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      08-07-2013, 12:41 PM   #38
Denk
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Drives: 2021 X5M
Join Date: May 2011
Location: PNW

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Quote:
Originally Posted by CSBM5 View Post
Re tire weight. Changing to a 275/35 from a 265/35 will have an UNMEASURABLE effect on the car's acceleration due to the minor weight addition. It will be within the repeatability window of the data logging in acceleration tests. Also, since it only has an effect when there is acceleration of the wheel, AND since that effect drops of exponentially with speed (i.e. 1st gear has the highest acceleration rate, then accel rates fall successively as speeds climb), there will be zero effect on measured gas mileage that you can measure. At minor acceleration rates (essentially all of daily driving), it's trivial, and at a rather constant speed (cruising) there is ZERO contribution to minor effect of a small increase in rotational inertia.
I A/B'd stock sizes with 255/35, 275/35 and it did have a measurable effect with my butt dyno. Besides weight there is also an increased OD which plays into the equation. Maybe on paper it shouldn't be noticeable but after real world testing I noticed a difference and that was just street driving. Stock size definitely feels better to me...that's a biggie to me.
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