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  #1  
Old 05-17-2014, 07:10 PM
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MPG change when upgrading to 20"?

looking to upgrade our 19" wheels to 20" along with the fender flares... Not going to run staggered as I want to be able to rotate the tires. (i'll just run spacers in the back)

for those of you who upgraded, did you notice a decrease in MPG? Love our 35d and would hate to lose the MPG just for some aesthetics.
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  #2  
Old 05-17-2014, 08:08 PM
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There shouldn't be any change if the width is the same, assuming you don't change you driving style.
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Old 05-17-2014, 09:34 PM
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Even if the width changes, the impact should be in the noise...imo

Diameter is all the same, so no change in force/torque/rpm/efficiency
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Old 05-17-2014, 10:54 PM
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There should be a negative impact due to increased rotational inertia, unless you never stop or start. I'd expect it to be small, though.
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Old 05-17-2014, 11:38 PM
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Quote:
Originally Posted by JCL View Post
There should be a negative impact due to increased rotational inertia, unless you never stop or start. I'd expect it to be small, though.
Yeah, but no more then 3 or 4 mpg, right?
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Old 05-18-2014, 07:54 AM
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Quote:
Originally Posted by JCL View Post
There should be a negative impact due to increased rotational inertia, unless you never stop or start. I'd expect it to be small, though.
LOL, that's assuming he's going OWM Wheels, what if he's going to replica wheels and from RFT to Non-RFT and lower the overall weight, I'll leave the math to you.. LOL

Oh don't forget, fender flares, additional drag..

Harry
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Old 05-18-2014, 08:35 AM
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With OEMs/run flats the drop would probably be 1..2 MPG.
My beyern/non run flats combo is lighter than stock 18s, and MPG remained exactly the same.
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Old 05-18-2014, 10:36 AM
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rotational mass remains the same but i'm going from 255/50R19 to 275/40R20. I know it already has more area in front of the wheel when it comes to aerodynamics but such a big car I don't know if its that significant.

3-4mpg is a pretty significant difference.....
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Old 05-18-2014, 11:02 AM
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Rolling resistance is probably more important than aero for the tires themselves. Wider patch implies more resistance. I think it is pretty hard to drive the same on tires that handle better - I'm guessing there is some right foot action that outweighs mass, rolling resistance and aero combined!
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Old 05-18-2014, 11:25 AM
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Originally Posted by 14thbmw View Post
Rolling resistance is probably more important than aero for the tires themselves. Wider patch implies more resistance. I think it is pretty hard to drive the same on tires that handle better - I'm guessing there is some right foot action that outweighs mass, rolling resistance and aero combined!
Now the truth comes out..
Harry
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