Wondering eyes... um, I mean steering.... '98 Disco

Happy New year all....
Just wondering if anyone can offer a pointer or confirm my suspicions on
a strange steering effect on the old beast.

A couple of months back I had a pair of new tyres in the form of
235/70x16 Insa Turbo Traction Track Extreme All Terrain
Initially (as I was trying to prove the diff that was fitted 15 months
prevuious was now w4nked) I had 'em mounted on the front to prevent the
garage blaming chunky tyres for rear axle noise.

I then got them re-fitted to the back so better braking efficiency with
the older less chunky AT's and fairly shortly after noticed the steering
a bit "lively" worst problem being in the nearside lane of the poorly
maintained M5 where you can see significant trenches from lorry wear. I
appreciate these grooves would give a problem to most cars   but the
Disco becomes a bit of a handfull as it jumps from track to track.

Front wheels are fairly low on tread Cooper A/T style  so diameter of
new must put the rear axle a good 3/4 inch higher then the front.

Does the group think this would change the castor angle geometry of the
front end enough to create such a marked difference in handling or could
it be something more evil like squidgy rubbers or dodgy dampers?

The beast has around 185,000 miles and due to business comitments  ,
garage serviced and maintained so generally kept  up together pretty well.

Cheers
Pete
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