Date:         Thu, 17 Apr 2003 17:23:19 -0700
Reply-To:     Damon Campbell <damoncampbellvw@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Damon Campbell <damoncampbellvw@YAHOO.COM>
Subject:      Re: Tires
In-Reply-To:  <68D40148-7120-11D7-B47B-00039398EEBC@mac.com>
Content-Type: text/plain; charset=us-ascii

Can i take my crack at armchair physicist?!?!? :-)

A heavier wheel takes more energy to GET going... once
it is going, it takes the same energy to keep moving.
First order approximation, of course.

A larger wheel, due to it's shallower angle of contact
actually has LESS rolling resistance.  First order of
approximation, or course.

Now, rubber compounds, tread profiles, contact patch
sizes, tire pressures, etc. all have a huge effect on
this, but simply saying bigger, heavier tires are
slower just ain't right.  They simply resist change in
speed more - not speed itself.

Oh yeah, i have a set of contis on my van that i like
very much :-)

-Damon

--- Kim Brennan <kimbrennan@MAC.COM> wrote:
> Not entirely. There are two factors to consider.
> Rolling diameter
> (determined by the tire) and weight.
>
> The weight matters because it takes more energy
> (read power) to spin a
> heavier wheel/tire than a lighter wheel/tire. AND,
> WHERE that weight is
> distributed makes a difference. Weight at the outer
> circumference takes
> more energy to spin  (or stop) than weight
> concentrated at the hub.
>
> When you go to a larger wheel you usually are adding
> additional weight
> to the wheel/tire, but you are also changing the
> weight distribution,
> usually by moving more of the weight away from the
> inner hub.
>
> This all affects acceleration times. A longer
> circumference is harder
> to spin, and a heavier circumference (even at the
> same size) is harder
> to spin.
>
> I certainly noticed it going from steel 14" wheels
> (205/70R14 tires) to
> alloy 15" wheels (215/75R15 tires).
>

=====
'84 Westy (Sparky)
'65 Kharma Ghia (Dharma)

__________________________________________________
Do you Yahoo!?
The New Yahoo! Search - Faster. Easier. Bingo
http://search.yahoo.com