>Even if the wheels weighed the
>same. the 14" wheel would
>spin more easily than a
>17" or 18". The distibution
>of mass is different. Because
>in the 14" wheel the
>weigh actually has a shorter
>path to complete around the
>axis of rotation. It's like
>an ice skater they spin
>the fastest when their arms
>and legs are tight against
>their body and and to
>slow themselves down they put
>their arms and leg out.
>So for a rotating mass
>the smaller the better. Hell
>find 13" rim for the
>track, and you'll have another
>gain.
>Sorry if this explanation didn't make
>sense I haven't had to
>do physics in a couple
>years now. If something doesn't
>make sense let me know
>I'll try to elaborate

You got it right Mike, that's a good explanation.

Going along those same lines, the mass at the VERY OUTER EDGE of the tire is what should affect the rotational inertia the most. The tire's tread is further out than the rim of the wheel, right? So the tire should affect the rotational inertia more than the rim. The larger rim should also have an affect, but I'm guessing the wider tire is causing most of the "power loss."

My tires were 225s, compared to 195s that's 15% more tread (and at least 15% more weight) at the very outer diameter of the tire, now multiply that by 4 tires and I guess it was enough to cost me that 2/10ths at the drag strip.

So, a heavier rim might not make all that much of a difference, a heavier/wider tire would. Of course lighter is always better, since you also have to accelerate that mass in a straight line, and it adds to suspension unsprung weight.

So as crazy as it sounds you might see a small negative difference with a 195 tire on a 18 inch rim (bear with me here, I know no one would do this) and a huge negative difference with a 225 tire on a 14 inch rim (if the outer diameter is the same)

Todd Scungio
98 RS
15.803 @ 86.48 MPH