larger wheels OF THE SAME WEIGHT do lower your gas mileage.
take an umbrella. the kind that has a hook on the end. put the umbrella between your two hands and roll the umbrella back and forth. you are spinning the umbrella but with relatively minimal effort. now, take that same umbrella and spin it around your hand by the hook on the end. the weight of the umbrella has not changed but the effort you expend has increased and you are most likely not spinning the umbrella as fast as you were before.
but i see it all the time. get some standard 16" wheels normal profile tires, get 30 mpg. then they decide to put on 20" wheels with low profile tires with difference in weight that does adds up to a few lbs.
but the mileage drops to 25 MPG and its the same story..."oh ya, new tires take time to break in but your mileage will go back up a bit" and it probably will...to 26 at the most.
there is a reason why early Japanese imports had 12 and 13 " wheels. it was because that is what they needed to do to get better mileage. now that technology has improved a bit, tires are getting larger. after all, they ride better
2011 SL; 44,598 miles. 2013 S; 44,840 miles.2016 S30 deceased
. 29,413 miles. 2018 S40; 5775 miles, 488 GIDs, 38 kwh 113.37 Ahr available, SOH 98.21, Hx 115.75
My Blog; http://daveinolywa.blogspot.com
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