Date: Mon, 2 Nov 1998 19:36:31 -0800
Reply-To: David Marshall <vanagon@VOLKSWAGEN.ORG>
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: David Marshall <vanagon@VOLKSWAGEN.ORG>
Subject: Re: Wheels, Tires and the Laws of Physics
In-Reply-To: <s63d9440.013@collchem.cchem.berkeley.edu>
Content-Type: text/plain; charset="iso-8859-1"
This all make sence is the performance car world... but I hardly consider
that average Vanagon Syncro a performance car. I think there are two main
reason for 15" and 16" wheels:
- more tire choices
- larger than 27" diameter
These two factors are important to someone who wants to take their Vanagon
off-roading and not driving fast.
At 11:14 11/2/98 -0800, YauMan Chan wrote:
>Pardon me for jumping in even though I don't have 16" wheels!!!
>
>We are comparing a 205/70-14 wheel and a 215/65-16 wheel. Radius of wheel
= height of tire +radius of rim
>
>205/70-14 --> 205mm wide 70%height, 7" radius rim
>Calculate: 205mm x .7=143.5mm + 7"x25.4mm=321.3mm=12.65" wheel radius
>
>215/65-16 -->215mm wide 65%height, 8" radius rim
>Calculate: 215mm x .65=139.75 + 8"x25.4mm=342.95mm=13.5" wheel radius
>
>The 16" wheel is therefore 7% "bigger" than the 14".. So the speedometer
will read 7% slower.. ie, when the speedometer reads 100mph, the van is
really going 107mph..no big deal
>
>The question is what is the advantage of going for the 16" rim. These are
two important consideration. (1) For safety and comfort, you want to keep
the "unsuspended" weight of a vehicle to be minimum ¯ conservation of
momentum and all that ¯ and (2) You want the wheels to be as stiff as
possible for good handling.
>
>1. The answer is not size (sorry guys!) but weight. What you should aim
for is to decrease the "unsuspended" weight of the vehicle. i.e., anything
not carried by the suspension system should be kept to a minimum. This
include all the wheels, brake components and drive shaft from inner CV
joint on out. Of these, the wheels are the heaviest. That's why alloy
wheels were introduced since aluminum alloy weighs a lot less than steel.
Then why bigger rims? ¯ by having less rubber and more alloy, the net
weight of the wheel can be decreased. (While rubber is lower density than
alu alloy, it takes more rubber to hold up a van than alu alloy.) In this
instants of 16" vs 14" wheel (with rubber), I don't know if the 16"
actually weights less than the 14" ¯ someone here can check it out.
>
>2. Rubber is squishy and is too flexible for good road feel. By lowering
the height of the tire and increasing the diameter of the rim, you get a
much stiffer wheel. This will greatly improve the handling of the vehicle.
>
>The side effect of all this is that the 16" wheel have a wider contact
surface.. This gives you more friction with the road and will give you
more traction.. But will decrease you gas mileage.
>
>My $0.02 worth.
>
>Yau-Man Chan
>87 GL
>
>
-- David Marshall --
-- 78 1.8L VW Rabbit, 80 2.0L VW Caddy, 87 Audi 5KSQ --
-- 85 VW Cabriolet, 88 2.0L VW Syncro 16" Double Cab --
-- Volkswagen Homepage http://www.volkswagen.org --
-- Volkswagen/Audi Parts http://parts.volkswagen.org --
-- mailto:david@volkswagen.org - Quesnel, BC, Canada --
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