Quote:
Originally Posted by newtlicious
You don't need a physics degree to see this in action. Next time you are in the grocery store get a big box of kitty litter and put it in the front of an empty shopping cart. Next, turn the cart around a corner and see how difficult it is. Now, move the kitty litter to the back of the cart closest to you and take the same turn. You will notice that it is much easier to turn the cart when the mass is closest to you. This is the same idea with the wheel. The mass is the same but it's distance from the center of rotation affects the force required to change it's direction. Resistance to change in direction is the layman's definition of inertia. It may not seem like an inch on a wheel would make much of a difference but then again, we are talking about hundreds of rpm, not a shopping cart hanging a left in the parking lot. Realistically, there wouldn't be much seat of the pants change in straight line acceleration with all things equal, grip, rolling diameter etc. There would, however, be a difference in seat of the pants acceleration if the rolling diameter changed which would cause a change in effective gear ratio. Hope that helps!
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Theres nothing wrong with your physics, but you like others above are making the assumption that the weight in the 19's is distributed in the exact same manner as the 18's, and therefore, having a slightly wider radius that means they must be slower.
But lets be honest. None of us know how the weight in these wheels is actually distributed, since they are different designs. For all we know the 18's have really dense and heavy barrells while the 19's have most of their weight at the hub.
So we are left with the basic equation of a slightly lighter wheel (19's) with a slightly larger diameter vs a slightly heavier wheel with a smaller diameter and bundles of usual internet speculation. I would be willing to bet that the difference between the two is negligible and people claiming they can really feel the difference are at best suffering from a placebo effect and at worst talking trash.
Mick