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CVT Mode & Highway Fuel Economy: D vs S

Palut

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I've done some experimentation with CVT drive modes while cruising in top gear, and I want to share them. I hope you might find this beneficial.

For anyone who hasn't noticed, the CVT's D mode utilizes a significantly taller top gear ratio than S mode. As an example, on level ground at 68 mph in S mode I will see approximately 2,700-2,800 RPM. The gear ratio is identical in both automatic S mode, and in S mode with 7th gear selected. The same vehicle speed in D mode yields approximately 2,100 RPM. This results in a significant improvement in fuel economy.

I've tested this on a 120 mile round trip highway route I frequently travel, and I've driven this route a few dozen times since buying this car in July 2022. I frequently fill up right before the drive, resetting the trip meter, so by the end of the drive I will see the ECU reported mileage for just this section of highway. I generally set the non-adaptive cruise at 68 mph due to very heavy speed enforcement on this route. Up until January I would do this exclusively using S mode, gear 7. This fairly large sample size was usually in the 34-35 mpg range, with 36.7 mpg being the best ever recorded. That best ever trip was in approximately 70° weather with absolutely no traffic slowdowns and no unnecessary braking.

Since late January I've done that same drive a half dozen times in D mode. The weather is typically 35°-50° F, and I've had light to moderate traffic slowdowns on most of these drives. Despite these conditions being tougher for fuel economy, D mode has consistently yielded 38+ mpg as per the ECU. I've seen as high as 40.1 on a trip, and that drive included a 10 mile side trip of stop & go city driving.
 
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Palut

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Ben
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Just as a comparison, my 2018 WRX CVT would return 25-26 mpg in pure highway driving, and 23 mpg when driven hard for an entire tank on my favorite spirited driving route. This Integra can get 40 mpg in pure highway driving, but that drops to 25 mpg when driven hard on that same route.

This powertrain is very sensitive to load.
 

jtrader

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That's interesting. In our CVT Civic Hatch Sport, while on the highway the D rpm and the 7th gear (S) rpms are identical. Only regular "S" has a higher rpm and worse MPG's. Now I'm curious why there is a different between your simulated gear ratios and mine.
 
 


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