Thread: Gearing
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Old 09-23-2008, 12:22 PM   #7 (permalink)
extragoode
EcoModding Apprentice
 
Join Date: Mar 2008
Location: Des Moines, IA
Posts: 155

Nerdcycle - '81 Honda CM400E
Motorcycle
90 day: 61.16 mpg (US)

Trouble - '06 Kawasaki Ninja
90 day: 74.69 mpg (US)

Edna - '13 Nissan LEAF SV
Last 3: 133.3 mpg (US)

Tank - '20 Ford Expedition Limited
Last 3: 17.4 mpg (US)
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Quote:
Originally Posted by Big Dave View Post
On pickups, bigger diameter wheels/tires ALWAYS result in LOWER MPG.

To repeat big tires = lower MPG.

Reason: Rotational inertia. When you accelerate away from a stop, you must not only translationally accelerate the vehicle but also those four "flywheels" attached to it. The rotational moment of inertia goes up with the square of the outside diameter. On a pickup, going from 235-85x16 to 305-75x16 tires costs the owner 2 MPG.
But you're also the one who is always preaching gearing. Rotational inertia means a lot in city stop and go, but I would think gearing would trump inertia on the highway. Choose the tires for the driving you do most.
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