Twitchy steering at speed
 

At 'motorway' speeds the steering on my XK8 if very, in fact too much so, positive. The slightest movement of the wheel creates quite a change in direction which can be somewhat disconcerting!

Just had the alignment checked and the only thing that is out is the front wheel castor, measuring -5deg 48min LH and -5deg 20min RH, so it is approx 12 deg out. Could this be the problem? If so, what could cause it?

BTW tyres are Avon rear and Dunlop front.

Sorry all, think I've been reading the printout incorrectly! The arrows are on the -ve side indicating that the readings are under the ideal setting not negative as I've assumed (idiot).
So I;'ve actually got positive at 5deg 48 and 5deg 20. Thus approx 1deg less than should be.

Without seeing the full before and after printouts, it would be like working with a blindfold on.

Lots of possibilities. Suspension or tires. Tire issues that come to mind include:

A) Beware of a broken belt inside one of the tires.

B) Also, If you are new to the XK8 and cars with tires of this size, it could just be tramlining. Disregard this if your issue is a recent development and was not this way at a prior time.

From Tirerack: High performance tires with short sidewalls that develop lots of cornering power at lower slip angles will be more susceptible to tramlining than standard All-Season passenger tires that develop less cornering force until their slip angle increases. A wider treaded tire will encounter more longitudinal ruts and/or grooves in the road than a narrow treaded tire (IE- As you barely pull the wheel to one side as soon as one edge of your tire catches a crown in the road it quickly pulls the rest of the wide tire over it).

C) Someone didnt realize the offset, rotated your tires and you have 8" inch wheels on one side and 9" on another as opposed to front and back.

Fair comment!

Please see below.....