maybe a Homer Simpson type dumb question. I have only had my hybrid for two months and about 1200 miles so far. The weather this summer has been almost perfect for battery environment, dry and temperatures generally peaking in the 80's. I got used to my general use mileage to average in the mid-40's, gets higher in the urban environment and down a bit in the open. Two days ago was a 120 mile round trip, 90% at 65+ speeds. Almost all of the trip, both directions, was in moderate to heavy rainfall, plus moderate winds. I noticed the throttle felt much less responsive and the mileage steadily decreased from 43.5 average at the start to <37mpg at the end. I missed noting the individual trip mileage I am wondering if the coating of water friction and the greater rotating mass may have a direct effect on a vehicle designed towards efficiency?
All my previous ICE vehicles over 55+ years generally liked humid and wet weather. A sort of crude water injection perha,ps? Maybe I am now more aware or the steady dose of high speed reflects normal reality??

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[Zotman]

9 years with a C-Max and always noted rain-related mpg decrease.

 

[sundog]

Headwinds and heavily saturated roads have an effect. You also didn't mention if you used the Defrost for condensation. Defrost = air conditioning = lower mpg

 

[jsus]

You're basically dealing with increased rolling resistance/reduced traction, meaning it takes more energy to actually spin the tires. Tires also need to be able to push through the water - think of it as perhaps a lesser version of the difference in moving your arm through a swimming pool vs. the air. Rain is often accompanied by wind, so unless it's a tailwind, that further decreases efficiency. Changing ambient temperatures may mean extra energy needed for climate, as does an increased use of defrost to clear condensation off the windshield. Technically the wiper blades may or may not have a small impact on aerodynamics as well.

Bottom line is that rain decreases efficiency in all vehicles, it's hardly limited to hybrids. It may, however, be more noticeable with more efficient vehicles as the same % drop in efficiency at a 20 mpg baseline is smaller in actual mpg than with a 40 mpg baseline - the drop is half as big in finite numbers. e.g. losing 10% at 20 mpg is 2 mpg, but at 40 mpg, it's 4 mpg. Efficiency drop % is arbitrary for the sake of making the point.

Per Freightliner (the same physics apply to a Maverick as do a semi):

Rain, snow, or slush on the road increases the vehicle’s rolling resistance, because in addition to moving the vehicle, the tires must also push their way through the precipitation on the roadway. The precipitation cools the tires, transmission oil and axle oils. These components operate less efficiently at lower temperatures. The increased rolling resistance and drive-train friction in just a light rain can increase fuel consumption by 0.2 to 0.3 mpg.

https://www.freightliner.com/blog-and-newsletters/how-adverse-weather-affects-fuel-economy

 

[2seater]

Thank you all.
No defrost, but valid thought. I imagined it is probably a combination and of course the operator is extra vigilant. The somewhat mushy throttle response was the catalyst for the question. As I said, it's my first hybrid, and I have been pleasantly surprised that its willingness to accelerate for passing is better than I expected. That feeling was notably absent in the rainy drive. Now I know I haven't imagined the effect.

 

[TedTX]

Its also, still sorta new. There is a longer period where the computer built in adjustments are being made, so on third tank of gas @ 1200, etc. 4000-6000 miles the mpg improves accuracy and numbers.

 

[FriscoTXJoe]

OK. Blowhard here. (Well, kinda. I'm really fun underneath this exterior.) I was giggling as I read the title and thought uphill vs downhill.....wind??? As if it were that simple.

Then I read all the different responses with totally valid reasons.......

And I realized, it's taken till I have gray hair but I do learn to think before I pop off every once in a while.

Great posting/responses. Thank you!

 

[72Maverick]

I was surprised how much a rainy day would effect efficiency of a vehicle. My plug in hybrid would lose about 10% of it's range (45mi vs about 40mi) when the road was wet. Especially when it was raining hard enough to keep a solid sheet on the road. I usually try straddle the puddles if possible just because of the extra drag. I never noticed or thought about it in my ICE vehicles because it not as noticeable unless you're tracking mpg down to the last drop.

 

[HughdMan]

This is my first hybrid so maybe a Homer Simpson type dumb question. I have only had my hybrid for two months and about 1200 miles so far. The weather this summer has been almost perfect for battery environment, dry and temperatures generally peaking in the 80's. I got used to my general use mileage to average in the mid-40's, gets higher in the urban environment and down a bit in the open. Two days ago was a 120 mile round trip, 90% at 65+ speeds. Almost all of the trip, both directions, was in moderate to heavy rainfall, plus moderate winds. I noticed the throttle felt much less responsive and the mileage steadily decreased from 43.5 average at the start to <37mpg at the end. I missed noting the individual trip mileage I am wondering if the coating of water friction and the greater rotating mass may have a direct effect on a vehicle designed towards efficiency?
All my previous ICE vehicles over 55+ years generally liked humid and wet weather. A sort of crude water injection perha,ps? Maybe I am now more aware or the steady dose of high speed reflects normal reality??

No, it hurts mpg on all vehicles, you just notice it more in a vehicle that gets a higher mpg. It's aerodynamic drive, the water on the wheels, road spray hitting the car and more.

I noticed it when my mileage dropped from 48mpg to 44mpg (10%). That is driving 40 miles in the mountains. In my Ram 1500 I don't notice it much going from 14 to 13, and also the non-hybrids don't always have "live" mpg estimators.

 

[MakinDoForNow]

Headwinds and heavily saturated roads have an effect. You also didn't mention if you used the Defrost for condensation. Defrost = air conditioning = lower mpg

The hybrid automatically can run the AC condenser to lower the humidity level to insure the dew point is not reached to prevent fogging of windows. Whether or not you have AC on. It will have slow airflow coming out floor vents so you may not readily notice it.

 

[Ozarkbeard]

The hybrid automatically can run the AC condenser to lower the humidity level to insure the dew point is not reached to prevent fogging of windows. Whether or not you have AC on. It will have slow airflow coming out floor vents so you may not readily notice it.

This.
Also, the rated highway MPG is only 33. If OP was getting 37 in the rain, above 65mph (with the a/c compressor likely running to lower cabin humidity), that's really not bad mileage.

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