Originally Posted by swamp2
Doubtful. 18" vs. 20", if the 18" are light and 20" are particularly heavy, will be measurable and probably fairly consistent. I doubt that tire width will be above the noise of the measurement for acceleration. Furthermore, the weight of wider rears will be offset by a bit more traction, given an identical compound and all else "apples to apples".
You might be right but I would love to know for sure, all the same.