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Re: RotoFlex Suspension

To: Triumphs <triumphs@autox.team.net>
Subject: Re: RotoFlex Suspension
From: "Power British Performance Parts, Inc." <britcars@powerbritish.com>
Date: Tue, 28 Nov 2000 09:08:30 -0500
References: <65.c6a59f6.2755083c@aol.com>
Chip19474@aol.com wrote:

> List,
>
> What a curiosity this is.....a rear suspension that transfers power to the
> wheels through a rubber donut.
>
> I'm familiar with the term but had never seen "it" until last week when I had
> a chance to see "it" (assembled and dis-assembled) on a GT6+.  At first I
> thought how clever it was to use a big rubber bushing donut to absorb changes
> in axle torque and loads to the rear wheels but after I saw the results of
> the rubber bushings delaminating from their metal washers, etc, I began to
> wonder why Triumph did this......well, I'm guessing that money was at the
> heart of the decision.
>
> I have a few books that address Spitfire & GT6 history but thought I'd ask
> the forum that question....."Why did Triumph use rotoflex in lieu of perhaps
> a sway bar/swing axle Spit suspension or even an IRS setup?"
>
> Chip Krout
> '76 TR6 CF57822U (chassis finished - working on body & engine)
> '70 Spit Mk3  FDU78512L (tucked away for a long winter's nap)

Hi Chip,

I'll throw my hat in on this one, but I bet Jonmac may have more insight.

Using a lower wishbone on the GT6+ rear suspension lowers the roll center and
thereby eliminates the 'jacking' effect for which the early Spits were notorious
for.  However, since the length of the wishbone is considerably shorter than the
axle itself, some provision must be made for the axle to 'telescope' in and out
as the suspension components follow different arcs throughout their travel.  On
the TR4A model of the same vintage, this was accomplished with the splined
driveshafts.  On the GT6, this same action was achieved through the use of rigid
axles and the rotoflex coupling in place of a conventional universal joint.  As
the end of the axle changes depth in relation to the hub, the rotoflex just
stretches side to side a bit in addition to distorting off axis as a u-joint
would.  My guess is that this was considerably cheaper than manufacturing
tight-tolerance sliding splines and that's why it was adopted for the lighter,
lower HP cars such as the Vitesse and GT6.  As we all know, the design only
lasted a few short years until the advent of the pivoted 'swing-spring' which
reverted to a true swing-axle design without the 'jacking' problem.  Of course,
this was far simpler (read cheaper) than even the rotoflex design.

Cheers!

Brian Schlorff
Power British
http://www.powerbritish.com/~britcars

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