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Old 01-08-2021, 08:24 PM   #1 (permalink)
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Tire/wheel weight and mpg

How much will rotational weight reduction help with fuel economy? I have to assume that it would help more than the same weight reduction elsewhere in the car.

My current front tire/wheels weigh 47 lbs each, 94 lbs total
The current rears weigh 55 lbs each, 110 lbs total

The new fronts Iím considering would weigh 41 lbs each, 82 lbs total
The new rears would weigh 48 lbs each, 96 lbs total.

While it not a lot of weight off the the entire car, itís a pretty good chunk off the rotating stock.

Should I see this in my mpg recordings?

1966 Chevelle w/ 3.6L (217 ci) 4 cam direct injected V6, 6 speed double OD auto trans and 3.07 rear end. 3260 lbs with full tank of gas.
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Old 01-09-2021, 12:02 AM   #2 (permalink)
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Some back of the envelope math suggests the rotational inertia of your wheels is around 6.5% of your total vehicle's inertia (I made what I felt were some reasonable assumptions about wheel moment of inertia). The wheels themselves are also, surprisingly, just about 6.5% of the total vehicle mass, so you're looking at affecting approximately 13% of the energy need to accelerate and decelerate. Or, in other words, my math supports that taking a pound out of the wheels is like taking two pounds out of the car.

Looks like the total inertial savings is ballpark 1.5% from the entire vehicle. I can only guess at how that would relate to fuel consumption. Maybe 1/3 to half that in mixed driving?

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