Not your avg. wheel and tire Q

[ralphyboy]

I was wondering if all other things being equal (IE size width etc) it is better to have the lighter tire or the lighter wheel. I am making an educated guess in the fact that 17 in tires are lighter than a 16 in counterpart (remember plus sizing in effect) however those 16 in wheels are lighter than the 17s . The outside rotational mass is more on which one, the 16 has the metal of the wheel closer to the center but the heavier tire. O-well I guess I'll see if anyone has any info on this...


By the way did the word orange come before the fruit or was it the other way around:D

[Halz]

All things being equal, the larger wheel will have a higher rotational mass.

I ran some numbers awhile ago trying to answer a similar question, and came up that with all things being equal, a 1" reduction in wheel diameter reduced rotational inertia by something like 6%. Conversely, a 1lb reduction in the weight of that wheel gave something like 15% less inertia.

I am looking around for the notebook I did all of the math in; my room is a mess :( While I don't have exact numbers at the moment, I know that a reduction in weight had a significantly larger effect on the wheels properties.

[ralphyboy]

I thought I was the only anal one about that subject. Thank you for that info I do appreciate it.

[S14mc]

I also heard that the bigger the wheel to spin, the loss of hp to the wheels (by a small percent)

[HippoSleek]

Something that I think ralphy is missing is where the mass is located. While you mention a larger wheel, you are fogetting about the heaviest part of both the wheel and the tire - the "foot" (as in footprint, i.e., not the "face"). If a tire is only 4" high and 7" wide, the bulk of the mass is with the width - which is the futhest out portion.

While this doesn't chance for the tire if you keep the basic diameter of the tire (from the hub) the same, it does for the wheel. When you go +1 or +2 on a wheel you are moving this foot/width portion of the rim (and hence the rotational mass) further out. So all things equal, you have moved more rotational mass out, which is bad.

(I hope someone can explain this better - b/c that is confusing me - and it's my thought :( )

[ralphyboy]

I get what you are saying Sleek but the inserts in the sidewall must weigh something those would be less in a larger size tire I guess I just did not know how much or what kind of effect they had on rotational mass. The tires I will likely end up with are the yokahama AVS sports ( I want the A520s back ). They have steel inserts, the diference in weight would be less in the tire than the wheel but it is also futher out from the center. I think I'm just nit picking but I thought the differance between the two might be less than one would think so the smaller sidewall would be more bennificial than weight vs issue. ( WHEW ) ( Now you know what it's like living in my brain ) ( why do I think of this crap )