"Dave Baker" wrote in message
...

"Dave Plowman (News)" wrote in message
...
With R&P steering if the wheel ends up off centre the tracking isn't
correctly done - the geometry will vary as the wheels turn.

Ummm no it won't. The straight-ahead position of the steering wheel has no
effect on Ackermann steering geometry which is created by the angles of
the steering pivots and tie rod.

http://en.wikipedia.org/wiki/Ackerma...ering_geometry

Imagine with tracking set correctly you move the steering wheel slightly
off centre and then recheck the tracking. The tie rod ends will now be too
long at one side and too short at the other. So you undo the locking nuts
and adjust everything until the wheels are straight again. All you've
actually changed is to lose a little steering lock on one side and gain a
little on the other. The steering geometry hasn't altered. The total
length of the tie rod (rack) is still the same, the steering pivot angles
are still the same, the wheels are still pointing straight, the steering
wheel and pinion have just moved relative to the rack is all.

A rack and pinion system has a completely linear mode of operation. A
little logical thought ought to make it apparent that it can't be the
movement of the pinion relative to the rack or their initial starting
positions that creates a non-linear steering output on opposite sides of
the car which indeed is created solely by the movement of the rack
relative to the steering pivots.

Unless the
steering wheel has been moved on its splines.

Again utterly irrelevant other than you lose steering lock on one side and
gain it on the other. I once had a Fiesta XR2 which I ran for years until
it gradually dawned on me that if I turned into my driveway from the usual
direction I approached the house in I had no difficulty but if I came back
home from the other direction which was pretty rare I struggled to get
enough steering lock on to make the turn. In normal driving there was no
other apparent fault or difficulty. After pondering this for a while I
started checking everything and finally found that from the straight ahead
position I had a lot less steering lock on one side than the other. In
fact after marking the steering wheel with a bit of masking tape and
counting the turns either way to the stop I calculated that I had one
third of a turn more on one side than the other which was a massive error.
Turns out that at some time in the past the steering wheel had been taken
off and moved round a notch on the steering column which had a hexagonal
fitting rather than a spline on this model. So I'd lost a sixth of a turn
on one side and gained a sixth on the other.

Checking the tie rod ends one side was indeed wound almost fully in and
the other side almost fully out. God knows how anyone had managed to screw
this up so badly and not realise. The garage I'd got the car from was run
by complete numpties though so that probably explains it. Anyway, with the
steering wheel back in the right place I had to make a massive tie rod end
correction and finally got everything back as it should have been. However
at no time was there any unusual tyre wear or strange steering or handling
behaviour. The steering wheel position simply makes no difference to this.

BTW it should also be apparent from the above that just because the car
tracks straight and the steering wheel is in the right position while it's
doing that is no indication that everything is correct. Before checking the
tracking you need to check the turns lock to lock either side of the
straight up position. If this is the same both ways then the steering wheel
is on correctly and the rack is properly centred. If not then the steering
wheel needs to be moved on its spline before the track rod ends are adjusted
to set the tracking.
--
Dave Baker