can someone clarify the whole 17" wheels thing hindering performance? Everyone is saying it's because wheels are heavier and stuff but I just weighed a set of 205/40/17 tires and they came in at 20lbs...that practically the same weight as one 17" rim would weigh (a heavy one as well)...so if someone goes from a 215/45/17 setup to a 215/55/15 setup (to keep same wheel diameter and width) then first, the tires would weigh more since there's more rubber(never weighed..it's just a theory of mine), which negates the few pounds you lose from going down a rim size..more weight torwards the outter part of your wheels (tires weighing more than rims)...and now you have more flex from the extra rubber(larger profile) added to your wheels which hinders cornering performance...is there something i'm missing?

btw this is all taking into consideration you keep the same diameter wheel+tire combination as to not throw your speedo off...if you make your wheel+tire combination smaller then it negates everything i said..but many people won't decrease the combination so they don't throw off the speedo(or have money for two different sets of rims)

 

polar moment of inertia.

15" tires are also cheaper.

 

You are correct. I much prefer short sidewall tires. Less flex, and les variable to deal with when adjusting suspension.

 

Two pieces of info. I've found out through experience/discussion:

1. On most wheels the rim is the heaviest portion.

2. Most tires of the same type/style but varying sizes weigh similarly (ie 205/50 15 Azenis is close to a 205/45 16 Azenis to a certain degree). Stiff sidewalls make up a significant portion due to the additional supporting rubber.

My point is that the 17s got more mass farther out => larger polar moment of inertia. The tires weigh almost the same, so a 17" tire has its mass concentrated farther out radially (it has a bigger hole).

So...what .RJ said, I'm just dorky enough to justify it.

 

your hypothetical is wrong in that a low profile tire weighs as much as a taller tire, or more.

the material used in the sidewall is conserved, since the low pros need more reinforcement to prevent popping off the bead.

thus, the moment of inertia becomes even more like a hoop, since more of the weight is on the outside of the spinning object. compound that with the fact that most of the weight of the wheel itself is on the very outside, and the extra 1" radius length also makes a big difference there.

sometimes 17's are necessary if you want to run a particular tire that only comes in the requisite width in the larger sizes (like the kumho MX).

 

cool..thanks guys makes sense to me

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bad-monkey &raquo;</TD></TR><TR><TD CLASS="quote">your hypothetical is wrong in that a low profile tire weighs as much as a taller tire, or more.

the material used in the sidewall is conserved, since the low pros need more reinforcement to prevent popping off the bead.</TD></TR></TABLE>

Tires are manufactured through a process of reaction injection molding. Every manufacture has their own "secret" method, but the basics are all the same. There is no constraint to use the same volume of material in each mold, and I highly doubt that it is conserved. My comments are specifically from weighing tires of varying sizes, and noticing that they are pretty close. I mentioned the "reinforcing blocks" of the low pros displacing more weight outward.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">thus, the moment of inertia becomes even more like a hoop, since more of the weight is on the outside of the spinning object. compound that with the fact that most of the weight of the wheel itself is on the very outside, and the extra 1" radius length also makes a big difference there.</TD></TR></TABLE>

Isn't that what I said?