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 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 8468.7 mi, 95.18% SOH
My Blog; http://daveinolywa.blogspot.com
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