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Re: Radial v Bias belted tyres

To: "Triumph List" <triumphs@autox.team.net>
Subject: Re: Radial v Bias belted tyres
From: "John Macartney" <jonmac@ndirect.co.uk>
Date: Fri, 6 Jul 2001 00:47:14 +0100
The original Michelin X tyre was developed and used extensively in
France and fitted as OE to many French cars. Because it was of radial
construction, it had substantially improved tyre life and offered much
better roadholding overall. French roads of the time left much to be
desired in terms of smoothness - though the same cannot be said today.
Early postwar French cars had incredibly soft suspension systems - e.g
Renault 4 and Citroen 2CV
There were disadvantages.
Because the wall was designed to flex more than a cross-ply (bias),
the tyres often looked as though they were running under-inflated. The
soft walls also left them more prone to tyre wall damage.
However, it didn't take long for the Michelin X tyre to gain a highly
regarded reputation and it soon became the benchmark for OE fit or as
a replacement. Because of its different rolling radius and if line
fitted as a factory option, it was necessary to specify a different
speedo head. Therefore, cars fitted with cross plies when new and
later changed to Michelins had inaccurate speedos thereafter.
As far as the sidescreen TR was concerned (and a few others as well)
the fitment of Michelins caused other problems. Because of its greatly
improved handling properties, owners exploited this to the full and
had some frigthening experiences and by no means just a few accidents.
A TR2-3B has a notoriously twitchy backend (TR4 as well) and when this
eventually broke away under very spirited cornering, you really had
your work cut out to keep the car under control. In wet weather the X
had some very unpleasant characteristics in a sidescreen TR because
the suspension had not been developed for this type of rubber. The
grip was good for a while - and then it would let go BIG TIME.
Two weeks ago, I was driving a TR3A up a former test hill at speed on
tyres that while they weren't true X's, had a very similar tread
pattern and steering feedback. We came to the first corner at about
45mph and at the apex of the bend (and it was a very hot day) I
floored the accelerator, entirely forgetting about the back end. It
came out viciously and then the grip returned at exactly the point
when it wasn't needed - just like the old Mich X. Fun - yes, but I
could have done without it at the time!
For its day it was a brilliant tyre - but modern alternatives are far
better.

Jonmac
MG 4305 DLO 1970 2.5PI
"Loving thy neighbour" is fine - until you get caught

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