Doc is quite right. In suspensions designed to use modern low profile tires
and larger diameter wheels, part of the benefit is that you can put the
suspension pivot points further apart. By the same token, if the tire/wheel
stresses
are focused on certain suspension components from a different angle (than the
angle it was designed for) there's potential for failure. On the Spitfire,
that would stress the trunnions, which are none too sturdy to begin with.
ISTR that when the LPT/LDW craze began, all the manufacturers took great
pains to tell everyone that they would void their warranty if they used such a
setup because ti stressed the suspension so. Maybe they still do??
I guess we will all have to consider 14" wheels if 13" tires start to
disappear, but 15"-16" rims might be a little extreme.
(Then again, I suppose that's the idea, right, Joe?).
Tom Burke
In a message dated 2/1/2005 11:54:22 AM Eastern Standard Time,
docnugent@yahoo.com writes:
> There won't be any change in a CAD drawing of the
> suspension's arcs, but the plus two wheels/tires WILL
> change the real-world geometry. Better grip between
> tire patch and road will compress the suspension
> bushings more, making their pivot points change, and
> slop from sidewall flex with "old style" tires will be
> gone, so the bushings and bearings can be expected to
> fail sooner. Small stuff, but real. For plus two
> wheels/tires to achieve their potential, you need
> non-flexing bushings (polygraphite, etc.) to keep the
> suspension pivots in one place.
>
> As to performance, I'd bet you could find a 13"
> autocross tire that would outperform 15" low profile
> street tires. All you really get with plus two
> wheel/tire combos is a different look - not
> automatically better performance.
>
> M D "Doc" Nugent
> Renton, WA
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